Thermomechanical Processing

Ceramic coatings tend to be brittle and devitrefy or spall on thermal cycling, but offer excellent resistance to oxidation and corrosion. Processing methods and the resultant coating microstructures are described. Degradation modes and testing methods are discussed. The following areas are identified for further research: phase diagram and diffusion data, adhesive energy and friction data, adhesion interlayers for ceramicto-metal coatings, multilayer coating formulations, barrier layers to stop siliciding of substrates, self sealing coatings, lower temperature CVD processing, adhesion and interparticle bonding improvements for flame sprayed coatings and lower porosity, prevention of microchipping of ceramic coats, factors influencing stress in coatings, effect of debris impact, grit inclusions and surface embrittlement, development of shear adhesion tests, thicker and more strain tolerant ceramic coatings.

Dynamic recrystallization of the AZ91 alloy was studied by conducting hot compression tests at temperature range of 325-400 • C and strain rate of 0.001-1 s -1 . The influence of the hot deformation variables on flow stress as well as recrystallized grain size was investigated. The results showed that by decreasing temperature and increasing strain rate, flow stress increases while dynamically recrystallized grain size decreases. A power-law relation developed between the characteristic peak strain and Zener-Hollomon parameter and the exponent was determined as 0.17. Besides, the linear regression between the Zener-Hollomon parameter and dynamically recrystallized grain size developed another power law equation, with a stress exponent equivalent to -0.13.

Extensive studies have been conducted to develop high strength linepipes with higher deformability. One of the key technologies for improving deformability is dualphase microstructural control. Steel plate with ferritebainite microstructure can be obtained by applying thermo-mechanical controlled processing (TMCP), a process of controlled rolling and accelerated cooling. Low carbon, boron-free steels were used to enable the ferrite formation during cooling after controlled rolling, and accelerated cooling with an ultimate cooling rate enhanced the strength up to the X120 grade. HOP ® (Heat-treatment On-line Process) was also applied after accelerated cooling in order to improve the Charpy energy of the base material. Trial production of X120 high deformability linepipe was conducted by applying dual-phase microstructural control. Microstructural and mechanical properties of X120 linepipe are introduced in this paper.

The subject of the work is the analysis of thermomechanical bending process of a thin-walled tube made of X5CrNi18-10 stainless steel. The deformation is produced at elevated temperature generated with a laser beam in a specially designed experimental setup. The tube bending process consists of local heating of the tube by a moving laser beam and simultaneous kinematic enforcement of deformation with an actuator and a rotating bending arm. During experimental investigations, the resultant force of the actuator and temperature at the laser spot are recorded. In addition to experimental tests, the bending process of the tube was modelled using the finite element method in the ABAQUS program. For this purpose, the tube deformation process was divided into two sequentially coupled numerical simulations. The first one was the heat transfer analysis for a laser beam moving longitudinally over the tube surface. The second simulation described the process of mechanical bending with the time-varying temperature field obtained in the first simulation. The force and temperature recorded during experiments were used to verify the proposed numerical model. The final stress state and the deformation of the tube after the bending process were analyzed using the numerical solution. The results indicate that the proposed bending method can be successfully used in forming of the thin-walled profiles, in particular, when large bending angles and a small spring-back effect are of interest.

The microstructural characteristic evolution was investigated during thermomechanical processing of Ti-29Nb-9Ta-10Zr (wt %) alloy, which consisted of, in a first stage, in a Multi-Pass Rolling with increasing thickness reduction of 20%, 40%, 60%, 80%, and 90%; in step two, the multi-pass rolled sample with the highest thickness reduction (90%) was subjected to a series of three variants of static short recrystallization and then to a final similar aging. The objective was to evaluate the microstructural features evolution during thermomechanical processing (phase’s nature, morphology, dimensions, and crystallographic characteristics) and to find the optimal heat treatment variant for refinement of the alloy granulation until ultrafine/nanometric level for a promising combination of mechanical properties. The microstructural features were investigated by X-ray diffraction and SEM techniques through which the presence of two phases was recorded: the β-Ti phase and the α″-Ti martensiti...

The evolution of the microstructure and mechanical properties during equal channel angular pressing processing has been studied in an extruded Mg-Gd-Y-Zn alloy containing long-period stacking ordered phases. After extrusion, the microstructure is characterized by the presence of long-period stacking ordered fibers elongated along the extrusion direction within the magnesium matrix. The grain structure is a mixture of randomly oriented dynamic recrystallized and coarse highly oriented non-dynamic recrystallized grains. Rare-earth atoms are in solid solution after extrusion at 400 °C and precipitation takes place during the thermal treatment at 200 °C. Precipitation of β’ prismatic plates and lamellar γ’ in the basal plane increases the tensile yield stress from 325 to 409 MPa. During equal channel angular pressing processing at 300 °C, the volume fraction of dynamic recrystallized grains continuously increases with the strain introduced during the equal channel angular pressing proce...

The development of microstructure and mechanical properties was investigated in a heavily cold-rolled and annealed AlCoCrFeNi 2.1 high-entropy alloy. The as-cast alloy having a eutectic morphology consisting of alternate bands of ordered L1 2 and B2 phases was 90% cold-rolled. The deformed microstructure showed profuse shear banding and disordering of the L1 2 , but no transformation of the B2 phase. A duplex microstructure consisting of ultrafine equiaxed grains ( ∼ 0.60 μm) of disordered face centered cubic and B2 was observed after annealing at 800°C. The annealed material showed remarkable strength-ductility combination having ultimate tensile strength ∼ 1.2 GPa and elongation to failure ∼ 12%.

The aim of the research presented in the paper is to design the cooling routes after plastic deformation ensuring the multiphase structure with a high fraction of retained austenite on the basis of DCCT diagram for a new-developed Si-Al microalloyed TRIP steel. Design/methodology/approach: The CCT and DCCT diagrams were developed. Eight variants of the thermomechanical processing were designed on the basis of the DCCT diagram. The thermomechanical processing consisted of a multi-stage compression and various cooling strategies in the γ→α transformation range and isothermal holding temperature at a bainitic transformation region. Findings: The usefulness of DCCT diagram for designing the thermomechanical processing conditions for TRIP steels was demonstrated. The fraction of ferrite and retained austenite are highly dependent on a cooling path applied in the γ→α transformation region and a fraction of retained austenite especially on the isothermal holding temperature. The highest fraction of retained austenite as irregular grains located in a ferritic matrix and fine islands or interlath regions in bainitic regions were obtained at temperature of 400 and 450°C. To determine precisely a fraction of retained austenite, the X-ray investigations has to be applied additionally to the image analysis. Practical implications: The designed cooling conditions are of great importance for the thermomechanical strategy for manufacturing the advanced high strength TRIP steels. Originality/value: The thermomechanical processing was carried out for a new group of TRIP steels with Si partially replaced by Al and containing microadditions of Nb and Ti.

In Additive Manufacturing AM, each volume of material experiences a complex thermal history due to both short-range effects, from the repeated overlap of the thermal field from each heat source pass, and long-range variation in the thermal boundary conditions, related to the part geometry and build height. With an  +  alloy, like Ti64, this can lead to significant local variation in the transformation microstructure, which can contribute to heterogeneity in the mechanical properties of a component. In order to better understand the transformation microstructure variability in AM parts, an automated microstructure analysis tool has been developed, and tested against independently measured data, that can accurately map the inter-lamellar spacing of the  phase and spheroidicity of the  phase, at both high resolution and over large distances. The approach used was based on automated batch image analysis of thousands of image tiles obtained using a mapping function in a high-resolution SEM with a scanning stage. Within a practical operating range of drift in the microscope parameters (e.g. working distance, detector contrast) the errors in the measurements were found to be minimal (< 3%). Results are discussed from applying the method to two example case studies from different ends of the AM spectrum; selective Electron Beam Melting (EBM) and Wire-Arc Additive Manufactured (WAAM). In the former case this revealed considerable drift in the microstructure with build height and geometry, but little short-range variation, whereas with the WAAM process more severe short range microstructural gradients associated with HAZ banding were fully quantified.

As an implant material, Cu-bearing austenitic stainless steels can possess the antibacterial property, but their mechanical strength is low. In order to improve the yield strength of a 304Cu (17%Cr-7%Ni-3%Cu) alloy through substantial grain refinement, a research investigation has been taken up to conduct the reversion annealing treatment comprising a heavy (71%) cold rolling reduction followed by annealing at various temperatures (650-950 °C) and durations (1-5400 s). The microstructure evolution was examined by electron backscatter diffraction and further characterized by magnetic measurements, and mechanical properties were determined by tensile and hardness testing. The precipitation of Cu was confirmed by transmission electron microscopy. It was found that the reversion of deformation-induced martensite to austenite took place by the shear mechanism, followed by subgrain formation and continuous recrystallization resulting in quite non-uniform grain size distribution. The finest reversed grains were around 0.6 µm in size, but also much larger austenite grains and a small fraction of unreversed martensite existed in the final structure despite annealing at least up to 800 °C. Coherent Cu particles were observed after aging for 1.5 h at 700 and 650 °C, while the yield strength could be improved to 507 and 791 MPa, respectively, i.e. by ~2-3 times that of the annealed steel. The ductility of the steel remains still high, the fracture elongation being 36%.

We present a computational method for calculating the phase transformation start for arbitrary cooling paths and for different steel compositions after thermomechanical treatments. We apply the method to quantitatively estimate how much austenite deformation and how many different alloying elements affect the transformation start at different temperatures. The calculations are done for recrystallized steel as well as strain hardened steel, and the results are compared. The method is parameterized using continuous cooling transformation (CCT) data as an input, and it can be easily adapted for different thermomechanical treatments when corresponding CCT data is available. The analysis can also be used to obtain estimates for the range of values for parameters in more detailed microstructure models.

A computational model based on the Johnson-Mehl-Avrami-Kolmogorov equation for simulating the onset and kinetics of austenite to bainite and martensite transformation has been fitted to experimental continuous cooling data for two different steels. We investigated how deformation below recrystallization temperature affected the transformation onset and kinetics in comparison to the same steel in the undeformed state. The fitted model can be used to simulate phase transformations occurring when the steel is cooled along any cooling path. The model can be fully coupled to heat transfer and conduction simulations in order to optimize cooling practice, for example in industrial thermomechanical processing of steel. The fitted model can also be used to predict the hardness of the steel after cooling.

In this study, equiaxed microstructures with various grain sizes ranging from 6.0μm to 0.3μm and bimodal microstructures with grain sizes of primary α ranging from 5.0μm to 0.6μm were successfully fabricated by hot deformation and subsequent annealing in α+β two phase region in Ti-6Al-4V alloy having a martensite initial microstructure. The mechanical properties of both microstructures with different grain sizes were tested at room temperature. It was found that the strength (yield and tensile strength) of both microstructures increased with the decrease of the grain size. In the equiaxed microstructure, the uniform elongation gradually decreased with the decrease of the grain size, which was in consistent with the behavior of other metallic materials with ultrafine grains. However, in the bimodal microstructure, relatively large uniform elongation (~8%) was stably obtained regardless of the grain size. The unique and superior balance between strength and uniform elongation in bimodal microstructures was discussed, considering the contribution of interfaces between primary α grains (α p ) and transformed β areas (β trans ).

Multiple extrusion of Al-4Mg-1Zr (wt.%) is presented as a severe plastic deformation technique to develop an ultra-fine grained material, using rapidly solidified needles as a feedstock. After each extrusion pass the microstructure is refined, the primary Al 3 Zr precipitates are broken down and <50-nm-scale cubic Al 3 Zr are precipitated from solution. Recovery dominates the initial passes with recrystallisation becoming dominant during later passes, but the grains remain at the sub-m scale. Interestingly, the yield stress and the ultimate strength increased significantly after the first pass, and then decreasedany strength increment gained from the grain refinement was offset by coarsening of the metastable nano-scale Al 3 Zr dispersoids.

Depending on the nature of the loading during service, the level and nature of residual stress can contribute to the lower service-life of a component. In this study the internal level of the residual stress of a 6061 Al-Mg-Si alloy with different thermomechanical processes was evaluated by residual stress neutron diffraction (RSND). Commercial tempers such as T6 (peak aged) and O (annealed) were compared with the 6061 alloy after different steps of a thermomechanical processing used for the manufacturing of nuclear fuel plates, R3 and R9H60. The results showed that the lowest level of residual stress was found for the peak age, T6 condition. This was associated with the highest microhardness value (highest density of "β″ phase) and lowest grain size. The O temper was the only condition which showed compressive residual stress and the most coarsened precipitates. The nuclear thermomechanical processes, R3 and R9H60, resulted in increased level residual stress related to the T6 and showed a tensile nature in relation to its parent material (6061-O). Moreover, the RSND technique allows observing that the texture is also higher for the samples processed by the nuclear thermomechanical process due the hot rolling stage.

The development of high-performance ultraelastic metals with exceptional strength and large elastic strain limits is critical for a wide range of industrial applications, including actuators, medical devices, and high-precision instruments. In this study, a novel strategy is proposed to construct a dual-phase lamellar heterogeneous structure in a CoNiV medium-entropy alloy (MEA) by pre-introducing a precipitated phase prior to cold drawing. This structure, composed of elongated κ phases and an FCC matrix, enables an outstanding combination of an ultrahigh tensile strength (2.6 GPa) and an elastic strain limit of 1.5 %. The cold-drawing performance of the CoNiV MEA containing the brittle κ phase is significantly enhanced by the pronounced twinning-induced plasticity (TWIP) effect and the transformation-induced plasticity (TRIP) effect (κ → FCC). The dual-phase lamellar structure effectively disperses cracks and delays stress concentration, contributing to high crack tolerance. Meanwhile, the presence of high dislocation density, fine grain size, residual κ phases, and various nanoscale defects imparts the alloy with exceptional strength. This work innovatively addresses the general limitation of elastic strain in high-strength materials through multi-phase structural design, offering new theoretical insights and a design paradigm for the development of advanced metallic materials with superior strength and elastic deformability.

In the present work, the high-temperature phase stability and the correlated flow stress softening of Ti-6 %Al-2 % Sn-4 %Zr-2 %Mo alloy (Ti-6242) fabricated through the laser powder bed fusion process were studied. Toward this end, a set of hot compression tests were conducted at 700, 800, 900 and 1000 • C under the strain rate of 0.001s-1. A distinct observation was the occurrence of a significant strength drop and notable flow softening after reaching the maximum stress at all thermomechanical conditions. The peak stress was significantly dropped (~490 MPa) with increasing temperature from 700 • C to 800 • C, proposing activation of a new emerging softening mechanism. The α′ martensitic starting microstructure extensively started to decompose at around 800 • C, leading to the formation of α and β grains, where the β phase fraction was considerably increased by approaching the β transus temperature. The reverse transformation of the martensite served as an effective softening mechanism, owing to the fact that the α and β phases represent higher capability for strain accommodation. At 900 • C and 1000 • C, the penetration of β phases through the α lamellae and the occurrence of α-globularization was clearly evident, contributing to the flow softening at elevated temperatures. A preferred texture towards the <2-1-10> and <0001> orientations was also recognized in the microstructure deformed at 800 • C and 900 • C, which proposed the contribution of texture weakening as an additional factor in flow softening.

The mechanical characteristics of polycrystalline metallic materials are influenced significantly by various microstructural parameters, one of which is the grain size. Specifically, the strength and the toughness of polycrystalline metals exhibit enhancement as the grain size is reduced. Applying severe plastic deformations (SPDs) has a noticeable result in obtaining metallic materials with ultrafine-grained (UFG) microstructure. SPD, executed through conventional shaping methods like extrusion, plays a pivotal role in the evolution of the texture, which is closely related to the plastic behavior and ductility. A number of SPD processes have been developed to generate ultrafine-grained materials, each having a different shear deformation mechanism. Among these methods, linear twist extrusion (LTE) presents a non-uniform and non-monotonic form of severe plastic deformation, leading to significant shifts in the microstructure. Prior research demonstrates the capability of the LTE process to yield consistent, weak textures in pre-textured copper. However, limitations in production efficiency and the uneven distribution of grain refinement have curbed the widespread use of LTE in industrial settings. This has facilitated the development of an improved novel method, that surpasses the traditional approach, known as the nonlinear twist extrusion procedure (NLTE). The NLTE method innovatively adjusts the channel design of the mold within the twist section to mitigate strain reversal and the rotational movement of the workpiece, both of which have been identified as shortcomings of twist extrusion. Accurate anticipation of texture changes in SPD processes is essential for mold design and process parameter optimization. The performance of the proposed extrusion technique should still be studied. In this context, here, a single crystal (SC) of copper in billet form, passing through both LTE and NLTE, is analyzed, employing a rate-dependent crystal plasticity finite element (CPFE) framework. CPFE simulations were performed for both LTE and NLTE of SC copper specimens having <100> or <111> directions parallel to the extrusion direction initially. The texture evolution as well as the cross-sectional distribution of the stress and strain is studied in detail, and the performance of both processes is compared.

The duplex stainless steels are materials, which present a better combination of mechanical properties and stress corrosion resistance than ferritic and/or austenitic stainless steels. However, in the processing of these materials, hot working is a critical step that leads in many cases to the generation of cracks and/or to an unacceptable surface finish. In the present work, it has been observed that severe localisation of plastic flow into superficial shear bands is the responsible for transversal cracking during hot rolling of duplex stainless steels. Torsion is a deformation mode involving pure shear and it has been found to be very useful in tackling the problem of damage formation in these materials under hot working. The effects of the strain, temperature and the strain rate on the damage formation in duplex stainless steels have been analysed in order to improve the hot workab ility of this material. Microstructural observations reveal that cracks mainly concentrate at the f...

Very often Nb contributes to the strength of a microalloyed steel beyond the expected level due to the grain size strengthening resulting from thermomechanical processing. Two different mechanisms are behind this phenomenon, and both of them have to do with the amount of Nb remaining in the solution after hot rolling. The first of them is the increase of the hardenability of the steel due to Nb, and the second one is the fine precipitation of NbC in ferrite. The contribution of the precipitates to the work hardening of two thermally and thermomechanically processed microalloyed steels is addressed in this work and this contribution has been integrated into previously developed models by the authors for ferrite-pearlite microstructures. An L eff is considered through the effective spacing associated to the different obstacles and their interactions with the moving dislocations. The model obtained shows good agreement with the experimental tensile curves from the end of yield point elongation to the onset of necking.

A Nb microalloyed steel has been thermomechanically processed at laboratory through the use of plane strain compression sequences followed by simulated coiling. Tensile samples have been machined from the obtained specimens in order to investigate the effect of different variables: recrystallisation or accumulated strain before transformation, holding in austenite and coiling temperature on the final mechanical behaviour. Transmission electron microscopy observation of the precipitates has been carried out after coiling at different temperatures. It has been shown that when Nb remains in solution in austenite after hot deformation, it can precipitate in ferrite, leading to an important strengthening effect which is directly related to the concentration of Nb in solution before transformation and coiling temperature.

Multipass torsion tests were carried on with several V-microalloyed high carbon steels, using different deformation sequences in order to modify the austenite state prior to transformation. Both recrystallized and deformed austenite microstructures were studied. After deformation, different cooling rates were applied. The results show that accumulating strain in the austenite before transformation seems to slightly increase the interlamellar spacing for a given cooling rate, this increase being related to the pearlite transformation taking place at higher temperatures because of the increase in the austenite grain boundary area per unit volume (S V ). On the other hand, the retained strain significantly contributes to a refinement of the "ferrite units", this effect being more significant as vanadium and nitrogen contents rise. A relationship between the mean "ferrite unit" size with S V and cooling rate was determined. Similarly, empirical expressions to predict strength as a function of vanadium microalloying addition, S V and cooling rate were derived.

In the present study, we propose a hybrid manufacturing route to produce high-quality Ti6Al4V parts, combining additive powder laser directed energy deposition (L-DED) for manufacturing of preforms, with subsequent hot forging as a thermomechanical processing (TMP) step. After L-DED, the material was hot formed at two different temperatures (930 • C and 1070 • C) and subsequently heat-treated for stress relief annealing. Tensile tests were performed on small sub-samples, taking into account different sample orientations with respect to the L-DED build direction and resulting in very good tensile strengths and ductility properties, similar or superior to the forged material. The resulting microstructure consists of very fine grained, partially globularized alpha grains, with a mean diameter ~0.8-2.3 µm, within a beta phase matrix, constituting between 2 and 9% of the sample. After forging in the sub-beta transus temperature range, the typical L-DED microstructure was no longer discernible and the anisotropy in tensile properties, common in additive manufacturing (AM), was significantly reduced. However, forging in the super-beta transus temperature range resulted in remaining anisotropies in the mechanical properties as well as an inferior tensile strength and ductility of the material. It was shown, that by combining L-DED with thermomechanical processing in the sub-beta transus temperature range of Ti6Al4V, a suitable microstructure and desirable mechanical properties for many applications can be obtained, with the advantage of reducing the material waste.

The effects of thermomechanical treatment on the microstructure and mechanical properties of a newly developed β titanium alloy, i.e., Ti-28Nb-35.4Zr (wt%, hereafter denoted Ti-Nb-Zr) were investigated. The as-cast Ti-Nb-Zr alloy was subjected to solution treatment at 890°C for 1h, after which its thickness was reduced by 20%, 56%, 76%, and 86% via cold rolling. Results indicated that annealing at 890°C for 1h after cold rolling at a thickness reduction ratio of 86% resulted in a phase transformation from the stress-induced α&quot; and ω into β, leading to a recrystallization of a uniform single β phase. The recrystallized Ti-Nb-Zr alloy exhibited a tensile strength of 633MPa, Young&#39;s modulus of 63GPa, and elongation at rupture of 13%, respectively. The cold rolled specimens showed a higher Young&#39;s modulus than that of the recrystallized specimen due to the stress-induced ω phase. Transmission electron microscopy (TEM) analysis revealed that ω, α&quot; and β phases co-existe...

This study investigates the effects of thermo-mechanical processing parameters, specifically cold rolling and annealing, on the ultimate tensile strength (UTS) of AA2024 alloy, employing a Box-Behnken experimental design. The deformation during cold rolling, the annealing temperature, and the time annealing were varied to evaluate their individual and combined effects on the UTS. The results demonstrated that the UTS increased with deformation from 50% to 60%, but decreased with higher annealing temperatures (460°C-500°C) and extended annealing times (10 to 30 minutes. Among the parameters, annealing time exhibited the most significant influence on UTS, followed by deformation level and annealing temperature. The optimized parameters-60% deformation, 460°C annealing temperature, and 10 minutes time annealing-predicted a UTS of 628 MPa, with experimental verification confirming a 3% deviation. This research underscores the critical importance of controlling thermo-mechanical parameters to optimize the mechanical properties of AA2024 alloy, offering valuable insights for industrial applications.

The prediction of damage for each material during plastic deformation processes is crucial yet challenging due to the significant variability of prediction results according to ductile fracture criteria. This paper presents a solution for determining the critical damage values of AA1050-O aluminum alloy sheets as well as predicting workpiece damage in combined deep drawing processes using a combination of experiments and numerical simulations based on Freudenthal, Cockroft-Latham, and normalized Cockroft-Latham ductile fracture criteria. First, the depth of indent obtained from the Erichsen cupping test was applied to identify the critical values through numerical simulation using the Freudenthal, Cockroft-Latham, and normalized Cockroft-Latham ductile fracture criteria. Then, the critical values were used to predict the fracture for AA1050-O alloy sheets in the combined deep drawing processes. The prediction was validated through the execution of a combined deep drawing process experiment on AA1050-O alloy sheets employing a hydraulic press. The results demonstrated the superiority of the Cockroft-Latham criterion over other criteria in predicting both failure and non-failure occurrences in the combined deep drawing processes of AA1050-O alloy sheets, particularly in forecasting failure initiation, moment, and position. The combination of experiments and numerical simulations exhibited its potential to predict fracture criteria in other forming processes.

In this study, the effect of different microstructures resulting from thermochemical processes of X65 pipeline steel on mechanical properties of welding in the presence of hydrogen was investigated. According to studies conducted, due to the charge of hydrogen, the hardness of base metal (BM) increased by 10% , the hardness of heat affected zone (HAZ) samples increased by about 13% , the yield strength of base metal increased by an average of 5% and the yield strength of HAZ increased by about 7%, indicating hardening. Elongation was reduced by 32-70% and the percentage of ductile fracture decreased by an average 46% which shows that the fracture of samples in the presence of hydrogen is brittle. In the study of hydrogen defect and concentration of hydrogen permeated to the material it was determined that, the ferrite-pearlite banded microstructure of base metal has a higher hydrogen defect sensitivity than HAZ with an acicular ferrite microstructure and hard phase. In base metal samples under various rolling conditions, the two-pass rolled and the final rolling temperature of 800 °C sample (2BM800), with a smaller grain microstructure and higher interface, had the most diffusive hydrogen content and therefore had the highest hydrogen defects. In the case of HAZ samples, the effect of hydrogen on the increase in hardness and strength properties is greater than that of the base metal samples due to the different microstructure (of the acicular ferrite) and the variable grain size (i.e. the presence of two coarse-grained and fine grained areas). Overall, the results of this study showed that the microstructure has a significant effect on mechanical properties, the amount of diffusive hydrogen and hydrogen defects in welds.

Two as-cast low-density steels grades (austenite-based duplex Fe-30.9Mn-4.9Al-4.5Cr-0.4C and austenitic Fe-21.3Mn-7.6Al-4.3Cr-1C) with an initial dendritic microstructure were subjected to hot working conditions to understand the influence of deformation parameters on flow behavior and microstructural evolution. The alloys were produced using electric arc melting, and their phase constituents were determined using optical microscopy and X-ray diffraction analysis. This was then corroborated with the phase predicted from Thermo-Calc simulation. The as-cast alloys were machined to 10 × 10 × 7 mm specimen configurations for rectangular axial testing on the Gleeble 3500 thermomechanical simulator. The samples were deformed to a total strain of 0.5 at different deformation temperatures (800, 900, and 1000 °C) and strain rates (0.1 and 5 s−1). Thereafter, a hardness test was conducted on the deformed samples, and post-deformed microstructures were analyzed using optical and scanning elect...

In the present research, the AISI 321 austenitic stainless steel was subjected to cold rolling with different amount of reductions. The 80% cold rolled samples were then annealed in the temperature range of 700-900 °C with different durations. The microstructural evolutions during cold rolling and subsequent annealing were investigated by XRD analysis, optical and scanning electron microscopy, and feritscope analysis. The mechanical properties were evaluated by room temperature tensile testing. Results showed that the amount of strain induced martensite is increased with increasing the rolling reduction. Annealing at 700 °C for 2 min resulted in the simultaneous increase of tensile strength and elongation due to the formation of ultrafine grain austenite. By annealing at 900 °C for 5, . 10, and 15 min the bimodal grain structure was obtained as a result of the occurrence of static recrystallization and martensite to austenite reverse transformation simultaneously. Results of tensile testing showed that the good combination of strength and elongation is obtained by the formation of bimodal grain structure.

Grain refinement in a plain carbon steel under intercritical warm deformation was studied by torsion testing. Based on the experimental results. tbp warm flow behaviour and microstructural evolution of ferrite were researched with particular emphasis on the effect of the strain rate in controlling the grain refinement mechanism of ferrite. The deformed microstructures were investigated at various strain rates using optical microscopy and electron back-scattered diffraction (EBSD). The EBSD observations indicate that an increase in the strain rate leads to the development of new fine ferrite grains with high angle boundaries. Furthermore, it shows that the annihilation of dislocations occurs more readily at lower strain rate. The elongated ferrite grains continuously dynamically recrystallize to form the equiaxed fine ferrite grains. Thereby, the aspect ratio of elongated grains decreases with increasing the strain rate. Furthermore, the peak stress and steady state stress of ferrite both increase with increasing strain rate. Based on the study, the effect of strain rate on the development of fine ferrite grains during continuous dynamic recrystallization of ferrite was analyzed in detail.

A combination of extrusion and equal channel angular pressing ( E C A P ) was used to deform a plain low carbon steel. This process consists of two successive deformations by extrusion and ECAP in a single die ( Ex-ECAP). Cylindrical samples were heated to predefined temperatures (650 and 850 -C ) and then pressed through a die channel with crosshead speed of 10 m m / s . Microstructure and resultant mechanical properties of processed mate rial were studied. The results showed that pressing temperature has a significant effect on the resultant microstruc ture. While at 650 'C , the cold worked structure with elongated ferrite grains were obtained, and at 850 "C the mi crostructure consisted of elongated ferrite grains and very fine grains at their boundaries as a consequence of continu ous dynamic recrystallization (CDRX) of ferrite phase. Also at 850 *C , a particular microstructure consisted of cold worked ferrite and static recrystallized grains on shear bands was obtained.

Hot torsion testing was performed on a low carbon Nb-Ti microalloyed steel to study the effects of hot torsion parameters, strain and strain rate, on ultrafine ferrite grains production through dynamic strain-induced transformation, at a deformation temperature just above A,a. The initiation and evolution of ultrafine ferrite grains were studied. The results show that the amount of strain and strain rate has conversely effect on the volume fraction and grain size of ultrafine ferrite grains. With increasing strain, the interior of austenite grains become activated as nucleation sites for fine ferrite grains. As a result, ferrite grains continuously nucleate not only at the former austenite grain boundaries but also inside the austenite grains which leads to a rapid increase in volume fraction of ultrafine grains. Increasing of strain rate reduces the tendency of ferrite grains coarsening so that ultrafine ferrite grains are achieved, while the volume fraction of ultrafine grains decreases at the same strain level.

A boron treated copper bearing HSLA steel containing austenite formers like manganese and nickel, somewhat lower in amount than that in HSLA 100 variety of steel is chosen for the study. The role of thermomechanical processing on the microstructure and mechanical properties of the above steel has been investigated. Differential scanning calorimetric study is carried out for understanding the precipitation behaviour of copper in HSLA steel under the influence of boron. The microstructure of the experimental steel is found to consist of laths of martensites and bainite. MA constituents of ribbon like morphology are observed at the lath boundaries. Higher strength properties of the steel are attributed to the presence of finely distributed precipitates of copper and microalloy carbides.

High-entropy alloys (HEAs) have generated interest in recent years due to their unique positioning within the alloy world. By incorporating a number of elements in high proportion, usually of equal atomic percent, they have high configurational entropy, and thus, they hold the promise of interesting and useful properties such as enhanced strength and alloy stability. The present study investigates the mechanical behavior, fracture characteristics, and microstructure of two single-phase FCC HEAs CoCrFeNi and CoCrFeNiMn with some detailed attention given to melting, homogenization, and thermo-mechanical processing. Ingots approaching 8 kg in mass were made by vacuum induction melting to avoid the extrinsic factors inherent to small-scale laboratory button samples. A computationally based homogenization heat treatment was given to both alloys in order to eliminate any solidification segregation. The alloys were then fabricated in the usual way (forging, followed by hot rolling) with typical thermo-mechanical processing parameters employed. Transmission electron microscopy was subsequently used to assess the single-phase nature of the alloys prior to mechanical testing. Tensile specimens (ASTM E8) were prepared with tensile mechanical properties obtained from room temperature through 800 °C. Material from the gage section of selected tensile specimens was extracted to document room and elevated temperature deformation within the HEAs. Fracture surfaces were also examined to note fracture failure modes. The tensile behavior and selected tensile properties were compared with results in the literature for similar alloys.

In this work, the dynamic material modelling (DMM) is employed to identify the hot working window that is suitable for hot processing of Duplex stainless steel 2205 (DSS). The Gleeble 1500 thermo-mechanical simulator was used to conduct the investigation, where several hot compression tests were conducted at a temperature range of 850 -1050 °C and strain rates of 0.001s -1 -5s -1 . The obtained experimental data were first corrected for friction and adiabatic heating, the correction of adiabatic heating was only done for a strain rate of 1 and 5s -1 . After the corrections, the corrected flow stress curves were plotted, and the flow stress data at the strain of 0.1, 0.3, 0.5 and 0,8 were generated. Using the generated flow stress data at a particular strain and combination of temperature and strain rates, the strain rate sensitivity values were calculated using constitutive modelling. The DMM was then applied to calculate the efficiencies and instability values followed by using cubic spline interpolation for more detailed data. The processing maps were then constructed from the results of cubic spline interpolation. The processing maps indicated that, the hot working process of 2205 DSS is more efficient at low strain rates and high temperatures, particularly at true strains below 0.3. With increase in strain to 0.5 and above, high efficiency seemed to spread to the regions of high strain rates and moderate high temperatures.

The thermomechanical parameters have a great influence on the restoration processes of the steels and, consequently, on the grain size and morphology during and after deformation. At higher deformation temperatures the ferritic grain refinement may occur by dynamic recrystallization of austenite (DRX) and at lower temperatures, the operating mechanism might be dynamic strain-induced austenite-ferrite transformation (DSIT). In the present work, the effect of thermomechanical parameters on DSIT was investigated. In this study, after soaking at 1 200°C, the samples were cooled to 1 100°C submitted to hot torsion deformation to decrease the austenite grain size and then cooled to 900, 850 or 800°C for further hot torsion deformation, at strain rates of 1 s Ϫ1 and 5 s Ϫ1 and total strains of 1.5, 2.5 and 3.5. The steels were deformed by torsion in a 'Gleeble' thermomechanical simulator and water cooled immediately after deformation. In the steel without Nb, recrystallization occurred before enough deformation could be accumulated to induce ferrite formation, so DSIT would only occurred at the lowest temperature investigated, 800°C. In the Nb steel, Nb addition delayed austenite recrystallization allowing DSIT ferrite to form at higher temperatures than the steel without Nb, 850°C. The dynamic recrystallization of austenite at 850°C was retarded by the Nb addition thus allowing the occurrence of DSIT at this temperature. Variations in strain rate and amount of strain did not significantly change the dynamic mechanism of grain refinement, but did change the critical strain to start DRX and DSIT, as well as the fraction of the strain-induced transformed ferrite.

This paper shows the laboratory experiments made on several grade steels by applying some intercritical thermomechanical treatments; Two variants were used: "down-up" thermomechanical treatment with heating and rolling in the intercritical range and "up-down" thermomechanical treatment with preliminary complete austenitizing and rolling in the intercritic interval. Structural changes, as well as changes of properties revealed in the experimental variants of the intrercritical treatment, have been compared to those revealed by controlled rolling and normalization states of delivery that are recommended to flat products from these steel grades. High values of the strength characteristics and a good plasticity have been obtained. The paper presents only a part of the results obtained when applying different regimes of thermal and thermomechanical treatment within experimental researches made at laboratory and industrial scale, on thick plates of different thicknesses and qualities of the weldable steels.

The compressive strength and creep resistance of cast Mg-6Al-3Ba-3Ca (ABaX633) alloy has been measured in the temperature range of 25 to 250 • C, and compared with that of its predecessor ABaX422. The alloy is stronger and more creep-resistant than ABaX422, and exhibits only a small decrease of yield stress with temperature. The higher strength of ABaX633 is attributed to a larger volume fraction of intermetallic particles (Al, Mg) 2 Ca and Mg 21 Al 3 Ba 2 in its microstructure. Hot deformation mechanisms in ABaX633 have been characterized by developing a processing map in the temperature and strain rate ranges of 300 to 500 • C and 0.0003 to 10 s -1 . The processing map exhibits two workability domains in the temperature and strain rate ranges of: (1) 380 to 475 • C and 0.0003 to 0.003 s -1 , and (2) 480-500 • C and 0.003 to 0.5 s -1 . The apparent activation energy values estimated in the above two domains (204 and 216 kJ/mol) are higher than that for lattice self-diffusion of Mg, which is attributed to the large back-stress that is caused by the intermetallic particles. Optimum condition for bulk working is 500 • C and 0.01 s -1 at which hot workability will be maximum. Flow instability is exhibited at lower temperatures and higher strain rates, as well as at higher temperatures and higher strain rates. The predictions of the processing map on the workability domains, as well as the instability regimes are fully validated by the forging of a rib-web (cup) shaped component under optimized conditions.

In this research, a series of secondary warm rolling was performed under various process conditions in order to evaluate the influence of thermo-mechanical treatment on the interface microstructure and subsequent mechanical properties of roll-bonded STS/Al/Mg 3-ply laminates. The variation of interfacial microstructure was observed by scanning and transmission electron microscopes equipped with energy dispersive X-ray detector. Uniaxial tensile, hardness and drum peel tests were then carried out to clarify major mechanical properties of STS/Al/Mg clad sheets. We revealed that annealing for 60 min followed by secondary warm rolling at 300 ℃ under the reduction ratio of 20% could effectively improve the bonding strength at the Al/Mg joint and the tensile properties of roll-bonded STS/Al/Mg 3-ply laminates.

The microstructural origins of premature fatigue failures were investigated on a variety of forged components manufactured from AZ80 and ZK60 magnesium, both at the test specimen level and the full-scale component level. Both stress and strain-controlled approaches were used to characterize the macroscopically defect-free forged material behaviour as well as with varying levels of defect intensities. The effect of thermomechanical processing defects due to forging of a industrially relevant full-scale component were characterized and quantified using a variety of techniques. The fracture initiation and early crack growth behaviour was deterministically traced back to a combination of various effects having both geometric and microstructural origins, including poor fusion during forging, entrainment of contaminants sub-surface, as well as other inhomogeneities in the thermomechanical processing history.             At the test specimen level, the fracture behaviour under both stress ...

This paper presents the results on the influence of different thermo-mechanical processing (TMP) on the mechanical properties and electrochemical behavior of new metastable β-alloy Ti-20.6Nb-13.6Zr-0.5V (TNZV). TMP included hot working in below β-transus, solution heat treatments at same temperature in different cooling rates in addition to aging. Depending upon the TMP conditions, a wide range of microstructures with varying spatial distributions and morphologies of equiaxed/elongated α, β phases were attained, allowing for a wide range of mechanical and electrochemical properties to be achieved. The corrosion behavior of studied alloy was evaluated in Ringer's solution at 37 • C using open-circuit potential-time and potentiodynamic polarization measurements.

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This paper presents Digital Image Correlation (DIC) and Infrared Thermography (IRT) methods to investigate the thermomechanical behavior of an aluminum at the microstructural scale. Electron BackScattered Diffraction (EBSD) is used to characterize the microstructure of a 3 mm thick specimen with centimetric grain size. This study combines the following imaging techniques: DIC to obtain displacement and strain fields during the test, and IRT to estimate temperature and heat source fields induced by the mechanical loading. Ultimately, the aim of this methodology is to provide energy balance during mechanical test at the scale of the microstructure, in order to propose thermomechanical constitutive modelling of crystalline plasticity.