Institute for Materials Research

Strengthening by grain refinement and increasing dislocation density through highpressure torsion (HPT), which is an attractive technique to fabricate ultrafine grained and nanostructured metallic materials, is expected to provide β-type Ti-29Nb-13Ta-4.6Zr (TNTZ) higher mechanical strength while maintaining low Young's modulus because they keep the original β phase. However, the ductility shows reverse trend. Greater strength with enhanced ductility can be achieved by controlling precipitated phases through HPT processing after aging treatment. Aged TNTZ subjected to HPT processing at high N exhibits a homogeneous microstructure with ultrafine elongated grains having a high dislocation density and consequently non-equilibrium boundaries and distorted subgrains with non-uniform shapes and nanostructured intergranular precipitates of α phases. Therefore, the effect of HPT processing on the microstructure and mechanical hardness of TNTZ after aging treatment was systematically investigated in this study. TNTZ, which was subjected to aging treatment at 723 K for 259.2 ks in vacuum followed by water quenching, subjected to HPT processing at rotation numbers (N) of 1 to 20 under a pressure of around 1.25 GPa at room temperature. The microstructure of TNTZ AT consisted of precipitated needle-like α phases in β grains. However, TNTZ AHPT at N ≥ 10 comprises very fine α and small amount ω phases in ultrafine β grains. Furthermore, the hardness of every TNTZ AHPT was totally much greater than that of TNTZ AT . The hardness increased from the center to peripheral region of TNTZ AHPT . In addition, the tensile strength of every TNTZ AHPT was greater than that of TNTZ AT . The tensile strength of TNTZ AHPT increased, but the elongation decreased with increasing N and then both of them saturated at N ≥ 10.

The mechanical properties and microstructure of commercial Al-15Si-2.5Cu-0.5Mg (Alumix-231 ® ) alloy was subjected to extrusion (EXTR), hot extrusion into rods at 565 • C at an extrusion ratio of 4:1 and high-pressure torsion (HPT) processing, one of the most severe plastic deformation (SPD) techniques, with an anvil rotation speed of 0.5 rpm under a quasi-hydrostatic pressure of 5 GPa. Afterwards, the microstructures of specimens were systematically investigated using XRD, SEM, EBSD, and TEM. Also, tensile properties of Alumix-231 processed by EXTR and HPT were determined at room temperature. The HPT specimen shows refined microstructure (around average 165 nm) having more spherical and homogeneously distributed eutectic silicon second phases in Al metal matrix as compared to EXTR specimen. The hardness values are greater on the surface of the HPT specimen (239.1 Hv) as compared to that EXTR specimen (71.2 Hv) and increase with distance from the center of HPT specimen (198.3 Hv). Tensile strength and ductility of HPT specimen increased approximately 2 times than that of EXTR sample, respectively. The results indicate that the morphological changes in eutectic silicon especially after HPT play a critical role in enhancing or limiting the overall properties of the Alumix-231 material.

In order to improve the poor surface hardness and the wear resistance, titanium has been nitrided with plasma (ion) nitriding which is one of the methods to treat surface properties of titanium alloys. The increment at surface hardness and so the wear resistance of nitrided titanium alloys has been provided by means of compound layer (ε-Ti 2 N+δ-TiN) and diffusion zone (α-Ti) occurred by plasma ion nitriding. The goal of the present paper is to investigate effects of nitriding temperature and nitriding time on the microstructure and hardness value of nitrided surface layers. A systematic study was undertaken with specimens of commercial pure Ti and Ti-6Al-4V alloy. As treatment parameters, we have used; nitriding time (from 2 to 9 hour), nitriding atmosphere (H 2 -80%N 2 ), total pressure (1 kPa) and cathode temperature (from 600 to 800 o C). The Vickers indenter was used for analysis of the micro hardness measurements. The thin hardened layer at the nitrided surface was characterized by glancing-angle X-ray difractometer. X-ray diffraction analysis has confirmed the formation of ε-Ti 2 N and δ-TiN phases on the nitrided specimens. Experimental details and characterization of plasma (ion) nitrided titanium have reported and discussed.

h i g h l i g h t s " Both polymeric support and extractant of SIR enhanced its adsorption capacity for chromium (VI). " Adsorption of chromium on SIR followed Freundlich isotherm and Thomas model. " Chromium from chromium-loaded SIR was eluted effectively by 0.1 M NaOH solution. " The SIR can be used for adsorption of chromium at least in three cycles.

Huge amounts of effluent of low copper content are generated in electrical and electronic parts manufacturing industries. Here we report an adsorption process using strongly acidic exchanger Dowex G-26 for copper recovery from dilute sulfate solution containing 0.5-0.7 g/L copper, which is similar to the chemical and mechanical polishing (CMP) waste generated in electronic industries. The structures of activated and copper-loaded resins were compared by FT-IR spectroscopic characterization to confirm the adsorption phenomena. Various process parameters viz. contact time, solution pH, resin dose were investigated for copper recovery from the waste effluent. Copper adsorption from the solution was complete within a contact time of 14 min for an aqueous/resin (A/R) ratio of 100 mL/g and equilibrium pH of 2.5. The mechanism for copper adsorption by Dowex G-26 resin was found to follow a Langmuir isotherm and second-order reaction rate. 99.7% of the copper was eluted effectively from the loaded resin by 10% sulfuric acid at an A/R ratio of 25 in a contact time of 20 min to produce a copper-enriched solution. After copper recovery, the raffinate generated could be disposed safely without affecting the environment.

Crystallographic features of needle-or lath-shaped phases generated from solid-state phase transformations can often be explained from the invariant line concept. This paper presents analytical expressions of crystallographic features, including the orientation relationship, the habit plane orientation and dislocation configuration in the habit plane, based on derivations in both reciprocal and direct spaces in two dimensions (2D). Examples are given by applications to face-centered cubic (fcc)/body-centered cubic (bcc) and bcc/hexagonal closepacked hcp systems, with results which are functions of lattice parameters. These results are consistent with available results from previous studies. Compared to the existing (2D) models for similar conditions, the present approach has overcome the limitation that the invariant line must lie in 2D space and provides a description of the dislocation configuration that was not available in other 2D models. Compared with the three dimensional (3D) O-line approach, the present approach is more transparent and simpler when a 2D treatment is allowed. Crown

Interfacial structures are the key features for understanding the crystallography and dynamics of a phase transformation. A general condition of the habit plane (HP) of martensite is that the misfit in the HP can be accommodated by a single set of defects. Based on this condition, HP orientations can be analytically expressed according to a simple vector analysis in either direct or reciprocal space. Generally, the possible HP normal is located on an elliptic cone. The application of present approach to FCC/BCC and HCP/BCC systems shows full consistency with previous work and it is easy to apply.

ABSTRACT This article presents a model of a secondary coincidence site lattice (CSLΙΙ). It is applied to interpret a truncated triangular morphology of β-Mg2Sn precipitates in an Mg-Sn-based alloy. With a slight long-range strain being accommodated elastically, the distribution of good matching sites (GMS) on interfaces between the β-Mg2Sn precipitates and α-Mg matrix exhibits double periodicity. One is within GMS clusters, and the other is carried by the constrained-CSLΙΙ (CCSLΙΙ) points at the centers of the GMS clusters. The calculated results fully agree with the experimental results, including the irrational orientation relationship, the habit plane, and the irrational side facets. The preferred state of the interfaces, the preferred ledge height, and the preferred Burgers vectors of secondary dislocations have been discussed.

ABSTRACT This paper presents the progress in phase transformation crystallography of the fcc/bcc system based on the O-line model. In contrast to previous numerical methods, closed-form expressions have been derived to describe the orientation relationship (OR), habit plane (HP) normal, dislocation direction and spacing as functions of the lattice parameter ratio (λ) and the angle between the Burgers vectors of the dislocations. Possible directions of the dislocation and the HP normal are presented as elliptical curves in stereographic projections and explicit expressions for the curves are provided. In the 3-D space defined by the OR, the O-line criterion only restricts two degrees of freedom in the OR, while various constraints have been applied to the remaining degree of freedom. A comparison of the calculations with those from existing models indicates the general applicability of the method. Furthermore, the property that the HP normal lays on the surface of an elliptic cone can be readily extended to other systems.

ABSTRACT A simple 2-D analytical method has been developed for calculating the crystallographic features, including the orientation relationship (OR), habit plane (HP) and the direction and spacing of dislocations in the HP, under the condition that a pair of Burgers vectors from both phases are parallel to each other lying in the HP. In contrast to previous 2-D models for the OR and HP, which are on the plane normal to the parallel Burgers vectors, the present 2-D model is based on vector analysis in the HP. Closed-form expressions for the crystallographic features have been derived as functions of lattice parameter ratios. While the results are in agreement with those from a 2-D method based on the O-line model, the present method is simpler and improves our understanding of crystallographic features.

ABSTRACT The O-line model is usually applied to precipitation crystallography. Its application to investigation of martensite crystallography has received little attention. In this paper, the relationship between O-line model and the prism matching model for martensite crystallography is established. The formulas in the O-line model are applicable to martensite crystallography. Analytical solution of the habit plane corresponding to the minimum shape strain has been derived. A calculation example of {3 10 15}f martensite in a ferrous alloy is provided. While the results are in agreement with the former models for martensite crystallography, the advantage of O-line model is that it offers analytical solutions, facilitating further systematic investigations.

The displacements of vectors in a habit plane (HP) are assumed to lie along a particular Burgers vector, so that the misfit in the interface can be fully accommodated by a set of dislocations with that Burgers vector. This assumption is consistent with many models and experimental observations. Based on this assumption, a simple method based on vector analysis has been developed. By applying this method to fcc/bcc system, the classical solutions from the phenomenal theory of martensite crystallography can be reproduced. In addition, a simple form of equation for general HP orientations satisfying the above assumption has also been derived. The present method provides a simple but general tool for analysis of irrational HP generated from either martensitic or diffusional transformations.

Lath martensite with a dislocation substructure is one of the most common forms of martensite in structural steels. Surface relief has been regarded as an important characteristic in the martensitic transformation. Crystallographic features on surface relief are essential to get into deep insight of the long range strain field in the transformation, and explore the mechanism of the phase transformation. However, very limited experimental data on the shape strain associated with the formation of surface relief caused by the lath martensite have been reported so far, especially for the quantitative study of the displacement vector. The present investigation was carried out to study the shape deformation in the formation of the lath martensite on the austenite matrix in an Fe–20.2Ni–5.5Mn (mass fraction, %) alloy. The shape strain accompanying surface relief, such as the magnitude and direction of the displacement vector, has been concerned in a quantitative way. The morphology of the ...

The preference of the habit planes (HPs) developed from precipitation in the fcc/bcc system has been investigated. The interfacial energy of different interface orientations has been examined with variation of the orientation relationships (OR) and lattice parameters by a classical molecular dynamics method. The results show that interface has the lowest interfacial energy when it contains parallel Burgers vectors and a set of dislocations. The local minimum of interfacial energy may not associated with a maximum of dislocation spacing. It is also found that the near Kurdjumov-Sachs OR is more preferable than the near Nishiyama-Wasserman OR. Contrary to the previous interfacial energy calculations, which usually limit to rational ORs, the present work allows ORs to be irrational, which agrees with the observations.

According to the structural ledge model, the irrational habit planes (interfaces with structural ledges) of precipitates are more energetically preferred than those atomic flat ones, e.g. the {111}f//{110}b interface in an fcc/bcc system. In this paper, based on atomistic calculation, we show that the well-known example of ledged interface {335}f in an fcc/bcc system with the Nishiyama-Wasserman orientation relationship has a higher energy than the interface parallel to {111}f//{110}b. The reason why this ledged interface has a higher energy is discussed in detail.

Thermal conductivity of Ni 3 Ga-X ternary alloys was comprehensively surveyed for 16 kinds of ternary elements X. The direction of ridge in thermal conductivity contours in g H single phase ®eld agrees with that of solubility lobe of g H phase in a ternary phase diagram. The ridge direction is determined by the sublattice occupation of a ternary element. #

A preliminary study of the mechanical properties of Rh-based L1 2 intermetallic compounds Rh 3 Ti, Rh 3 Nb and Rh 3 Ta is carried out by micro-vickers hardness tests at room temperature and compression tests at various temperatures ranging from room temperature to 1673 K. A cold-rolling test is also conducted on a Rh 3 Ti plate. Although high temperature ductility-loss is observed in all compounds, Rh 3 Ti shows good ductility at all temperatures investigated. Both Rh 3 Nb and Rh 3 Ta show a weak positive temperature dependence of strength (stress anomaly) at around 1273 K which is about half the melting point for both intermetallic compounds. The stress anomaly is discussed in terms of a phase stability concept based on the Kear±Wilsdorf (K±W) mechanism. High work hardening rates of Rh 3 Nb and Rh 3 Ta, which cause high vickers hardness at room temperature, are also attributed to the K±W mechanism. #

The evolution of L1 2 -long-range order in Cu 3 Au was studied as a function of temperature by means of residual resistivity measurement. Kinetics as well as temperature dependence of equilibrium values of the LRO-parameter were studied during isothermal annealing and the LRO-equilibrium values obtained were compared with model calculations and X-ray diraction measurements. Comparing the analyses of order-order relaxations with those of disorder±order relaxations, information is gained on the growth kinetics of ordered antiphase domains. #

For explaining asymmetry in the flow stress of Ni 3 Al alloy as a function of aluminum content, the structural energy of ordered NiAl alloy with the L1 0 structure is obtained with the electronic structure calculations based on the density functional theory. Quite a large distortion in the c-direction is found at the equilibrium, which means an L1 0 -like local structure appearing in the Al-rich region of the Ni 3 Al phase undergoes a large tetragonal strain. This tetragonal strain will give an explanation for the strengthening mechanism using the framework of Cochardt et al. The effect of the Al concentration on the structural stability of L1 0 in terms of the DOS is also discussed to explain the concentration dependence of the B2-L1 0 martensitic transition temperature. q

Ternary addition generally degrades an excellent conduction properties of NiAl. The contour map of thermal conductivity in NiAl±X b single phase ®eld is drawn for the ternary elements X=Ti, Cu and Ge. It is revealed that each element has a characteristic ridge direction in the contour map. This feature is discussed based on the preference substitutional site of a ternary element, and eighteen ternary elements with a sucient solubility into NiAl are classi®ed into three groups according to the ridge direction. Thermal conductivity of NiAl-based alloys increases with increasing temperature, however the ridge direction in the contour map remains unchanged. #