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Ming Jen Tan

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Papers by Ming Jen Tan

Fabricating Protruded Micro-Features On Aa6061 Substrates By Hot Embossing Method

Metallic micro parts are playing an important role in micro-fabrication industry. Recently, we ha... more Metallic micro parts are playing an important role in micro-fabrication industry. Recently, we have demonstrated a new deformation mechanism for micro-formability of polycrystalline materials. Different depressed micro-features smaller than the grain size have been successfully fabricated on 6061 aluminum alloy (AA6061) substrates with good fidelity. To further verify this proposed deformation mechanism that grain size is not a limiting factor, we demonstrate here that in addition of depressed features, protruded micro-features on a polycrystalline substrate can similarly be fabricated.

$Research paper thumbnail of Evaluation of Residual Stress by X-Ray Diffraction and Correlative Stress Modelling$

Evaluation of Residual Stress by X-Ray Diffraction and Correlative Stress Modelling

Residual Stresses 2016, Dec 22, 2016

Residual stress is an unavoidable problem which occurs during any manufacturing process or during... more Residual stress is an unavoidable problem which occurs during any manufacturing process or during repair when it is unwanted or uncontrolled, and becomes a limitation to the service life of a component. Welding is one of the common repair methods used on gas turbine engine components that develops high residual stress, and uncontrolled residual stress may appear in several manufacturing processes which involves uneven distribution of heat, mainly in a localised manner (i.e. at the cutting/welding tip/zone). This study is mainly focused on the estimation of the surface residual stress after welding on aerospace material; here X-Ray diffraction (XRD) is used for analysis since it is an accurate NDT method used for measuring residual stress. X-ray diffraction is made a semi-destructive method by removing material using electropolishing to micron level for analysis of sub-surface stresses, as X-ray diffraction method has low penetration depth. Residual stress measurement is carried out at surface level and correlated with numerical simulation of residual stress due to welding.

Approaching high-performance of ordered structure Sb2Te3 film via unique angular intraplanar grain boundaries

Scientific Reports, 2020

In this paper, we present an innovative electric-field-assisted magnetron-sputtering deposition m... more In this paper, we present an innovative electric-field-assisted magnetron-sputtering deposition method for films preparation. By grain boundary-engineering, we successeful obtained the ordered Sb2Te3 film with greatly high figure of merit via controlling external electric field. It has been found that the electric field can induce the change in the angle of intraplanar grain boundaries between (0 1 5) and (0 1 5) planes, which leads to the enhanced holes mobility and maintained low thermal conductivity. The energy filtering takes place at the angular intraplanar grain boundaries. At room temperature, a high ZT value of 1.75 can be achieved in the deposited Sb2Te3 film under 30 V external electric field. This is a very promising approach that the electric field induced deposition can develop high-performance Sb2Te3-based thermoelectric films.

The bonding time effects on the transient liquid phase bonding of Inconel 718 using nickel-based sintered brazing preform

Applied Surface Science, 2019

Tilt-structure and high-performance of hierarchical Bi1.5Sb0.5Te3 nanopillar arrays

Scientific Reports, 2018

The uniquely tilted nanopillar array favorably influence carrier and phonon transport properties.... more The uniquely tilted nanopillar array favorably influence carrier and phonon transport properties. We present an innovative interfacial design concept and a novel tilt-structure of hierarchical Bi1.5Sb0.5Te3 nanopillar array comprising unique interfaces from nano-scaled open gaps to coherent grain boundaries, and tilted nanopillars assembled by high-quality nanowires with well oriented growth, utilizing a simple vacuum thermal evaporation technique. The unusual structure Bi1.5Sb0.5Te3 nanopillar array with a tilt angle of 45° exhibits a high thermoelectric performance ZT = 1.61 at room temperature. The relatively high ZT value in contrast to that of previously reported Bi1.5Sb0.5Te3 materials and the Bi1.5Sb0.5Te3 nanopillar array with a tilt angle of 60° or 90° evidently reveals the crucial role of the unique interface and tilt-structure in favorably influencing carrier and phonon transport properties, resulting in a significantly improved ZT value. This method opens a new approach ...

Time gap effect on bond strength of 3D-printed concrete

Virtual and Physical Prototyping, 2018

An advancing technology that combines the concrete extrusion with a motion control to create stru... more An advancing technology that combines the concrete extrusion with a motion control to create structures with complex geometrical shapes without the need for formwork is known as 3D concrete printing. Since this technique prints layer by layer, the time taken to reach the same position in the subsequent layer is important as it will create an anisotropic property that has a weaker tensile strength at the bond interface of the two printed filaments. Through rheological measurement, which reveals the material deformation and flow behaviour, it is possible to examine the material structural build-up due to time-gap effect by measuring at different time delay. This paper focuses on investigating the time-gap effect on the printed filament with rheological and observation at macroscopic-scale to understand the material behaviour of the initial and subsequent printed layer during its fresh phase. Rheological experiment findings reveal that the tensile strength of the printed specimen is correlated to the material modulus at the initial layer.

Fresh and hardened properties of 3D printable cementitious materials for building and construction

Archives of Civil and Mechanical Engineering, 2018

The main advantage of 3D concrete printing (3DCP) is that it can manufacture complex, non-standar... more The main advantage of 3D concrete printing (3DCP) is that it can manufacture complex, non-standard geometries and details rapidly using a printer integrated with a pump, hosepipe and nozzle. Sufficient speed is required for efficient and fast construction. The selected printing speed is a function of the size and geometrical complexity of the element to be printed, linked to the pump speed and quality of the extruded concrete material. Since the printing process requires a continuous, high degree of control of the material during printing, high performance building materials are preferred. Also, as no supporting formwork is used for 3DCP, traditional concrete cannot be directly used. From the above discussion, it is postulated that in 3DCP, the fresh properties of the material, printing direction and printing time may have significant effect on the overall load bearing capacity of the printed objects. The layered concrete may create weak joints in the specimens and reduce the load bearing capacity under compressive, tensile and flexural action that requires stress transfer across or along these joints. In this research, the 3D printed specimens are collected in different orientations from large 3DCP objects and tested for mechanical properties. For the materials tested, it is found that the mechanical properties such as compressive and flexural strength of 3D printed specimen are governed by its printing directions.

Measurement of tensile bond strength of 3D printed geopolymer mortar

Measurement, 2018

The structural capacity of construction joints in concrete bridges, deck and pavements mainly dep... more The structural capacity of construction joints in concrete bridges, deck and pavements mainly depends on the bond strength between the old substrate and new overlaid concrete. Sometimes, a mismatch in the properties of old and new concrete may lead to early age failure and shortened service life. Since in 3D concrete printing (3DCP), the whole object is made by layer by layer, bond strength is considered as one of the key parameters to ensure stability in the structure. For understanding bond mechanism, it is essential to measure bond strength at the interface between new and old layer and investigate significant parameters affecting this property. In this direction, our current work targets to analyse tensile bond strength of 3D printed geopolymer mortar with respect to printing time gap between layers, nozzle speed and nozzle standoff distance. A novel formulation of fly ash based geopolymer was made and printed using four-axis automated gantry system. Experimental findings reveal that the bond strength is a function of state of interface material between two nearby layers which can be influenced by material strength development rate and 3D printing parameters.

Microstructure versus substructure size effect

AIP Conference Proceedings, 2016

In metal deformation, size effect is generally attributed to the interactive effect of grain size... more In metal deformation, size effect is generally attributed to the interactive effect of grain size and specimen dimension. This work shows, however, that relative substructure dimensions should also be considered. Micro-compression tests on the micro-pins having different grain sizes revealed no significant size effect with respect to the mechanical behavior, even if the number of grains over the diameter of the micro-pins falls below its critical value. To justify the reason laying under this fact, a recovery annealing cycle was applied on the micro-pins to change the substructure properties without altering the mean grain size. A surprising drop in the flow stress of the recovery-annealed micro-pins implied the importance of considering subgrain size rather than grain size over the diameter of component for the size effect investigation.

Effect of Nano-Particle Addition on Grain Structure Evolution of Friction Stir-Processed Al 6061 During Postweld Annealing

JOM, 2016

The fabrication of nano-composites is quite challenging because uniform dispersion of nano-sized ... more The fabrication of nano-composites is quite challenging because uniform dispersion of nano-sized reinforcements in metallic substrate is difficult to achieve using powder metallurgy or liquid processing methods. In the present study, Al-based nano-composites reinforced with Al 2 O 3 particles have been successfully fabricated using friction stir processing. The effects of nano-Al 2 O 3 particle addition on grain structure evolution of friction stir processed Al matrix during post-weld annealing were investigated. It was revealed that the pinning effect of Al 2 O 3 particles retarded grain growth and completely prevented abnormal grain growth during post weld annealing at 470 °C. However, abnormal grain growth can still occur when the composite material was annealed at 530 °C. The mechanism involved in the grain structure evolution and the effect of nano-sized particle addition on the mechanical properties was discussed therein.

Enabling Wider Use of Magnesium Alloys for Lightweight Applications by Improving the Formability by Groove Pressing

Procedia CIRP, 2015

In the last decade or so, severe plastic deformation (SPD) has been shown to be an effective mean... more In the last decade or so, severe plastic deformation (SPD) has been shown to be an effective means for the production of fine grained microstructure in magnesium alloys at relatively low temperatures while altering the material texture to improve its formability. SPD of sheet geometry is particularly attractive in order to encourage wider use of magnesium alloys for lightweight applications. In this study, the microstructure evolution of magnesium alloy AZ31 sheet in the groove pressing process was examined at different processing conditions. The average grain size of the material was reduced from 13.3 μm to 1.9 μm after 4 cycles of deformation under the condition of progressive decreasing temperature and specimen rotation between cycles. The final microstructure was observed to be homogenous in both the transverse and rolling directions consisting of fine grains of 0.6-1 μm and a small fraction of coarser grains of 3-5 μm. The average hardness of the material was increased from 62 to 91 Hv with a uniform distribution along the thickness direction. This study has demonstrated that groove pressing is a highly effective method for production of fine grained microstructures in magnesium sheet using the technique of progressive decreasing temperature while alternate specimen rotation is necessary to prevent premature failure of the material.

Superplasticity in CP-Titanium Alloys

Materials Science Forum, 2007

In this work, studies were carried out to investigate the superplasticity of a commercially pure ... more In this work, studies were carried out to investigate the superplasticity of a commercially pure (CP) titanium alloy during high temperature deformation. Uniaxial tensile tests were carried out at 600, 750 and 800°C with an initial strain rate from 10-1s-1 to 10-4s-1. It was found that the alloy do not show good superplasticity due fast grain growth at high temperature and cavity. The effects of temperature on the grain growth and cavity phenomena as well as the dynamic recrystallization of the alloy were studied and a ‘two-step-method’ was introduced to increase the superplasticity of the alloy.

Effect of cold-work on the Hall–Petch breakdown in copper based micro-components

Mechanics of Materials, 2015

Effect of cold-work on the Hall-Petch breakdown in copper based micro-components.

Enhanced superplasticity in commercially pure titanium alloy

The superplasticity of commercially pure titanium alloy at high temperature was studied and the d... more The superplasticity of commercially pure titanium alloy at high temperature was studied and the dynamic recrystallization phenomenon of the alloy was investigated by using electron back scattered diffraction. A two-step deformation method was used to increase the ductility of the alloy from 188% to 243%.

Investigation of Microstructure and Hardness in Microfoming of Pure Copper Pins

KEM, 2010

ABSTRACT Microforming is defined as the process of production of metallic micro-parts with sub-mi... more ABSTRACT Microforming is defined as the process of production of metallic micro-parts with sub-millimeter dimension. There is as strong interaction between the scale of the microstructure and the size of the part affecting material flow, the so-called &quot;size effect&quot; in microforming processes. Conventional forming rules cannot be directly applied to the micro-scale forming. To better understand the implications for part geometry and properties, further investigation of the material flow related events is necessary. The aim of this work is to investigate microstructural evolution of pure copper during a micro-extrusion process - for production of micro-pins with diameters varying from 300 to 800 mu m - by means of optical microscope (OM). Qualitative strain gradient distribution could be observed by those pictures. The results showed that change of micro-pins diameter and die angle affect the microstructure and strain distribution of the final product remarkably, that affect the mechanical properties of the pin formed. Furthermore, microhardness results were consistent with the microstructural observations.

Microstructure Evolution of Ti-6Al-4V during Superplastic-like Forming

Procedia Engineering, 2014

Superplastic-like forming is a recent developed sheet-forming process that combines hot drawing (... more Superplastic-like forming is a recent developed sheet-forming process that combines hot drawing (mechanical pre-forming) with gas forming. It is an efficient way to form sheet metals into complex parts for automotive and aerospace industries. In comparison with conventional superplastic forming process, the forming time for superplastic-like forming can be significantly shortened as the hot-drawing step would have produced a pre-formed component before gas forming. The other advantage of the superplastic-like forming is its capacity for lower temperature forming, for which superplasticity is not possible. Nonsuperplastic grade Ti-6Al-4V sheets were successfully formed by superplastic-like forming at 800 °C in 16 min. The maximum percentage thinning of 54 % occurred at the outward corners. In this paper, electron backscatter diffraction (EBSD) was used to examine the microstructure evolution of Ti-6Al-4V at different forming stages during superplastic-like forming process. Some small equiaxed grains, regarded as newly recrystallized grains, were observed near the deformed area after hot drawing. Grains became more randomly distributed as the recrystallization continued during gas forming stage. The as-received structures were finally replaced by the equiaxed grains with an almost random misorientation distribution after the forming process. Dynamic recrystallization was considered as the main deformation mechanism for the non-superplastic grade Ti-6Al-4V alloy.

Grain size and workpiece dimension effects on material flow in an open-die micro-forging/extrusion process

Materials Science and Engineering: A, 2013

B.V. It incorporates referee's comments but changes resulting from the publishing process, such a... more

Re-examination of “missing strain” during superplastic deformation of AA7475

Materials Science and Engineering: A, 2004

Missing strain", a discrepancy between the total macroscopic strain and the strain contributed by... more Missing strain", a discrepancy between the total macroscopic strain and the strain contributed by grain boundary sliding (GBS) during superplastic deformation, appears to exist in previous investigations. In this work, the contribution of GBS (ξ GBS ) and intragranular strain (ξ IG ) were simultaneously measured using scratch test conducted on AA7475 samples after deformation at 500 • C at initial strain rate of 10 -3 s -1 . The result shows that the missing strain results most probably from the neglect of the intragranular strain as well as the anisotropic GBS-induced underestimation of ξ GBS . The calculation of ξ GBS was re-examined, based on the fact that anisotropic shrinkage of samples along width and thickness during superplastic deformation was noted.

Microstructure Evolution During High-Temperature Deformation of 8090 Al-Li Alloy

Materials and Manufacturing Processes, 2004

ABSTRACT

Finite Element Modeling of Superplastic Sheet Metal Forming for Cavity Sensitive Materials

Journal of Engineering Materials and Technology, 2003

In this paper, a constitutive equation for superplasticity, which is based on the microstructural... more In this paper, a constitutive equation for superplasticity, which is based on the microstructural mechanism of superplastic deformation taking into account the effects of deformation damage, is incorporated into the finite element method to simulate the superplastic forming process. The effects of strain rate sensitivity, cavity growth and imposed hydrostatic pressure on the strain limit are studied. The predicted results are validated through the comparison with the existing experimental data. It is found that the present model produces accurate results in all cases.