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Wei Quan Toh

Bio: Wei Quan Toh is an academic researcher from Nanyang Technological University. The author has contributed to research in topics: Diamond-like carbon & Cavity magnetron. The author has an hindex of 6, co-authored 10 publications receiving 316 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors report α' martensitic transformation and α/β interface evolution in varied printing thicknesses of EBM-printed Ti-6Al-4V block samples by means of atom probe tomography.
Abstract: As an important metal three-dimensional printing technology, electron beam melting (EBM) is gaining increasing attention due to its huge potential applications in aerospace and biomedical fields. EBM processing of Ti-6Al-4V as well as its microstructure and mechanical properties were extensively investigated. However, it is still lack of quantitative studies regarding its microstructural evolution, indicative of EBM thermal process. Here, we report α' martensitic transformation and α/β interface evolution in varied printing thicknesses of EBM-printed Ti-6Al-4V block samples by means of atom probe tomography. Quantitative chemical composition analysis suggests a general phase transformation sequence. By increasing in-fill hatched thickness, elemental partitioning ratios arise and β volume fraction is increased. Furthermore, we observe kinetic vanadium segregation and aluminum depletion at interface front and the resultant α/β interface widening phenomenon. It may give rise to an increased α/β lattice mismatch and weakened α/β interfaces, which could account for the degraded strength as printing thickness increases.

168 citations

Journal ArticleDOI
TL;DR: In this paper, the physical, mechanical and tribological properties of various surface coatings and their impact on the replication efficiency and lifetime of micro/nano-molds that are used in micro-nano hot-embossing and injection molding processes are discussed.
Abstract: Micro/nano hot-embossing and injection molding are two promising manufacturing processes for the mass production of workpieces bearing micro/nanoscale features. However, both the workpiece and micro/nano-mold are susceptive to structural damage due to high thermal stress, adhesion and friction, which occur at the interface between the workpiece and the mold during these processes. Hence, major constraints of micro/nano-molds are mainly attributed to improper replication and their inability to withstand a prolonged sliding surface contact because of high sidewall friction and/or high adhesion. Consequently, there is a need for proper surface coating as it can improve the surface properties of micro/nano-molds such as having a low friction coefficient, low adhesion and low wear rate. This review deals with the physical, mechanical and tribological properties of various surface coatings and their impact on the replication efficiency and lifetime of micro/nano-molds that are used in micro/nano hot-embossing and injection molding processes.

65 citations

Journal ArticleDOI
TL;DR: In this article, columnar carbide chains or clusters consisting of nanometer-sized, cuboidal particles are precipitated coherently with surrounding γ Co phase within interdendritic regions.

53 citations

Journal ArticleDOI
TL;DR: In this paper, CoCrMo and Ti6Al4V coatings were deposited on 6061-T651 aluminum alloy substrates via a high pressure cold spray process, and they were systematically investigated.
Abstract: In this study, CoCrMo and Ti6Al4V coatings were deposited on 6061-T651 aluminum alloy substrates via a high pressure cold spray process. Adhesion, tribological and corrosion properties of the CoCrMo and Ti6Al4V coatings were systematically investigated. The CoCrMo and Ti6Al4V coatings had good quality with low porosity levels and high hardnesses. X-ray diffraction patterns showed that there were no phase change and oxidation for the CoCrMo and Ti6Al4V coatings with reference to the CoCrMo and Ti6Al4V powder feedstocks. The shear bonding tests indicated good adhesion quality between the coatings and substrates. The tribological results showed that the CoCrMo coatings significantly enhanced the wear resistance of the Al alloy substrates. The corrosion results showed that the CoCrMo and Ti6Al4V coatings had higher anti-corrosion performances compared to the bare Al alloy substrates in a 3.5 wt% NaCl solution as the corrosion current densities for the CoCrMo and Ti6Al4V coated samples were substantially reduced.

51 citations

Journal ArticleDOI
18 Nov 2016
TL;DR: In this article, powder-bed-based electron beam melting (EBM) was used to additively manufacture Ti-6Al-4V (Ti64) parts of varying thicknesses.
Abstract: Ti-6Al-4V (Ti64) parts of varying thicknesses were additively manufactured (AM) by the powder-bed-based electron beam melting (EBM) technique. Microstructure and wear properties of these EBM-built Ti-6Al-4V parts have been investigated in comparison with conventionally cast Ti64 samples. Sliding wear tests were conducted using a ball-on-disc micro-tribometer under ambient conditions. Experimental results reveal that EBM-built Ti64 samples exhibited higher microhardness and an overall larger coefficient of friction as compared to the as-cast counterpart. Of interest is that the corresponding specific wear volumes were lower for EBM-built Ti64 samples, while the as-cast Ti64 showed the poorest wear resistance despite its lower coefficient of friction. Wear mechanisms were provided in terms of quantitative microstructural characterization and detailed analysis on coefficient of friction (COF) curves.

44 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the authors provide a basic understanding of 3D printing processes and the recent development of novel materials such as smart materials, ceramic materials, electronic materials, biomaterials and composites.

860 citations

Journal ArticleDOI
TL;DR: A broad range of metal additive manufacturing (AM) technologies and reviews literatures on the anisotropy and heterogeneity of microstructure and mechanical properties for metal AM parts are presented in this paper.

799 citations

Journal ArticleDOI
Noam Eliaz1
TL;DR: The body environment is analysed in detail and the possible effects of the corrosion of different biomaterials on biocompatibility are discussed, followed by description of the most common corrosion processes in vivo.
Abstract: Metallic biomaterials are used in medical devices in humans more than any other family of materials. The corrosion resistance of an implant material affects its functionality and durability and is a prime factor governing biocompatibility. The fundamental paradigm of metallic biomaterials, except biodegradable metals, has been “the more corrosion resistant, the more biocompatible.” The body environment is harsh and raises several challenges with respect to corrosion control. In this invited review paper, the body environment is analysed in detail and the possible effects of the corrosion of different biomaterials on biocompatibility are discussed. Then, the kinetics of corrosion, passivity, its breakdown and regeneration in vivo are conferred. Next, the mostly used metallic biomaterials and their corrosion performance are reviewed. These biomaterials include stainless steels, cobalt-chromium alloys, titanium and its alloys, Nitinol shape memory alloy, dental amalgams, gold, metallic glasses and biodegradable metals. Then, the principles of implant failure, retrieval and failure analysis are highlighted, followed by description of the most common corrosion processes in vivo. Finally, approaches to control the corrosion of metallic biomaterials are highlighted.

423 citations

Journal ArticleDOI
TL;DR: This paper presents a state-of-the-art overview mainly on manufacturing, topological design, mechanical properties and biocompatibility of cellular Ti-6Al-4V scaffolds via SLM and SEBM methods.

366 citations

01 Jan 2001
TL;DR: In this paper, experimental and theoretical aspects of applying electrochemical methods in tribology are discussed and recent results obtained with passivating metals in the authors' laboratory are presented, and it is shown that these parameters can significantly affect the electrochemical response of a tribocorrosion system.
Abstract: Tribocorrosion is an irreversible transformation of a material resulting from simultaneous physico-chemical and mechanical surface interactions in a tribological contact. Electrochemical methods are well suited for the study of tribocorrosion phenomena because they allow one to simulate the corrosive effect of the environment by imposing a fixed potential. Furthermore, the measurement of the anodic current permits one to determine the amount of material removed by oxidation as opposed to mechanical wear. In the present paper, experimental and theoretical aspects of applying electrochemical methods in tribology are discussed and recent results obtained with passivating metals in the authors' laboratory are presented. The importance of controlling the mechanical parameters and the contact geometry is stressed, and it is shown that these parameters can significantly affect the electrochemical response of a tribocorrosion system.

352 citations