Yusheng Zhang

Bio: Yusheng Zhang is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Microstructure & Alloy. The author has an hindex of 21, co-authored 63 publications receiving 1263 citations. Previous affiliations of Yusheng Zhang include University of Science and Technology of China.

Friction and wear behaviors of nanocrystalline surface layer of pure copper

Abstract: Surface mechanical attrition treatment (SMAT) was employed to fabricate a nanocrystalline surface layer on a pure copper plate. The grain size is about 10 run in the top layer and increases with an increasing depth from the treated surface. The tribological behavior of the nanocrystalline surface layer was investigated under dry conditions. Experimental results show that the load-bearing ability is markedly enhanced with the nanocrystalline surface layer relative to the coarse-grained form. The friction coefficient of the nanocrystalline layer is lower than that of the coarse-grained copper when the applied load is below 20 N. With increase of the load, the difference in wear resistance between the SMAT and the conventional Cu decreases. When the load exceeds 40 N, for the SMAT Cu, there occurs a transition of wear regime from local damage to delamination of a mechanical mixed layer. There is an abrupt increase of the wear volume, which corresponds to the wearing away of the nanocrystalline layer. The enhanced wear properties of the nanocrystalline surface layer are correlated with the stability of the mechanical mixed layer and the high hardness of the nanocrystalline structure. (c) 2005 Elsevier B.V All rights reserved.

Recent progress in development of tungsten-copper composites: Fabrication, modification and applications

Abstract: Tungsten copper (W-Cu) composites, as a traditional refractory material, are promising materials for manufacture of electrical contacts and electrodes, heavy duty electronic contacts, welding and electro-forging dies, heat sinks, packaging material, arcing resistance electrodes and thermal management devices owing to their excellent properties. This critical review presents and discusses the current progress of W-Cu composites. Starting with an introduction of the synthesis methods for W-Cu composites, including the conventional and modern preparation approaches. After that we focus on the description of the improvement of mechanical properties and arc-erosion properties by modification techniques. Finally, the advantages of W-Cu composites in applications such as electrical contacts, electronic packaging materials, and heat sinks, as well as military materials, are described, respectively.

Warm formability and post-forming microstructure/property of high-strength AA 7075-T6 Al alloy

Abstract: Formability of peak-aged AA 7075-T6 sheet across a temperature range from room temperature to 250 °C as well as post-forming microstructure/property were investigated in this paper. It showed that the optimized formability was obtained at 200 °C, due to the higher ductility and work hardening capacity at this temperature. The dominant phases in 7075-T6, 200 °C warm formed, and 250 °C warm formed samples were fine η′ and GP zones, well-developed η′, and coarser η phases, respectively. Post-forming and post-paint-baking mechanical property of 7075 samples was closely associated with those corresponding microstructures. Specifically, 200 °C warm forming caused limited coarsening of matrix precipitates (MPts) and generated a certain number of dislocations, due to the combined effect of the decreased precipitation strengthening and increased dislocation strengthening, the inherent high strength of 7075-T6 was perfectly preserved after 200 °C forming. However, 250 °C forming led to severely decreased hardness due to the sharply coarsened MPts. Furthermore, the paint-baking treatment exerted little influence to MPts, grain boundary precipitates (GBPs) and precipitate free zone (PFZ), thus the hardness loss caused by paint-baking was unobvious. Overall, 200 °C was the appropriate temperature under which the peak-aged 7000 alloys exhibited enhanced formability and maintained high post-forming strength, after paint baking, the drawn component possessed microstructure/property similar to those of retrogression and re-aged (RRA) samples.

Electrochemical corrosion characteristics and biocompatibility of nanostructured titanium for implants

Abstract: In the present study, a nano-grained (NG) surface layer on a commercial pure (Grade-2) titanium sheet was achieved by means of sliding friction treatment. The surface characteristics, in vitro corrosion behavior and biocompatibility of NG Ti were investigated, compared with those of the conventional coarse-grained (CG) substrate. The protective passive film on NG Ti surface is thicker than that on CG Ti, leading to its enhanced biological corrosion resistance in simulated body fluid (SBF) solution. In addition, NG Ti shows a much higher hydrophilicity and nano-roughness, which is related to its significantly improved cell attachment, spreading, proliferation and maturation relative to CG Ti. The enhanced biological anti-corrosion properties and biocompatibility render NG Ti a promising biomaterial for implants.

Sintering effect on microstructural evolution and mechanical properties of spark plasma sintered Ti matrix composites reinforced by reduced graphene oxides

Abstract: Ti matrix composites reinforced with 0.6 wt% reduced graphene oxide (rGO) sheets were fabricated using spark plasma sintering (SPS) technology at different sintering temperatures from 800 °C to 1100 °C. Effects of SPS sintering temperature on microstructural evolution and mechanical properties of rGO/Ti composites were studied. Results showed that with an increase in the sintering temperature, the relative density and densification of the composites were improved. The Ti grains were apparently refined owing to the presence of rGO. The optimum sintering temperature was found to be 1000 °C with a duration of 5 min under a pressure of 45 MPa in vacuum, and the structure of rGO was retained. At the same time, the reaction between Ti matrix and rGO at such high sintering temperatures resulted in uniform distribution of micro/nano TiC particle inside the rGO/Ti composites. The sintered rGO/Ti composites exhibited the best mechanical properties at the sintering temperature of 1000 °C, obtaining the values of micro-hardness, ultimate tensile strength, 0.2% yield strength of 224 HV, 535 MPa and 446 MPa, respectively. These are much higher than the composites sintered at the temperature of 900 °C. The fracture mode of the composites was found to change from a predominate trans-granular mode at low sintering temperatures to a ductile fracture mode with quasi-cleavage at higher temperatures, which is consistent with the theoretical calculations.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Review on titanium and titanium based alloys as biomaterials for orthopaedic applications.

Abstract: Variety of implant materials have been employed in various disciplines of medical science depending on the requirement of a particular application. Metals, alloys, ceramics, and polymers are the commonly used biomaterials. The main focus of this study is to review the various structural and microstructural properties of titanium and titanium based alloys used as orthopaedic implants. Orthopaedic implants need to possess certain important qualities to ensure their safe and effective use. These properties like the biocompatibility, relevant mechanical properties, high corrosion and wear resistance and osseointegration are summarized in this review. Various attempts to improve upon these properties like different processing routes, surface modifications have also been inculcated in the paper to provide an insight into the extent of research and effort that has been put into developing a highly superior titanium orthopaedic implant.

Stabilizing nanostructures in metals using grain and twin boundary architectures

Abstract: Forming alloys with impurity elements is a routine method for modifying the properties of metals. An alternative approach involves the incorporation of interfaces into the crystalline lattice to enhance the metal's properties without changing its chemical composition. The introduction of high-density interfaces in nanostructured materials results in greatly improved strength and hardness; however, interfaces at the nanoscale show low stability. In this Review, I discuss recent developments in the stabilization of nanostructured metals by modifying the architectures of their interfaces. The amount, structure and distribution of several types of interfaces, such as high- and low-angle grain boundaries and twin boundaries, are discussed. I survey several examples of materials with nanotwinned and nanolaminated structures, as well as with gradient nanostructures, describing the techniques used to produce such samples and tracing their exceptional performances back to the nanoscale architectures of their interfaces. The incorporation of structural defects, in particular of interfaces, into crystalline lattices results in enhanced material properties. In this Review, different types of boundaries and interfaces are discussed, including high- and low-angle grain boundaries, twin boundaries, nanotwinned and nanolaminated structures, and gradient nanostructures.

Recent advances in the development of aerospace materials

Abstract: In recent years, much progress has been made on the development of aerospace materials for structural and engine applications. Alloys, such as Al-based alloys, Mg-based alloys, Ti-based alloys, and Ni-based alloys, are developed for aerospace industry with outstanding advantages. Composite materials, the innovative materials, are taking more and more important roles in aircrafts. However, recent aerospace materials still face some major challenges, such as insufficient mechanical properties, fretting wear, stress corrosion cracking, and corrosion. Consequently, extensive studies have been conducted to develop the next generation aerospace materials with superior mechanical performance and corrosion resistance to achieve improvements in both performance and life cycle cost. This review focuses on the following topics: (1) materials requirements in design of aircraft structures and engines, (2) recent advances in the development of aerospace materials, (3) challenges faced by recent aerospace materials, and (4) future trends in aerospace materials.