Yinong Wang

Bio: Yinong Wang is an academic researcher from Dalian University of Technology. The author has contributed to research in topics: Alloy & Microstructure. The author has an hindex of 20, co-authored 73 publications receiving 2125 citations. Previous affiliations of Yinong Wang include City University of Hong Kong & National Sun Yat-sen University.

Texture analysis in hexagonal materials

Abstract: Textures in the hexagonal metals have attracted significant interest over the years because of the use of some hexagonal metals and alloys, e.g. Zircaloy cladding for nuclear reactor fuels, Ti alloys for aerospace and aircraft industry, and Mg alloys for automobile and computer, communication and consumer electronic (3C) appliances. From a mechanistic point of view, hexagonal metals are different from cubic metals due to the restricted slip systems and the activation of twinning. In this paper, a brief summary of the texture in hexagonal structural materials is carried out, mainly dealing with the deformation and recrystallization texture as well as the anisotropy of textured hexagonal materials.

The role of twinning and untwinning in yielding behavior in hot-extruded Mg–Al–Zn alloy

Abstract: This paper examines the effect of compressive pre-deformation on subsequent tensile deformation behavior in a hot-extruded AZ31 Mg alloy bar with a ring fiber texture, and with the basal planes parallel to the extrusion direction. Such an orientation favors extensive { 1 0 1 ¯ 2 } twinning under compressive loading, resulting in a comparably low compressive yield stress. In contrast, the basal slip and { 1 0 1 ¯ 2 } twinning are difficult to operate under tensile testing, resulting in a high tensile yield strength. Compressive pre-deformation causes a significant drop in tensile yield strength, from ∼265 to ∼160 MPa, irrespective of the amount of pre-deformation strain. The latter value of ∼160 MPa nearly coincides with the compressive yield strength. The lattice reorientation of 86.3° caused by twinning during compressive loading favors untwinning in the twinned areas during subsequent tensile reloading, leading to a significant drop in tensile yield strength.

Texture and weak grain size dependence in friction stir processed Mg–Al–Zn alloy

Abstract: The Mg–Zn–Al alloy processed by hot extrusion typically exhibits strong grain size dependence of yield stress. However, the same friction stir processed Mg–Zn–Al alloy samples exhibited much weaker grain size dependence. The high Schmid factor of around 0.3 of the friction stir processed samples is responsible for the low parameters in the Hall–Petch relationship.

The effect of ageing treatment on shape-setting and superelasticity of a nitinol stent

Abstract: Ageing treatments were performed on Ti–50.7 at.% Ni (nitinol) stent wires. The results of shape-setting, austenite finish temperature and the non-linear mechanical properties of nitinol stent wires at body temperature were investigated. The experimental results show that the shape-setting results were stable when wires were constrain-treated at 500 and 550 °C and the ageing time was longer than 10 min. Austenite finish temperatures of the wires increased with ageing time, and decreased with ageing temperature after an initial increase. The peak value of the transition temperature was found to be 400 °C. For the same ageing temperature, both the upper and lower plateau stresses decreased slightly with ageing time. Most of the treated nitinol wires retained good recovery ability at body temperature; permanent sets were less than 0.05% when the ageing treatment was performed at 500 °C for not more than 60 min.

Effect of solution heat treatment on the precipitation behavior and strengthening mechanisms of electron beam smelted Inconel 718 superalloy

Abstract: Inconel 718 superalloy was fabricated by electron beam smelting (EBS) technique. The effect of solution heat treatment on the precipitation behavior and mechanical properties of EBS 718 superalloys were studied, the strengthening mechanisms were analyzed and related to the mechanical properties. The results indicate that the optimized microstructures can be acquired by means of EBS, which is attributed to the rapid cooling rate of approximately 280 ℃/min. The solution heat treatment shows a great impact on the microstructures, precipitation behavior and mechanical properties of EBS 718 superalloy. The γ`` phase shows an apt to precipitate at relatively lower solution temperatures followed by aging, while the γ` precipitates are prone to precipitate at higher temperatures. When solution treated at 1150 ℃, the γ` precipitates are dispersively distributed in the matrix with size and volume fraction of 8.43 nm and 21.66%, respectively, a Vickers hardness of approximately 489 HV0.1 is observed for the aged superalloy. The precipitation strengthening effect of EBS 718 superalloy could be elucidated by considering the interaction between the dislocations and γ``/γ` precipitates. The shearing of γ` is resisted by the coherency strengthening and formation of antiphase boundary (APB), which shows equal effect as weakly coupled dislocation (WCD) model. And for γ``, the strengthening effect is much more prominent with the primary strengthening mechanism of ordering. Moreover, it is interestingly found that the strengthening mechanism of stacking fault (SF) shearing coexists with APB shearing, and SF shearing plays a major role in strengthening of EBS 718 superalloy.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Deformation twinning in nanocrystalline materials

Abstract: Nanocrystalline (nc) materials can be defined as solids with grain sizes in the range of 1–100 nm. Contrary to coarse-grained metals, which become more difficult to twin with decreasing grain size, nanocrystalline face-centered-cubic (fcc) metals become easier to twin with decreasing grain size, reaching a maximum twinning probability, and then become more difficult to twin when the grain size decreases further, i.e. exhibiting an inverse grain-size effect on twinning. Molecular dynamics simulations and experimental observations have revealed that the mechanisms of deformation twinning in nanocrystalline metals are different from those in their coarse-grained counterparts. Consequently, there are several types of deformation twins that are observed in nanocrystalline materials, but not in coarse-grained metals. It has also been reported that deformation twinning can be utilized to enhance the strength and ductility of nanocrystalline materials. This paper reviews all aspects of deformation twinning in nanocrystalline metals, including deformation twins observed by molecular dynamics simulations and experiments, twinning mechanisms, factors affecting the twinning, analytical models on the nucleation and growth of deformation twins, interactions between twins and dislocations, and the effects of twins on mechanical and other properties. It is the authors’ intention for this review paper to serve not only as a valuable reference for researchers in the field of nanocrystalline metals and alloys, but also as a textbook for the education of graduate students.

Friction stir processing technology: A review

Abstract: Friction stir processing (FSP), developed based on the basic principles of friction stir welding (FSW), a solid-state joining process originally developed for aluminum alloys, is an emerging metalworking technique that can provide localized modification and control of microstructures in near-surface layers of processed metallic components. The FSP causes intense plastic deformation, material mixing, and thermal exposure, resulting in significant microstructural refinement, densification, and homogeneity of the processed zone. The FSP technique has been successfully used for producing the fine-grained structure and surface composite, modifying the microstructure of materials, and synthesizing the composite and intermetallic compound in situ. In this review article, the current state of the understanding and development of FSP is addressed.

Superior light metals by texture engineering: Optimized aluminum and magnesium alloys for automotive applications

Abstract: Aluminum and magnesium are two highly important lightweight metals used in automotive applications to reduce vehicle weight. Crystallographic texture engineering through a combination of intelligent processing and alloying is a powerful and effective tool to obtain superior aluminum and magnesium alloys with optimized strength and ductility for automotive applications. In the present article the basic mechanisms of texture formation of aluminum and magnesium alloys during wrought processing are described and the major aspects and differences in deformation and recrystallization mechanisms are discussed. In addition to the crystal structure, the resulting properties can vary significantly, depending on the alloy composition and processing conditions, which can cause drastic texture and microstructure changes. The elementary mechanisms of plastic deformation and recrystallization comprising nucleation and growth and their orientation dependence, either within the homogeneously formed microstructure or due to inhomogeneous deformation, are described along with their impact on texture formation, and the resulting forming behavior. The typical face-centered cubic and hexagonal close-packed rolling and recrystallization textures, and related mechanical anisotropy and forming conditions are analyzed and compared for standard aluminum and magnesium alloys. New aspects for their modification and advanced strategies of alloy design and microstructure to improve material properties are derived.