Yanqing Yang

Bio: Yanqing Yang is an academic researcher from Northwestern Polytechnical University. The author has contributed to research in topics: Microstructure & Ultimate tensile strength. The author has an hindex of 25, co-authored 175 publications receiving 2116 citations. Previous affiliations of Yanqing Yang include German Aerospace Center & Nanjing University.

Influence of substrate material on oxidation behavior and cyclic lifetime of EB-PVD TBC systems

Abstract: EB-PVD NiCoCrAlY/P-YSZ TBCs on several polycrystalline, directionally solidified, and single crystalline (SX) substrate alloys were thermally cycled at 1100°C. TBC spallation does not correlate solely to TGO thickness, but depends also very much on the substrate alloy. The longest lifetimes are achieved on Hf-containing alloys while SX alloys suffer from early TBC spallation. The formation of the thermally grown oxide was investigated in detail by TEM. A mixed layer of alumina and zirconia exists in the as-coated condition. After initial slight thickening, the thickness of this mixed layer remains constant over a long period of time. During thermal exposure, a continuous layer of pure α-alumina forms and grows underneath the mixed zone by oxygen inward diffusion.

Robust self-cleaning and micromanipulation capabilities of gecko spatulae and their bio-mimics.

Abstract: Geckos have the extraordinary ability to prevent their sticky feet from fouling while running on dusty walls and ceilings. Understanding gecko adhesion and self-cleaning mechanisms is essential for elucidating animal behaviours and rationally designing gecko-inspired devices. Here we report a unique self-cleaning mechanism possessed by the nano-pads of gecko spatulae. The difference between the velocity-dependent particle-wall adhesion and the velocity-independent spatula-particle dynamic response leads to a robust self-cleaning capability, allowing geckos to efficiently dislodge dirt during their locomotion. Emulating this natural design, we fabricate artificial spatulae and micromanipulators that show similar effects, and that provide a new way to manipulate micro-objects. By simply tuning the pull-off velocity, our gecko-inspired micromanipulators, made of synthetic microfibers with graphene-decorated micro-pads, can easily pick up, transport, and drop-off microparticles for precise assembling. This work should open the door to the development of novel self-cleaning adhesives, smart surfaces, microelectromechanical systems, biomedical devices, and more.

Precipitation process along dislocations in Al-Cu-Mg alloy during artificial aging

Abstract: The heterogeneous nucleation and growth of precipitates at dislocations in Al–Cu–Mg alloy were investigated by examining sample aged at 195 °C for various times from 10 min to 9 h. High resolution transmission electron microscopy (HRTEM) observations and electron energy loss spectrometers (EELS) analysis show that the precipitation sequence of the S (Al 2 CuMg) phase along dislocations should be SSS → GPB zones → S (Type I) → S (Type I) + S (Type II). Type II S precipitate can nucleate and grow separately at some dislocation parts which are unfavorable for Type I S precipitate formation, or can transit from Type I S precipitate during lateral growth along dislocations by means of continuous or stepped changing in lattice orientations. Both of these modes are accomplished under the action of dislocation strain field. The deviation extent of Type II S precipitate is considered not changing with time but closely related with the interactions between the transformation strain during nucleation and the dislocation strain field.

Nano-scale precipitate evolution and mechanical properties of 7085 aluminum alloy during thermal exposure

Abstract: As a new generation of Al-Zn-Mg-Cu alloy, 7085 aluminum alloy is a promising structural material in the field of aerospace industry. However, research on its thermal stability is still lacking. In the present work, thermal exposure was carried out on the T7452-treated 7085 aluminum alloy under different temperatures (100 °C, 125 °C, 150 °C and 175 °C) for 500 h. Variations of tensile properties and hardness were exhibited. The microstructure, nano-scale precipitates and fracture characteristics of the alloy were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that with the increase of exposure temperature, the strength and hardness increase first and then decrease while the elongation and the reduction of area increase continuously as compared to those of the non-thermal exposed alloy. The transformation from η′ phase to η phase during thermal exposure occurs continuously during thermal exposure. In addition, as the exposure temperature increases, the average dimensions of precipitates and the average spacing of neighbor precipitates become larger. The influence of precipitates on mechanical properties of the alloy is discussed.

Variant selection and the strengthening effect of S precipitates at dislocations in Al-Cu-Mg alloy

Abstract: The heterogeneous precipitation of the S (Al2CuMg) phase along dislocations is investigated using high-resolution transmission electron microscopy various configurations of the S precipitate group form according to the initial dislocation morphology and no more than two S variants coexist along a single dislocation line. The most favorable combination of two S variants is observed to be variants 1 and 4 (or variants 2 and 3), and the variant selection criterion for S precipitate with the classic orientation relationship is proved to be that the dislocation line direction lies in the habit plane of the precipitate. The contribution of S precipitate groups to strengthening is evaluated by comparing the difference in total system energy increment induced by precipitate loop and the equivalent number of Guinier–Preston–Bagaryatsky zones and discrete S particles during plastic deformation. The results show that the average size of the precipitate loops as well as other kinds of precipitate groups has an important influence on the final strengthening effect. By keeping the precipitate groups below a critical size and increasing their density, the strength and thermal stability of the alloy are expected to be improved.

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.

The Superalloys: Fundamentals and Applications

Abstract: 1. Introduction 2. The physical metallurgy of nickel and its alloys 3. Single crystal superalloys for blade applications 4. Superalloys for turbine disc applications 5. Environmental degradation: the role of coatings 6. Summary and future trends.

The Diffusion of Solids

Abstract: IN view of the interest attaching to the vaporisation and diffusion of solids, the following observations may be worthy of record.

A selective laser melting and solution heat treatment refined Al-12Si alloy with a controllable ultrafine eutectic microstructure and 25% tensile ductility

Abstract: This study shows that a eutectic Al–12Si alloy with controllable ultrafine microstructure and excellent mechanical properties can be achieved by using selective laser melting and subsequent solution heat treatment. This provides a novel and promising approach to the refinement of eutectic Al–Si alloys. Unlike Al–12Si alloys fabricated and refined by traditional methods, the as-fabricated Al–12Si in this study contains nano-sized spherical Si particles surrounding a supersaturated Al matrix. During solution heat treatment, precipitation and coalescence of the Si particles occur, which decreases the Si concentration in the matrix and sub-micron to micron-sized spherical particles embedded in an Al matrix form. The as-fabricated Al–12Si exhibits significantly better tensile properties than the traditionally produced counterparts; while the solution treated Al–12Si has an extremely high ductility of approximately 25%. Importantly, the mechanical properties of the Al–12Si can be tailored through controlling the precipitation and coalescence of the Si particles by varying the solution heat treatment time. A detailed transmission electron microscopy study was conducted to investigate this Al–12Si alloy with ultrafine eutectic microstructure. The excellent tensile properties have been attributed to the refined eutectic microstructure containing spherical Si particles. The formation of this unique microstructure is due to the super heating and an extremely high cooling rate during selective laser melting and the subsequent solution heat treatment, which enables Si to grow along its most stable plane {1 1 1}Si.

Carbon fiber reinforced metal matrix composites: Fabrication processes and properties

Abstract: This paper reviews the research and development works conducted over the past few decades on carbon fiber reinforced metal matrix composites (CFR-MMC). The structure and composition of carbon fiber and its bonding to metal matrix have an impact on the properties of the resulting CFR-MMC remarkably. The research efforts on process optimization and utilizing of carbon fibers are discussed in this review. The effect of carbon fiber on structural, physical and mechanical properties of metal matrix composite are studied as well. This review also provide an overview of the research to date on various fabrication methods that is used for production of CFR-MMC.