Zhi-Hua Nie

Cobalt has been used as sputtering target materials for integrated circuit fabrication. A sputtering target with a homogeneous microstructure is crucial for ensuring sputtering uniformity. Pure cobalt exhibits a hexagonal close-packed (HCP) crystal structure at room temperature. The limited deformability of HCP cobalt restricts microstructural homogenization during plastic deformation. Thermomechanical processing below the phase transformation temperature (∼ 420°C) offers a promising method to enhance deformability without inducing phase transformation. In this study, twinning behavior and texture evolution during warm rolling at 360°C are studied in pure cobalt. A preferred // ND crystallographic orientation is established during warm rolling. The activation of { 10 1 ¯ 2 } and { 11 2 ¯ 1 } tension twins, as well as { 11 2 ¯ 2 } , { 10 1 ¯ 3 } and { 10 1 ¯ 1 } compression twins are identified. Experimental results reveal that both electrical resistivity and microhardness increase with the increase of rolling reduction.

Nickel‐based single‐crystal superalloys significantly enhance creep rupture strength and high‐temperature stability due to their structural advantage of eliminating grain boundaries. Plastic strain can be induced in the single‐crystal superalloys during investment casting and cooling, which provides a sufficient driving force for recrystallization during subsequent postcasting heat treatment. In this study, a single‐crystal superalloy is stretched along the primary dendrite growth direction (parallel to [001]) with different plastic strains to simulate the deformation induced during investment casting. X‐ray Laue diffraction and transmission electron microscopy are performed to study the structural evolutions in the single‐crystal superalloys during tensile deformation and subsequent annealing. The slip system is activated in the single‐crystal superalloy during tension along [001] direction. A nonuniform distribution of local orientation gradient is observed in the deformed specimens, where slip steps and slip bands are detected with a high kernel averaged misorientation (KAM) ranging from 0.5° to 1°. After annealing treatment, the mean KAM angle is still large but the number fraction of the KAM exceeding 0.5° is reduced when compared to the corresponding deformed state. The relative lattice rotation induced by the plastic deformation is unchanged after annealing treatment.

There has been a growing surge of interest in examining the shock response of titanium alloys, owing to their considerable potential for military applications. The present study aims to reveal the influence of phase stability on the shock-induced mechanical response and substructure evolution of a metastable β titanium alloy, namely, Ti-17. This investigation included extensive work, such as plate impact tests, quasi-static reloading compression tests, and electron microscope analyses. The microstructural evaluations following the shock-wave loading unveil planar slip as the prevailing deformation mechanism in Ti-17 with a bimodal microstructure with stable α and β phases. However, when the shock stress exceeds 10 GPa, the activation of {101¯1}α nano-sized twins was observed, leading to improved reloading ductility. This implies a novel strategy to achieve excellent strength-plasticity compatibility in titanium alloys through appropriate shock-wave loading. Conversely, in Ti-17 with an equiaxed β microstructure, the metastability of the β phase leads to the activation of shock-induced α″ martensite, shock-induced ω, and planar slip. Two distinct forms of interaction involving the α″ laths, i.e., shear and truncation, were also observed. Phase stability greatly influences substructure evolution, which ultimately controls the reloading mechanical properties of the postshock Ti-17 alloy.

MCrAlY (M = Ni and/or Co) metallic coatings are essential for the protection of hot-end components against thermal and corrosion damage. Increasing the Al content is considered a feasible solution to improve the high-temperature performance of MCrAlY coatings. In this paper, the effects of high Al contents (12–20 wt.%) on the phase constituents and cast microstructures in MCrAlY alloys were studied by high-energy X-ray diffraction and electron microscopy techniques combined with phase equilibria calculations. High Al content improved the stability of β, σ, and α phases. Meanwhile, an evolution of the cast microstructure morphology from a dendrite structure to an equiaxed grain structure was observed. The thermal properties were analyzed, which were closely related to the phase constituents and solid-to-solid phase transitions at evaluated temperatures. This work is instructive for developing high-Al-content MCrAlY coatings for next-generation thermal barrier applications.