Qingshan Dong

The microstructures of copper (Cu) materials were investigated by electron backscatter diffraction, showing that electrodeposited (ED) Cu has a homogenous polycrystalline microstructure, while cold spray (CS) Cu has a heterogeneous microstructure with varying grain size, pores, and interfacial splat regions. The corrosion rate was examined by corrosion potential (E_CORR) and polarization resistance (R_p) measurements on Cu specimens in solutions containing 0.1 M NaCl + 1 × 10⁻³ M Na₂S. Although the as sprayed CS-Cu was the least corrosion resistant, the corrosion rate of the heat-treated CS-Cu was similar to that of the ED-Cu and wrought Cu (SKB-Cu). Electrochemical behaviours of Cu materials were investigated by either a potentiodynamic scan or a potentiostatic polarization at a more positive potential (E > E_CORR) for various experiment durations up to 4 h, showing that the heat-treated CS-Cu, SKB-Cu and ED-Cu exhibited very similar behaviour while the as sprayed CS-Cu showed erratic behavior consistent with a variable surface reactivity. Nanoscale scanning transmission electron microscopy analysis has been performed at the cross-section of an anodically-oxidized CS-Cu specimen, revealing a two-layer film structure, mostly composed of Cu sulfide, with a minor diffusion of sulfur in the local area of an interfacial splat boundary tip.

In this work, commercial AISI 304 stainless steel rods were subjected to cyclic forward/reverse torsion (CFRT) treatments at low-speed and high-speed torsion at room temperature. Microstructures in the core and surface layers of the CFRT-treated samples were systematically characterized. Results show that the CFRT treatment can introduce martensite phase on the surface of the rods via strain-induced martensitic transformation. High-speed twisting is more effective in inducing martensite in the surface layer compared to low-speed twisting. During the stretching process, the overall strain-hardening behavior of the gradient material is related to the content of its gradient defects. Higher gradient martensite content results in a higher surface hardness of the material, but less overall tensile properties. The effect of twisting speed on torsion behavior and the strain-hardening mechanisms in tensile of the gradient structured steels was also addressed.

The irradiation induced microstructure of heavy ion irradiated Zr-2.5Nb alloy has been characterized by X-ray diffraction and transmission electron microscopy (TEM). Diffraction line profile analysis is used to analyze the X-ray diffraction data and anisotropic responses to irradiation in terms of peak broadening in axial direction (AD; sample surface normal aligned with axial direction) and transverse direction (TD; sample surface normal aligned with transverse direction) samples. More specifically, AD samples demonstrate a significantly higher peak broadening than TD for the same irradiation dose level. TEM characterization shows that heavy ion irradiation induces small <a> type dislocation loops in the range of 2-10 nm in diameter. However, up to 0.2 dpa, the dislocation densities calculated from X-ray diffraction and TEM characterization both show comparable quantities for AD and TD samples. The considerable additional peak broadening of AD samples is attributed to an intergranular strain distribution. Chemi-STEM analysis shows that Fe is depleted from β-phase to α-β phase boundary and then into the α matrix, mainly due to ion sputtering during heavy ion irradiation.

Cr-coating was deposited on AISI 5140 steel by electro brush-plating, followed by annealing treatment at different temperatures, from 300 to 1100 °C. The microstructure evolution of the Cr-coating was characterized by backscattered electron imaging (BSEI) and energy dispersive spectrometry (EDS). The results show that the brush-plated sample has a nodular shaped microstructure, which is very stable at 300 °C of annealing. At 500 °C of annealing, the constitution of the microstructure changes from nodules to grains. As the annealing temperature further increases, the grains grow significantly. When the temperature reaches 1100 °C, a Cr-Fe solid-solution layer is formed within the original pure Cr-coatings. With increasing annealing temperature, the number of micro-cracks in the coating increases first and then decreases, reaching a maximum at 500 °C. The hardness and wear-resistance of the coating are improved when the annealing temperature increases to 1100 °C, owing to the decrease of micro-cracks that formed during brush-plating.

The stability of precipitates in Zr–2.5Nb–0.5Cu alloy under heavy ion irradiation from 100 °C to 500 °C was investigated by quantitative Chemi-STEM EDS analysis. Irradiation results in the crystalline to amorphous transformation of Zr2Cu between 200 °C and 300 °C, but the β–Nb remains crystalline at all temperatures. The precipitates are found to be more stable in starting structures with multiple boundaries than in coarse grain structures. There is an apparent increase of the precipitate size and a redistribution of the alloying element in certain starting microstructures, while a similar size change or alloying element redistribution is not detected or only detected at a much higher temperature in other starting microstructures after irradiation.