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Abstract: In this study temperature and grain size dependent plastic instability and strain rate sensitivity (SRS) were investigated for coarse grained (CG) and ultrafine grained (UFG) austenitic Fe–14Cr–16Ni alloys. As tensile testing temperature increased from 20 to 200°C, UFG alloys exhibited much more prominent decrease of uniform strain compared with CG counterparts. Transmission electron microscopy (TEM) analysis of deformed UFG alloys revealed temperature dependent evolution of microstructures. Through grain refinement, the SRS of Fe–14Cr–16Ni alloy increased and activation volume decreased, which may be related to the interactions of dislocations with grain boundaries. The SRS of UFG alloys exhibited greater temperature dependence than CG alloys. [Copyright &y& Elsevier]

Abstract: Equal channel angular pressing was used to refine the microstructure of a Fe–14Cr–16Ni (wt.%) alloy. The as-processed alloy had predominantly equiaxed austenite fine grains with an average grain size of 0.4μm and a low fraction of deformation induced martensite. Ex situ isothermal annealing experiments showed the fine microstructure was thermally stable up to 673K, and abnormal grain growth occurred at ∼873K. In situ annealing studies in a transmission electron microscope revealed the coarsening of grains. Analysis of grain growth kinetics from 873 to 1073K yielded average activation energy of grain growth to be ∼207kJ/mol. The grain growth mechanisms and annealing induced evolution of mechanical properties were discussed. [Copyright &y& Elsevier]

The annealing induced grain growth (GG) and heterogeneous interface evolution of Cu/Ag multilayers with individual layer thickness ( h ) varying from 5 to 50 nm were investigated by transmission electron microscopy (TEM). The results demonstrate that the thermal stability of Cu/Ag multilayers exhibits strong length scale dependence. For samples with h <20 nm, the heterogeneous interfaces completely disappear when the annealing temperature exceeds 200 °C. However, the temperature for stable layered structure can reach 300 °C as the h ≥20 nm, w h ere the interfaces remain remarkably intact. The existence of a large number of grain boundaries (GBs) decrease the stability of multilayers, while more heterogeneous interfaces contribute to resisting atomic diffusion, inhibiting GG. The equilibrium is achieved by a competitive process between GBs diffusion and heterogeneous interfaces resistance. Moreover, the formation of annealing twins in multilayer also significantly improve the microstructural stability. [ABSTRACT FROM AUTHOR]

Abstract: The microstructural evolution of the NiCrAlY/CrON system during vacuum heat treatment and thermal exposure was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The elastic modulus and residual stress of the coating system were measured by nanoindentation and photo-stimulated luminescence spectrum (PSLS) methods, respectively. It was shown that the series reaction of β→γ′→γ took place in the NiCrAlY coating, which contributed to a decrease in the Young’s modulus. The replacement of Cr2O3 by Al2O3 during thermal exposure resulted in an increase of the Young’s modulus of the barrier layer. A change in the residual stress in the barrier layer was due to a combination of thermal and growth stresses. [Copyright &y& Elsevier]