Papers by Author: Z.G. Wang

Abstract: Investigations have been conducted on the fatigue behavior of Ti-6Al-4V alloy with the bimodal microstructure in air at room temperature, in vacuum at room temperature and in vacuum at low temperature (100K), respectively. The results show that the fatigue life of this alloy is longer in vacuum and/or at low temperature than that in air at room temperature. The combination of vacuum and low temperature can much improve the fatigue properties of this alloy because of their purifying effect on fatigue cracks propagation. SEM observation of fatigue fracture surface indicates that all the fatigue cracks initiate in the sample surface when Nf ≦106 cycles. The above three testing conditions lead to different modes of fatigue crack propagation and therefore much different morphology of fatigue fracture.

Abstract: Nano-scale Au/Cu multilayers were investigated by nano/microindentation. It was found that the hardness of the multilayers increases with decreasing individual layer thickness (λ), and shear band deformation can occur more easily in the multilayer with small λ. For comparison, the same experiments were also performed on Cr/Cu multilayers with the same layer structure. The results show that the Cr/Cu multilayer can be more effective in resisting shear band deformation than the Au/Cu multilayer. Finally, the λ dependence of shear band deformation and the difference between plastic deformation behaviors of the two multilayers were analyzed based on dislocation plasticity.

Abstract: Thermal barrier coatings (TBCs) were prepared by the recently-developed detonation gun spray process. The oxide scale formation and micro-damage evolution of these coatings during oxidation in air at 1100 °C were investigated. It was found that duplex oxide scales, the upper oxide mixture scale and α-Al2O3 subscale, form at the interface between bond coat (BC) and top coat (TC) during the oxidation. Microcracks usually nucleate within the porous oxide mixture layer. With the increase of oxidation time, some microcracks coalesce to form a long crack. Residual stress in the thermally grown oxides (TGO) was measured using photo-stimulated luminescence spectroscopy. It was found that compressive residual stress exhibits a fast increase at the beginning of oxidation up to maximum value for about 10h. Then, the compressive stress begins to decline up to 100h. Local stress distribution showed that the micro-damage in the TGO causes a remarkable decrease in the magnitude of compressive residual stress.