Microstructural evolution of graded W-Cu materials under repeated thermal shocks

Abstract

To investigate the stability of W-Cu functional graded materials (FGMs) under transient-state heat load, continuous W-Cu FGMs from pure W to W-36 Cu(vol%) layer and W/W-30 Cu(vol%) joints were employed for thermal shock tests at temperatures of 1000 °C-RT under different cycles (50, 100, 150, 200). The results show that the thermal shock damage mainly occurs in the forms of Cu exudation to the sample surface, pores, and cracks caused by various thermal stresses, which were induced by the mismatch of coefficients of thermal expansion (CTEs) between W and Cu, temperature gradient and composition gradient inside W-Cu FGMs. For the continuous W-Cu FGMs, Cu exudation to the surfaces and the maximum exudation occurs in the W-22Cu region, and some microcracks appear in this region after 200 times of thermal shocks. However, for the W/W-30 Cu joints, a macrocrack appears through the entire interfaces between W and W-30Cu layer after 50 thermal shock cycles, and the crack width gradually becomes larger with the increase of the times of thermal shocks.