Influence of heat treatment on mechanical properties, microstructure, and fracture surface morphology of V-5Cr-5Ti alloy

Nuclear fusion reactors are becoming an efficient source of energy in next generation energy. The development of structural materials is a foremost step towards building the environmentally friendly reactors. The structural components require superior mechanical and thermal properties to sustain under extreme heat, and radiation fluxes. V-5Cr-5Ti alloy is considered as promising structural material for vessel first wall components and blanket applications in fusion reactors due to its high melting point and superior mechanical and thermal properties. In this study, the influence of heat treatment on mechanical properties, microstructural changes, and fracture surface morphology of V-5Cr-5Ti alloy were investigated. The result showed that the tensile residual strength was increased by 40% but the elongation dropped significantly by 67% after the heat treatment at 650 degrees C due to dynamic strain aging (DSA) after significant plastic deformation and work hardening. At the higher temperature window from 400 degrees C to 700 degrees C, the diffusion of chromium and titanium possibly facilitate the DSA phenomenon, which enhances the strength at elevated temperatures. The microstructure of the V-5Cr-5Ti alloy showed that grain sizes were reduced to 20-60 mu m after the heat treatment at 650 degrees C from the grain sizes of 50-100 mu m at room temperature. The fracture surface at room temperature displayed ductile tearing ridges and pulled-up features. After the heat treatment to 650 degrees C, the sample showed brittle fracture features with intergranular cracks and cleavage facets. The morphological features can be correlated with the mechanical properties to analyze the microstructural origin of strength and toughness of the materials.