The behavior and mechanism of void self-shrinkage in diffusion bonded 1Cr11Ni2W2MoV steel joint: Effect of temperature and void morphology

The aim of this study was to investigate the void self-shrinkage behavior and mechanism in the diffusion bonded 1Cr11Ni2W2MoV martensitic stainless steel joint. Two void morphologies, i.e., ellipse and long penny-shaped voids, were firstly manufactured by two kinds of prepared surfaces using diffusion bonding, and then heat treated at different temperatures. Results showed that for the ellipse voids the void self-shrinkage behavior hardly occurred at the lower heat treatment temperatures of 700 ℃ and 800 ℃ while it occurred to transform the ellipse voids into smaller round voids at the higher temperatures of 900 ℃ and 1000 ℃. For the penny-shaped voids, there was no obvious void self-shrinkage at the temperatures of 800 ℃ and 900 ℃ while the void self-shrinkage was greatly improved at the temperature of 1000 ℃. Joint shear strength could be significantly improved by the void self-shrinkage behavior. The void self-shrinkage mechanism was also analyzed, indicating that the void self-shrinkage behavior only occurred when the sum of internal driving force and external driving force was greater than the resistance for void self-shrinkage. The void self-shrinkage was mainly operated by diffusion of atoms, in which surface diffusion altered the void morphology, and grain boundary diffusion and volume diffusion reduced the void volume. Relative to ellipse voids, the void self-shrinkage of penny-shaped voids occurred at higher temperature due to the lack of surface diffusion.