Solid-state interfacial reaction in molybdenum-carbide systems at high temperature-pressure, and its application to bonding technique

TLDR: In this paper, diffusion couples of molybdenum with several carbides, i.e., SiC, B4C, TiC, ZrC, HfC and TaC, were heated at various temperatures ranging from 1500 to 1840°C under high pressures of 3GPa and 100MPa for up to 4hr.

Abstract: Diffusion couples of molybdenum with several carbides, i.e. SiC, B4C, TiC, ZrC, HfC and TaC, were heated at various temperatures ranging from 1500 to 1840°C under high pressures of 3GPa and 100MPa for up to 4hr. The couples were then examined for the composition of reaction products, the growth rate of reaction layers, interfacial structures, and tensile strength. In case of Mo-transition metal carbides, Mo2C layer was mainly formed, so that the carbides, which had supplied carbon, resulted in having the nonstoichiometric composition near the interface. The activation energy for the growth of Mo2C layer in Mo-TiC system was 332kJ/mol, and that in Mo-TaC system was 366kJ/mol. In Mo-SiC system, Mo2C layer, the mixed phase of Mo2C and Mo5Si3, and Mo5Si3C layer were formed in order from the Mo side. In Mo-B4C system, the mixed phase of Mo2B and MoB, and Mo2BC layer appeared. The decomposed graphite from B4C was also observed between B4C and Mo2BC phase. The activation energy for the growth of total reaction layer in Mo-SiC system was 531kJ/mol, and that in Mo-B4C system was 183kJ/mol. It can be said that the growth of reaction layers is controlled by diffusion. The orientation of crystals was observed in all reaction products except for Mo2BC phase in Mo-B4C system and (Mo, Ta)2C phase in Mo-TaC system. In HIPed couples, the magnitude of tensile strength was dependent on the difference in thermal expansion coefficient between Mo and carbides. HIPed Mo-TaC couple had the best weldability among the systems examined in the present investigation.