Influence of Fe-W intermetallic compound on fracture behavior of Steel/Tungsten HIP diffusion bonding joint: Experimental investigation and first-principles calculation

Abstract

The influence of Fe-W intermetallic compound on fracture behavior of steel/tungsten HIP diffusion bonding joint was investigated using both experimental investigation and first-principles calculation. The research results indicate that, the fracture of steel/tungsten joint shows brittle fracture characteristic due to the existence of Fe2W intermetallic compound (IMC), and the fracture process can be divided into four stages, which are crack initiation stage, crack extension stage, imminent fracture stage and complete fracture stage, respectively. The crack generates at (or near) Fe2W/W interface at crack initiation stage and extends in Fe2W IMC at crack extension stage decides the joint property. Fe-W atomic bonds in Fe2W IMC not only weak causing the easy-destroy feature, but also exhibit covalent characteristic leading to the large brittleness, is the essential reason that Fe2W IMC shows the poor mechanical performance, and becomes the crack extension area in steel/tungsten joint. Crack initiation processes at Fe2W/W interface are various and depend on interfacial bonding behavior and charge vacancy distribution. For the weak Fe2W/W interface, which represented by Fe2W (001)/W (111) interface with Fe-W terminated structure, the crack occurs exactly at the interface (1−1' layer) due to the large area of charge vacancy region and the weak interfacial binary Fe-W bonding. While for the strong Fe2W/W interface, which represented by Fe2W (001)/W (111) interface with W-W terminated structure, because of the large charge density at interface and the strong interfacial W-Fe-W ternary bonding, the crack will occurs not at the interface exactly but the interior of Fe2W IMC (2′-3′ layer) near the Fe2W/W interface.