PNNL

Abstract

We report on the effects of alloying transition metals on the interfacial cohesion of W S27{525} symmetrical tilt grain boundary (GB). Density-functional-theory calculations show that the effects are related to the sensitivity of the d-orbital’s occupation with respect to the atomic enviroments at the GB. Systematic trends of cleavage energy as a function of the electronic valence of the impurities were observed across different interfacial positions. Segregation formation energies were calculated to study the stability of the substitutional sites. All of the energetically preferred sites also correspond to the positions at which the alloying elements increase the GB cleavage energy. For each element, the more stable the configuration, the higher the cleavage energy. This finding is crucial in designing polycrystalline W-alloys with improved fracture toughness. Considering the solubility limit, the results suggest that Ta, Nb, Re, Ru, and Os are potential additives against intergranular fracture.