Embrittlement by liquid U in some group VB and VIB metals and alloys during tensile loading at 1473 K

Abstract

An investigation was conducted to determine the effect on tensile behavior of Ta, W, V, Nb, and a Ta-2.5 wt pct W alloy when they were exposed to liquid U. Tantalum, wolfram, and the Ta-2.5 wt pct W alloy were embrittled with a negligible reduction of cross section at failure, whereas V and Nb showed ductile behavior, with the samples necking down to a point. Tensile deformation of Ta in liquid U was also investigated at different displacement rates. It was found that ductility and strength increased with increasing displacement rate. The embrittlement in Ta, W, and the Ta-2.5 wt pct W alloy was associated with intergranular penetration of U, and the fracture surfaces showed evidence of grain boundary dissolution. At higher displacement rates, however, this evidence was less obvious. These results indicate that intergranular penetration of liquid U and tensile embrittlement in some of the Group VB and VIB metals correlate with low mutual solubility between the solid and liquid elements. It was also found that the thermo-dynamic criterion for intergranular penetration of liquid into a solid (grain boundary energy > 2 × liquid/solid interfacial energy) only applies to these systems.