Effects of W content on high temperature oxidation resistance and room temperature mechanical properties of hot-pressing Nb–XW alloys

Abstract

Oxidation behaviors at 1300°C, room temperature flexural strength and fracture toughness of hot-pressing Nb–XW (X=10, 20, 30wt%) alloys were investigated by isothermal oxidation, three-point bending (TPB) and un-precracked single edge notch bending (SENB) tests. It is shown that the oxidation resistance of Nb–XW alloys was improved with the increasing of W content due to WO3 in oxidation scale reducing the oxygen-vacancy concentration and preventing Nb5+ from outward diffusing. However, 30% W was a limit concerning the effectiveness of W in improving oxidation resistance of Nb–W alloys. W addition to Nb gives rise to an increase in room temperature flexural strength due to solid solution strengthening, but W content must meet or even exceed 30% which can efficiently strengthen the alloy. Fracture toughness first increases obviously and then decreases slightly with W changing from 10% to 30%, which was attributed to ductile fracture propensity in 20W alloy and remarkable solid solution strengthening in 30W alloy, respectively. Considering the good balance of high temperature oxidation resistance, room temperature flexural strength and fracture toughness, W content of 30% was optimum for Nb–W alloys.