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

Oxidation behaviors at 1300 degrees C, room temperature flexural strength and fracture toughness of hot-pressing Nb-XW (X = 10, 20, 30 wt%) 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 20 W alloy and remarkable solid solution strengthening in 30 W 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. (c) 2012 Elsevier B.V. All rights reserved.