Effect of Ta on the oxidation resistance of a cast Nickel-base die material with low Cr and high W content

摘要

A conventional cast nickel-base superalloy with the chemical composition of Ni-16W-2Mo-1.5Cr-6Al wt % has been recently developed as isothermal forging die material operating at temperatures above 1000℃. The oxidation test results showed that the oxide scale spalled heavily after exposure in air at 1050℃ for 100 h, which is unacceptable for the process of isothermal forging. To improve the high temperature oxidation resistance, 3 wt% Ta was added into the alloy. Specimens after oxidation test were analyzed by the scanning electron microscope (SEM) and the X-ray diffraction analysis (XRD). The results showed that the oxides were mainly NiO, NiWO_4, and NiAl_2O_4 for all the samples. The oxidation resistance of the alloy with 3wt%Ta was fairly good at 1050℃ with the mass gain rate of around 0.016g/m~2·h and spallation of oxides less than 2g/m~2 within 100h.The SEM results showed that a continuous protective layer of Al_2O_3 has been formed under the layer of NiO for the alloy containing Ta.