Role of metallic carbides on high temperature mechanical properties of wire arc additive manufactured GH4099 Ni-based superalloy

Abstract

Wire arc additive manufactured (WAAMed) γ′-strengthened Ni-based superalloy always suffers from the undesired and excessive carbides, due to the rapid cooling rates, resulting the degradation of the alloy's mechanical properties. To solve this issue, GH4099 γ′-strengthened Ni-based superalloy was prepared by melt inert-gas welding additive manufacturing, followed by both high and low temperature post-heat treatments. Both high density larger MC and tiny-dispersive M₂₃C₆ carbides were observed at the subgrain boundary in the as-built alloy, causing a higher strength but normal ductility due to the micro-cracks at the MC carbide/matrix interface. 1200 °C 4 h heat treatment, induced the growth of the large MC carbide and dissolved M₂₃C₆ carbides, resulting the improvement of the ductility of the alloy by scarifying the strength. 900 °C 4 h treatment has limited effects on the carbides’ morphology and sizes, but 900 °C 50 h treatment caused the dissolving of the large MC carbide and the growing of the tiny M₂₃C₆ carbide. Such carbide evolution can not only introduce more strengthening phase, but also suppressing the crack initiation at the large carbide/matrix interface, which simultaneously improve the strength and the ductility of the as-built alloy.