Temperature-dependent tensile deformation and plasticity loss mechanism of a novel Ni-Cr-W-based superalloy prepared by laser powder bed fusion

Abstract

The Ni-Cr-W-based Haynes 230 alloy fabricated by laser-beam powder bed fusion (PBF-LB) has garnered considerable attention for its ample shaping freedom and remarkable strength-plasticity synergy at room temperature. However, the limited strengthening effects provided by solid-solution atoms and carbides might restrict the practical applications of the alloy at high temperatures. In this paper, the high-temperature microstructural evolution and tensile properties of a novel γ′-strengthened based on Haynes 230 prepared by PBF-LB were systematically explored. The γ′ strengthening mechanism at 25–1000 °C and plasticity loss mechanism at 800–900 °C were first discussed. The results show that the precipitation of nanoscale γ′ phases after heat treatment (HT) can significantly improve the alloy strength at 25 °C, but dramatically sacrifice the alloy plasticity. With the testing temperature increasing, the ultimate tensile strength (UTS) and yield strength (YS) of the HT sample continue to decrease, while its elongation (EL) decreases first and then increases. A sharp decrease in EL appears at 900 °C, which is mainly attributed to the formation of acicular δ phases. The YS of the as-built (AB) sample from 25 °C to 800 °C increases, even higher than that of the HT sample, which is ascribed to the appearance of nanosized γ′ particles. The precipitation of γ′ particles and δ phases in the AB sample is the main reason for the more significant plasticity loss at 800–900 °C. Due to the increase in γ′ size and decrease in γ′ volume fraction, the dominant deformation mechanism in the HT sample changes from SF shearing at 25–800 °C to Orowan looping at 900–1000 °C.