Tailoring the microstructure and mechanical properties of laser metal deposited Hastelloy X superalloy via heat treatment and subsequent hot plastic deformation

Abstract

The laser metal deposition technology, characterized by its inherent rapid cooling rate and high thermal gradient, poses significant challenges in fabricating large-scale, complex thin-walled Hastelloy X components that necessitate precise dimensional accuracy and structural integrity. To tackle this issue, a novel compound forming process is proposed, wherein a near-net-shaped preform is produced using laser metal deposition technology, followed by shape and properties regulation through the hot metal gas forming process. This investigation systematically explores the hot formability, pre-deformed microstructure and properties of Hastelloy X superalloy sheets fabricated through laser metal deposition, aiming to identify optimized process parameters and to validate the feasibility of this advanced forming process. Results indicate that: (1) The laser metal deposited Hastelloy X superalloy, subjected to solution and aging heat treatments, demonstrates remarkable microstructural integrity and exceptional hot formability, attributed to its pronounced overall crystalline texture and minimal dislocation density. (2) The optimal processing domain was established within a temperature range of 900 °C to 1000 °C and a strain rate of 0.001s-1, as derived from hot processing maps based on dynamic material model. (3) Pre-deformation at 950 °C facilitates uniform and stable precipitation of nanoscale M23C6 carbides and the formation of a high-density dislocation network, significantly enhancing strength. Overall, through appropriate heat treatment and subsequent hot plastic deformation, the microstructure of Hastelloy X superalloy was optimized, yielding exceptional mechanical properties at both room and elevated temperatures. The feasibility of forming laser metal deposited preforms using the hot metal gas forming process was confirmed, laying a foundation for the future application of this innovative process. The methodologies and insights derived from this research are particularly relevant to the fabrication of large-sized, complex thin-walled components, especially within demanding aerospace applications and next-generation transportation systems.