| Abstract Scope |
Ni-superalloys are overwhelmingly relied upon in aerospace, power generation and automotive sectors, yet, are seldom considered as materials for hot tooling. The operational conditions of hot forming dies potentially exceed those experienced by aircraft turbine discs. Fortunately, new disc alloys have pronounced elevated temperature capabilities and the current study focuses on implementing two advanced alloys, VDM 780 and Haynes 282 (H282) as hot tool materials. There is, however, inadequate evidence of their life-limiting properties and mechanisms in the in-service temperature regime of 700 – 900 ºC. Thus, realistic operating conditions were replicated by combining interrupted short and long-term thermal-mechanical tests. To begin, isothermal ageing in the furnace, assisted in comparing the extent of 𝛾′ coarsening between the alloys, and subsequent in-situ ageing and compression testing reflected the accompanying loss in strength. Compression creep testing at stresses near appropriate yield point (250 – 750 MPa) revealed accelerated creep rates at high temperatures with creep behaviour directly transitioning from primary to tertiary regime, the steady-state creep region being absent. The results indicated that even as exposure duration, temperature, and applied stress all influence microstructural evolution, the exposure temperature was pivotal in determining the effective life of these 𝛾′-strengthened alloys. Dissolution kinetics of γ' around near-solvus temperatures was crucial and was governed by elemental additions. As a result, the research paves the way for better understanding and design of superalloys with improved thermal integrity for hot tooling. |