Sub-Solidus HIP Process for P/M Superalloy Conventional Billet Conversion

Abstract

Recent studies have identified thermo-mechanical conditions for powder UDIMET@alloy 72Oi which resulted in significantly higher ductility of HIP compacts [l]. In this process, the compact is produced by hot isostatic pressing (HIP) at temperatures just below the solidus of the alloy (slightly sub-solidus HIP or SS-HIP). The workability of the resulting as-HIPed material is high enough to allow billet conversion using conventional forging. This new process has the potential of reducing the cost of powdered metal (P/M) billet manufacturing. The results of the present study provide some insight on the mechanisms leading to the enhanced forgeability of the SS-HIP processed UDIMET alloy 720. In addition, a full-scale trial has shown that this new processing route has potential application for future production of high performance turbine disks, with equivalent microstructural and mechanical properties as parts manufactured with the conventional compact plus extrude plus isothermal forging route.

Process Development and Mechanical Properties of Alloy U720LI for High Temperature Turbine Disks

“…-HIP B material is not subjected to a sub-solidus heat treatment like in [5] and therefore the grain growth is possible while maintaining a fine gamma prime microstructure, and the risk of incipient melting is eliminated.…”

“…The PPBs have also a detrimental effect on the workability of as-HIPed material, and initial attempts to use conventional forging routes were unsuccessful [5]. Therefore, high-cost extrusion processes were developed to ensure the minimum forging ratios imposed for critical applications [6].…”

Numerical and physical simulation of rapid microstructural evolution of gas atomised Ni superalloy powders

“…In order to select the targeted isothermal holding temperatures ( s -1 to 300 K s -1 using a holding time of only 0.5 s, but changed little with higher heating rates. In the present study, precipitates (including ') actually started to form in the powders during the HIP process, moving the alloy phase fractions closer to equilibrium [18,19]. Therefore, while some difference in  from DSC measurements and during Joule heating and holding for 10 s of HIPed powders can be expected, it was likely less than the 12 K measured for the atomised powders over much shorter timescales.…”

Effect of Powder Characteristics and Oxygen Content on Modifications to the Microstructural Topology During Hot Isostatic Pressing of an Austenitic Steel

“…However, presence of PPBs in the as-HIPed condition has been a perennial problem, and has necessitated post-HIP thermomechanical processing of these alloys, which not only increases the manufacturing cost, but also restricts the efficient use of HIPing as a process for manufacturing near net shape components. Specifically, processing involves canning of gas-atomised powders and HIPing, followed by hot extrusion and/or isothermal forging [20,21]. Post-HIP thermomechanical processing is performed in order to "break" the PPB network present in the as-HIPed products (i.e., via recrystallization).…”