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HOT isostatic pressing (HIP), a form of near-net shape (NNS) manufacture, is the consolidation of metal alloy powder in a mold under high temperature and pressure and has been shown to be effective for producing complex geometry components without the need for welds; thus reducing costs, accelerating manufacturing time, and improving performance.[1,2] The advantages of HIP are well documented,[3–6] the most significant being HIP’s ability to produce components with exceedingly complex geometries that do not require subsequent machining/welding procedures on the manufactured component.[4,7] Through the elimination of welded joints, HIP can produce components exhibiting homogenous metallurgy; omitting common issues associated with problematic welded components

A.J. COOPER and W.J. BRAYSHAW are with the School of Materials, University of Manchester, Oxford Road, M13 9PL, UK. Contact e-mail: [email protected] A.H. SHERRY is with the School of Materials, University of Manchester and also with the National Nuclear Laboratory, Birchwood Park, Warrington, WA3 6AE, UK. Manuscript submitted November 10, 2017.

METALLURGICAL AND MATERIALS TRANSACTIONS A

such as hot cracking, heat-affected zones, and induced residual stresses.[8–10] The lack of heat-affected zones and lower residual stresses as a result of the HIP diffusion bonding could enhance resistance to environmentally assisted cracking (EAC).[11,12] Furthermore, the ability to completely avoid welding and subsequent machining not only reduces production lead times, costs, and volume of wasted material, but also eliminates significant expenses associated with costly manufacture and through-life weld inspection procedures. HIP’s finer and isotropic microstructure improves strength and aids non-destructive examination,[1,2] and HIP produces isotropic and homogeneous materials that display microstructures with little-to-no directionality and uniform material properties throughout. Finally, HIP produces material with a comparatively smaller grain size than that of forgings and castings, which not only improves the yield strength and ultimate tensile strength, but also lends itself to easier inspection view non-destructive examination techniques.[13] Because of these advantages, there have been increased efforts to demonstrate that components produced by HIP have equivalent or better material properties than those of equivalently graded forged materials, driven by the more demanding levels of regulatory control associated with the nuclear industry,

It has been shown[20] that the yield strength and ultimate tensile strength of HIP’d Inconel 718 are independent of the material’s oxygen content in the range of 25 to 850 C, and although the ductility is insensitive to oxygen content at room temperature, it decreases significantly with increasing oxygen content at elevated testing temperatures. However, to our knowledge no comparative study has hitherto been reported on the Charpy impact toughness fracture behavior between equivalently graded HIP’d and forged Inconel supera