Effect of Hot-Isostatic-Pressing Parameters on the Microstructure and Properties of Powder Ti-6Al-4V Hot-Isostatically-P
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T-SHAPE hot-isostatic-pressing (‘‘HIPping’’) is becoming an accepted technology for the manufacture of a range of engineering components.[1–4] The potential economic advantages of net-shape HIPping of powder to produce complex-shaped and fully dense components from titanium and nickel-based alloys[5–7] and other expensive metal powders have been investigated. In this process, a containing capsule, together with internal tooling, is filled with powder; the geometry of the capsule and tooling is defined via computer modeling of the shrinkage of the powder compact during the densification process occurring during HIPping. The capsule is pumped to backing pump pressure and sealed vacuum tight, prior to HIPping under defined conditions. The tooling and capsule (commonly of mild steel) are then removed by machining or pickling.[7] Net-shape HIPping can be used with titanium-based materials to obtain cost reduction by reducing the amount of difficult titanium machining and the large amount of material loss.[8] It is essential that the factors that influence the properties of such components are understood and that the HIPping process parameters are optimized according to specific application requirements. K. ZHANG, formerly Research Fellow, with the IRC in Materials, The University of Birmingham, is Metallurgist, with Intertek Derby, ELT14 Rolls Royce, Elton Road, Derby, Derbyshire, DE24 8BJ, United Kingdom. J. MEI and N. WAIN, Research Fellows, and X. WU, Professor, are with the IRC in Materials, The University of Birmingham, Edgbaston B15 2TT, United Kingdom. Contact e-mail: [email protected] Manuscript submitted August 20, 2009. Article published online February 25, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
The surface finish is known to be the major factor that influences the fatigue properties of a component, and net-shape hot-isostatically-pressed (‘‘HIPped’’) products are designed to retain much of the as-HIPped surface. Thus, the influence of the ‘‘as-HIPped surface’’ on the fatigue properties of a component produced using netshape HIPping is an important aspect of the work reported here. The term as-HIPped surface is used to describe the final surface of the component after HIPping after the tooling has been removed. This surface is in direct contact with the mild steel tooling during HIPping, and the as-HIPped surface is generated after HIPping by acid etching to remove the tooling. The overall aim of the work reported in this article is to study the effect of HIPping variables (HIPping temperature and HIPping procedure) on microstructure, surface finish, and mechanical properties (tensile, fatigue, and fracture toughness) of HIPped Ti-6Al-4V powder; the main interest is the properties of samples that contain the ‘‘as-HIPped’’ surface. There is a wealth of data on properties of conventionally processed samples (e.g., References 9 through 13) with which these data can be compared. In earlier work, it was shown, using conventional HIPping, that the surface roughness downgraded the fatigue properties of as-HIPped samples.[1
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