Hot deformation mechanisms in a powder metallurgy nickel-base superalloy IN 625
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I. INTRODUCTION
THE nickel-base superalloy IN 625* possesses an attrac* IN 625 is a trademark of INCO Alloys International, Inc., Huntington, WV.
tive combination of properties such as high strength, corrosion resistance,[1] and fatigue strength, for which it is picked commonly in a sheet form by the designers of gas turbine engines, heat exchangers, and reaction vessels. Its hightemperature strength is achieved primarily by solid solution strengthening of nickel by iron, molybdenum, and niobium. However, by increasing the aluminum and titanium contents in the alloy, a special age hardenable grade is manufactured.[2] Since it is required mostly in a sheet form, considerable mechanical processing is involved in its manufacture, which includes several stages of hot working followed by a few steps of cold rolling for achieving additional strength, dimensional accuracy, and surface finish. For the design and
S.C. MEDEIROS, Materials Research Engineer, and W.G. FRAZIER, Research Leader, are with the Materials Process Design Branch, Manufacturing Technology Division, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 454337746. Y.V.R.K. PRASAD, formerly NRC Research Associate, Materials Process Design Branch, Manufacturing Technology Division, Materials and Manufacturing Directorate, Air Force Research Laboratory, is Professor, Department of Metallurgy, Indian Institute of Science, Bangalore 560012, India. Manuscript submitted August 30, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
optimization of hot working processes and for microstructural control, studies on the evaluation of the hot deformation behavior will be very useful. Zhao et al.[3] recently studied the flow behavior of three different commercially available types of IN 625 alloys during hot deformation. On the basis of a detailed microstructural study, the temperature and strain rate conditions for DRX, and partial to complete recrystallization, have been established. In the microstructure of IN 625 alloy, several microstructural phases are present, which include Ni3Nb (d) precipitates, Laves phases, and complex carbides such as MC, M6C, and M23C6. The alloy is usually solutionized at 1100 8C, where all phases except the carbides go into solution.[4] The aim of the present investigation is to study the mechanisms of hot deformation in IN 625 over a wide range of temperature and strain rate regimes so that these may be explored for optimizing bulk metal working processes such as rolling, forging, or extrusion. The IN 625 alloy investigated has been produced by a powder metallurgy (P/M) route, which gives the advantages of reducing segregation of alloying elements, distributing the carbides and other microconstituents more uniformly in the matrix, and producing finer grain sizes. It is generally recognized that the prior processing history has a significant influence on the hot deformation behavior, and therefore, this study will provide an opportunity to compare the hot deformation behavior of th
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