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Hot deformation is an effective way to tackle major problems in powder metallurgy, i.e., inferior mechanical properties and low relative density. To characterize the hot deformation behavior of NiAl-based alloy manufactured by hot pressing sintering, the isothermal compression tests were performed in the deformation temperature range of 1100–1300 °C with strain rate of 0.001–1 s
1. The result indicates that calculated hot activation energy Q is 326.31 kJ/mol. The processing efficiency maps and instability maps of NiAl-based alloy were established to optimize deformation parameters on the basis of dynamic material model. They were validated through microstructure evolution. The microstructure observation revealed that fine grains, dislocation pile-up, cracks appear in high efficiency, low efficiency, and instability domains, respectively. According to effective processing window revealed by processing maps, hot forging of sintered billets was performed. The elevated temperature elongation increases from 17.86% to 74.87% after forging. The stripping feature is found on fracture surface after forging.

I. INTRODUCTION

The NiAl-based alloy is promising to serve in high temperature environment for its high oxidation and corrosion resistance, relatively low density, high melting point, high Young’ modulus, the ability to retain strength and stiffness at elevated temperature, etc.1–4 These excellent elevated temperature properties make NiAl based alloy potential candidate for replacing superalloy.5,6 The conventional routine for fabricating NiAl-based alloy is ingot casting which leads to a coarse-grained microstructure. Some researchers tried to find alternative ways to produce NiAl-based alloy like rapid solidification7 and directional solidification.8–12 Another promising way is powder metallurgy (PM) such as hot pressing sintering (HPS). However, the NiAl-based alloy prepared via metallurgical routine shows low-temperature brittleness owing to lack of sufficient independent slip systems below the ductile-to-brittle transition temperature (DBTT).13,14 Lots of researchers have carried out investigation on improving low-temperature ductility of NiAl-based alloy. Eryong Liu used mechanical alloying to produce nanocrystalline NiAl intermetallic to improve mechanical properties.15 Liyuan Sheng investigated the effect of Au and Ho additions on ductility.16,17 LinZhi Tang analyzed the relationship of Ti, Nb, Hf, W additions and mechanical behaviors.18 An effective way to improve mechanical Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.315

properties, especially for room temperature ductility, is plastic deformation which is particularly beneficial to PM since it can eliminate some essential problems such as low relative density. There is a large deformation temperature range of plastic processing, especially for alloys with high melting point. Combined with the consideration that mechanical properties may be sensitive to strain rate, it is of great i