Abstract
Powders of heat-resistant NiAl-8Cr-6Co-xMo-1 Nb-0.9Hf (x = 0, 2, 4 and 6 at% Mo) alloys were successfully obtained by high-energy ball milling (HEBM) and combustion synthesis. Powders with the grain size of 10–55 μm were characterized by high flowability (up to 30 s) and bulk density (up to 3.1 g/cm3) due to the absence of submicron-sized particles. Compacted samples having a finer-grained (<5 μm) structure were produced from the combustion-synthesized powders by hot isostatic pressing (HIP). Molybdenum doping gave rise to a duplex structure consisting of NiAl and (Cr, Mo) grains. High-resolution electron microscopy (HRTEM) and selected area electron diffraction studies of the fine structure of the alloys detected that there are nanoparticles of refractory compounds (Co2Nb, Cr2Nb, (Hfx, Nby)C, and Ni2AlHf) along the grain boundaries and in grain bulk, which improve resistance to viscoplastic strain at temperatures above 800 °C. Molybdenum was shown to affect the mechanical properties of the base alloy in compression tests at 500–1100 °C. Two predominant mechanisms of alloy deformation were identified: glide of matrix dislocations and mechanical twinning.
NSTL
Elsevier