NiAl based alloy produced by HIP and SLM of pre-alloyed spherical powders. Evolution of the structure and mechanical behavior at high temperatures

The microstructure of Ni alloy produced by hot isostatic pressing (HIP) and selective laser melting (SLM) using pre-alloyed Ni41Al41Cr12Co6 spherical powders was studied by scanning electron microscopy (SEM) and high-resolution electron microscopy (HRTEM). In-situ studies of the evolution of the fine structure of Ni41Al41Cr12Co6 alloy during the heating at 20, 350… 850 °C has been performed. Homogeneous precipitation and growth of the spherical Guinier-Preston zones rich in Cr (size < 5 nm) on concentration fluctuations of dopants in the β-NiAl matrix by spinodal decomposition was detected in the range of 20-450 °C. In addition, the precipitation of the Guinier-Preston zones by heterogeneous nucleation on the crystalline defects of β-NiAl matrix has been revealed. Prismatic dislocation loops 10-25 nm in size with a stacking fault are formed from a vacancy cluster in the β-NiAl grain at 750 °C. In the 750-850 °C interval, heterogeneous nucleation and growth of α-Cr nanocrystallites having a prismatic shape and longitudinal size of 20-50 nm was observed on the prismatic dislocation loops. Also, high-temperature strength characteristics of the alloy produced by HIP in the temperature range of 600-1100 °C on a Gleeble System 3800 testing system was studied. The high-temperature strength of the HIP samples produced using pre-alloyed spherical powders is higher by 80-100 MPa compared to that of the as-cast alloy.