Thermal stability of the multicomponent nanocrystalline Ni–ZrNbMoTa alloy

A single-phase nanocrystalline Ni–ZrNbMoTa alloy with a grain size of below 10 nm was prepared by 30 h ball milling. This nanocrystalline nickel-based alloy with multicomponent solute co-segregation showed good thermal stability during high-temperature annealing. The stability of the nanocrystalline alloy at a low alloying level (x < 1.0 at%) and/or low temperature (T < 900 °C) is due to grain boundary segregation. A fully nanocrystalline microstructure with a grain size of 40 nm was retained at temperatures of up to 1000 °C for an alloying level of 1.5 at% Zr, Nb, Mo, and Ta. A small amount of second-phase precipitation (ZrTa-rich and NbTa-rich) was also observed at the grain boundary at annealing temperatures of over 900 °C. The stability of the high-composition alloy at high temperatures is due to the coupling effect of thermodynamics (the reduction of grain boundary energy caused by multicomponent segregation) and kinetics (sluggish kinetics and second-phase pinning).