Formation of nanocrystalline B2-structured (Ru,Ni)Al in the ternary Ru–Al–Ni system by mechanical alloying and its thermal stability

B2-structured single-phase (Ru,Ni)Al is synthesized directly from the three components by mechanical alloying. Complete solubility between pseudo-binary RuAl–NiAl is realized in a range between 10 and 25 at.% Ni, while the range for Al remains at 50 at.%. B2-structured (Ru,Ni)Al is formed by an abrupt reaction at the beginning of milling and a certain quantity of Ru was found to remain in all three compositions after the reaction. Further alloying and reaction between Ru and Al sticking on the surfaces of milling tools require a much longer time and finally result in single-phase B2-structured (Ru,Ni)Al. The alloying element Ni is found to improve the sluggish reactivity of Ru by promoting the abrupt reaction. No decomposition process has been observed for the as-milled single-phase (Ru,Ni)Al either after high-temperature XRD or after isothermal annealing (1273 K), demonstrating the complete mutual solubility between pseudo-binary RuAl and NiAl. The structural evolution of as-milled materials includes reordering, strain relaxation and grain growth. The grain size of the as-milled (Ru,Ni)Al after exposure to elevated temperatures (up to 1273 K) turns out to be less than 35 nm and reflects its strong thermal stability.