Phase equilibria in the Ni–Al–Ga system at 700 °C

Abstract

Phase relations in the ternary Ni–Al–Ga system at 700°C have been established by the X-ray powder diffraction methods. In addition to already known Ni3(Al,Ga) continuous solid solution, Ni(Al,Ga) continuous solid solution as well as Ni2(Al,Ga)3 and Ni5(Al,Ga)3 extended solid solutions were found to exist in this system. It was shown that the ternary Ni2(Al,Ga)3 and Ni5(Al,Ga)3 compounds do not belong to the continuous solid solutions because of two-phase gaps on the Ni2Al3–Ni2Ga3 (∼30–50at.% Ga) and Ni5Al3–Ni5Ga3 (∼12–25at.% Ga) isolines at 700°C. Some crystal structure peculiarities such as atomic ordering–disordering and presence of structural vacancies have been revealed for all solid solutions existing in the Ni–Al–Ga system. It was found that the compressive strength of the Ni3(Al,Ga) solid solution increases with small additions of gallium (about 2.5at.%).The isothermal section (700°C) of the ternary Ni–Al–Ga system including four extended solid solutions (Ni3(Al,Ga), Ni5(Al,Ga)3, Ni(Al,Ga) and Ni2(Al,Ga)3) has been constructed and plotted.