The Mn-Ni-Ti system was reviewed by [1991Gup]. Available limited information indicated only the phases observed in a few alloys along the MnNiTi line (up to approx 20 at. percent Ti) and along the MnNi_3-Ni_3Ti line (up to approx 10 at. percent Ti). More information on the MnNi_3-Ni_3Ti psendobinary is now available and reported here. The phases existing in the Mn-Ni, Mn-Ti, and Ni-Ti were reviewed earlier, and their structure data were reported [1991Gup]. The cubic AuCu_3-type MnNi_3 (gamma') phase exists over a small composition region and forms through a peritectoid reaction, fcc gamma + alpha-Mn reversible gamma' at 520 deg C. Above this decomposition temperature of MnNi_3 the line of 75 at. percent Ni stoichiometry passes through a two-phase region, alpha-Mn +gamma, and at and above approx 560 deg C continues through the fcc gamma phase (disordered solid solution of Mn in Ni). The MnNi_3 stoichiometry continues to rise through the Mn-Ni isomorphous region to cross the solidus and liquidus lines at approx 1230 and approx 1260 deg C, respectively. The hexagonal Ni_3Ti (eta) phase is a single composition stoichiometric compound with a melting point of 1380 deg C.
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