Microstructure and tensile properties of Ni3 (Si,Ti) alloys containing second phase dispersions

Abstract

The alloying behaviour, microstructure, and high temperature mechanical properties of quaternary polycrystalline Ni3 (Si,Ti), which was alloyed with transition elements V, Nb, Zr, and Hf beyond their maximum solubility limits, were investigated. The solubility limits of the quaternary elements in the L12 Ni3 (Si,Ti) phase were determined to be ranked in the sequence of Nb > V > Hf > Zr, and correlated with the size misfit parameter between Si and the quaternary element X, and with the difference in formation enthalpy between Ni3 Si and Ni3 X. The second phases (dispersions) formed beyond the solubility limit were identified as a face centred cubic type Ni solid solution for the V containing Ni3 (Si,Ti) alloy and Ni3 X type compounds of the Nb, Zr, and Hf containing Ni3 (Si,Ti) alloys. The second phase dispersions in the L12 phase matrix resulted in strengthening over a wide range of temperatures. The high temperature tensile elongation was improved by the introduction of the second phase dispersions. Among the quaternary Ni3 (Si,Ti) alloys observed in the present study, the Nb containing Ni3 (Si,Ti) alloy with the Nb containing second phase dispersion was shown to have the most favourable mechanical properties.