Thermodynamics of the solid solution of hydrogen in β-titanium alloys: [formula omitted] and [formula omitted

Abstract

The solid solution of hydrogen has been investigated in a series of random β-TiMo alloys ranging from 0–65 atom % Mo via determination of pressure-composition-temperature relationships; additionally, one ( β- Ti Re alloy ( Ti 37 atom % Re) was investigated. The thermodynamic parameters of hydrogen solution were generated from the p- c- T data. The relative partial molar enthalpy at infinite dilution, Δ H ̄ H o , exhibited by β- Ti Mo alloys were adjusted to conditions of fixed volume, that of pure β-Ti. It was found that variations in the resulting Δ E ̄ H o correlated roughly with variations in the electron density of states at the Fermi level. The relative partial molar entropy at infinite dilution was found to vary linearly with Mo content and it is suggested that this trend reflects a blocking of potentially available interstitial sites to hydrogen occupation by Mo atoms at small hydrogen contents. Examination of the excess free energy vs hydrogen content relationships indicates that effects resulting from accommodation of hydrogen electrons by the metal conduction band are significant even at small hydrogen contents in the Ti Mo alloys; thus, explicit determination of the H-H interaction is not possible in the alloys. By contrast, electronic effects in pure β-Ti are negligible at small H M and under fixed volume conditions, the H-H interactions in β-Ti are attractive.