Precipitation at low strains in Nb 46.5 wt% Ti

The effects of a given heat treatment at 300 to 500 C in the 2 phase region in cold worked Nb 46.5 wt%Ti have been studied. Empirically it has been observed that the effect of such heat treatments on the critical current density are not predictable unless the treatments are delayed until a prior strain of 5 to 7 has been given. In this study, heat treatments at strains of 2 and 5 are discussed. It is shown that precipitation is strongly dependent on the heterogeneous nucleation site density. Precipitation is thus much more non-uniform at ε=2 than at ε=5. The ω phase is seen after heat treatment at 375 C at a strain of 2 but only α was seen on increasing the temperature or strain. Grain boundary film precipitation was only seen at a strain of 5.