The phase decomposition and mechanical property change occuring during the heat treatment of rapidly solidified Cu-Ti alloys has been investigated by a combination of X-ray diffractometry and microhardness investigation.
During the rapid solidification process of Cu-Ti alloys, single α- phase (disordered f.c.c.) and α+ $Cu_3Ti$ mixture were formed respectively in the range of 2-11 at.%Ti and 12 - 20 at.%Ti. The lattice parameter of single α-phase obeyed the following linear relationship with the Ti content in nm unit:
$a_\alpha=0.3611+0.000426\times(at.%Ti)$
The heat treatment experiments of supersaturated α-phase alloys in the 4.9 -10 at%Ti composition range showed that the aging process was dependent upon the temperature in the following two ways;
1) When the alloys were aged at intermediate temperature (723 - 873K), they first developed sidebands around $(200)_\alpha$ main diffraction line of the supersaturated α-phase, and then decomposed into disordered Ti poor $\alpha_1$ and Ti rich $\alpha_2$ phases.
2) When the alloys were aged at high temperatures (873 - 1023K), they decomposed directly from the supersaturated α-phase into $\alpha_1$ and $\alpha_2$-phases entailing line broadening at the low angle side of $(200)_\alpha$ main line.
Rapid hardening was observed in the aged alloys with side-bands. A complete miscibility gap could not be determined. However, the miscibility curve at the low composition limit as well as the coherent spinodal which may as well mark the composition boundary between the sidebands formation and the line broadening of the diffraction patterns of the alloys after aging treatment was determined in this study.