Microstructure and properties of a Cu-Ti-Co alloy

It is now well established that dilute Cu-Ti alloys with titanium in the range of 2.5-5 wt.% decompose by a spinodal mechanism and, also, that the decomposition begins during the process of quenching itself from the temperature at which the alloy is solution treated. To study the initial stages of the decomposition reaction, the necessary suppression of the decomposition was attempted and achieved either by addition of a small quantity of a third element, namely, cobalt to the binary Cu-Ti alloy or by melt-spinning the binary alloy. Both the approaches were found to be successful. The results obtained through the second approach were recently published. The present work reports the results obtained through the former approach. In this work, the decomposition reaction in the ternary alloy was studied at temperatures of 673 and 723 K. The important findings relate to the effect of cobalt on the precipitation process and the properties of the alloy. During aging, the metastable Cu4Ti (D1a) was seen to evolve in this ternary alloy without the initial 1 1/2 0 ordering in the titanium enriched regions and the formation of the special point N3M phase that were seen to precede the formation of the metastable Cu4Ti (D1a) in the melt spun alloy. Also, the ternary alloy was found, in the aged condition, to be extremely strong and ductile. Moreover, unlike the Cu-Ti binary alloy, the ternary alloy was found to be resistant to over-aging.