Structural aspect of overageing in CuTi alloys

The role of decomposition mechanism of supersaturated Cu-Ti solid solution in the lowering the hardness due to overageing has been studied. Three CuTi alloys were investigated to find the influence of titanium content on the growth of the cellular structure caused by discontinuous precipitation. For CuTi5.6 alloy the volume fraction of cellular precipitate (VFCP) increases sigmoidally with the overageing time and VFCP growth correlates with the decrease of hardness. For CuTil alloy the cellular structure was observed incidentally, which suggests that continuous precipitation is responsible for overageing of low alloyed copper-titanium alloys. No difference in mechanical effect of overageing due to continuous (CuTi2.5 alloy) or discontinuous precipitation (CuTi5.6 alloy) was found if alloys were aged at temperature 650°C, It has been also shown that in alloys plastically strained before ageing the decrease of strength in consequence of overageing was most prominent in a highly alloyed material.