Effect of Dislocations on Spinodal Decomposition, Precipitation, and Age-hardening of Cu–Ti Alloy

Abstract

In age-hardenable Cu–Ti alloys, cold work before aging enhances their mechanical properties and shortens the aging time for obtaining the maximum hardness. In order to discuss hardening behaviors, microstructural evolutions such as dislocation rearrangements, progress of spinodal decomposition, and subsequent precipitation from the spinodal region during aging need to be analyzed precisely. Therefore, we employed a probing method combining the small- and the wide-angle X-ray scattering methods to characterize the precipitate size and the progress of spinodal decomposition, respectively. Sideband peaks appearing adjacent to Bragg reflection peaks in the X-ray diffraction patterns of a copper matrix were analyzed to estimate the development of compositional modulations of titanium accompanied by spinodal decomposition. The results of these analytical procedures revealed that the growth rates of the spinodal region and nanometer-scales precipitates in Cu–Ti alloys are less susceptible to dislocations introduced during cold working before aging, and that dislocations introduced during prior cold working annihilate in the initial aging stage. Consequently, overaging, which is mainly induced by dislocation annihilation, in a cold-worked Cu–Ti alloy occurs after a shorter aging time than in an unworked alloy.

Keywords

• copper–titanium alloy
• spinodal decomposition
• dislocation
• precipitation
• x-ray diffraction
• small-angle x-ray scattering
• 81.40.-z
• 61.05.c-