Isothermal aging behavior in Ti-10 Cr-Al alloys for medical applications

The effect of Al addition on the elastic modulus and aging behavior in Ti-10 Cr alloys was investigated by means of electrical resistivity, X-ray diffractometry and Vickers hardness measurements. All of the alloys used were formed from solutions treated at 1173 K for 3.6 ks and then quenched into ice water (STQ). Following STQ, all Al-containing specimens exhibited a beta phase, with the athermal omega appearing only for alloys with zero Al addition. The elastic modulus was found to decrease with addition of Al from approximately 80 to 70 GPa, due to the suppression of the athermal omega. The specimens following STQ were isothermally aged at 573 K, 673 K and 773 K. The addition of Al was found to retard the onset of precipitation of the isothermal omega phase and decrease the upper limit temperature for precipitation of this phase. On the other hand, as the Al content was increased, precipitation of the alpha phase was accelerated in the presence of an existing isothermal omega phase. By contrast, this precipitation was suppressed under single beta phase conditions. Surface modification for osteointegration was also performed. When the modified specimens were immersed in simulated body fluid, the surface modification was found to promote the deposition of HAp.