Experimental and Computational Study of Interphase Properties and Mechanics in Titanium Metal Matrix Composites at Elevated Temperatures

Abstract

Abstract : The high temperature interfacial properties, in the tangential and normal direction, of a continuous SiC fiber reinforced Ti matrix composites, primarily SCS-6/Timetal- 21S, have been examined in this experimental/numerical study. An elevated temperature fiber pushout apparatus has been built and used to test the interfacial shear strength and frictional shear stress at various temperatures. It was found that as temperature increases, both interface properties decrease, but the debonding behavior changes for test temperatures above 400 deg C. Additionally, transverse loading tests have shown a similar decrease in normal separation stress with increasing temperature. The pushout apparatus, coupled with thermal aging studies, was used to investigate the influence of temperature and thermal exposure on tangential interfacial shear strength and frictional shear stress. It was found that thermal exposure under vacuum for temperatures up to 650 deg C conditions results in no noticeable increase in the interphase size, composition, or interphase strength properties. Aging in air causes a degradation of the interphase, resulting in deterioration of interphase properties, particularly at higher temperatures. The effect of variation of processing conditions, including variation of fiber volume fraction and of the time-temperature-pressure profile during consolidation, has been examined using concentric cylinder numerical mode, and compared to experimental test results. It was found that the processing conditions required for full consolidation of the material allow little variation in the composite stress state.