07-06-2009, 09:52 AM
Titanium matrix composites (TMCs) have been extensively evaluated for their potential to replace conventional superalloys in high temperature structural applications, as they provide significant weight-savings while maintaining comparable mechanical properties. Gamma titanium aluminide alloys and an appropriate fiber could offer an improved TMC for use in intermediate temperature applications (400-800°C). The purpose of this investigation is aimed at evaluating the potential of a gamma titanium aluminide alloy with nominal composition Ti-46.5Al-4(Cr,Nb,Ta,B)at.% as a matrix material in future aerospace transportation systems, where very light-weight structures are necessary to meet the goals of advanced aerospace programs. Monotonic tests were performed on thin rolled sheet product to evaluate basic mechanical properties and stress-strain behavior of the gamma titanium alloy. Coupons of SCS-6/gamma TiAl were manufactured at NASA LaRC. Analytical predictions were made of the optimal composite stress-strain response using AGLPLY. An [0]4 composite lay-up was modeled to estimate residual stresses after consolidation and the potential of these composites as structural materials. The analysis considered various fiber volume ratios and two potential reinforcing fibers: Ultra-SCS and Nextel 610. High residual stresses were observed due to the CTE mismatch in the materials. Laminates with Nextel 610 fibers were found to offer the best potential for a composite in this comparison. The laminate coupons manufactured cracked during cooling due to the large thermal mismatch between the silicon carbide fibers and the matrix material.