Friday, October 23, 2009
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Evaluation of a Gamma Titanium Aluminide for Hypersonic Structural Applications
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.
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