Controlling Residual Stress in Metal Matrix Ceramic Fiber Composite
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Controlling Residual Stress in Metal Matrix Ceramic Fiber Composite Marwan S Al-Haik1, Hamid Garmestani2, and Yousef Haik3 1 Mechanical Engineering, University of New Mexico, Albuquerque, NM, 87131 2 Materials Science and Engineering, Georgia Institute of Technology, 71 Ferst Drive, N.W., Atlanta, GA, 30332 3 Mechanical Engineering, United Arab Emirates University, Al Ain, United Arab Emirates
ABSTRACT
In metal matrix composites the nature of the reinforcement can influence the development of residual stresses not only as a result of the mismatch in the thermal expansion coefficient between the fiber and the matrix but also caused by the interface of the materials during the processing cycles. The residual stress can be minimized through controlling the processing path and the thermal environment. We studied the residual stress formation and evolution in gamma titanium aluminide (Ti-47AL-2Ta) matrix. The matrix was reinforced with three different types of fibers: Alumina, Sapphikon, and Tiboride through hot isostatic pressing. The composite was heat treated for various combinations of time: 100, 200 and 500 hours; and temperature: 590°C, 815°C and 982 °C respectively. Residual stresses were measured in the gamma phase of the matrix using X-Ray diffraction. INTRODUCTION Titanium aluminide-based intermetallic matrix composites (IMCs) are prone to the existence of high residual stresses during processing which can result in localized plastic deformation, matrix cracking, and ultimately in premature failure [1-4]. Residual stresses in composites are typically thermal in nature and are the result of the difference in coefficients of thermal expansion (CTE) between the fibers and the matrix. Composites are typically produced at elevated temperatures where both the fiber and the matrix are essentially stress-free. During cooling to ambient temperatures, however, residual stresses arise due to the thermomechanical (i.e., CTE, strength, etc.) mismatch between the fibers and the matrix. Though it is not possible to completely eliminate the residual stresses that develop during processing, it is possible to minimize their influence by carefully controlling the processing path and the temperature cycles. EXPERIMENT Three Ti-47Al-2Ta matrix composites reinforced with Alumina, Sapphikon or Tiboride were employed in this investigation. The alumina fiber has a diameter of 40-50 µm compared to 184.26µm and 84.57µm for Sapphikon and Tiboride fibers, respectively. Alumina fiber manufactured by DuPont and the Tiboride fibers manufactured by Dow Corning. The composite material was fabricated at the McDonnell-Douglas Research Center using hot isostatic pressing (HIP’ing) of powdered matrix material over the different fiber types. Pre-
alloyed powders were milled in SPX800 mills [5]. All powder handling and milling operations were carried out in argon glove boxes and Titanium lined vials to minimize contamination. Due to the larger quantities of powder milled in SPX800, this material was sealed in TI-3AL2.5V(wt%) tube 6.
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