Mechanical behavior of TiNb/Ti-48-2-2 composite fabricated by PM technology

Abstract

Titanium aluminizes system offered great potential for weight savings of jet engines [1–3]. But the material shows lower mechanical properties. Ti-48Al-2Cr-2Nb (Ti-48-2-2), developed by Huang of the General Electric Corporation [2], offers better combinations of ductility, toughness and creep resistance. Aigetinger et al. [4] and Breme et al. [5] reported that it was possible to improve mechanical performance of the intermetallics further by mixing ductile phase, and believed that the key of effective toughening was to get an appropriate boundary layer. In our previous work, Ti-48-2-2 matrix composites had been fabricated through the method of sheeting [6–8], and there existed many defects in the boundary layer, which reduced the property of the material. In this work, we have fabricated TiNb/Ti-48-2-2 composite through powder metallurgy (PM) technology and hot pressing (HP) process. The mechanical behavior of the material was measured and compared with Ti-48-2-2 prepared using same method. Because the components with high melting point in Ti-48-2-2 make it difficult to smelt the matrix directly, intermediate alloy (the composition was listed in Table I) was prepared first. The intermediate alloy was resmelted five times in medium frequency induction furnace (1700 Hz, 59 KW) to assure homogenization. Some extra elements were added to make for the weight loss because of the volatilization at high temperature. Spongy Ti and 99.9% Al powder were added to prepare Ti-48-2-2 alloy (chemical composition is listed in Table II). In a vibration ball-milling machine, the alloy was pulverized into fine powder. TiNb fibers were twined around a frame made of Ti. The frame and Ti48-2-2 powder were filled in to a steel-made wrap that was vacuumized and sealed using electron beam subsequently. The composite was manufactured by means of HP processing (20 MPa, 1250 ◦C/2.5 h). The volume percentage of fiber in composite accounts for 12%. Specimens of composite were spark cut, and fixed using an epoxy resin. Consequently, the cross-section of fixed specimens was polished with various grades of silicon carbide paper: 400, 800 and 1200, and subsequently was polished down to 3 and 1 μm with diamond paste. LEICA MEF4M optical microscope is