Fabrication of carbide-particle-reinforced titanium aluminide-matrix composites by laser-engineered net shaping
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2/20/04
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Fabrication of Carbide-Particle-Reinforced Titanium Aluminide–Matrix Composites by Laser-Engineered Net Shaping WEIPING LIU and J.N. DuPONT TiAl-based titanium aluminide alloys and their composites reinforced with ceramic particles are considered to be important candidate materials for high-temperature structural applications. Laser-engineered net shaping (LENS) is a layered manufacturing process, which involves laser processing fine powders into three-dimensional components directly from a computer-aided design (CAD) model. In this work, the LENS process was employed to fabricate carbide-particle-reinforced titanium aluminide–matrix composites using TiC and gas-atomized Ti-48Al-2Cr-2Nb powders as the feedstock materials. The composites deposited by the LENS process were susceptible to solid-state cracking due to high thermal stresses. The microstructures of the laser-deposited monolithic and composite titanium aluminide materials were characterized using light optical microscopy (LOM), scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS) analysis, electron-probe microanalysis (EPMA), and X-ray diffraction (XRD) techniques. Effects of the LENS processing parameters on the cracking susceptibility and microstructure were studied. Crack-free deposits were fabricated by preheating the substrate to 450 °C to 500 °C during LENS processing. The fabricated composite deposits exhibit a hardness of more than twice the value of the Ti-6Al-4V alloy.
I. INTRODUCTION
TITANIUM aluminide alloys based on TiAl and their composites reinforced with ceramic particles have been considered and are being developed for high-temperature applications in the automotive, aerospace, and power-generation industries.[1] The TiAl-based alloys have several advantages over the conventional titanium alloys, such as higher elasticity modulus, lower density, better mechanical properties at elevated temperatures, and higher oxidation resistance due to the formation of a surface-passivated alumina layer.[2] The intermetallic-matrix composites (IMCs) reinforced with ceramic particles generally possess an even higher specific strength and specific stiffness, increased creep strength, improved toughness, and hightemperature strength retention.[3,4] Discontinuously reinforced intermetallic-matrix composites have been produced by a variety of techniques, most of which rely on a powder processing route, including mechanical alloying and a combustionreaction synthesis or reactive sintering technique, cryomilling, reactive hot isostatic pressing, and exothermic dispersion (XD) synthesis.[3] Despite a number of advantages, fabrication of IMCs by powder-metallurgical processing generally requires the use of dies for pressure-aided densification, which limits its applications. Laser-engineered net shaping (LENS) is a solid freeform fabrication process, which involves laser processing fine powders into fully dense three-dimensional components directly from a computer-aided design (CAD) model. The LENS process
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