Evaluation of Centrifugal Casting Process Parameters for In Situ Fabricated Functionally Gradient Fe-TiC Composite
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INTRODUCTION
RECENTLY, ceramic materials with high wear resistance and high melting point properties have been widely applied for reinforcement in metal matrix composites, which leads to the fabrication of high-performance cermets materials.[1,2] Also, an additional advantage can be achieved in composite using functionally graded materials (FGMs), which are defined as a class of composites characterized by gradual variations in composition and microstructure across the material’s body thickness. Systematic research on manufacturing FGMs was first reported in the 1980s by Japanese researchers.[3–6] The gradual variation of properties can be achieved by means of a gradual force field such as magnetic, electrophoresis, or centrifugal force field gradient.[7,8] For instance, centrifugal casting techniques have been applied successfully for manufacturing FGMs composites based on different density between floated particles and molten medium such as Al-SiC composites.[9,10] Because titanium carbide (TiC) is one of the most suitable reinforcements in iron matrix composites as a secondary phase due to its high hardness and high chemical stability, researchers suggested various methods and developed them for Fe-TiC composites.[11–13] Fe-TiC composite was prepared via an in situ technique by milling of the starting powders (Ti, Fe, and carbon black) and then sintering of pressed sample at about 1673 K (1400 C). The authors reported that the formation of titanium carbide occurred due to a reaction between melted Fe2Ti and carbon at 1411 K (1138 C).[14] The formation mechanism of TiC-reinforced Fe based composites, with the spark plasma sintering technique
MOHAMMAD REZA RAHIMIPOUR, Professor, and MANOOCHEHR SOBHANI, Ph.D. Student, are with the Department of Ceramic, Materials and Energy Research Center, Karaj 31787-316, Iran. Contact e-mail: [email protected] Manuscript submitted January 14, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
using similar raw materials, can include a hybrid formation mechanism containing solid–solid diffusion reaction and solid–liquid solution-precipitation reaction.[15] In another study using high-purity titanium and graphite powders as TiC precursor and ductile iron as a matrix alloy, the reaction casting technique has been applied to synthesize Fe-TiC; the formation of titanium carbide occurred under 1403 K (1130 C) due to a direct chemical reaction as follows with its free energy equation[16]: ½Ti þ ½C ¼ TiCðsÞ DG ¼ 139; 046:31 þ 98:96TJ=mol ½1 This study focused on a process of induction melting of raw materials plus centrifugal casting to produce gradient ferritic matrix composite that is reinforced with TiC particles. The density difference between Fe and TiC, not only limits the process but also was the critical point to produce the ideal FGMs composite in this study. II.
EXPERIMENTAL PROCEDURE
The starting raw materials were cast iron and ferrotitanium, which are listed with their chemical composition in Table I. Cast iron and ferrotitanium slices (weighing 84 and 16 g, respectively)
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