Influence of reinforcement volume fraction and size on the microstructure and abrasion wear resistance of hot Isostatic
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INTRODUCTION
WEAR is a major problem in many industrial applications and the development of wear resistant materials is therefore both a technical and an economic advantage. Obviously, a content of hard particles in metals can decrease the amount of abrasive wear. This concept is utilized in high speed steels and in high-Cr white cast irons, which contain large amounts of carbides. These materials are widely used in a number of industries where good resistance to abrasive wear is required. High-Cr white irons are generally considered to be the most abrasion resistant class of ferrous alloys. They consist of a high volume fraction of hard eutectic M7C3 carbides in a strong supporting matrix.[1,2] The hardness of these carbides is about 1500 to 1800 HV and it is substantially greater than that of the austenitic or martensitic matrix and also greater than that of quartz. Quartz is one of the hardest and most common abrasives in mining and earth-moving operations where white irons are widely used. The good wear resistance of these materials is accompanied with poor impact strength which may restrict their use. Composites with steel matrix and ceramic reinforcements bring new possibilities in the production of wear resistant materials. Their microstructure can be rather easily modified to offer high hardness and sufficient fracture toughness. Common ceramic particles used to reinforce steel matrix composites include oxides (Al2O3, ZrO2), nitrides (TiN, E. PAGOUNIS, Research Scientist, and V.K. LINDROOS, Professor, are with the Laboratory of Physical Metallurgy and Materials Science, Helsinki University of Technology, 02150 Espoo, Finland. M. TALVITIE, Product Manager, is with Rauma Materials Technology Oy, 33101 Tampere, Finland. Manuscript submitted January 17, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
Si3N4), and carbides (TiC, Cr3C2, VC, B4C). Titanium carbide (TiC) has proven to be suitable for this purpose, owing to its extremely high hardness and its thermodynamic stability in iron alloys.[3,4] The abrasive wear resistance of composites depends on various microstructural parameters such as hardness, volume fraction, size, shape, and distribution of the embedded particles; the properties of the matrix; and the interfacial bonding between the two phases. Axen and Zum Gahr[5] have reported that the first requirement for obtaining maximum abrasion resistance in a particle-reinforced steel matrix composite is to use a reinforcing phase with higher hardness than the abrasive grit. In addition, the matrix hardness should be as high as possible and l , Dg , d, where l is the interparticle spacing, Dg is the groove size, and d is the reinforcement particle size. The hot isostatic pressing (‘‘hipping’’) technique possesses great attraction as the production route for composites because fully densified materials and near net shapes can be achieved. Furthermore, for steel matrix composites, the only additional step in a commercial powder metallurgical (P/M) steel production route is the mixing with the ceramic po
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