Spray-Formed Stainless Steel Matrix Composites with Co-Injected Carbide Particles
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cent years, there has been a significant interest in developing particulate-reinforced iron-based metal matrix composites for wear-resistant applications, because they combine high hardness and excellent wear resistance of the reinforcements as well as good toughness and other desirable properties of the matrix materials.[1–5] The matrix materials can be tool steels, stainless steels, or other alloy steels used for specific applications. The common ceramic reinforcements for iron-based matrices are Al2O3, ZrO2, TiN, Si3N4, TiC, B4C, VC, etc. Among them, TiC and VC have proved their suitability in iron-based alloys due to their extremely high hardness, good wettability, low density, and chemical stability in iron-based matrices. The conventional production process used to fabricate iron-based composites is mainly powder CHENGSONG CUI, Research Scientist, ALWIN SCHULZ, Research Team Leader, VOLKER UHLENWINKEL, Research Group Leader, and HANS-WERNER ZOCH, Professor and Director, are with the Foundation Institute for Materials Science, University of Bremen, 28359 Bremen, Germany. Contact e-mail: cscui@iwt. uni-bremen.de Manuscript submitted October 5, 2010. Article published online February 23, 2011 2442—VOLUME 42A, AUGUST 2011
metallurgy,[2,4] which involves blending of reinforcement particulates with iron-based alloy powders, pressing the powders into desired shape and final consolidation by extrusion, forging, rolling, or hot isostatic pressing. This process can be used to produce near-net-shape products, and it allows the possibility of using a wide range of reinforcement volume fractions and sizes. However, this process also has several limitations such as nonuniform distribution of the reinforcements caused by powder demixing, powder contamination, and complex and costly processing steps. Attempts were also made to produce iron-based composites through the conventional melting and casting method.[2,4] The reinforcement particulates can either be added externally and mixed with the liquid alloys or formed in situ in the liquid alloys by reaction between the added pure elements or compounds. This casting process has the advantages of simplicity, flexibility, cheapness, and ease of production of composites in complex shape. However, the presence of the reinforcement particles decreases the fluidity of the melts, the reinforcement volume fraction is restricted to a low range, and segregation of the reinforcement particles arises easily. Harmful chemical reaction at the interface between the matrices and the externally added reinforcements may also occur due to high processing temperature. METALLURGICAL AND MATERIALS TRANSACTIONS A
Spray forming is emerging as a viable processing route for the fabrication of discontinuously reinforced metal matrix composites.[6–8] In the spray forming of metal matrix composites, reinforcement particles are injected into the atomizing gas or downstream into the spray of droplets and embedded in the metallic matrices of the spray-formed products. In the last two decades, attempts to produce
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