JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 200(2008)12-24 13 1. Introduction explore the potential of MIM for the fabrication of metal- and ceramic-based composites and components.Companies Powder injection molding (PIM)is a near net-shape manu- facturing technology th combines the shaping efficiency for ied compo (German.1).The PIM process normally involves four steps: nts in a trate flow and mold in rquirements of the PrM proces deter of powders,bi nding route mine that it is most applicative for processing the feedstoc process to date are strengthened by discontinuous reinforcements. production This paper provide r the reproducible shapes can be achieved at a notably reduced cost For completeness.bimetal structures and surface-engineered 50 manufa ng pro s.Par components manufa veg即tsC cally produc as well in the context even though it is still green at funda- fabricated relatively easily with MIM.whereas conventional mental investigation stage metallurgy methods are limited to the fabr 2. Metal matrix composites (MMCs)by MIM Based on the matrix mat rials,the fabricated by with matenal systems that are difhcult to sinte using con based intemmetallic basedand steel based.Bimetal structure are also discussed in this section.The MIM route has enable matrix compo many MMC or CMC offer unique erties that cannot he nor. conventional routes(Diehl and Detlev.1990). mally achiev onolit ma turing 2.1 Refractory metal based MMCs ving the Mi process the cost for con cial use of composite materials can e significantly reduced.In Tungsten and molybdenum are two refractory metals that recent years,comprehensive has been conducted to have attracted great interest for high-temperature applica Solver Therma Injection 修一 Sintering Fig.1-Schematic diagram of powder injection molding journal of materials processing technology 200 (2008) 12–24 13 1. Introduction Powder injection molding (PIM) is a near net-shape manu￾facturing technology that combines the shaping efficiency of plastic injection molding with the capability of pow￾der metallurgy for processing metal and ceramic powders (German, 1990). The PIM process normally involves four steps: mixing, injection molding, debinding and sintering, as illus￾trated in Fig. 1. The evolution of the PIM technology has resulted in many variations, reflecting different combinations of powders, binders, molding techniques, debinding routes, and sintering practices. Metal injection molding, commonly known by its acronym MIM, is by far the most widely used PIM process. The process offers many unique advantages for the mass production of small and complex parts. First, precise and reproducible shapes can be achieved at a notably reduced cost as compared to conventional manufacturing processes. Part quantities varying from 5000 per year (e.g., specialty firearm sights) to over 100 million per year (e.g., cell phone vibra￾tor weights) can be economically produced by MIM (Johnson and German, 2003, 2005). Second, complex shapes can be fabricated relatively easily with MIM, whereas conventional powder metallurgy methods are limited to the fabrication of parts with simple geometries. Third, the use of very fine powders in the feedstock promotes densification during sin￾tering and hence high-performance parts can be produced with material systems that are difficult to sinter using con￾ventional processes. The attractive features of the MIM process can be applied advantageously to the fabrication of metal matrix compos￾ite (MMC) or ceramic matrix composite (CMC) parts. Although many MMC or CMC offer unique properties that cannot be nor￾mally achieved by monolithic materials, their commercial use are often restricted by the high cost of materials and manufac￾turing. By applying the MIM process, the cost for commercial use of composite materials can be significantly reduced. In recent years, comprehensive work has been conducted to explore the potential of MIM for the fabrication of metal￾and ceramic-based composites and components. Companies have even been established to discover the commercial capac￾ity of the MIM technology for the fabrication of composites (Decker, 1989; H.C. Starck Inc., 2003). The most widely stud￾ied composites by PIM are metal-based, including stainless steels, refractory metals, intermetallic compounds, and tita￾nium alloys. Although theoretically the reinforcements in a composite can take either continuous (typically long fibres) or discontinuous (particles and short fibres/whiskers) form, the flow and mold filling requirements of the PIM process deter￾mine that it is most applicative for processing the feedstock containing particles or short fibres. Consequently, it is not sur￾prising that all of the metallic composites fabricated by MIM to date are strengthened by discontinuous reinforcements. This paper provides a review of the research activities related to composite fabrication through the MIM route. For completeness, bimetal structures and surface-engineered components manufactured by MIM are also included in the metal matrix composites. Furthermore, fabrication of micro￾components by mircometal injection molding will be covered as well in the context even though it is still green at funda￾mental investigation stage. 2. Metal matrix composites (MMCs) by MIM Based on the matrix materials, the composites fabricated by MIM can be divided into refractory metal based MMC, titanium based, intermetallic based and steel based. Bimetal structures are also discussed in this section. The MIM route has enabled the fabrication of MMCs containing ingredient materials that are not compatible in molten state and difficult to fabricate by conventional routes (Diehl and Detlev, 1990). 2.1. Refractory metal based MMCs Tungsten and molybdenum are two refractory metals that have attracted great interest for high-temperature applica￾Fig. 1 – Schematic diagram of powder injection molding