Ductile iron is used in structural parts such as hubs, gears and crankshafts, which require not only high mechanical properties, but also high wear resistance[1–4]. Austempered ductile iron can generally meet the above requirements, but its preparation process is relatively complex, requiring complex alloying and strict heat treatment process on the basis of casting[5–7]. Therefore, it is necessary to develop a simpler preparation process for wear-resistant ductile iron.
Adding ceramic particles to alloys is one of the important means to improve the wear resistance of materials[8]. This is because the reinforcing phase improves the hardness and strength of the material, which can hinder the initiation of microcracks during the sliding friction process and improve the wear resistance[9]. Based on this, Zheng et al.[10] fabricated aluminum matrix composites reinforced by SiC ceramics using powder metallurgy. The study found that SiC ceramics and the matrix formed a mixed layer with high hardness during the wear process, which played an effective role in protecting the matrix. However, SiC cannot be used in iron alloys because of the strong interfacial reaction between SiC and Fe, which affects the strengthening effect[11]. In recent years, TiC particles have been used more and more as reinforcing phase in steel materials because TiC has high elastic modulus, high hardness, good wear resistance and chemical stability[12–14]. More importantly, it has better wettability with the iron matrix and no interfacial reaction occurs[15]. Qiu et al.[16] added a small amount of TiC to medium carbon steel, by promoting the heterogeneous nucleation of the matrix during the phase transformation, resulting in the effect of grain refinement, and finally improving the strength and toughness of the matrix material at the same time. Razavi et al.[17] added a small amount of high-hardness TiC particles to cast iron, and the combination of TiC and the matrix improves the hardness, strength and wear resistance. It can be found that adding a small amount of TiC has an important effect on the improvement of the mechanical properties and wear resistance of steel materials. Consequently, it is expected to improve the wear resistance of ductile iron by adding a small amount of TiC particles. But if the addition content is increased, the TiC particles tend to agglomerate in the melt due to the large specific surface area. Thus Yi et al.[18] prepared TiC particles reinforced iron matrix composites by hot isostatic pressing. The results revealed that TiC particles were uniformly dispersed in the matrix, and the strength, hardness and wear resistance of the composites were enhanced. However, this method still cannot be applied to ductile iron, because spheroidization and inoculation treatment are necessary in the preparation process of ductile iron. In addition, the density of TiC is only 4.93g/cm3, which is much smaller than that of iron. If it is directly added to the iron melt, it will float up[19]. Hong et al.[20] put TiC into the same container as the base material, then put the container into the melt, and poured after the container was melted. But this method could not make TiC particles evenly distributed in the melt. The lost foam casting can be used to solve the problem of particle floating. TiC particles can be added to foam to be pre-dispersed. During the pouring process, the foam is sucked away by the negative pressure system after being vaporized by heat, making the particles stay in the added molten[21].
This paper mainly studies the effects of different TiC contents on the microstructure, mechanical properties and especially wear resistance of ductile iron prepared by lost foam casting. The purpose is to simplify the preparation process of wear-resistant ductile iron and provide theoretical guidance for its application in commercial factory structural parts.