In recent years, the demand for durable materials for long-lasting machine parts, which are used at manufacturing plants, is increasing. For this reason, vanadium carbide-dispersed cast iron (high V-Cr-Ni cast iron) with excellent corrosion resistance and abrasion resistance was developed. This high V-Cr-Ni cast iron was prepared by dispersing vanadium carbide (VC) in a matrix. Further improvements to the mechanical properties can be achieved by dispersing spheroidal VC in the matrix through magnesium treatment. The development of these materials is expected to contribute to improved productivity and reduced labor cost as a result of decreased replacement frequency of machine parts.
  In this study, we focused on niobium (Nb), which is less expensive than V and is a strong carbide-forming element. High Cr-Ni cast iron was prepared by dispersing niobium carbide (NbC) in an austenitic matrix, and the abrasion resistance and corrosion resistance were evaluated. We found that NbC-dispersed cast iron containing up to 11.6mass% Nb could be made.

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  Aluminum alloy composites reinforced with short potassium titanate fibers were fabricated by squeeze casting, and the effects of the fiber volume fraction and cutting conditions on the machinability of the composites were investigated. Composites reinforced with potassium titanate whisker and aluminum borate whisker were also fabricated to compare their machinability with the short potassium titanate fiber reinforced composite. The reinforcements were randomly arranged in the alloy matrix, and no agglomeration of the fibers or porosity was observed. While the change in cutting force values during the cutting was sometimes pronounced for AC8A alloy, it was relatively small and stable for the composite. The average cutting force was lowered by the reinforcement. This is probably due to the fact that the potassium titanate fibers or whiskers in the composite facilitated the shear deformation of the alloy. The cutting force of the potassium titanate fiber reinforced composite was lower than that of the whisker reinforced composites. The roughness of the machined surface was lowered by the reinforcement. The roughness of the AC8A alloy was considerably greater than theoretical roughness. On the contrary, the roughness of the composites was close to the theoretical roughness. This indicates that the reinforcements in the composite suppress the formation of the built-up edge. Continuous chips were formed after cutting the AC8A alloy, while serrated chips were formed after cutting the composites. These results lead to the conclusion that the machinability of the potassium titanate fiber reinforced composites is superior to that of the AC8A alloy and not less than that of the whisker reinforced composite.

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  Alloy tool steel castings, whose chemical compositions are 1.5% C and 12% Cr, have good wear resistance owing to continuous crystallization of M₇C₃ type Cr carbides. However, the continuity of these carbides reduces the strength of the castings in comparison with that of alloy tool steels which have the same hardness.
  This study aims to determine the optimum C and Cr contents for dispersing continuous Cr carbides and develop castings satisfying both good mechanical characteristics and good wear properties. The melts were adjusted varying the alloy composition between 0.5 and 1.5mass% C, and between 8 and 12mass% Cr in a high frequency induction furnace by investment casting. The amount of carbides was found to decrease with decreasing C and Cr contents. Cr carbides also dispersed in the matrix microstructure, and decreasing the C content increased mechanical properties such as tensile strength and bending strength. Especially, samples with 0.5% carbon content exhibited superior characteristics such as 1300MPa tensile strength and 2450MPa bending strength compared to other samples.
  On the other hand, decreasing the C content was found to deteriorate wear properties greatly due to reduced area fraction of crystallized carbides in the matrix microstructure. Based on these experimental results, we prepared samples adding Ti to the base melt. The results revealed improvements in the mechanical properties and wear properties of these Ti-added samples due to the fine TiC type carbides which crystallized preferentially than Cr type carbides in the matrix microstructures.

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  Grain refinement of magnesium alloys is required for improving mechanical properties to expand their application fields. Ultrasonic vibration has been applied to a variety of liquid phase processes such as grain refinement and degassing in aluminum alloys. In the present study, ultrasonic radiation was applied to the continuous casting of magnesium alloy to refine its grain size. The microstructures of continuously cast billets was observed as a function of immersing depth of an ultrasonic horn into molten magnesium alloy, which is the distance between the solidification front and ultrasonic horn tip. Microstructures with grain size of 22μm were attained in the area with a small distance between the solidification front and horn tip. However, well refined regions were limited to the central area in the horizontal cross-section of the billets. In order to obtain refined grains over the whole billet, it was proposed that the ultrasonic horn be rotated around the center line to expand the area with a small distance between the solidification front and horn tip over the whole cross-section of the billet. By providing additional rotating motion to the ultrasonic horn, average grain size of 50μm was achieved in sono-solidified continuously cast billets. Furthermore, the effects of immersing depth of the ultrasonic horn on the microstructure were also examined from the viewpoint of acoustic cavitation by using luminol solution. The luminescent area was found to become much wider due to acoustic cavitation in continuous casting with a rotating ultrasonic horn compared to that with a fixed horn. Pressure measurements below the ultrasonic horn showed that the peak to peak pressure amplitude is strongly attenuated at one tenth of wave length, thereby limiting the generation of acoustic cavitation to the area with a short distance between the solidification front and horn tip.

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