Development of TiB2/Steel Composites with High Termal Conductivity

Die-cast process is important for mass-production of the aluminum, magnesium and zinc alloy used in industrial parts such as automobile. In order to improve the life-time of die, the improvement of the thermal conductivity is required because of the degradation of the thermal stress. In this study, the improvement of the thermal conductivity is attempted by using steel matrix composites with titanium diboride (TiB2). Staring powders were 40CrMoV5 steel alloy (ISO standard) and TiB2. The powders were mixed by V shape type ball milling in ethanol. 4vol.%, 8vol.%, 20vol.%TiB2 containing 40CrMoV5 steel alloy composites was prepared by spark plasma sintering under the conditions of 1273 K, 10 min. in temperature keeping time, and 50MPa in applied pressure. The composites with low content of TiB2, has lower thermal conductivity for theoretical value because of the reaction of TiB2 with Fe and C. As increasing TiB2 content, many TiB2 remains in composites because of the improvement of chemical stability aggregation of TiB2, and the thermal conductivity increased. Although the relative density of 20vol. %TiB2 / 40CrMoV5 steel alloy composites were about 92.6%, the thermal conductivity of the composites with 8 vol. % TiB2 was 35.0W/mK, which is better than 40CrMoV5 monolithic alloy. As increasing TiB2 content, the tensile strength decreased but elongation increase.