Development of Tool Steel Matrix Composites with High Thermal Conductivity

The improvement of thermal conductivity of tool steel is extremely important for order to achieve life prolongation of metal die used in die-casting. In order to improve the thermal conductivity without the degradation of mechanical properties, VGCF (vapor grown carbon fiber) and TiB2 particles added in tool steel (SKD61) and to obtain the composites. Composites was fabricated by spark plasma sintering (SPS). Before sintering, SKD61 powders with 70 mu m in diameter and 1.9 -3.8 vol. % VGCF with 0.15-0.2 mu m in diameter and 10-20 mu m in length or 4-8 vol. % TiB2 particles with 2.62 mu m in average diameter was mixed by V shape type ball milling or planetary ball milling. Composites were sintered at 1273K with 50 MPa. The relative density of all composites is higher than 97%. The thermal conductivity improved from 20W/mK to 36W/mK by adding 8 vol. % TiB2 particles, and to 25W/mK by adding 1.9 vol. % VGCF. On the other hand, the tensile strength of 1.9 vol. % VGCF/SKD61 composites prepared under the condition of V shape type ball milling has 2200MPa. Composites with addition of 4vol. % TiB2 particles with V shape type ball milling and 1.9 vol. % VGCF with planetary ball milling is almost equal to the monolithic alloy. Good mechanical properties of the composites are caused by the grain refinement or interfacial strengthening by adding dispersants. But as increasing the contents of dispersants, the aggregation of the dispersants degrade the mechanical properties.