Research On High-temperature Friction And Wear Characteristics Of SiCP/A356Composite

The material employed in the present investigation was SiCp/A356compositesupplied by KIMS. It is used for high-speed train brake disc (diameter635mm). Thecomposite used SiC particle with20μm grain size and20%volume as reinforcement. Thehigh temperature friction and wear characteristics of SiCP/A356composites after differentheat treatments was investigated in detail at UMT-2tribometer by using Al2O3ceramic ballas dual material. The high temperature friction and wear behavior of the composite materialwas analyzed by SEM, EDS, and OLS4000Olympus confocal laser scanning microscope.The results show as follows:SiCp/A356composite material consists of SiC particles, the eutectic silicon particlesand the matrix metal. The low-temperature annealing can improve the conductivity of thematerial. However, T6heat treatment, not only can change the size and morphology of theeutectic silicon in the material, but also improve the conductivity of the material, thehardness and strength at a certain extent.The wear rates of material after different heat treatment processes increase as thetemperature rises, there is evident critical transition value during the transition from theslight wear to the severe wear. Friction coefficient can appear different degrees of volatilitywith increasing temperature, which directly related to the wear resistance and hardness ofthe material. While the friction coefficient are related to the bonding strength between theSiC particles and the matrix, So compared to the material of different heat treatmentprocess, after T6treatment the friction and wear characteristics of material is relativelygood. The wear mechanism of material can be divided into three stages as the temperaturechanges: First, slight wear, this stage is mainly oxide and abrasive wear. With thetemperature increasing, it will change into the abrasive and fatigue wear. While it enters thehigh-temperature zone, it will get into the severe wear stage, and the wear rate willsuddenly increase, which is mainly adhesive wear and along with some of oxidation wearand fatigue wear.Applied load and velocity have a certain impact on the wear rate and frictioncoefficient. As the heat treatment processes are different, there are some differences in thewear rate and friction coefficient of the material. As the increase of the load, the material ismainly oxidation wear and fatigue wear, which belongs to slight wear stage; As the further increase in the load, the wear enters into a critical stage, and the mainly adhesive wearaccompanied by oxidation wear. At low speeds, the wear of the material is in the slightstage, as-cast material is mainly oxidation wear and fatigue wear. While the material afterannealing and T6treatment is mostly oxidation wear, along with peeling wear a period oftime. When at high speed, the wear of materials enter into a severe stage, as-cast material ismainly severe adhesive wear, along with fatigue wear, while annealing and T6treatmentmaterial is mainly abrasive wear and fatigue wear.In conclusion, comparing with the others heat treatment processes, thehigh-temperature friction and wear characteristics of T6treated composite is best. Heattreatment can improve the mechanical and high-temperature friction and wearcharacteristics of composite well.