The Studies On Thermal Shock Test Of Wc Particles Reinforced Steel Substrate Surface Composites

Recently, steel-based surface composites reinforced with hard ceramic particles become a new class of advanced materials, but the application in thermal shock specific conditions was limited because the thermal physical properties did not match between substrate and composite layer, matrix and reinforcing particulate in the composite layer, which led to of their thermal shock performance is low. In this paper, the preparation process and thermal shock resistance of WC particles reinforced steel substrate surface composites were studied, and effects of heating temperature and WC particles volume fraction on their thermal shock resistance, crack initiation and expansion were focused on.In the paper, the high-carbon chromium steel substrate surface composites containing different volume fractions of WC particles were fabricated successfully by V-EPC infiltrating casting process. In the surface composites, interface between particles and matrix is metallurgical bonding and the transitional zone is gentle.The thermal shock experiment results showed that, with the increase in temperature, the velocity of crack initiation and expansion increased. During 700℃to 800℃temperature, WC particles were completely oxidized and changed into powder during the preparation of metallographic, so that some pinholes were found in the surface of the composite layer. When the volume fraction of WC particles is changed, the metallographic of matrix and the volume fraction of the matrix are changed, thus affecting the rate of crack initiation and direction of expansion.In order to study thermal fatigue failure mechanism, high-temperature oxidation behavior of the composite were studied, the results showed that, high-temperature oxidation behavior of the composite layer could decrease their ability of anti-fatigue damage, and with the increase in the temperature the oxidation rate become faster. When the test temperature was above 650℃, oxidation rate of WC particles was increased obviously, and oxidation product was WO3, which was osteoporosis structure and harmful to the thermal shock resistance of the composites.According to high-temperature oxidation behavior and the crack initiation and expansion patterns after thermal fatigue, the thermal fatigue failure mechanism of the surface composites was discussed. The results showed that, the thermal fatigue failure of the surface composites was the result of harmonious effects of the high-temperature oxidation and thermal stress, and crack initiation and expansion occured in the interface of WC particles and matrices and the defects of the composite layer.In order to enhance the thermal shock resistance of ceramic particles reinforced metal substrate surface composites, ceramic particles should have good anti-oxidant capacity at high temperature, and compared with metal sustrate, the thermal expansion coefficient and elastic modulus of the ceramic particles should be controlled in little difference.