Study Of Matrix Microstructure Variation And Interface Continuity Of Tungsten Carbide Particle Reinforced Steel Substrate Surface Composite

Recently, tungsten carbide particles reinforced steel substrate surface composite is developed greatly, and it is expected to be applied in many industries, such as metallurgy, machinery and so on. Because of its complex microstructure, the study on the relationship between microstructure, interface and thermal fatigue property is important for realizing practical application. In this paper, the microstructure and interface of the composite are adjusted through alloying, e.g. alloying element powders such as nickle powder, molybdenum powder and so on were added into the performs, respectively. The influences of alloying powder addition on the microstructure and properties of matrix, interface, interface continuity are studies. Some valuable research conclusions are obtained. The research could enrich the interface theories of tungsten carbide particles reinforced steel substrate surface composite and support its widely practical application.Vacuum expendable pattern casting infiltration is used to fabricate the cast tungsten carbide particle reinforced steel substrate surface composites with different kind and quantity alloying powders. The influence of process parameters on microstructure and properties are studied. The results show that:(1) the surface of the composite is smooth relatively, the interface between the surface composite and the substrate has a transition area, the interface between the particle and matrix in the composite have a metallurgical bonding;(2) With the increasing of nickle powder in the composite, the microstructure of composite becomes flawless, and the quantity of carbide in the matrix increases;(3) With the increasing of molybdenum powder, the thickness of the composite increases, the microstructure becomes flawless and harder, and the quantity of eutectic carbide in composite increases;(4) With the increasing of cobalt powder, the quantity of Co3W3C phase increases, and the quantity of (Cr, Fe)7C3decreases, and the tungsten carbide becomes sharply in shape. the hardness of the composite increases.The interface continuities of the composites with different process parameters are studied. The results show that:(1) a standard is proposed for the interface continuity measurement for the macroscopic interface between the surface composite and the substrate, and the interface continuity of the macroscopic interface could be influenced by adding alloying powder, in which the nickle powder addition could improve the interface continuity of macroscopic interface;(2) the interface continuity measurement of the microscopic interface between the particle and matrix, is also proposed, the interface tradition effect index of the composite without alloying powder, with nickel, molybdenum, cobalt powder are19.0919,18.1604,19.8705,20.3745, respectively, the microscopic interface continuity of the composite with nickel powder has the best tradition effect.(3) the formation mechanism for the microscopic interface has been revealed. The decomposition of the tungsten carbide particles offers W and C atoms to the matrix, then they react with Fe to produce Fe3W3C. Besides, the original W2C in WC particles and the W2C formed by phase transformation in WC particles react with Fe to produce Fe3W3C. The Fe3W3C from the two reactions form the microscopic interface reaction zone.The connection between the microstructure variation and the thermal fatigue property of composite is investigated by thermal shock test and observation on the crack. The results that:(1) the thermal fatigue property of the composite is in proportion to the interface continuity;(2) the crack propagation speeds for the composites with molybdenum and cobalt powder addition are higher, and that for the composite with nickle powder addition is lower. The cracks in composites with molybdenum and cobalt powder addition propagate through the surface of composite after5and3thermal shock cycles. However, after36thermal shock cycles, the crack does not propagate through the surface of composite with nickle powder addition.