The interface between matrix and casting tungsten carbide particle is produced by the the particles’ decomposition. Casting tungsten carbide particle is a kind of eutectic product,which is composed of two phases: WC and W2C. The two phases have differing chemical and physical properties, and thus follow different paths to achieve their decomposition process. By observing the decomposition of the particle, a hypothesis was put forward about how the casting tungsten carbide particle decomposes in steel/iron composites. An experiment was then designed to prove this hypothesis. The experimental result shows that heat gain plays a significant role in the decomposition process of casting tungsten carbide particles.
In order to provide a theoretical basis for the study of thermal fatigue properties on surface composites, thermal shock cracks initiation and propagation of WCP reinforced high chromium steel substrate surface composites were studied by thermal shock test method at 500 °C. The results show that cracks initiation and propagation begin within a few thermal shock cycles, and after 15 thermal shock cycles, the composites remain intact, indicating a good thermal shock resistance. The thermal shock cracks consist mainly of longitudinal and transverse cracks. Within a few thermal shock cycles, the initiation and propagation of longitudinal cracks play a dominant role; however, with the increase in the number of thermal shock, the transverse cracks may play a key role as the length and number of both types of cracks increases. However, the increase is slow. The longitudinal cracks are mainly caused by the first class thermal stress and the transverse cracks result from the culminant effects of the first and second thermal stress, interacting with each other.
The casting WC particles reinforced steel matrix composite coatings on Cr15 steel substrate were fabricated using the vacuum infiltration casting technique, meanwhile, investigated the relationship between the structure, hardness and the volume fraction of tungsten-iron powder in the composite coatings. The fabricated composite coatings contained tungsten-iron powder of 4.96, 9.31, 17.15 and 23.64 vol%, respectively. The microstructures and phase of the composite coatings were analyzed using Optical Microscope (OM), Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The results shows that, with increase in volume fraction of tungsten-iron powder, the amount of martensite and in situ synthesized Fe3W3C have increased. The changes of the hardness in the composite coatings with the volume fraction of tungsten-iron powder, and the hardness has been improved greatly, the highest hardness value can reach HRC 65. In addition, the reacted layers have been formed around the WC particles and mainly consist of Fe3W3C, therefore, the interfacial strength is increased significantly. However, tungsten element in the matrix hampered the melting of the WC particles.
The WC particles reinforced iron matrix composites were prepared by utilizing energy ball milling powder mixed and vacuum powder sintering method in this paper. The effects of two kinds of matrix on the micro-structure, interface and fracture mechanism of the composites were studied emphatically, and it provided a theoretical guidance for the design and engineering application of particle reinforced metal matrix composites. The results show that: in the two kinds of matrix composites, WC particles and interface had different degree of melting, WC particles and the matrix were metallurgical combination; ferritic matrix composites had better compressibility than pearlite matrix composites (1089Mpa); the fracture mode of ferrite matrix composites was quasi-cleavage fracture and pearlite matrix composites was pure cleavage fracture; the compressive micro-cracks of the two matrix composites generated at the interface and expand at the interface to a broad macroscopic crack, which eventually the material fails.
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