Quan Shan

Thermo-Physical Characteristics of WC Particle-Reinforced Steel Substrate Surface Composites

Surface composites of WC reinforced steel matrix were fabricated by vacuum-expendable pattern casting(V-EPC) technology in order to provide theoretic direction for designing surface composites with high thermal fatigue performance, and then the thermo-physical properties of the composites, such as thermal expansion coefficients and thermal conductivities were characterized. The influence of process parameters on the thermo-physical characteristics was investigated. The results show that the thermal expansion coefficient the sampled layer decreased when the distance of which to the transition layer becomes lager. For the layers sampled at the same distance, their thermal expansion coefficient increased with the increase of WC particles size. For the surface composites reinforced with different sizes of WC particles, the thermal conductivities increased with the increasing temperature. When the temperature was higher(above 170℃), the thermal conductivities of the composites decreased with increase of the sizes of WC particles, and when the temperature was lower(40℃ and 105℃), the thermal conductivities of the composites did not change remarkably. The composite with Ni addition has lower thermal expansion coefficient and thermal conductivity than that of those without Ni.

Effects of Different Matrix on Interface and Compression Fracture Behavior of WC Particles Reinforced Iron Matrix Composites

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.

The Particle Shape of WC Governing the Fracture Mechanism of Particle Reinforced Iron Matrix Composites

In this work, tungsten carbide particles (WCp, spherical and irregular particles)-reinforced iron matrix composites were manufactured utilizing a liquid sintering technique. The mechanical properties and the fracture mechanism of WCp/iron matrix composites were investigated theoretically and experimentally. The crack schematic diagram and fracture simulation diagram of WCp/iron matrix composites were summarized, indicating that the micro-crack was initiated both from the interface for spherical and irregular WCp/iron matrix composites. However, irregular WCp had a tendency to form spherical WCp. The micro-cracks then expanded to a wide macro-crack at the interface, leading to a final failure of the composites. In comparison with the spherical WCp, the irregular WCp were prone to break due to the stress concentration resulting in being prone to generating brittle cracking. The study on the fracture mechanisms of WCp/iron matrix composites might provide a theoretical guidance for the design and engineering application of particle reinforced composites.

Effect of Heat Treatment Process on Mechanical Properties of a Medium Carbon Low Alloy Steel

Effect of heat treatment processes on the microstructure and mechanical properties of a medium carbon low alloy steel was studied by means of color metallography, XRD and mechanical tests.The adopted heat treatment processes included air quenching and then austempering in salt bath, watercooling and then austempering in salt bath, as well as directly austempering in salt bath. The results show that after treatments according to the above three processes the steel may exhibited microstructure composed of different amount of bainite and martensite, and better mechanical properties in comparison with the cast ones, i.e. its impact toughness and hardness were increased by 92%-183% and 31%-55% respectively. For the case of air cooling and then austempering in salt bath, the amount of bainite decreased gradually with the increase of air cooling time while the amount of martensite progressively increased, correspondingly its hardness and impact toughness showed a tendency of increase and decrease respectively.The mechanical performance of the medium carbon low alloy steel is closely related to the ratio of bainite to martinsite in the microstructure. It is noted that the steel with a duplex microstructure of 50%-60% bainite and 30%-40% martensite exhibited an optimal comprehensive mechanical performance.

Effect of Co Addition on the Microstructure of Matrix in Tungsten Carbide Reinforced Surface Composite

WC-Co surface reinforced composite was formed by V-EPC (vacuum-expendable pattern casting), and the microstructure of the matrix in the composite was investigated. The results show that the Co addition caused the appearance of granular pearlite and troostite in the matrix, therefore the brittle tendency of the composite was lighten. After the molten steel infiltrating into the preform, the component diffusion in matrix decreased from the substrate to the surface of composite, the composition of the matrix became more uneven, and the formation of the granular pearlite and troostite were facilitated. When the atomic concentration of W and C in the matrix increased, Co3W3C, η type carbide, was easier to separate out. Before the temperature of the composite drop to 1200°C, Co3W3C could precipitate in the interface reaction between the matrix and the tungsten carbide particles, the hardness of the matrix would be increased, and then the abrasive resistance of the composite could be improved.

Microstructure and Interface of TiC In Situ Synthesized Reinforced Steel-Based Surface Composite Prepared by V-EPC Infiltrating Method

In order to optimize the processing parameters of TiC/steel composite materials, in-situ TiC particle reinforced steel-based surface composites were prepared by vacuum evaporative pattern casting (V-EPC) infiltration process, and the structure and interface of the composites were investigated. The results show that, TiC particle size with Ti-C-20wt%Fe reaction system was much smaller than the composite with Ti-C reaction system in the same location of the composites. In the composites, the TiC particle size and volume fraction increased and spherical degree dropped from the tradition layers (interface between the substrate and the composite layer) to the outer surface. But the increase of TiC particle size (1-3μm) and volume fractions (25.8%-43.5%) in the composite with Ti-C-20wt%Fe reaction system was obviously lower than that of TiC particle size (1-10μm) and volume fractions (12.3%- 67.7%) in the composite with Ti-C reaction system. The bond zone between TiC particles and the matrices was totally metallurgical bonding without apparent interface. Comparing with the composite with Ti-C-xFe reaction system, the tradition layer with Ti-C reaction system has a poorer internal quality. The forming process of TiC in situ synthesized reinforced steel substrate surface composites prepared by V-EPC infiltrating process was infiltrating of the melting and carbothermal reactions of C and Ti powder the result of joint action.

Influence of Addition of Tungsten-Iron Powder on Microstructure of WC/Steel Composite Coatings

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.

Decomposition of Two Phase WC and W2C in Casting Tungsten Carbide Particles in Steel/Iron Substrate Composites

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.

Effects of Alloy Powder for WC/Steel Base Surface Composite Structure and Interface

Use Cr15 high chrome steel as base, WC particles as reinforcing particles, and adopting casting-infiltration method, a kind of quite steel-base surface wear-resistant material was prepared. The effect of Alloy powder for WC/steel base surface composite structure and interface was tested by OM, SEM and EDS. The results showed that after adding nickel powder into the composite layer, martensite, austenite, pearlite and eutectic carbide distributed in the matrix; after adding tungsten iron powder into the composite layer, more martensite distributed in the matrix; after adding molybdenum iron powder into the composite layer, martensite, austenite, pearlite and carbide distributed in the matrix. If the base material was high chrome (Cr15) and adds molybdenum iron powder in the composite layer, composite layer interface transition is good, more WC particles and irregular small carbide particles in composite layer.

Effect of Alloying Element Addition on Transition Interface Reaction Zone in Metal Matrix Composite Processing by Cast Infiltration

In metal matrix composite, the matrix and reinforced body is different in physical and chemical properties. The transition effect of reaction zone between the matrix and reinforced body is the hot point in research aboat metal matrix composite. The steel substrat casting tungsten carbide particle surface reinforced compostie is research object in this article. The interface reaction zone is measured by EDS line scaning. The problem is solved by statistic that interference between scaning neighbour points leads to the emergence of sawtooth wave, the processed curve is beneficial to observe. The effect and effect curve of W、Mo、Ni addion is received in the interface reaction zone.