Study Of Tungsten Carbide Composite Produced By In-Situ Metallurgy

Tungsten carbide (WC) is produced traditionally by powder metallurgy (PM) technology. The PM technology is complex, flow process is long, energy consumption and costs are fairly high, and WC particles have essential heredity, which limits its application in some areas. In order to prepare WpC(WC+W2C) composite materials rapidly, in this paper, we have developed plasma in-situ metallurgical technology and consumable electrode direct current (DC) arc in-situ metallurgical technology, and WpC composite materials were prepared efficiently and low costly by W based alloy powder. The WC, W2C crystals are generated and growed up in-situ in the high temperature melt pool. The reaction system is clean, the alloy's structure is compact and uniform, and wear-resistant properties of them are excellent. The devices of in-situ metallurgical technology are efficient in processing, low in cost and easy to control, it's more likely to be applied in industrial production processes.In this paper, bulk WpC composite materials were prepared in 42CrMo cutting pick crest hole separately by plasma in-situ metallurgical technology (PISM) and consumable electrode DC arc in-situ metallurgical technology(CEDISM), and prepared in Al2O3 refractory cavity by CEDISM. The microstructure, phases and ingredients were examined separately by SEM, XRD, EDS and EMPA. The skimming wear performance and fixed abrasive wear performance of the WpC composite materials were measured by friction wear tester.The structure analysis results reveal that the microstructure of the specimens those were prepared in cutting pick crest hole separately by the two preparation methods are approximate, the phases of the specimens are WC, W2C, M6C(Fe3W3C),γ-Fe, Cr7C3 and small amount of (Fe, Ni)3C, the alloy and substrate have excellent metallurgical bonding. From bonding area to internal alloy area, the microstructure shows in turn planar interface, eutectic region and cross shaped dendrite region. The phases of the herringbone shape eutectic are mainly Fe3W3C (bright area) andγ-Fe (dark area), the phase of the cross dendrite is Fe3W3C, the total thickness of the three regions is generally less than 200μm; From the cross dendrite region to alloy centre, the microstructure is uniform, the character of it is that Fe3W3C dendrite which has four to hexagonal branches distributed in theγ-Fe matrix which has long strips characteristics. Hard particles-WC and W2C have measured triangular or quadrilateral shape, tend to show concentrated growth, and the size is around 0.5-20μm, the growth form of them is approximate peritectic and eutectic transformation.The internal microstructure of the WpC composite materials prepared in refractory cavity is more compact and uniform due to slow cooling rate and adequate time for gases escaping. The WC and W2C crystals grow larger and the length of a triangular crystal side can reach more than 70μm, Fe3W3C is more rounding and the branch structure of it is reduced greatly.The reaction of the pure W and C powder in DC arc is also studied. With 500A electricity, when the stoichiometric ratio of WC is ensured,4% weight percentage Al is added to the reaction system, the pure WC powder can be obtained, and the crystal shape is lamellar; If 4% weight percentage Cu is added to the reaction system, and other conditions are same, the powder contains WC, W2C, WO3 and unreacted C element. With 1000A electricity, Cu is used as reaction assistant element; the dense sintering alloy of the D08 specimen with WC and W2C phases is obtained from W and C powder according with stoichiometric ratio. The nucleation and growth form of WC and W2C phases are eutectic.Under the interaction of the plasma beam and DC arc, the characteristics of the above specimens are similar. The WC crystals in-situ react, then nucleate and grow up from melt pool, the WC crystals have facet growth form; the interfacial energy of each crystal face in the WC crystal is different, so the growth speed of each crystal face is different; the result is that the WC particles are lamellar in structure.The average hardness of all the prepared WpC composite materials can reach more than HRA82, and the average hardness of D08 specimen is HRA87.8. The WpC phase has highest hardness and the microhardness of it can reach above 2000HV0.2; the microhardness of the Fe3W3C phase can reach above 1100HV0.2; the microhardness of the matrix can reach around 600-800 HV0.2 because of high solid solubility of alloy elements.In the dry sliding wear condition, quenched 45# steel as the grinding ring, the specimens produced in the cutting pick crest hole separately by PISM and CEDISM and the specimen in the refractory cavity produced by CEDISM are studied. When the load is 250N and the relative slipping speed is 400r/min, the wear resistant performances of the three specimens are close to YG13C and the wear trends of them are similar with the time extended, the wear resistant performances of P01 and D05 specimens are similar and slightly better than D04 specimen; when the rotate speed is 400r/min and wear time is 2 hours, the weight losses of the three specimens are less than YG13C when the loads are 200N and 250N, and the weight losses of the three specimens are slightly higher than YG13C when the load is 300N, and the best anti-skimming wear resistant abilities of the three specimens can reach 15 times higher than the 42CrMo steel. In the fixed abrasive wear conditions, the weight losses of all the specimens increase with the loads increase; the anti-abrasive wear performance of the specimen produced in the refractory cavity is best among the three specimens, the wear performance of it is similar while comparing with YG13C under the loads of 100N,125N, and when the load is 150N, the wear performance of it is slightly worse than YG13C; the abrasive resistance of the two specimens produced in the cutting pick crest hole are similar, and the anti-abrasive resistance performances of them are worse than YG13C under the loads of 100N,125N and 150N. The anti-abrasive resistance abilities of all the three specimens are at least 77 times higher than 42CrMo steel, and the resistance performances of them are even better compared with 42CrMo steel when the loads are lower, so the three specimens show excellent abrasive wear resistance performances.Preliminary trial-manufacture of WpC composite materials used in cutting picks were proceeded which was produced by CEDISM, the results shows that the bonding strength of the WC composite materials and substrate is excellent.