Research And Development Of Diamond-Metal Composites With Ultra-High Wear Resistance

Metal materials are widely used as equipment components around the world.However,many of these components operate in harsh environments and are subjected to destructive effects such as impact,wear and corrosion.The most common and extensive failure modes for mechanical equipment components are wear and corrosion.Therefore,it is of great economic and social benefit to research wear-resisting technology for equipment in harsh environments by reducing equipment loss under these conditions.To improve the wear resistance of metal equipment under harsh conditions,one of effective technical method is to prepare wear-resistant coatings on the surface of parts by laser cladding.However,the performance of currently used alloy coating materials is difficult to meet requirements for ultra-high wear resistance of parts in modern mechanical equipment.In order to solve this problem,the wear resistance of the coating has been enhanced by adding the diamond as a strengthening phase to alloy powder in this work.However,the application of diamond in wear-resistant coatings meets several key technical difficulties.(1)The diamond has poor affinity and bonding ability with other materials due to its strong surface chemical inertia,making it difficult to form metallurgical bonding with metal matrix at their interfaces.(2)The diamond is prone to oxidation and graphitization under the high temperature condition during welding,leading to a loss of its structure and properties.In this work,fine diamond particles with plated-Cr and plated-(Cr-Ni-Fe)were used as strengthening phase and mixed with Ni-Cr-B-Si or Fe-Cr-B-Si alloy powder produced by gas-atomized method respectively.The mixed power was then used to prepare wear coatings with ultrahigh-resistance on the surface of metal specimens by laser cladding technique.Finally,the coatings were characterized by several methods including metallographic analysis,XRD、SEM、EDS、Vickers hardness and abrasive resistance test to obtain the following results.1.The XRD test analysis of the wear-resistant coating revealed that only the diamond phase was present while the graphite phase was absent.Moreover,the microscopic morphology analysis indicated that the diamond structure inside the cladding layer was fully intact,with no cracks or gaps observed at the junction with the metal substrate.It shows the plating layer on diamond can effectively avoid the thermal damage of raw diamond at high temperature,addressing the technical challenges of oxidation/graphitization of diamond as well as the difficulties of metallurgical bonding between diamond and matrix metals.The metallographic analysis results reveal that the addition of coated diamond to the clad layer has led to a reduction in the number of columnar crystals,dendrites,and cytosol crystals and an increase in the number of equated crystals,herringbone crystals,and needle crystals,as compared to the metal structure of the clad layer without the addition of coated diamond,which can refine the clad layer structure.2.The influences of different addition ratios of the plated-diamond on the hardness and wear resistance of the laser cladding prepared by Ni-Cr-B-Si and Fe-Cr-B-Si alloys were also investigated in this work.The results indicate that the hardness and wear resistance of the clad layer is significantly improved by the addition of diamond plating.The highest hardness of the laser cladding prepared by the Ni-Cr-B-Si alloy can be obtained with the addition of 10wt% diamond with plated-Cr.Compared to the coating without diamond,the hardness of the cladding layer is increased by 1.6 times.It is also found that when 20wt% Cr-plated diamond was added into the Fe-Cr-B-Si alloy powders,the cladding layer exhibited the best friction resistance which is improved by12 times compared to the coating without diamond.3.The hardness of Ni-Cr-B-Si and Fe-Cr-B-Si clad layers with 10wt% Cr-plated diamond addition prepared with different experimental parameters was examined in this research.The results reveal that the maximal hardness of the Ni-Cr-B-Si layer with10wt% Cr-plated diamond was 11.39 GPa at a laser power of 1000 W,a traverse speed of 10 mm/s and a spot diameter of 5 mm.The maximal hardness of the Fe-Cr-B-Si layer with 10wt% Cr-plated diamond was 11.65 GPa at a laser power of 800 W,a traverse speed of 10 mm/s and a spot diameter of 4 mm.