The Microstructure And Tribological Behavior Of Ti B₂+TiN/Ni Coating By Argon Shielded Arc Cladding

As an effective way to improve the properties of material, coating has been widelyused in engineering, especially, its excellent anti-friction, corrosion and oxidationresistance abilities. The plasma spraying and laser cladding have been used to improve the wear-resistance of coating as the main methods. High costs and complicated operation influence development of the methods. However, argon shielded arc cladding is an especially promising technique for improving the shearer picks of wear resistance. It is of a very great importance to improve the productivity effect in enterprises.In this paper, the coating were in situ fabricated on 35 Cr Mn Si steel substrate by argon shielded arc cladding technology with Ti, BN and Ni60 A mixed alloy powder as raw material respectively. The effect of arc power, cladding speed, powder feeding rate, the ratio of BN to Ti and the（Ti+BN） contents on phases’ morphology and distribution have studied systemly.The optimal powder formulation and cladding procedures for preparing cladding coatings were determined after a large number of experiments. The phases and microstructures of the cladding specimens were analyzed by X-ray diffraction（XRD）, optical microscope（OM）, scanning electron microscopy（SEM）, transmission electron microscope（TEM） and high resolution transmission electron microscope（HREM） and energy dispersive spectrum（EDS）. And the properties of the cladding coatings were carried out by microhardness and wear resistance tests. It can be used to control microstructures and properties and have further study on in-situ synthesized mechanism and wear mechanism. The test results show that:（1） The dilution of the cladding coat is the least at the 120 A and 2mm/s. The grain of microstructures grew coarse with the cladding current changed as 100Aâ†'120Aâ†'140Aâ†'160A, the size of phases alter as follow: small particle phases with size of 2⁵μmâ†'particles, whisker and rod-like microstructureâ†'needle and rod-like microstructure with grain size range from5μm×600nm¹5μm×1.2μmâ†'coarse needle microstructure with size of 20μm×1.2μm²Î¼m. The grain size of synthesized become small with the cladding speed increased and the coating is mainly composed of Cr23C6, TiB, TiB₂, Ti N and γ-Ni. With the cladding speed increased from 1mm/s to 4mm/s, the microstrue of phases at the top field varied much: coarse needle microstructure with mean grain size of 30μm×1μmâ†'needle microstructure with size of 10μm×1μm and particle microstructure with grain size range from1μm to 2μmâ†'mixed particle and whisker micrsture. However, the ration of BN to Ti has great effect on the microstructure and distribution of phases. The particles of reinforcing phase TiB and Ti N phases in the clad layer with the ratio of BN to Ti being 0.33. With BN content add the nucleated amount of TiB₂ increased. The content of B play an important role on the crystal of TiB₂.（2） It is analyzed that what the possibility of reaction and reaction outcome among the substances in alloy are and that what condition of thermodynamics and dynamics in the Ti N and TiB₂ forming reaction are needed. A dynamics model of Ti N and TiB₂ in-situ synthesis is presented. The reaction process of Ti+BN+Ni alloy in induction heating is as follows:（1） at first Ni60 A melt to liquid state;（2）Ti and BN liquate in the liquid Ni60A;（3）Ti diffuse to the surface of N in the Ni60 A liquid;（4）Ti reached the surface of N reacted with N into Ti N;（5） Ti reached the surface of Ti N reacted with B into TiB₂. Finally, a lot of Ti N and TiB₂ nucleus are made.（3） The in situ synthesised TiB have a whisker-like shape with the ratio of BN to Ti being 0.33. It exhibits typical crystallographic planes of（100）,（101） and（101）, and a zone axis along [010] direction. The in situ synthesised Ti N crystal is typically faceted when the molar radio of BN/Ti=0.67. The form of petal shape Ti N is the result of eutectic occurred in the last period of solidification, growing in the direction of on the cross and along the edge. The orientation relationship between Ti N and γ-Ni was observed by HREM as relationships between TiB₂ and Ti N can be determined as follows: {111}Ti N//{0001}TiB₂,<110>Ti N//<11 2 0>TiB₂, and then TiB₂ nucleus extended along the Ti N nucleus.（4） In-situ synthesized TiB₂-Ti N reinforced Ni based coating exhibited excellect microhardness and wear performance by argon shielded arc cladding. With the cladding current and cladding speed increasing, the cladding coat of microhardness first increase and then decrease, the average hardness of cladding coating is 1320HV0.5（I=120A;v=2mm/s）, which is about 5 times as high as that of substrate hardness. With an increase in the BN/Ti ratio, the cladding coat of microhardness increased. The microhardness of the layer of BN/Ti=1.0 is up to 1360HV0.5 with uneven distribution.The influence of predispose dope components and content to the coating quality is studied, with the content of（Ti+BN） increasing coating micro-hardness increased, the amount of particle phases increased, and the structure of in-situ synthesis changed.（5） Dry friction parallel test results show that the friction coefficient and weight loss of 35 Cr Mn Si steel substrate increased with the increasing of load, and the wear mechanism of the 35 Cr Mn Si steel is changed from main oxidation wear and adhesion wear. when the（Ti+BN） content reached 20% and the BN/Ti=0.67, the wear resistance of cladding coat adds up 6¹4 times compared with 35 Cr Mn Si steel substrate under different loads. The frictional coefficient of coating is decreased when frictional load is increased, and the average friction was about 0.25 under the 300 N. Meanwhile, analysis the bonding strength between TiB₂+Ti N coating and matrix, friction and wear behavior, set up some easy models, explain some test phenomenons.