The Effect Of Heat Treatment On The Structure And Properties Of Ni-based Coatings By High-frequency Induction Cladding

The wear and tear problem of the sucker rod has an important impact on the safety,efficiency and cost of oil and gas resources exploitation in China.In order to improve the hardness and wear resistance of the surface of the sucker rod and prolong its service life,the TiC/Ni composite coating was prepared on the surface of the sucker rod 35CrMo by high frequency induction cladding.Due to the defect and the unbalanced structure problems,the coating composition was uneven and the structure was unstable,resulting in unstable per formance.Therefore,in this paper,the solution treatment and aging treatment were used to improve the properties of the TiC/Ni composite coatings.By studying the microstructure and mechanical properties of the coating under different heat treatment parameters,the better solution and aging heat treatment was preferred.Then,the substrate 35CrMo was heat treated by using the preferred heat treatment process parameters to verify whether the properties of 35CrMo met the H-class sucker rod standard.The microstructure and phase of the coating were analyzed by means of optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD).The Vickers hardness tester was used to characterize the microscopic coating.Hardness,and the wear resistance of the coating was evaluated by friction and wear test and wear morphology analysis.The mechanical properties of 35CrMo alloy steel after heat treatment were evaluated by standard tensile test and Rockwell hardness test.Then the following conclusion were gotten,(1)The TiC/Ni composite coating can be successfully prepared on the surface of 35CrMo alloy steel by high frequency induction cladding technology.The TiC/Ni composite coatings were metallurgically bonded to the substrate and the microstructures are compact and uniform with little defects.The coating consists mainly of y-Ni solid solution Ni3Fe,Ni3Si and Ni3B eutectic structure and hard phase Cr23C6,CrB and TiC.The hardness was 1.3 times higher than that of the matrix.(2)After solution treatment,the composition of the coating surface and the substrate was more uniform,and the main phases of the coating were ?-Ni,Ni3Fe,Cr23C6,CrB,TiC,SiB6,NiCr2O4 and Fe2O3.The microhardness of the coating decreased with the increase of the solution treatment temperature,and it increased with the temperature increase after 910?.And the wear resistance decreases first and then decreases with the increase of the solution treatment temperature.When the solution treatment temperature was 950?,the coating had the highest hardness and the best wear resistance.The wear mechanisms of the coating were brittle fracture,adhesive wear and abrasive wear caused by hard phase spalling.(3)After aging treatment,the coatings structures were more uniform and compact.The composite coatings were mainly composed of y-Ni solid solution,Ni3Si and Ni4B3 eutectic structure,nano-scale carbide(Fe,Ni)23C6,TiC,SiB6 and other hard particles,such as Cr23C6 and Cr2B hard phases,and ? phase(Fe-Cr)particles.Appropriate aging temperature and aging time could significantly improve the hardness and wear resistance of the coating.The coating after aging at 510? for 8 h and aging at 540? for 4 h had a hardness of about 4.2 times that of the 35CrMo matrix,and the wear whight loss was reduced by 62.2%and 61.5%,respectively,compared with the 35CrMo matrix material.The wear mechanisms of the coatings changed from brittle fracture,adhesive wear and abrasive wear gradually to only adhesive wear and abrasive wear.(4)The preferred heat treatment process parameters that can obtain the optimal performance of the coating wouldn't significantly reduce the me chanical properties of the substrate 35CrMo alloy steel.Its tensile strength,yield strength,elongation and core hardness can reach the standard of H-class sucker rod in SY/T 5550-2012 Hollow Sucker Rod,which met the actual production requirements.