Research On Nickel Electroplating As A Transition Layer Of Laser Cladding Gradient Coating

Despite the use of laser cladding technology has been successfully prepared a very good surface wear resistance composite materials, but the crack is difficult to avoid serious effects. On how to reduce and prevent domestic and crack a lot of research, generally considered gradient coating helps to reduce and avoid cracks. Current gradient intermediate layer coating by laser cladding or the general thermal spray and other thermal processing methods available. Transition layer of thermal processing methods exist to obtain the internal stress, transition will affect the internal stress and surface metallurgical bonding of the laser cladding layer. In most cases, transition layer and the cladding layer after cooling performance of macro-tensile stress. The greater the internal stress of transition layer, the impact of the laser cladding layer is also greater. Therefore, if the transition layer can reduce the internal stress, can reduce the stress of the transition layer of the inner cladding stress, which further enhance the improvement effect of interlayer on crack. In this paper, obtained by plating cold stress that the smaller buffer layer, and from many of its cladding layer.Q235 steel plate in the plating layer of nickel as the transition layer gradient coating, the surface of the nickel coating, the use of high-power CO2 laser, powder feed with synchronized methods, preparation of Ni60A+25% WC clad layer from the alloy powder. In order to play a role in the transition of nickel plating, nickel plating in order to prevent the cladding through the process of being molten pool, can not let the pool is deeper than the thickness of nickel coating. Therefore, before the experiment in the laser cladding, cladding need mathematical model predicts the pool depth, the development process parameters. In this paper, heat transfer theory and the principle of superposition, proposed by Alireza Fathi TEMoo fundamental mode laser cladding temperature field model based on multi-mode derived mathematical model of temperature field in laser cladding. The experimental parameters of the physical properties of materials, process parameters and dimensions on behalf of the cladding layer into the mathematical model of temperature field by a double integral equations. Demand the use of double integral composite trapezoidal formula as the basic numerical solution algorithm, using Matlab software, programming, solve the double integral equations. By comparing the results of operations to optimize process parameters, finally got a set of compliance requirements of experimental design parameters, and use this set of parameters for laser cladding experiment.Using optical microscopy, scanning electron microscopy, X-ray diffraction and microhardness of the samples cladding, coating and matrix for composition, organization and performance testing. The results show that through the rational process and the plating parameters can be relatively, uniform and compact 0.3mm thick layer of nickel plating; numerical simulation and experiments using the same laser cladding process parameters, numerical simulation and prediction of the cladding layer of depth and laser cladding experiments close to the depth of the cladding layer to prove mathematical model can accurately predict pool depth; successfully obtained Ni60+25% WC laser cladding, cladding layer depth is less than the thickness of nickel plating, to experimental design requirements, the hardness range of cladding layer between 476-533HBV; by scanning electron microscopy revealed cladding layer and the interface between the plating layer to form a thin banded structure, Q235 plating layer and the interface between substrate not found banded structure, the interface boundary was, EDS scan the surface of cladding layer and the formation of metallurgical bonding plating, plating layer and the Q235 substrate not formed between the metallurgical bonding; laser cladding, the cladding layer in the substrate surface where no found that coating cracks or coating and matrix stripping phenomenon; base structure of the heat-affected zone thickness is about 0.1mm, the formation of a martensite structure and the fine grain zone, near the nickel coating matrix hardness 159HBV, heat affected zone around the The average hardness of the matrix high 30HBV.In this paper, this cold was obtained by plating transition layer, and multi-mode laser cladding derived mathematical model of temperature field, in order to further reduce cracking and improve the quality of laser cladding, access to the smaller interlayer stress laid a foundation.