Investigation On Texture And Internal Stress Of Electrodeposited Ni-ZrC Composite Coating

Texture, internal stress and microstructure of electrodeposited Ni matrix composite coating is the dependence for the properties and behavior of the coating. The existence of the second phase particles in the composite coating, leads the texture, internal stress and microstructure of composite coating different from those of pure metal coating. In this dissertation, ZrC nano-particles(nZrC) and Zr C micro-particles(mZr C) enhanced Ni matrix composite coatings are prepared by composite electrodeposition technique. The influence of electrodeposition parameters and Zr C particles on the microstruct ure of Ni-ZrC composite coating has been investigated. By using X-ray diffraction(XRD) analysis technique, the investigation focuses on the influence parameters, modification methods, and formation and evolution mechanisms for the texture, internal stress and microstructure of Ni-Zr C composite coating.By using relative texture coefficient(RTC), polo figures reconstructed by Rietveld refinements and measured by XRD, texture evolution of nickel matrix coatings has been investigated. The results of those three methods are consistent with each other. With increasing of current density, Ni-Zr C coating gradually exhibit [200] fiber texture, which is depressed with increasing of Zr C particle concentration in electrolyte. At the same current density and particle concentration, intensity of [200] fiber texture of Ni-nZr C coating is lower than that of Ni-mZr C coating. At the initial stage of electrodeposition, both Ni and Ni-Zr C coatings exhibit [111] initial texture. With the prolonging of electrodeposition, texture of pure Ni coating is gradually changed to be strong [200] texture and the crystalline preferred orientation of Ni-Zr C coating is gradually disappearing. The texture evolution of Ni-ZrC coatings with Zr C concentration in the electrolyte can be divided to two stages. At the first stage, fiber texture of Ni-Zr C coating is gradually depressed with the increasing of Zr C concentration. However, there is almost no crystalline preferred orientation in the Ni-Zr C coating and the texture is not changing with the increasing of Zr C concentration at the second stage.Combining Voigt and Reuss model, by using the modified Hill model, X-Ray stress measure fuction for the coating with fiber texture has been improved. The internal stress of electrodeposited Ni-Zr C coating has been studied by the improved X-Ray internal stress analysis. It has been found that the internal stress of Ni-Zr C coating doesn’t change much with the increasing of applied current density, but decreases with the increasing of particle concentration in electrolyte. The internal stresses of Ni and Ni-Zr C coatings are first decreasing then increasing with the increasing of thickness during the electrodeposition. By using ultrasound treatment during electrodeposition, pre-tension stress treatment on substrate, the tensile internal stress of Ni-Zr C coating can be reduced. By using thermal treatment, the internal stress of Ni and Ni-Zr C coating can be turn fro m tensile to compression, and the compression stress increases with increasing of the temperature.By using Voigt line profile analysis and Rietveld refinement, microstructure evolution of Ni-Zr C coating with electrodeposition parameters and Zr C particles concentration and particles size have been studied. The evolution of microstructure can also be devided into two stages. At the first stage, [200] related crystallite size of Ni-ZrC coating decreases, [111] and [220] related crystallite sizes change not much with the increasing of Zr C concentration in electrolyte. At the second stage, crystalline preferred orientation of Ni-ZrC coating no long change, crystallite sizes gradually decrease, microstrains gradually increase with the increasing of Zr C concentration in electrolyte. Combining the result of texture analysis, those two stages can be named as texture-modified stage and crystallite-refined stage. By using thermal annealing treatment and in-situ XRD analysis technique, the activation energy for crystallite growth of Ni-ZrC coating has been investigated, which is calculated to be 51.88 KJ/mol at low temperature and 112.9 KJ/mol at high temperature.The relationship between mechanical properties and electrodeposition conditions of electrodeposited Ni matrix coating has also been discussed. With the increasing of Zr C concentration in electrolyte or the decreasing of applied current density, microhardness of Ni-mZrC coating is increasing and the highest value is 475 HV, microhardness of Ni-nZrC coating is first increasing then decreasing with the highest value of 435 HV. By using in-situ XRD analysis technique, mechanical behavior of Ni-mZr C coating has been studied. The Young’s modulus, Poisson’s ratio and yield strength of Ni-mZr C coating are calculated to be 236 GPa, 0.297 and 290 MPa, respectively.