激光重熔/电化学沉积交互处理铜涂层的微观组织及机理研究

Microstructure and Mechanism of Copper Layer Processed with Laser Remelting and Electrochemical Deposition Interaction Process

为解决钛合金上直接电沉积铜沉积质量和结合力差的问题,本团队采用激光重熔/电化学沉积交互进行的方法在TC4合金上制备铜涂层,并采用光学显微镜、扫描电子显微镜、X射线衍射仪、自动划痕仪等分析了铜涂层的表面形貌、截面元素组成、截面厚度、物相、结合力、导电性和抗高温氧化性能。通过激光重熔获得了含有CuTi、Cu_(2)Ti、Cu_(4)Ti等金属间化合物的复合涂层,这使得沉积表面获得更多的活性位点,进而提高了沉积速率与沉积质量。实验结果显示:相比于传统的电沉积,激光重熔/电化学沉积交互处理可使重熔层表面的电极响应速率提高约44%,沉积层表面的孔隙明显减少,晶粒间结合更紧密;激光重熔/电化学沉积交互处理能显著提高钛合金表面铜沉积层的沉积质量、抗高温氧化性能以及涂层与基体间的结合力。

Objective To improve the poor deposition quality and binding force of copper electrodeposited directly on titanium,a new laser remelting/electrochemical deposition interaction process is proposed to prepare a titanium-copper alloy layer and thicken the copper layer.The micromorphology,cross-sectional elements,coating thickness,and phase of the composite remelting layer obtained from laser remelting/electrochemical deposition interaction process are investigated.The effect mechanism of the laser electrochemical interaction on the electrical conductivity,high-temperature oxidation resistance,and adhesion to the substrate of the composite coating is discussed.Methods First,laser melting pretreatment is performed to replace the conventional chemical pretreatment,which simplifies the process,reduces environmental pollution,and reduces hazard to the human body.Thickening of the copper layer and its metallurgical binding to the matrix are achieved via laser remelting and electrochemical deposition.The first laser remelting is performed to obtain a titanium-copper seed layer,whereas the second laser remelting is performed to modify the surface of the deposited layer and reduce defects,such as porosity,crevices,and grain agglomeration.Consequently,the copper layer particles become refined and denser,which can facilitate the subsequent electrodeposition as well as thicken and improve the performance of the copper layer.The morphologies of the composite coating and composite remelting layer are characterized via scanning electron microscopy(Sigma HV-01-043,Carl Zeiss),and the elemental distribution on the cross-section of the composite remelting layer is analyzed using an X-ray energy-dispersive spectroscope connected to a scanning electron microscope.The cross-sectional morphology and thickness of the composite coating and composite remelting layer are observed using an optical microscope(Axio Imager A2M,ZEISS).The composite remelting layer obtained via interactive treatment is analyzed using an Xpert Pro X-ray diffractometer(PANAlytical Company,Netherlands).The adhesion between the composite coating and composite remelting layer achieved via the interactive treatment is evaluated using an automatic adhesion scratch tester(WS-2005).Results and Discussions The grains of the deposited layer obtained via the conventional electrodeposition are relatively coarse.Large gaps appear in the intergrain bonding sites.The surface of the deposited layer is loose and porous,and sediment agglomeration is severe.After laser remelting and electrochemical deposition are performed,the pores on the surface of the deposited layer are reduced significantly,the grain-to-grain binding is firm,and the compactness is improved.Although the number of laser remelting/electrochemical deposition interaction processes is increased,the electrode response rate and polarization do not decrease(Figs.3,4,5,and 6).Laser remelting causes mutual diffusion between titanium and copper,thus resulting in a composite remelting layer containing titanium-copper intermetallic compounds such as CuTi,CuTi2,and Cu_(4)Ti.The generation of these intermetallic compounds increases the deposition surface active sites,enhances the polarization of electrodeposition,and accelerates the electrodeposition reaction rate.Under the same electrodeposition time(30 min),the thickness of the deposited layer obtained via the conventional electrodeposition is 79.67μm,and the thickness of the composite coating obtained via laser remelting and electrochemical deposition is 145.36μm(Figs.7,8,and 9).The copper deposited layer achieved via laser remelting and electrochemical deposition shows a higher binding force with the matrix than that achieved by conventional electrodeposition.Under a 50 N load force,the scratch morphology of the deposited layer obtained via laser remelting and electrochemical deposition remains relatively complete.The composite coating indicates good adhesion to the matrix(Figs.10,11,and 12).The composite remelted layer achieved via laser remelting exhibits better resistance to high-temperature oxidation than the copper layer.In addition,the copper layer achieved via conventional electrodeposition is more oxidized than the copper layer achieved via laser remelting and electrochemical deposition(Fig.13).Owing to the effect of laser remelting,interdiffusion occurs between titanium and copper,thus resulting in the formation of titanium-copper intermetallic compounds and a slight decrease in the conductivity of the composite coating.However,as the deposition time increases,the titanium content in the composite coating achieved via the subsequent laser remelting and electrochemical deposition decreases gradually,thus resulting in an increase in the electrical conductivity of the composite coating(Fig.14).Conclusions Compared with conventional electrodeposition,the combination of laser remelting and electrochemical deposition can increase the electrode response rate on the surface of the remelted layer by approximately 44%.The pores on the surface of the deposited layer are reduced significantly,and the grains are bonded firmly.The results show that the combination of laser remelting and electrochemical deposition can significantly improve the deposition quality of the copper deposited layer on the titanium alloy surface,the bonding force with the substrate,and the high-temperature oxidation resistance.