Technology And Friction-wear Behavior Of Laser Clad Cu-TiB₂Coating On Pure Copper

High strength and high conductivity materials have been widely used in mechanical and aerospace industry, such as vacuum electronic devices, electrical contact materials, rail materials of electromagnetic launcher, etc. Copper and copper alloy are the traditional materials with high conductivity. However, their applications are greatly confined because of their low strength and poor wear resistance.Cu-TiB2composites coatings were prepared by laser cladding on the pure copper to meet the requirement of high electrical conductivity and good wear resistance. In view of the interfacial bonding between the coating and the substrate, several solutions were tried in the paper for obtaining appropriate processes. The microstructure of Cu-TiB2composites coatings and their interfacial bonding were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Through the pin-on-disc friction and wear test at room temperature and elevated temperature, the tribological behaviors of the Cu-TiB2coatings were investigated at different speeds and under different loads. The wear surfaces of Cu-TiB2coatings were studied by SEM, and the friction and wear mechanism under different conditions were investigated. This work provided experimental and theoretical basis for related real applications.In order to obtain suitable process parameters, the Cu-5wt.%TiB2coatings were clad on the pure copper by CO2laser and YAG pulsed laser respectively. The structure and properties of the coatings, e.g. the macro morphology, microstructure and electrical conductivity, were compared and studied. The YAG pulsed laser was chosen for preparing the coatings. With the increase of TiB2content, the micro-hardness of Cu-TiB2coatings increased while the conductivity decreased. When the content of TiB2was2wt.%,5wt.%and10wt.%, the micro-hardness of the coatings was approximately95HV0.1,105HV0.1and152HV0.1, and the electrical conductivity was39.5%IACS,35.2%IACS and28.2%IACS respectively.The friction and wear behavior of pure copper and Cu-TiB2coatings under various loads and different speeds were studied at room temperature. The results shown that, the wear-resistance of the coatings was improved with the increase of TiB2content and the wear mechanism should be influenced by the change of load and sliding speed. The wear mechanism of the coatings is mainly attributed to abrasive wear and adhesion wear under low load and velocity. With the increase of loads and sliding speed, the heat produced per unit time and plastic deformation on contact surface increased, and oxide films tended to form on the friction surface layer. As the heat increased to a certain value, the oxidation layer peeled off. The wear mechanisms of the coatings transferred to adhesion wear, oxidation wear and delamination wear.The friction and wear properties of Cu-TiB2composites at elevated temperatures were evaluated. The friction coefficient and wear rate of the coatings decreased with the increase of TiB2content, indicating improved tribological properties at evaluated temperature with the addition of TiB2particle. The plastic deformation and softening phenomena easily occurred, and oxide films were formed on the friction surface layer. The abrasive wear, adhesion wear and oxidation wear under low load and sliding speed were involved in the friction process. With the increase of loads and sliding speed at elevated temperatures, the coatings suffered severe wear because of the acceleration of the plastic deformation and softening phenomena and the main wear mechanism was delamination wear and adhesion wear.