Study On Nano-ZrO₂/Cu Composite Fabricated By In-Situ Chemical Route

The particle reinforced copper matrix composite is a kind of excellent candidate material for the applications of electrical resistive welding electrode, leading frame, electric contact material and so on because of its high specific strength, high specific modulus, excellent electric conductivity and high temperature performance. But its application is restricted to avoid the poor wetting and inhomogeneous dispersion between the reinforcement and the matrix by traditional powder metallurgy and casting techniques. Nano-sized ZrO₂ reinforced copper matrix composite powders were fabricated by in-situ chemical route and then nano-ZrO₂/Cu composites were fabricated by powder metallurgy.ZrO₂-Cu composite powders with 0⁸wt% ZrO₂ content were fabricated by in-situ chemical route. The influence of technical parameters, which include reactive concentration, calcination temperature, reductive temperature and time on the performance and microstructure of composite powders was analyzed. The influence of 3mol%Y2O3 addition on ZrO₂ crystal structure, composite microstructure and properties was discussed. The results showed that the stabilizer Y2O3 was helpful to decrease copper crystal size and to improve composites comprehensive properties such as hardness and electric conductivity. When ZrOCl2 was 0.1mol/L, ammonia was 0.5 mol/L, calcination temperature was 500℃, reductive temperature was 650℃and time was 45min, nano-ZrO₂ particles were fine and dispersed in copper matrix homogenously. Composite powder sizes were uniform and less agglomeration. Consequently, nano-ZrO₂ reinforced copper matrix composite had the best comprehensive properties.ZrO₂/Cu composites were fabricated by powder metallurgy. ZrO₂-Cu composite powders were cold pressed and sintered. The optimize PM technical parameters were acquired by analyzing the influence of initial pressure, sintering temperature, sintering time and repressing pressure on composite microstructure and properties.At the same time, the effect of ZrO₂ content on composite performance was discussed. The results showed that the reinforcement of nano-ZrO₂ could improve composite tensile strength and hardness, but would decrease composite electric conductivity. Resistive softening property was improved obviously with the increase of ZrO₂ content.Nano-ZrO₂/Cu composite microstructure and interfacial characterization were analyzed by transmission electron microscope(TEM) and scanning electron microscope(SEM). The influence of ZrO₂ morphology on stress distribution and composite mechanical properties was analyzed by means of finite element method. Effect of fine grain and dispersive strengthing on nano-ZrO₂/Cu composite was discussed. The results demonstrated that nano-ZrO₂/Cu composite structure was compact, grain was fine and the ZrO₂ particles were homogenously dispersed in matrix. With the increase of nano-ZrO₂ content, defects in compose increased. Two crystal structures of monoclinic and tetragonal ZrO₂ existed in the copper matrix. Interfaces between monoclinic ZrO₂ and matrix were directly integrating interfaces which were clear and had no reaction. Interfaces between tetragonal ZrO₂ and matrix were solving dispersion and direct integrating interfaces. The stress in interface of monoclinic ZrO₂ particle tip was much larger than that of tetragonal ZrO₂. Therefore, inner cracks were more easily induced in the tip of monoclinic ZrO₂. Fine grain strengthening and dispersive strengthening were main reinforcement routes. Fine grain strengthening took 67.43% of total composite strength increment, while dispersive strengthen took 11.73%.Abrasive and wear properties of nano-ZrO₂/Cu composite were studied by pin-on-disk wear process. The influence of load, rotating speed and number on composite abrasive properties were discussed. The results showed that wear circls properties improved with the increase of nano-ZrO₂ particles. Composite wear rate increased gradually with the increase of load, rotating rate and rotating circles. While friction coefficient increased in different forms, which were resulted from different wear mechanisms. The process of ZrO₂/Cu composite main wear mechanisms was oxidation wear→oxidation wear+adhesion wear→oxidation wear+adhesion wear+ shell layer wear→adhesion wear+shell layer wear. When main wear mechanisms were oxidation wear and adhesion wear, nano-particles were helpful to improve composites wear resistive properties. When main wear mechanisms were shell layer wear and three body grain-abrasion, agglomeration region of nano-particles, cavity and loosen deteriorated composite wear resistive properties.