Sintering process optimization for Cu-Al2O3 powders synthesized by novel method

Abstract

This paper presents sintered materials for use as contacts produced via novel synthesis method of starting powders by combination of explored conventional routes of thermochemical synthesis and mechanical alloying. Starting raw materials for powder synthesis by thermochemical route were soluble salts, nitrates of copper and aluminum of p.a. quality, dissolved in distilled water (50wt.% solution) in suitable ratio for final powder to contain 50wt.% of Al2O3 in structure. Nitrate solution was spray dried and subjected to heat treatment (900 ºC/1h). Obtained oxides were reduced in hydrogen atmosphere (flow rate 20L/h at 350 °C for 1h) in order to obtain composite of Cu-Al2O3. Produced powders were used for mechanical alloying of atomized copper (5h, 300 min-1). Final amount of alumina Al2O3 in composite powder were 1, 1.5 and 2 wt.%. After mechanical alloying obtained powders were compacted by a uniaxial pressing (8×32×3mm, 500 kN). Sintering of samples was performed in hydrogen atmosphere in isothermal conditions at five different temperatures in the range from 725-925 °C for 15 to 120 min. Results of characterization show, that increase of Al2O3 content has more noticeable effect on the electrical conductivity and hardness than sintering temperature and time. With increase of Al2O3 from 1 to 1.5 wt.% there is a slight decrease in both investigated properties, while with increase up to 2 wt.% Al2O3 significant decrease in electrical conductivity and hardness of sintered samples is observed. According to achieved results optimum sintering parameters for composite materials produced by novel synthesis method based on copper with dispersed 1% Al2O3 are 875 ºC/60 min. Based on the achieved results, this method provides production of contact materials with good combination of electrical and mechanical properties, but with estimated lower production costs.