The thermal and mechanical properties of W-20wt%Cu nanocomposites were investigated. W/Cu nano crystalline powders were fabricated by spray conversion process. Spray conversion process using W and Cu salt as start-up materials was one of the chemical method to fabricate nano crystalline powders. Fabricated W/Cu nano crystalline powders using spray conversion process had average W particle size ranging from 30 to 50nm. The W/Cu nanocomposites were fabricated by the liquid phase sintering in $H_2$ atmosphere at temperature ranging from 1200℃ to 1450℃ for 1hr using these nano crystalline powders. The W-20wt%Cu sintered at 1250℃ for 1hr showed the relative density of 99% and the coefficient of thermal expansion of 7.8 ppm/K. The thermal conductivity was 235W/mK which was about 20% higher than commercial product. The coefficient of thermal expansion was insensitive to porosity but the thermal conductivity was very sensitive to porosity in sintered W-20wt%Cu. When the sintering temperature ranged from 1200℃ to 1400℃, the W grain size and the relative density of sintered W-20wt%Cu were increased. The W-20wt%Cu sintered at 1200℃ for 1hr showed the relative density of 95% and its thermal conductivity was 205W/mK which was lower than others. When the sintering temperature was over 1300℃, the relative density of sintered W-20wt%Cu was higher than 99% and the thermal conductivity was ranged from 235 to 240W/mK. The thermal conductivity change with porosity in sintered W-20wt%Cu was predicted using modified Maxwell`s Model. In these results, the thermal conductivity decreased with increasing pores because pores inhibit the thermal conduction of Cu matrix. Mechanical properties of W-20wt%Cu were observed sensitively dependant on the porosity. Tensile strength and elongation enlarged with increasing the relative density. The sintered W-20wt%Cu which had relative density of 99.8% showed 864MPa, 235GPa in tensile strength and Young`s modules, respectively. When Co or Ni was added to W-20wt%Cu and sintered at 1250℃ for 1hr, the W grain size and the relative density enlarged with increasing Co or Ni additive. The coefficient of thermal expansion was insensitive to amount of Co or Ni additive up to 0.5wt%, but the thermal conductivity was greatly decreased with increasing Co or Ni additive. In case of Ni additive, All Ni was solved in Cu matrix. The thermal conductivity of Cu-Ni solid solution is much lower than that of pure Cu and this lower thermal conductivity of Cu matrix decreases the thermal conductivity of overall W-20wtCu nanocomposites. Apposite to Ni, Co makes intermetallic compounds with W instead of solution in Cu matrix. In this reason, Co additive showed more effective on densification and higher thermal conductivity than Ni additive.
