Investigations On Microstructure And Properties Of Tungsten-copper Alloys Prepared By Activated Sintering

Tungsten-copper alloys combine the excellent properties of the two components,such as the high temperature resistance,high strength,high density and resistance to arc corrosion of tungsten and high ductility,high electrical and thermal conductivity of copper.It is widely used in the fields of electrical contact materials,electronic packaging materials,armor materials and nuclear fusion materials.However,due to the mutual insolubility of the two components of the tungsten-copper alloys,the wettability of the tungsten-copper interface is poor.And it is difficult to be dense during the sintering process and to obtain an ideal microstructure and performance.Therefore,improving the wettability of the tungsten-copper interface has become an urgent problem to be solved.In this study,the tungsten-copper composite powder was activated by adding activating elements.Activated sintering was combined with spark plasma sintering to improve the sinterability of the tungsten-copper alloys,and a uniform and compact structure and excellent comprehensive performance of the alloys were expected.In this paper,the third phase activating element was added by chemical plating method and mechanical alloying method to prepare tungsten-copper composite powder.The structures and properties of the alloys under different powder preparation processes and different activating elements were compared and analyzed.W-Ni-Cu alloys with different compositions were prepared by chemical plating and SPS sintering technique.The coated tungsten powder exhibited a spherical shape.The surface of the coatings was uniform and integrated,and the oxygen content was low.The tungsten-copper composite powder prepared by chemical plating was used to study the SPS sintering process of tungsten-copper alloys.It was found that the alloys had the highest density and mechanical properties when sintered at 1030°C.The W-Ni-Cu alloy prepared by chemical plating had a preliminary network structure.The tensile strength of W/Ni/Cu-15Cu alloy was 379 MPa.Compared with pure tungsten prepared by SPS sintered at1700°C and alloys without Ni element,the tensile strength of W/Ni/Cu-15Cu was 1.5 times and 4 times higher respectively.Different compositions of W-Ni-Cu alloys were prepared by mechanical alloying of two-step ball milling and SPS sintering technique.The alloy prepared by mechanical alloying of Cu(Ni)exhibited a dense network structure of copper-net and tungsten-island.And its structure was uniform and W-W connectivity was low.The distribution of tungsten and copper of alloys prepared by W(Ni)mechanical alloying was uneven,there were more"blank areas"without tungsten or copper.The mechanical properties and densities of alloys prepared by mechanical alloying method were higher than those prepared by chemical plating method.The tensile strength of Cu(Ni)series alloys reached 488 MPa and the elongation was 3.30%,which was 2.21 times and 0.83 times higher than that of pure tungsten.However,the addition of Ni element greatly affected the thermal conductivity of the alloys.Thermal diffusivities of W-Ni-Cu alloys was much lower than that of pure tungsten.W-Cr-Cu alloy was prepared by mechanical alloying method and SPS method.Compared with Ni element,Cr had more obvious effect on improving the sintering performance of tungsten-copper alloys when it was used as activating element.And Cr element had a less negative effect on the thermal conductivity of the alloys.With the method of mechanical alloying,the mechanical properties and thermal conductivity of W-Cr-Cu alloys were better than W-Ni-Cu alloys.Alloys prepared by Cu(Cr)mechanical alloying had good W-Cu interface and continuous network structure with best tensile strength of 669MPa,elongation of 3.85%,which was 3.4 times and 1.13 times higher than pure tungsten respectively,and 0.37 times and 0.17 times higher than W-Ni-Cu alloys.The best thermal diffusivity of W-Cr-Cu was 64.05 mm~2/s,which was 50%higher than pure tungsten.In tensile fracture,the Cu(Cr)series alloys were mainly tungsten-copper interface fracture and cleavage fracture of tungsten particles.The addition of the activating element increased the interfacial strength of the tungsten-copper,and made the structure of alloys more uniform,the W-W connectivity less.Thereby the particle debonding of the tungsten particles and the debonding of the tungsten-copper interface reduced and the cleavage of the tungsten particles increased in tensile fracture.Finally,the properties of the alloys were improved.