Investigation On The Prepration And Characterization Of The W-Cu-Zn Alloy With Low W-W Contiguity

This study is a basic research undertaken for the research and development of a new type of military tungsten alloy. Contraposing the high W-W contiguity and low tensile ductility of the W-Cu alloy fabricated by the traditional infiltration method, we designed and fabricated a type of W-Cu-Zn alloy with low W-W contiguity. The electroless plating process was used to prepare the copper-coated tungsten powders, and three different preparation methods were used to fabricate the W-Cu-Zn alloy with low W-W contiguity. In the first method, the copper-coated tungsten powders were mixed with zinc powder, and the mixed powders were sintered into a bulk by SPS(Spark Plasm Sintering). In the second method, the copper-coated tungsten powders were mixed with zinc powder, and the mixed powders were pressed into a W-Cu-Zn preform by CIP(Cold Isostatic Pressing), and then the W-Cu-Zn preform was sintered into a bulk by SPS. In the third method, the copper-coated tungsten powders were pressed into a W-Cu preform by CIP, and then the W-Cu preform was infiltrated with H80 brass, and finally got a dense bulk. A systematic analysis on the microstructure of the prepared W-Cu-Zn alloys was conducted using SEM, TEM and XRD analysis methods. The static and dynamic mechanical properties of the W-Cu-Zn alloys prepared by three different methods were studied. The process factors which affect the microstructure of the binder phase and the mechanical properties of the alloy were analyzed. Meanwhile, the main failure mechanism of the alloy was revealed.The results of the analysis on the preparation process show that, the 80W-14Cu-6Zn alloy with a relative density of 96% and low W-W contiguity of 25% was prepared by the combined process of electroless plating and SPS method. The 80W-14Cu-6Zn alloy with a relative density of 99% and aW-W contiguity of 42% was prepared by the combined process of electroless plating, CIP and SPS method. The results of the analysis on the mechanical properties show that, the strength and ductility of the alloy were improvd after the introduction of CIP process which can increase the relative density of the alloy. The increased relative density is beneficial to the improving of the mechanical properties of the W-Cu-Zn alloy. While, the mechanical properties of the prepared W-Cu-Zn alloys were still lower than the 80W-20 Cu alloy prepared by traditional infiltration method. The results of the analysis on the microstructure and failure mechanism show that, the Zn element was non-uniformly dispersed in the Cu-Zn matrix of the W-Cu-Zn alloy prepared by the above two methods. The cracks can easily generate and propagate in the Zn enrichment region, and propagate through the Cu-Zn matrix and W-W interface, thus decreasing the strength and ductility of the alloy.In order to solve the problems of low componential homogeneity and low mechanical properties of the W-Cu-Zn alloy prepared by the first two methods, the processes of electroless plating, CIP and infiltration method were used to fabricate the W-Cu-Zn alloy with low W content of only 66%, low W-W contiguity of only 10% and high relative density of 98%. Microstructure analysis shows that, the alloy has high microstructural homogeneity and the Zn element is uniformly dispersed into the Cu-Zn matrix. The Cu-Zn matrix is composed of α-phase Cu-Zn solid solution and nano Cu3 Zn particals. The results of the analysis on the compressive mechanical properties show that, the dynamic compressive strength of the alloy reaches 1061 MPa, and when the true strain reaches 0.8, the alloy still has not failed. By contrast, the dynamic compressive critical failure true strain of the W-Cu-Zn alloy prepared by the traditional infiltration method is only 0.38. The results of the analysis on the quasi-static tensile mechanical properties show that, the ductility of the alloy is evidently improved, and the tensile enlongation reaches 7.8% which increased by 56% compared with the tensile enlongation of 80W-20 Cu alloy prepared by traditional infiltration method.The failure mechanism of the W-Cu-Zn alloy prepared by the combined process of electroless plating, CIP and infiltration method show that, the entire deformation of the alloy is mainly accomplished by the plastic deformation of the Cu-Zn matrix, and the W particals hardly deformed under the applied load. Thus, the strength of the alloy is mainly decided by the strength of the Cu-Zn matrix. The low W-W contiguity and high structrural and componential homogeneity of the alloy is beneficial to the plastic deformation of the alloy, thus increasing the ductility of the alloy. Meanwhile, the introduction of Zn into the matrix has the solid solution strengthening effect, and the homogenously dispersed Cu3 Zn particals show the precipitation strengthening effect. These two strengthening effect both increase the strength of the alloy. Besides, the tensile failure mechanism show that, the tensile fracture mode of the alloy is maily comprised of the transgranular cleavage fracture of the W particles and ductile tearing of the Cu-Zn matrix. The low W-W contiguity of the alloy effectively avoids the problem of decreased ductility caused by the failure of the W-W interface. The transgranular cleavage fracture of the W particles also indicates the high bonding strength beween W-matrix interface.