Estudo da densificação e microestrutura de um compósito (Mo-Cu) preparado a partir do pó de heptamolibdato de amônia e cobre

Abstract

The Mo-Cu system is a composite used in the electronics industry as electrical contact material and welding electrode resistance and also as a heat sink and microwave absorber in microelectronic devices. The use of this material in such applications is due to the excellent properties of thermal and electrical conductivity and the possibility of adjusting its coefficient of thermal expansion to satisfy those of materials used as substrates of semiconductors in the microelectronics industry. The powder metallurgy, through grinding processes, pressing shaping and sintering, is a viable technique for the consolidation of this material. However, the mutual insolubility of both phases and low liquid wettability of Cu on Mo difficult their densification. Mechanical alloying is a powder preparation technique used to produce nanocrystalline composite powders with amorphous phase or extended solid solution, which increase the sinterability of immiscible systems such as Mo-Cu. This work investigates the influence of ammonia heptamolybdate (HMA) and high-energy ball milling on the preparation of HMA-20%Cu and HMA-50%Cu composite powders as well as the effect of their preparation on the densification and structure of the Mo composite -Cu produced. HMA and Cu powders in the proportion of 12.66% and 35.21% by mass of Cu were prepared by manual mixing and high energy ball milling techniques in a planetary mill. These powders were milled for up to 50 hours. To observe the evolution of particle characteristics, powder samples were collected after 2, 20 and 50 hours of milling. Cylindrical samples with 5 and 8mm diameter and 3 to 4mm thickness were obtained by uniaxial pressing at 200MPa for both mixed and milled powders. These samples were sintered at 1200°C for 60minutes under an atmosphere of H2. To verify the effect of the heating rate on the structure of the material during the decomposition and reduction of the HMA, the rates of 5 and 10°C/min were used. To verify the effect of the heating rate on the structure of the material during the decomposition and reduction of the HMA, the rates of 5 and 10°C/min were used. The powders and structures of the sintered bodies were characterized by XRD, SEM and EDS. The densities of the green and sintered bodies were measured using the geometric (mass/volume) method. Vickers microhardness measurements with 1N load for 15s were performed on the sintered structures. Electrical characterizations were performed to measure the resistivity of sintered specimens. The density of the sintered structures at a heating rate of 10°C/min. reached 97% of the theoretical density of the material, while the density of the sintered structures at 5°C / min. reached only 96% of theoretical density.