Influência da moagem de alta energia e do precursor heptamolibdato de amônia na densidade e microestrutura do compósito Mo-27,82%vCu

Abstract

The Mo-Cu composite is a material used for electrical contact and heat sinks due its excellent properties of thermal and electrical conductivity and cooper good workability allied to its great resistance welding and electrical arc erosion of molybdenum. In the first case, simple shapes are required and the infiltration of the pre-sintered molybdenum skeleton with liquid copper is the technique of consolidation normally used. On the second case, more complex geometries and a density near or equal the theoretical density are required for the application as heat sink. The powder metallurgy is a very viable route for the production of these components, through the techniques of powder preparation processed by mechanical alloying, compaction or casting. However, the low dissolution of one component in the other and the liquid copper high contact angle on the molybdenum phase difficult the obtainment of a density near or equal the theoretical density. This research investigates the obtainment of the Mo-27,82%𝜈Cu composite prepared by mechanical alloying and mechanical mix of the copper powders and ammonium heptamolybdate (HMA) of chemical formula (NH4)6Mo7O24 .4H2O, decomposed and reduced by 𝐻2 before and during the sintering, showing two different fabrication routes for the material. The compaction pressure influence at the densification and microstructure of the Mo-27,82%𝜈Cu composite were also investigated. For this, the powder milled for 50 hours and the mixed powder were pressed at 200, 400 and 600 MPa. In order to understand the temperature effect at the density and microstructure were sintered at 1000, 1100 and 1200 °C. The bodies pressed at 200 and 400 MPa and sintered at 1200°C reached 94±0,4 % of the theoretical density. However, those which were decomposed and reduced during sintering showed manufacturing cracks. On the other hand, the bodies sintered at 1100 °C reached the highest microhardness value (571,70±78,82 HV), despite a low theory density (79.17 ± 1.78%).