Estudo do tempo de moagem e da sinterização na microestrutura e densificação de um compósito Mo-Cu

Abstract

The combination of a metallic material such as molybdenum (Mo) and an external transition metal such as copper (Cu) allows the formation of a compound that has both good workability and high electrical and thermal conductivity of copper and high wear resistance of molybdenum. These compounds are widely used in applications that require high thermal and mechanical performance, such as electrical contacts, heat sinks, and encapsulation of microwave devices. The production of these materials through powder metallurgy rotation, consisting of the steps of powder mixing or high-energy milling, compaction, and liquid-phase sintering, enables the manufacture of parts with complex geometries and controlled compositions. However, obtaining densified compounds faces considerable challenges due to the mutual insolubility between molybdenum and copper. This work investigates the influence of the milling time of HMA-15.34%Cu powders on the characteristics of Mo-25%Cu powders and on the densification, microstructure, and properties of the sintered compacts. The HMA-15.34%Cu powders were ground in a Pulverisset 7 planetary mill with a container and carbide balls. The mass ratio of powder to balls used was 1:5. These powders were milling under ethyl alcohol at 400 rpm for 20h. Then, they were reduced to 800°C in a tubular resistive furnace under a hydrogen (H2) atmosphere of 316 ml/min. The Mo-25%Cu powders found were compacted at 250 MPa in a uniaxial cylindrical die and their compacts sintered at 1200°C for 1h under an H2 atmosphere. The sintered Mo-25%Cu powder compacts from manual mixing reached a relative density of 86.11%, while the compacts from powders ground for 20h reached 96.81% relative density. The powder-mixed compacts achieved microhardness and electrical conductivity values of only 165 HV and 35% IACS, respectively, while the powder-milled compacts for 20h achieved values of 239.61 HV and 46.78% IACS.