Investigation of microstructure and mechanical properties of powder metallurgy (PM) copper-based composites welded by diffusion technique

Copper remains one of the major groups of commercial metals, ranking third behind only iron/steel and aluminium in production and consumption. Copper has found extensive applications because of its high thermal and electrical conductivity, plasticity, softness and formability. However, copper in pure form has poor strength, wear and fatigue resistance and hence is unsuitable for high-end applications like contact terminals of electrical switches and sliding surfaces. The use of carbides in metal or ceramic matrices is becoming increasingly popular in the production of abrasion-resistant materials, and the industry has an important share of usage. A copper-based composite matrix is reinforced with ceramics like B4C particles. Boron carbide (B4C) also has low density, high strength, high hardness and high Young's modulus, which are considered to be reinforcement for metal matrix composites (MMCs).Diffusion welding processing (DWP) overwhelmed the above limitations of pure copper. At the beginning of the last century, have developed this innovative solid-state processing technology, which is being used to enhance locally the mechanical properties of conventional materials by producing ultrafine-grained structures, which is rather attractive in situations where strength and/or fatigue crack initiation are serious concerns. DWP is a unique process to modify the microstructure and other mechanical properties at selective locations. In this investigation diffusion welding method is used to join copper boron carbide Cu+ B4C composites. The composites are manufactured by powder metallurgy (PM). Cu powders were blended with 2,5; 5 and 7,5% by weight B4C. Cu-% wt; %B4C, milled in a ball-milling machine for up to 45 minutes; compacted by the hot press at 40 MPa and sintered in the Ar atmosphere at 800°C for 4 min. Cu+B4C composites were bonded to Cu+B4C composites at various temperatures of 900°C and times of 90; 120 and 180 min through diffusion bonding. 5 and 8 MPa uniaxial load was applied during the diffusion bonding. Microstructural characterization of the joints was shown, optical microscopy and scanning electron microscopy weres carried out on the welded interfaces, and mechanical characterization by shear strength, bending strength, and hardness measu rements. It is found that the optimal parameters in the process of jointing copper matrix composites observed at samples welded at Cu+2,5% B4C; Cu+5% B4C by using diffusion bonding are the pressure of 5, 8 MPa, and 90 and 120 minutes of the bond time to achieve the highest tensile strength and bending strength of 142,65; 166 MPa respectively.