Microstructure, mechanical and tribological properties of (APC+B4C)/Al hybrid composites prepared by hydrothermal carbonized deposition on chips

Abstract

Abstract A hybrid reinforced Al matrix composite (AMC) was prepared by hydrothermal carbonized deposition on chips (HTCDC) and a hot extrusion process. The microstructure, tensile strength, hardness and tribological properties of the (APC+B4C)/Al hybrid composites were investigated. The results reveal that nanosized B4C particulates (nano-B4Cp) can be used as nucleation sites to facilitate nucleation and growth of amorphous carbon (APC) by encapsulating nano-B4Cp. It was found that the strength of APC spheres formed by encapsulating nano-B4Cp is higher than that of the original APC spheres. The dislocation density of the Al matrix increases in the conventional hot extrusion process because of the presence of nano-B4Cp, which promotes recrystallisation nucleation. With increasing nano-B4Cp content, the grain size of the Al matrix decreases from 18.80\xa0µm to 8.62\xa0µm. The strength and hardness of the (APC+B4C)/Al hybrid composites first increase and then decrease. For a nano-B4Cp content of 3%, the (APC+B4C)/Al hybrid composite shows the highest strength and hardness of 95.8\xa0±\xa00.7 HV and 235.41\xa0±\xa01\xa0MPa, respectively. The main reinforcement mechanisms for AMC were analysed, which include the grain refinement strengthening mechanism, the dislocation strengthening mechanism and the load transfer mechanism. The coefficient of friction (COF) and wear rate of the composites decrease with increasing nano-B4Cp content from 0.41 and 2.87\xa0×\xa010−5 mm3/(Nm) to 0.296 and 0.82\xa0×\xa010−5 mm3/(Nm), respectively. The increased wear resistance is attributed to the increase in hardness of the composites and the formation of an APC lubricating film and oxide layer between the wear surfaces.