Diamond tools wear in drilling of SiCp/Al matrix composites containing Copper

Although SiCp/Al matrix composites possess numerous excellent physical and mechanical properties, high hardness and high wear resistance characteristics of SiC reinforcement lead to low tool life and resultant poor machined surface quality in cutting. The aim of this paper is to investigate the micromechanism underlying the macro-scale wear of diamond tools in drilling of high volume fraction SiCp/Al composites. To achieve this, the worn morphologies and possible crystal structure evolution of diamond tools after drilled 10 holes were examined using Laser Scanning Microscope and Raman spectroscopy, respectively. Additionally, based on drilling forces and hole quality, the machinability assessment of SiCp/Al6063 composites was carried out. The results indicate that the mechanically induced abrasion and thermodynamically activated chemical graphitization is the dominant and common wear mechanisms for PCD and CVD diamond coated tools in drilling of 65 vol% SiCp/Al6063 composites containing copper. The reciprocating actions of thin graphite layer formed by oxidizing hydrogen chemisorbed on diamond surface by Copper oxides and graphite removal due to SiC particulates' high frequency scrape lead to continual and significant occurrence of diamond graphitization. In air atmosphere, the thermodynamic conditions of diamond-graphite transformation in machining of SiCp/Al6063 composites containing Copper are investigated. The coupled abrasive-chemical wear model is formulated based on analytical description of diamond wear mechanisms above. In terms of machinability of high volume fraction SiCp/Al composites, CVD diamond coated carbide drill is preferred, due to its stable cutting force, less wear and its ability to produce acceptable machined quality with increasing hole number.