Microscopic Studies of Flank Wear on Alumina Tools

The flank wear of alumina cutting tools in the machining of annealed steels, AISI 1045 and 4340, which were approximately the same hardness, was studied microscopically. The intent was to establish whether any chemical wear occurred in addition to the mechanical wear on the flank surface. While the hardness of the two steels was essentially the same, the chemistry and the carbide present in the microstructure differed. The flank wear morphology was studied and three regions within the wear land could be defined. The flank wear of the alumina tools, which increased with an increase of cutting speeds, was found to be strongly dependent upon the chemistry of the work material being machined. At the higher speeds, the flank wear when cutting AISI 1045 steel was approximately twice that of AISI 4340. It was observed that different wear mechanisms could be associated with the material being machined. The thermally activated chemical and mechanical wear processes were predominant in the AISI 1045 machining, but the chemical wear was not significant in machining AISI 4340. At lower temperatures, the mechanical wear predominated for both steels. The wear pattern consisted of three regions on the flank wear surface, which varied with cutting speed, cutting distance, and position within the wear land. The surface roughness on the worn tool was also related to these same test parameters. The flank wear appears to depend upon not only the workpiece, but also upon an interfacial oxide layer that forms during cutting. The physical and mechanical properties of the interfacial oxide depend upon its constituents, which relate back to workpiece composition and thermal conditions at the interface.