Influence of cutting damage on the bending strength of Ti₂AlC MAX phase machinable ceramics

Abstract

Ti₂AlC MAX phase ceramics are excellent candidates for high-temperature heat resistant materials. In addition, they are machinable using cemented carbide tools. However, heavy machining induces many surface cracks, reducing the mechanical strength and reliability of ceramic parts. Herein, we investigated the influence of the machining process on the bending strength and microstructure of Ti₂AlC ceramics. Nearly fully dense Ti₂AlC ceramics with elongated grains were machined using a carbide end mill in brittle mode, producing numerous cracks; however, the roughness of the ceramic was similar to that of tool steel cut in ductile mode. Despite its rough surface, the bending strength of the machined Ti₂AlC was only slightly lower than that of polished Ti₂AlC. The cracks in the machined Ti₂AlC ceramics were induced with a kinking structure; however, they stopped at a length equivalent to one grain. The minimum strength of the machined Ti₂AlC ceramics with a fracture toughness of 6.9 MPa·m^1/2 was estimated by assuming a machining through-crack shape that was as deep as the maximum grain size. Cutting damage was limited to a single grain; thus, the bending strength of the machined Ti₂AlC was not significantly reduced.