Wear of WC-Co inserts in dry high speed machining of micron-sized particle aeronautical grade near β titanium alloy

Current demands of higher damage-tolerance in the Aerospace industry resulted in resurging interest in beta, or near beta, titanium alloys. The combination of attractive properties of this class of alloys also led to the consideration of beta alloys for castings. Such alloys, however, are more difficult to cut than alpha-beta titanium alloys due to their limited ability to work harden and the effect of beta-stabilizers on ductility. These factors affect failure modes and active wear mechanisms of cutting inserts. This paper investigates some of the wear modes exhibited by WC-Co inserts when end milling the alpha near-beta alloy Ti-x. In addition to being of near-beta composition, this alloy is characterized by a fine sized microstructure (range of 1-5 mu m). The study focuses on SEM and EDS observations of the wear patterns exhibited by two groups of inserts. The first is uncoated WC-Co, whereas the second is coated with multi layers of TiAlN. The results of this post-mortem study are compared to wear patterns, observed under identical conditions, while milling the alpha-beta alloy Ti6Al4V. Results show that inserts used in machining the Ti-x alloy exhibit wear modes that contrast those exhibited when machining Ti64. The paper discusses factors leading to such occurrences and studies the influence of the alloy microstructure on tool effectiveness and failure modes.