The primary tool material when machining Ti6Al4V titanium alloy is uncoated straight cemented carbide. This study examines the performance of these materials during high-speed finish turning, and uses the advanced microscopy methods of SEM, (S)TEM, XEDS, and SAED to explore the fundamental tool wear mechanisms. The wear modes include a combination of flank wear and rake cratering. Four individual TEM lamellae were extracted from the crater and flank of one as-worn tool to investigate the wear mechanisms of cemented carbide exposed to different temperatures and contact conditions. The main wear mechanism identified is temperature-driven diffusion. Outward carbon diffusion occurs from surface WC grains into the adhered Ti alloy, which results in a layer of metallic tungsten. Dissolution of the W layer leads to doping of the α-Ti, thus causing its transformation into the β-Ti phase. At the same time, carbon-depleted WC grains interact with the Co binder, inducing formation of Co3W. Additional wear mechanisms include inward titanium diffusion, resulting in formation of TiC on both sides of the W layer. Simultaneously, TiCo2 is formed in Co-rich regions in the vicinity of the tool-chip interface. These reaction products retard direct dissolution of tool material in Ti6Al4V, thus acting as localized tool protection layers.
|Status||Published - 2021 juli 18|
- Bearbetnings-, yt- och fogningsteknik