An experimental and theoretical investigation on Ti-5553/WC–Co(6%) chemical interactions during machining and in diffusion couples

Abstract

Chemical interactions that drive crater wear in turning are often studied using diffusion couples where the tool and workpiece are fixed. In contrast, in actual turning, there is a constant supply of new workpiece material at the tool-chip interface. In this work, diffusion simulations of a WC–Co(6%) and Ti–5Al–5V system were conducted, with constant replenishment of titanium at the interface (open system) and a fixed amount of material (closed system). The simulations showed that the formation of W(bcc), η-phase, and TiC is dependent on the activity of C and the permeability of Co and C in titanium. Scanning and transmission electron microscopy-based techniques were used to analyse a Ti–5Al–5V–5Mo–3Cr and WC–Co(6%) diffusion couple and a worn WC–Co(6%) insert. The sequence of phases in the closed system simulation was similar to that observed in the diffusion couple. The open system simulation indicated that W(bcc) can form at WC–WC boundaries (where Co is low) within the subsurface of a WC–Co(6%) that has adhered titanium, and at the WC/Ti interface. Additionally, high densities of stacking faults and dislocations were found within subsurface WC grains, indicating a significant reduction of the tool’s integrity.