Response of titanium aluminide alloy to abrasive waterjet cutting: Geometrical accuracy and surface integrity issues versus process parameters

Due to their low thermal conductivity, high abrasion of cutting edges and a tendency to crack during machining, titanium aluminide (TiAl) alloys are notoriously difficult-to-cut materials when using conventional (e.g. turning, grinding, drilling, milling) cutting operations. Despite their low machinability TiAl alloys find niche application areas in the manufacture of complex shaped components for aerospace gas turbine engines. Abrasive waterjet (AWJ) machining is one of the most promising non-conventional machining processes for difficult-to-cut materials because of the reduced mechanical and thermal damage to workpiece surfaces produced using this technique. However, there is no information about the AWJ machining of TiAl alloys in the open literature. Based on a generic design of an aeroengine component, this paper investigates the response of a TiAl alloy to AWJ cutting process variables to enable generation of high-integrity surfaces. The effects of operating parameters (pump pressure, material removal rate, abrasive flow rate, and stand-off distance) on the output process quality measures have been investigated as follows: geometrical accuracy (kerf straightness); surface roughness homogeneity (measured along cutting direction on the cutting front surface to study the striation formation); workpiece surface integrity (grit embedment and possible recast micro-layers or material pull-out / micro-cracking after cutting). Advanced surface topography and metallurgical (e.g. SEM, EDX) analyses have been carried out to characterize the response of TiAl alloy to various AWJ conditions leading to the fulfilment of quality criteria of a group of targeted aeroengine components. It was found that the AWJ process has a very high capability (e.g. satisfactory geometrical accuracy, surface quality, minimum surface anomies) to cut TiAl alloy despite grit embedment. However, the authors have addressed this problem by plain waterjet cleaning know-how. In addition, a surprising phenomenon (bubble-like 'TiO₂-based spot') caused by a strong exothermic reaction was found on the AWJ cut surfaces.