Specific Energy and Scratch Hardness of Gamma Titanium Aluminides Subjected to Single-Grit Pendulum Scratching

Two gamma titanium aluminides (Daido RNT650 and HOWMET 45XD) with fully lamellar structure but with different colony sizes were studied using a single-grit pendulum (rotational) scratch tester in order to assess their abrasive wear resistances. The maximum depth of groove was ∼ 0.07 mm and the scratch velocity used was ∼ 1 m/s. Normal and tangential forces were monitored during each scratch. The material removal mechanisms were examined using a scanning electron microscope (SEM) and also measured using a laser profilometer. Extensive thermal softening was observed. Sizable fractures were revealed in the transverse direction; however, the role of these fractures in the chip formation depends on the microstructure of materials and the size of groove. The tribological properties were characterized by instantaneous specific energy and scratch hardness as related to the depth of the groove. The overall response of materials can be effectively characterized by the HEM (Hwang-Evans-Malkin) model and the PSR (proportional specimen resistance) model, even though the underlining material removal might be subjected to the different mechanisms. The TiAl with the larger colony or grain size exhibits a strong resistance to material loss or material removal (higher depth-independent specific energy) while exhibiting lower scratch hardness. The obtained depth-independent specific energy and scratch hardness can be used to screen the candidate materials depending on whether the application is sliding or impact dominant.