Study of surface integrity of milled gamma titanium aluminide

Abstract

This paper presents a comprehensive investigation of the effects of cutting parameters on the surface integrity of milled γ-TiAl alloys. Surface topography, surface roughness, surface defects, plastic deformation, micro-hardness, chip morphology, and tool wear of the milled γ-TiAl alloys were analyzed. The results indicate that the feed rate had the greatest influence on the surface topography and surface roughness. The value of surface roughness increased with the increase in cutting depth and feed rate. However, with the increase in cutting speed, it initially increased and then decreased. The minimum surface roughness was found to be 0.066 μm. The thickness of the plastic deformation layer and the micro-hardness value increased with the increase in cutting depth and feed rate. Also, they initially increased and then decreased with the increase in cutting speed. The minimum thickness of the plastic deformation layer was 15 μm and the depth of the hardened layer on the processed surface varied between 55 and 70 μm. The chip morphology was closely related to the quality of the processed surface. When the cutting depth and feed rate decreased, the chip morphology was transformed from segmented to nearly smooth. When the cutting depth and feed rate reached a critical point, plastic processing of γ-TiAl was achieved. Compared to brittle deformation, a more favorable processed surface was obtained. Finally, the comparison tests of tool wear were carried out with dry and flood coolant cutting. When the cutting speed reached 120 m/min in dry cutting, the tool life was very poor, and the cutting distance was only 1 m. However, the tool life was generally good when cutting with low cutting speed under the following conditions: vc = 60 m/min, ap = 0.1 mm, and fz = 0.01 mm/tooth. Under these conditions, the cutting distance was 60 m in dry cutting with the tool wear of 0.2 mm and 120 m in flood coolant cutting with the tool wear of 0.1 mm. The tool life in flood coolant operation was better than that of dry operation. The tool life decreased to 30 m when cutting with high cutting speed or feed rate (ap = 0.25 mm or fz = 0.025 mm/tooth).