Surface integrity in high-speed milling of gamma titanium aluminide under MQL cutting conditions

Abstract

Intermetallic alloys based on gamma titanium aluminide (γ-TiAl) are considered to be one of the best replacements for nickel-based super alloys (used in gas turbine blade) because of their unique set of properties. However the machinability of γ-TiAl is faced with restrictions and limitations due to the alloy's mechanical and metallurgical properties. Some of the most restricting properties include high temperature yield strength and wear resistance, even at elevated temperatures. Machining of γ-TiAl can also cause defects such as the formation of micro cracks on the machined surfaces. To explore the surface integrity of γ-TiAl under different cutting conditions, a series of machining experiments were carried out. High-speed and ultra-high-speed milling of γ-TiAl were examined under dry and minimum quantity lubrication (MQL) conditions. This research outlines the effects of cutting conditions on the surface integrity and Machining Affected Zone (MAZ). Two- and three-dimensional surface parameters were measured. In addition, the effects of machining parameters were studied using an analysis of variance (ANOVA). In addition, a mathematical model for the surface roughness measurements was developed in the present work. Likewise, other effects of surface alterations, including material pullout, deformations of the lamellae and micro cracks, were studied with optical microscopes (OM) and Scanning Electron Microscopes (SEM). Microhardness evaluation of the surface and subsurface indicated a significant difference between the surface and the bulk of the material (subsurface layers). X-ray diffraction analysis showed a phase transformation on the machined surfaces. Finally, the results of the present work are compared with previous works on machining of gamma titanium aluminide.