Machinability assessment of beta-solidifying TiAl-based alloy with Zr, Cr, and Gd content variability

Abstract

An experimental machinability assessment of a new six-component TiAl-based alloy Ti-44.5Al-2V-1Nb-(0.5…1.5)Zr/(1.5…2.5)Cr-(0…0.1Gd) (at.%) with variable Zr, Cr, and Gd content has been accomplished. The machining was carried out by means of cutting, turning, and milling on triple remelted ingots (VAR + VAR + VIM) with a diameter of 70 mm and separately cast samples of 22 mm in diameter. It has been shown that the ingots of all the studied compositions possess satisfactory processability upon cutting by 4420 × 34 × 1.1 HM Titan Z3/4 carbide saw blades with Emulsol coolant, as well as upon abrasive cutting by discs of the 07P/NF/CBN series with Cool-2 coolant. The duration of the ingots cutting, regardless of Zr/Cr/Gd content, as well as the quality of post-cut surfaces, correspond to those for structural titanium alloys like Ti6Al4V. It has been established that the machinability of the (Zr + Gd)-containing cast samples upon turning with a carbide tool is unsatisfactory due to failure in dimensional accuracy achievement because of microchipping of surface fragments and cleaving of thin sections of parts. The turning machinability of the (Cr + Gd)-containing cast samples is satisfactory as evidenced by the absence of surface microchipping, cleaving, and intense chip fragmentation. It has been revealed that upon milling of Cr- and (Cr + Gd)-containing compositions the forces (by 20%) and tool wear (by 30–40%) are less compared to the processing of Zr- and (Zr + Gd)-containing compositions. The best combination of tool life and minimal cutting forces was shown by the pair “Iscar HM90 milling tool vs. (Cr + Gd)-containing composition”: the cutting force was 440.5 ± 4.5 N, and the cutting edge wear was 0.42 ± 0.01 mm upon the duration of 1200 sec. Microadditions of Gd in the amount of 0.1 at.% do not lead to any noticeable effect on the machinability of ingots and castings of the studied TiAl-based alloy.