Cutting ability features for new high-strength titanium alloys with an ultrafine-grained structure used for aircraft parts

The results of experimental studies of the cutting parameters effect (cutting speed, feed, depth-of-cut) on the roughness of Ra, the microstructure of the surface layer of Ti-6Al-4V alloy samples with a conventional coarse-grained (CG) and ultrafine-grained (UFG) structure obtained by equal-channel angular pressing are presented. In framework of solving the problem connected with studying the machinability of a new VT6 alloy having an UFG structure, the development of a methodology for experimental research under turning was carried out. Physical parameters such as vibrations and noise under cutting, power consumption, numerical parameters of roughness, the magnitude and the pattern of residual stresses distribution and others are determined according to cutting modes and the tool used for the operation. It is shown that when turning at a low cutting speed, the roughness of CG sample is better than UFG of the alloy. With an increase in the cutting speed by 1,5 times, on the contrary, a sample with an UFG structure has a lower roughness Ra compared to a CG sample. Differences in the morphology and microstructure of the chips formed within comparative machining are discussed, taking into account types of microstructure of the alloy being treated, namely, presence of plastic flow lines in the chip microstructure after turning an UFG sample, the formation of large shifts, chips and tiny fractures in the chips after turning a CG alloy. It is found that new titanium alloys under turning obtain better cutting machinability in terms of such parameters as surface roughness, noise and vibration under cutting, and a more favorable character of residual stresses and riveting in the surface layer. Studying these factors, it is possible to predict a significant reduction of tool wear and stabilization of its durability compared to conventional coarse-grained titanium treatment.