Microstructural characteristic of Ti-15V-3Al-3Sn-3Cr chips

Titanium alloys like Ti-15V-3Al-3Sn-3Cr, a precipitation hardenable β -titanium alloy, are widely used in aerospace applications. Machining of Ti-15V-3Al-3Sn-3Cr, however, is difficult and expensive as its machinability is extremely poor. A thorough understanding of the chip formation process of Ti-15V-3Al-3Sn-3Cr is needed to improve related metal cutting operations. The aim of this article is to present the microstructure of Ti-15V-3Al-3Sn-3Cr chips prepared by turning. Chips from three states of the alloy were analyzed and compared: as-received, solution treated and aged. Chips were obtained in different speeds with different depths of cut. The microstructure was analyzed by means of optical, electron microscopy and hard XRD. During the experiments, depending of the cutting conditions, continuous or segmented chips were formed. Narrow highly deformed and grain oriented zone so-called “shear zone” separated individual segments. Different materials properties have been observed in shear zones and the segments. The results of the chips analyses have finally been used, to develop free-machining alloys based on Ti-15V-3Al-3Sn-3Cr. (segmented regime). For low cutting speeds (10 and 20 m/min) no clear localized deformation (continuous regime) is observed.