B. Zahra, F. Depentori, C. Siemers, J. Rösler
Proceedings of the 12th World Conference on Titanium (Ti-2011), Beijing, China, June 19th - 25th 2011, Science Press Beijing, 2012, Vol. 2, pp. 1597 - 1601
Titanium alloys like the metastable β-titanium alloy Ti15V3Al3Cr3Sn are widely used in aerospace applications. Machining of this alloy, however, is difficult and expensive as its machinability is extremely poor. This difficulty arises from the chemical, physical and mechanical properties and the formation of long chips. Metal cutting operations especially turning and drilling cannot be automated as the machining process must be interrupted as often as it is necessary to remove the chips from the process zone by an operator. Depending on the cutting conditions, either continuous or segmented chips are formed. In the second case a so-called shear band, a narrow zone showing a heavily deformed nano-crystalline microstructure, separates the segments. Small amounts of the rare-earth metal element lanthanum have been added to Ti15V3Al3Cr3Sn alloy to improve its machinability. Due to the formation of La5Sn3 precipitates instead of pure metallic lanthanum particles, the machinability was not improved. As an alternative, a new beta titanium alloy has been developed replacing tin by zirconium. The promising modified alloys form short breaking chips during turning at conventional cutting speeds. The alloys have been analysed by use of synchrotron radiation, SEM-EDX and LM. Their mechanical as well as their corrosion properties have been investigated. The free machining alloys exhibit similar strength and corrosion resistance compared to the commercially available Ti15V3Al3Cr3Sn alloy.