Free-machining Titanium Alloys Based on Ti 15V 3A1 3Cr 3Sn

摘要

Titanium alloys like the metastable β-titanium alloy Ti 15V 3A1 3Cr 3Sn are widely used in aerospace applications. Machining of these alloys is difficult and expensive as their machinability is extremely poor. Metal cutting operations cannot be automated as the machining process must be interrupted as often as it is necessary to remove the chips from the process zone. 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 lanthanum have been added to Ti 15V 3A1 3Cr 3Sn alloy to improve its machinability. Due to the formation of La5Sn3 precipitates instead of pure metallic lanthanum particles,machining operations were not improved. As an alternative,a new metastable β-titanium alloy has been developed replacing tin by zirconium. The modified alloys form short breaking chips at conventional cutting speeds. The alloys have been analysed by means of synchrotron radiation,scanning electron microscopy and optical microscopy. Their mechanical as well as their corrosion properties have been investigated. The freemachining alloys exhibit similar strength and corrosion resistance compared to the commercially available Ti 15V 3A1 3Cr 3Sn alloy.