Ti-6Al-4V α-β titanium alloy is the standard titanium alloy used in the aerospace industry, and in terms of tonnage it represents a significant portion of all alloy titanium. The alloy is known in the space industry not to be cold worked at room temperature. The lower oxygen grade Ti-6Al-4V alloy, designated Ti-6Al-4V ELI(" Ultra-low clearance ") alloy (UNS 56401), generally exhibits improved room-temperature ductility, toughness, and formability compared to higher oxygen grades. However, with the decrease of oxygen content, the strength of Ti-6Al-4V alloy decreases significantly. Those skilled in the art would consider the addition of oxygen to be detrimental to cold forming capacity and beneficial to the strength of Ti-6Al-4V alloy.
However, despite having a higher oxygen content than the standard grade Ti-6Al-4V alloy, Ti-4al-2.5V-1.5Fe-0.25o alloy (also known as Ti-4Al-2.5V alloy) is known to have excellent forming capacity at or near room temperature compared to Ti-6Al-4V alloy.
Another high strength α-β titanium alloy that can be cold deformed is Ti-4.5Al-3V-2Mo-2Fe alloy, also known as SP-700 alloy. Unlike Ti-4Al-2.5V alloy, SP-700 alloy contains a higher cost alloy composition. Similar to Ti-4Al-2.5V alloy, SP-700 alloy has reduced creep resistance relative to Ti-6Al-4V alloy due to increased β phase content.
Ti-3Al-5Mo-5V-3Cr alloy also showed good room temperature forming ability. However, this alloy includes a significant beta phase content at room temperature and therefore exhibits poor creep resistance. In addition, it contains significant levels of expensive alloy components such as molybdenum and chromium.
It is generally understood that cobalt does not affect the mechanical strength and ductility of most titanium alloys in comparison to alternative alloy additives. It has been described that while cobalt additions increase the strength of binary and ternary titanium alloys, cobalt additions also generally reduce ductility more dramatically than the addition of iron, molybdenum, or vanadium (typical alloy additions). It has been shown that while the addition of cobalt to Ti-6Al-4V alloys can improve strength and ductility, intermetallic precipitates of type Ti3X can form during aging and have harmful effects on other mechanical properties.
The advantage is to provide a titanium alloy that includes relatively low levels of expensive alloy additions, exhibits a favorable combination of strength and ductility, and does not produce a significant beta phase content.
