Near alpha titanium alloys

Heat-treated bar. Thermal expansion is typical of other near-alpha titanium alloys. Sovirce IMI Titaniiun High-Ttemperature Alloys brochure... 

Therefore, the basic properties of titanium and its alloys strongly depend on their basic metallurgical structure and the way in which this is manipulated in their mechanical and thermal treatment during manufacture. Four main types of titanium alloy have been developed, and hence titanium alloys fall into the four categories alpha, near alpha, alpha plus beta, and beta. 

Titanium alloys have the best corrosion resistance of the metals and alloys typically used in seawater. Titanium is a passive film-forming alloy and retains excellent resistance in both low and high velocity seawater. Some titanium alloys, specifically the all alpha and near-alpha alloys, do exhibit a susceptibility to stress corrosion cracking [72]. 

Source R.E. Lewis et al., The Elevated Temperature Ductility Dip Phenomenon in Alpha, Near-Alpha, and Alpha-Beta Alloys, Titanium, Science and Technology, Vol 2, G. Lowering, U. Zwicker, and W. Bunk, Ed., Deutsche Gesellschaft fur Metallkunde, Gemnany, 1985, p 895-902... 

Ti-1100 is a near-alpha alloy developed for elevated-temperature use up to 600 °C (1100 °F). It was developed to be used primarily in the beta-processed (beta-worked or beta-annealed) condition. Ti-1100 offers the highest combination of strength, creep resistance, fracture toughness, and stability of any commercially available titanium alloy. It is also recommended for castings. 

IMI 685 is a titanium alloy specifically developed to meet aerospace-engine reqmrements. It was the first of the near-alpha alloys, and represented a significant step forward in combining... 

The modulus of IMI 829 is typical of other high-aluminum, near-alpha alloys and is therefore somewhat Ngherthan alpha-beta alloys. Source IMI Titanium High-Temperature Alloys brochure... 

Corrosion/Chemical Properties. The corrosion-resisting characteristics of Ti-5Al-5Sn-2Zr-2Mo-0.25Si are comparable to unalloyed titanium and to other near-alpha and a-P titanium alloys. This alloy is unaffected after 1000 h in the standard ASTM salt-spray test. 

An alloy ideally should be homogeneous, but in practise it can contain segregations, for example hard alpha in titanium. Beeause of their different mechanieal properties sueh segregations can be the origin of eracks when the component is operated near to its temperature and stress limits. 

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