Effect of Oxidation Resistant Al3Ti Coating on Creep Behaviour of a Near α-Ti Alloy Titan 29A

Abstract

The effect of oxidation resistant Al3Ti coating, applied through pack aluminizing method on creep properties of near α Ti-alloy Titan 29A has been examined at 823 and 873 K and in the stress range of 250–650 MPa. The creep properties of the coated alloy are found to be inferior to those of uncoated alloy. While rupture lives of the coated alloy are 4–25 % lower than those of the uncoated alloy, minimum creep rate (MCR) is only marginally affected. The increase in MCR of the coated alloy is as a consequence of brittle and non-load bearing nature of the Al3Ti coating. The extent of deterioration in creep properties in particular stress rupture life of the coated alloy is more predominant at lower stresses. This can be attributed to the fact that aluminide coating is present prior to creep test in case of the coated alloy, hence surface cracks either pre-exist or form early during creep test, while α-casing forms only during creep test and hence there is delay in formation of brittle α-case at the surface of the uncoated alloy and subsequent development of surface cracks in it.