Les relations entre structures et propriétés de fatigue des alliages de titane

Sructure-fatigue properties relations in titanium alloys

S.N.E.C.M.A.

Abstract

The studies of structure-fatigue properties relations in titanium alloys have been deve- lopped in two directions. The first one is to establish a macroscopic correlation between the processing route and the mechanical characteristics of the final product. The second one aims to explain the metallurgical mechanisms which occur during the successive stages of fatigue.

As far as the macroscopic approach is concerned, studies have focussed upon the processing routes (β forging, β solution treatment, casting, P/M,...) that can produce microstructures including patterns of large elongated α platelets, as this is known to have a beneficai influence upon the toughness of Ti alloys, but a detrimental one, sometimes drastic, on their Low Cycle Fatigue resistance.

Little interest has been devoted to the study of the crack initiation mechanisms, however the propagation of fatigue cracks has received a great attention and the proeminent role played by the combination of microstructure with microtexture is by now recognized within the fatigue propagation life, the regime of « short cracks » needs a special attention because of the high rates which are often observed, here again in close relationship with the microstructure (planar slip).