The influence of laser glazing on fatigue crack growth in Ti-24AI-11Nb
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I.
INTRODUCTION
LASER surface treatment is one of several surface modification techniques being studied to improve fatigue resistance through modification of surface properties and the introduction of residual stresses in the surface layer. Laser glazing is one such treatment during which a thin surface layer is melted and rapidly solidified by selfquenching, thereby forming amorphous, microcrystalline, or metastable phases depending on the nature of the alloy and the cooling rates encountered. Among titanium alloys, Ti-6A1-4V has been widely investigated, t~-4] These studies have focused mainly on the evaluation of high-cycle fatigue resistance in terms of stress v s the number of cycles to failure and revealed beneficial as well as detrimental effects of glazing. Glazing in a nitrogen atmosphere reduced fatigue strength, while no variation in fatigue properties was observed when glazing was done in a helium atmosphere, t3j On the other hand, Mordike t41 reported reduced fatigue life under the same atmosphere. Mille e t al.t2] observed that a soft surface treatment confined to a shallow layer of about 0.1 mm improves fatigue strength, while a deeper layer has a detrimental effect. There are no reported investigations on the effects of laser glazing in titanium aluminides, a new class of materials being developed for high-temperature, fatigue-critical structural applications. In this article, the influence of laser surface glazing on the fatigue crack growth (FCG) in a titanium aluminide (Ti3A1) alloy is studied and the results presented. II.
EXPERIMENTAL DETAILS
The titanium aluminide alloy chosen for this study contains, by atomic percent, 61.4Ti, 27.3A1, 10.8Nb, G. MALAKONDAIAH, National Research Council Associate, on leave from Defence Metallurgical Research Laboratory, Hyderabad, India, and T. NICHOLAS, Senior Scientist, are with W L / M L L N , Wright Laboratory, Wright-Patterson Air Force Base, Dayton, OH 45433-6553. Manuscript submitted May 3, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS A
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