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arXiv · 2108.08786

Crystallographic evaluation of low cycle fatigue crack growth in a polycrystalline Ni based superalloy

Kaustav Barat·Abhijit Ghosh·Alok Doharey·Shreya Mukherjee·Anish Karmakar
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Abstract

The present work discusses the micro-mechanism of low cycle fatigue (LCF) crack growth in smooth bar specimens of Haynes 282. Two parametric approaches, i.e. crack tip opening angle (CTOA) and maximum tangential stress (θMTS) have been opted to characterize the cracks. CTOA variations along with a propagating crack, exhibit a non-linear decay followed by a stabilized regime. Mixicity of local KI and KII fields is directly proportional to θMTS and that can be assessed by measuring local deflections. Around the crack, the role of grain incompatibility has been addressed through EBSD and slip transfer analysis. There is a critical bound for Elastic Modulus (EM) and Schmid factor (SF) for the grains favouring subsurface crack propagation, and these values exist beyond a limiting threshold. The SF-EM maps mark the regions of cracked and uncracked grains in the material. The favourable twin-matrix incompatibility of the microstructure has also been identified about the fatigue crack growth and twins in (211) plane is abundant in the cracked region. A detailed slip transfer analysis based on the Luster-Morris parameter (LMP) has been carried out for investigating the interrelation between slip activity, elasto-plastic incompatibility, and grain boundary geometry.

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Kaustav Barat, Abhijit Ghosh, Alok Doharey, Shreya Mukherjee, Anish Karmakar. 2021-08-19. Crystallographic evaluation of low cycle fatigue crack growth in a polycrystalline Ni based superalloy. https://arxiv.org/abs/2108.08786

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