Coated bolt weakening mechanism and processing improvements

YING Shaojun; CHEN Zhitong; LI Jianwei; ZHAO Yue

doi:10.16511/j.cnki.qhdxxb.2022.22.038

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Journal of Tsinghua University(Science and Technology) ›› 2022, Vol. 62 ›› Issue (9) : 1539-1547. DOI: 10.16511/j.cnki.qhdxxb.2022.22.038

MECHANICAL ENGINEERING

Coated bolt weakening mechanism and processing improvements

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Abstract

Some key coated joint bolts on helicopter rotor systems had poor fatigue lives. This study investigated the microhardness distribution in these bolts using the scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD) tests. The tests showed that the deteriorated layers induced by turning, machining and shot blasting overlapped at the bolt substrate surface, which negatively impacted the bonding strength between the WC-10Co4Cr coating and the substrate. The poor fatigue life was found to be mainly due to premature cracking of the substrate-coating interface. The grinding depth was then increased to eliminate the overlapping deteriorated layers to more uniformly distribute the microhardness between the coating and the bolt substrate which lengthened the fatigue life 3 folds relative to the original bolt. This result is mainly due to the removal of the overlapping deteriorated layers which improves the hardness as well as the bolt surface homogeneity and relieves the hardness gradient between the substrate and the coating, which significantly improves the adhesion between the coating and the substrate.

Key words

coated bolt / fatigue life / substrate-coating interface / microhardness / electron back-scattered diffraction

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YING Shaojun, CHEN Zhitong, LI Jianwei, ZHAO Yue. Coated bolt weakening mechanism and processing improvements[J]. Journal of Tsinghua University(Science and Technology). 2022, 62(9): 1539-1547 https://doi.org/10.16511/j.cnki.qhdxxb.2022.22.038

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