Wear Resistance of Coatings on Titanium Alloy Double-wire Locking Threads

SHI Yuxi; GONG Xuan; LI Jingyu; LIAO Ridong; LI Weihao

doi:10.16490/j.cnki.issn.1001-3660.2026.17.006

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Surface Technology ›› 2026, Vol. 55 ›› Issue (17) : 68-76. DOI: 10.16490/j.cnki.issn.1001-3660.2026.17.006

Friction, Wear and Lubrication

Wear Resistance of Coatings on Titanium Alloy Double-wire Locking Threads

SHI Yuxi¹, GONG Xuan¹, LI Jingyu¹, LIAO Ridong², LI Weihao^2,*

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Abstract

The work aims to investigate the wear resistance of titanium alloy double-wire locking bolt-nut assemblies which are critical components such as hatch locks in major equipment. As these fasteners require frequent assembly and disassembly in service, their reusability is a vital performance indicator. Wear-induced failure at the thread surface is a common issue due to the specific locking structure. To address this limitation, an innovative surface engineering approach was proposed and evaluated, involving the modification of thread surfaces with organic lubricant (paraffin wax and hexadecanol)-reinforced MoS₂ composite coatings. In this work, the fundamental wear mechanism of a standard MoS₂-coated thread pair was deciphered. A torque-tension testing machine was employed to simulate repeated tightening cycles. Through synchronized analysis of the torque curve evolution and post-cycle surface morphology, five distinct and sequential wear stages were identified: the run-in stage of the MoS₂ coating, its stable wear stage, its severe wear stage, followed by the severe wear stage of the underlying metallic thread substrate, and finally, a stable wear stage of the metallic substrate itself. This analysis established a clear correspondence between the frictional state at the thread interface and the characteristic locking torque signature, with the specific torque change features and associated surface conditions for each stage being thoroughly documented. Building on this mechanistic understanding, a comprehensive performance evaluation of the modified coatings was conducted. Pin-on-disc tests were carried out to measure and compare the friction coefficients and specific wear rates of the baseline MoS₂ coating against the organic lubricant-modified versions. The practical efficacy was then directly validated through repeated tightening tests on bolt-nut assemblies coated with composites containing varying types and concentrations of organic lubricants, where the locking torque evolution served as the direct measure of in-service durability. The results demonstrated that the organic lubricant modification successfully reduced the average friction coefficient of the coating to approximately 0.05. This modification profoundly extended the duration of the critical stable wear stage during tightening, thereby delaying the transition to severe metallic wear. The performance was found to be highly dependent on the type and concentration of the organic lubricant. A key finding pertained to the thermal limitations of the MoS₂/paraffin wax composite. Furthermore, under high-power sliding conditions in pin-on-disc tests, the MoS₂/paraffin wax composite was observed to be prone to adhesive wear at elevated temperatures, accompanied by a sharp increase in the friction coefficient. This further corroborated its relatively poor thermal stability and underscored the necessity of carefully evaluating its applicable temperature range in practical service. Despite this thermal sensitivity under extreme conditions, the composite coating delivered remarkable functional improvement in standard assembly simulations, increasing the failure cycle of the titanium alloy locking bolt-nut assembly from 450 to over 1 500 uses. It is concluded that the reusable lifespan of such threaded connections is predominantly governed by the longevity of the coating's stable wear stage. The application of organic lubricant-modified MoS₂ coatings presents a highly effective strategy for dramatically improving wear resistance. The work highlights that while coatings like MoS₂/paraffin wax offer exceptional performance gains in typical scenarios, their thermal stability must be a key consideration for application-specific design, ensuring reliable performance across the intended service envelope.

Key words

hatch lock bolt / MoS₂ lubrication / organic lubricant / paraffin / wear characteristics / simulated installation experiment

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SHI Yuxi, GONG Xuan, LI Jingyu, LIAO Ridong, LI Weihao. Wear Resistance of Coatings on Titanium Alloy Double-wire Locking Threads[J]. Surface Technology. 2026, 55(17): 68-76

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