The fretting fatigue damage issue of nickel-based single crystal (NBSC) fir-tree tenon joints is the core bottleneck restricting the reliability and service durability of aero-engine turbine blades. In this paper, systematic research on the fretting fatigue damage mechanism of NBSC fir-tree tenons is carried out through high-temperature fretting fatigue tests under various loads, combined with crack observation systems and crystal plasticity finite element (CPFE) simulations. The results indicate that plastic deformation of the fir-tree tenon joint intensifies with increasing load, accompanied by aggravated fretting damage in the contact area. Consequently, the crack initiation life of each tooth is shortened and the crack propagation rate is accelerated. Under all loading conditions, cracks preferentially initiate at the first tooth of the tenon, then successively emerge and continuously propagate at the second and third teeth until structural failure occurs. All cracks nucleate at peeling or microcracks induced by fretting wear at the lower edge of the contact zone, which is consistent with the stress concentration locations obtained from CPFE results. In the early stage, cracks formed on all tenons propagate along the {111} slip planes. In contrast, the crack propagation path of the second tooth exhibits obvious load-dependent evolution characteristics. As the applied peak load declines, crack propagation morphology sequentially shifts from straight to zigzag and finally to smooth. This transition arises from the combined synergistic effects of varying crack propagation driving force and microstructural evolution.
The reliable operation of ferromagnetic tribological pairs in high-end mechanical equipment is critically challenged by magnetic field environments. However, the underlying mechanism of a magnetic field on wear evolution remains poorly understood, particularly regarding debris behavior. Using a medium carbon steel block against a bearing steel ball, the effect of a magnetic field on the tribological performance was systematically investigated across rotational speeds after eliminating normal force variation induced by magnetic attraction. The results showed that, as rotational speed increased, wear debris was progressively ejected from the wear track by centrifugal force. Upon application of a magnetic field, this ejection was suppressed, and debris retention at the friction interface was significantly enhanced, while oxidation was also markedly accelerated. The retained debris triggered repeated cold welding and tearing, forming a thick compacted debris layer and coarse plowing ridges, and promoted a transition toward a composite wear regime involving adhesive and abrasive mechanisms. The wear-promoting effect of the magnetic field was most pronounced at the intermediate rotational speed of 60 r/min, where the wear volume increased by 219.1% compared with the non-magnetized condition. At high rotational speed (300 r/min), the coefficient of friction increased by approximately 38.2% and approached 1.0 with pronounced fluctuations, while the wear volume still increased by 12.9%. These findings reveal specific conditions for magnetic field induced wear deterioration, providing guidance for sliding component design and lifetime assessment in magnetic field environments.
Progressive wear in rolling bearings involves coupled changes in surface morphology and vibration response, yet their stage-resolved evolution remains insufficiently quantified. This study develops a stage-resolved framework based on a 326 h rolling-contact wear experiment with 29 successive surface inspections. Three-dimensional raceway topographies were characterized using hierarchical descriptors of height distribution, spatial organization, and extreme-depression topology. Principal component analysis combined with piecewise-linear segmentation identified three morphology-resolved regimes corresponding to Running-in Wear, Steady-State Wear, and Severe Wear, with nominal transition times of approximately 95 h and 245 h. Moving-block bootstrap analysis indicated a gradual first transition and a more distinct onset of severe wear. Inspection-grouped ResNet50 analysis showed strong morphological separability among the three stages, with a pooled image-level accuracy of 90.42%. After controlling for operating time and multiple testing, surface roughness Rq remained positively associated with vibration RMS (rpartial=0.716, q=0.00132) and negatively associated with spectral entropy (rpartial=−0.639, q=0.00906). Incorporating Rq into a time-based RMS model reduced temporally blocked cross-validation RMSE by 27.8%. These results demonstrate that severe rolling-contact degradation is characterized by increasingly heterogeneous and localized surface morphology together with a stronger morphology–vibration association.
The high-speed rubbing behavior between Ti alloy blade tips and Al-based abradable seal coatings becomes more complex at elevated temperatures, particularly under compressor surge conditions. In this study, high-speed rubbing tests between Ti6Al4V blade tips and Al-hBN seal coatings were conducted from room temperature to 500 °C. The thickness of the Al transfer layer on the blade tip increased from 55 μm at room temperature to 178 μm at 300 °C, and then decreased to 71 μm at 500 °C. Above 400 °C, part of the Al transfer layer detached from the blade tip and re-adhered to the seal coating, thereby reducing its further accumulation on the blade tip. HRTEM and GPA analyses showed that the defect-rich nanocrystalline-amorphous structure near the Ti/Al reaction front promoted rapid interfacial reaction. Meanwhile, thick and brittle Ti-Al interfacial reaction layers detached together with the Al transfer layer and re-adhered to the seal coating wear track. These re-adhered Ti-Al reaction layers acted as hard phases during subsequent rubbing and aggravated Ti6Al4V blade tip wear. The results indicate that high-temperature blade tip wear is controlled by the coupled processes of adhesion, interfacial reaction, detachment, and re-adhesion.
