Fatigue Spalling Research Articles

Effect of Ni additions on microstructure, interfacial diffusion behavior and properties of Fe-based/B4C composite coating by vacuum cladding

In order to improve the hardenability and toughness of Fe-based/B 4 C composite coatings, which were bonded on ASTM 1045 steel by vacuum cladding, nNi ( n = 0, 1, 3, 5, weight %) were added into the coatings. The influences of Ni additions on the microstructures, interfacial diffusion behavior, impact toughness and three-body abrasive wear behavior of composite coatings were investigated systematically. The results indicated that coatings were completely fused with steel substrate without micro-defects. When the amount of Ni was increased, the activity of the C atom on the coating side was enhanced, the decarburization zone near the interface disappeared, and the metallurgical bonding state of interface was strengthened. Furthermore, the increment of Ni improved the hardenability of coating and promoted the transformation from pearlite to martensite in the matrix structure of the coating. The impact toughness of the coating samples also increased with the increment of Ni additions, and reached the maximum of 4.8 J/cm 2 at 5Ni sample. The three-body abrasive wear test implied that when 3 wt% Ni was added to the coating, the mass loss was 0.14 g, which was much lower than that of other samples and exhibited the best wear resistance. The wear mechanism of coatings changed from partial plastic cutting and fatigue spalling to single fatigue spalling. • Ni addition strengthens the metallurgical bonding state of the coating interface. • The increase of Ni addition improves the hardenability of the coating matrix. • Ni addition improves the impact toughness and wear resistance of the coating.

A combined experimental and analytical method to determine the EHL friction force distribution between rollers and outer raceway in a cylindrical roller bearing

Friction force is a crucial factor causing power loss and fatigue spalling of rolling element bearings. A combined experimental and analytical method is proposed to quantitatively determine the elastohydrodynamic lubrication (EHL) friction force distribution between rollers and outer raceway in a cylindrical roller bearing (CRB). An experimental system with the instrumented bearing and housing was developed for measuring radial load distribution and friction torque of bearings. A simplified model of friction force expressed by dimensionless speed, load, and material parameters was given. An inequality constrained optimization problem was established and solved by using an experimental data-driven learning algorithm for determining the uncertain parameters in the model. The effect of speed, load, and lubricant property on friction force and friction coefficient was discussed.

Effect of Cu additions on the microstructure, wear resistance and corrosion resistance of Fe-based/B4C composite coating by vacuum cladding

Fe-based/B4C composite coatings with different Cu contents were prepared on the surface of ASTM 1045 steel by vacuum cladding. The influence of Cu contents on the microstructure, hardness, wear behavior and corrosion resistance of coatings was investigated. The results demonstrated that the microstructure was finer owing to the dissolution and dispersion of Cu, although the type of boride M2B and carboboride M23(C, B)6 in Cu-free and Cu-added coatings did not change. Since the Cu additions improved the hardenability of coating matrix and transformed its microstructure into martensite, the microhardness of coating matrix reached over 600 HV, and the macrohardness also increased and reached the maximum of 57.85 HRC for 5Cu sample. The wear volume of Cu-added coating was significantly lower than that of Cu-free coating, and the wear rate of 5Cu sample decreased by 50.40 %. The number of spalling pits on the worn surface decreased, showing the best wear resistance, and the main wear mechanism was fatigue spalling. Furthermore, the coating with high Cu contents possessed higher Ecorr, lower Icorr and higher Rct, which was attributed to the composite oxide passive film formed on the corrosion surface effectively isolated the coating from corrosive medium and greatly improved the overall corrosion resistance of coating.

Investigation on WEA fatigue spalling of U71MnG rail material subject to laser quenching surface treatment

In this study, the fatigue spalling process and mechanism of the white etched area (WEA) caused by the laser quenching surface treatment of U71MnG rail material were investigated. The results demonstrate that the surface pearlite is visibly deformed under normal stress and creep force during the initial wear stage, whereas the WEA is not deformed. Discordant plastic deformation results in the formation of cracks at the contact between the initial position of the WEA and the substrate, which then propagates into the WEA. As the number of rolling cycles increases, the formation and propagation of cracks gradually shift into the middle of the WEA and branch cracks form, which eventually intersect and cause spalling. The substrate's plastic flow covers the WEA terminal position surface; the WEA edge fracture is formed due to bending under normal stress. Plastic deformation enhances the surface hardness of WEA. The substrate's apparent plastic deformation beneath the WEA suggests that the WEA flows under the influence of creep forces.

Microstructural response and surface mechanical properties of TC6 titanium alloy subjected to laser peening with different laser energy

In this paper, the main purpose was to investigate the effects of laser peening (LP) on the microstructural evolution and frictional wear resistance of TC6 titanium alloy. The surface topographic features, microhardness and residual stress distribution in the depth direction of differently treated specimens were measured using three-dimensional topography instrument, digital microhardness tester and residual stress instrument. The frictional wear test was carried out using a multifunctional friction wear tester. Meanwhile, X-ray diffraction (XRD), optical microscope (OM) and transmission electron microscopy (TEM) were utilized to investigate the effects of LP on the microstructural response of TC6 titanium alloy. The results indicated that the micro-pits induced by LP increased the surface roughness to a maximum of 6.94 μm. LP technique effectively improved the microhardness and frictional wear resistance of TC6 titanium alloy, and the wear form changed from abrasive wear, adhesive wear and fatigue spalling wear to abrasive wear at the laser energy of 8 J. Compared to the untreated specimens, the surface microhardness of the specimens treated by LP with 8 J increased from 356 HV to 442 HV, and the affected layer depth was approximately 500 μm. Moreover, the friction coefficient decreased from 1.2 to 0.5, the abrasion depth of the abrasion track was reduced by approximately 32 % compared to the untreated specimen. Additionally, the surface compressive residual stress induced by LP with 8 J reached about −510 MPa. The microstructural evolution of the specimens processed by LP was dominated by twin formation and dislocation slip, while the intercalation between multidirectional twins and the formation of sub-grain boundaries promoted grain refinement of TC6 titanium alloy. Refined grains, high density of dislocations, mechanical twins and the implantation of compressive residual stresses effectively improved the friction and wear resistance of TC6 titanium alloy.

Study on the impact wear mechanism and damage modes of compacted graphite cast iron

The impact wear mechanism of compacted graphite cast iron (CGI) at different temperatures (room temperature, 300 °C, 400 °C, and 500 °C) and impact frequencies (10 Hz, 12 Hz, and 14 Hz) was analyzed. The mass losses increase with test temperatures, impact frequencies and numbers. When the temperature increases to 500 °C, shallow, deep-spalling, and oxidation are the main wear mechanism of CGI. Metal oxides are generated and shed repeatedly, which can accelerate the impact wear of CGI. In addition, there are mainly two cracking modes during the impact wear test (I) Micro-cracks can generate preferentially in the graphite cavities, caused by surficial graphite falling off affected by the high-frequency shocks. The graphite cavities and micro-cracks can coalesce with each other to form the main crack (Ⅱ) The hard metal particles due to fatigue spalling can inset in the soft matrix and cause cracking.

Root Cause Failure Analysis of Deep-Groove Ball Bearing Used in a Governor

Premature failure of a deep-groove ball bearing used in an aeroengine governor took place during service. In this paper, the failure mode and root cause of the bearing were studied by macroscopic and microscopic examination, metallographic analysis, hardness test, calculations of contact stress and L10 life, flatness measurement and comparative experiment. The results show that the failure modes of the inner ring raceway and steel balls are contact fatigue spalling, the failure modes of the outer ring raceway are wear and contact fatigue spalling, and the failure mode of the cage is fatigue fracture. The root cause and direct cause of the bearing failure were the unqualified machining process of the spring end face and the high unbalanced axial load, respectively. The unqualified machining process induced high points of the spring end face, which caused misalignment of the outer ring and inner ring and thereby resulted in the high unbalanced axial load. The characteristic damages induced by high axial load were climbing with the morphology of metal extrusion and accumulation at the border of the raceway for the inner and outer ring, and multiple fatigue fractures with the characteristic of multi origins for the cage. The unqualified machining process can be prevented by adopting the refined grinding process and adding detection requirements of flatness.

A Dynamic Wear Prediction Model for Studying the Interactions between Surface Wear and Dynamic Response of Spur Gears

Surface wear, as a major failure mode of gear systems, is an unavoidable phenomenon during the whole life of gears. It also induces other gear damages, such as fatigue cracks, surface pitting and spalling. Ultimately, those defects may result in the sudden failure of a gearbox transmission system, which can lead to a serious accident and unexpected economic loss. Therefore, it can provide huge cost and safety benefits to industries to monitor gear wear and predict its propagation. Gear wear raises the error rate of gear transmission systems, typically leading to improvements in dynamic loads, vibration, and noise. In return, the increased load conversely aggravates wear, creating a feedback cycle between dynamic responses and surface wear. For this purpose, a wear prediction model was incorporated into a tribo-dynamic model for quantitatively investigating how surface wear and gear vibration are mutually affected by each other. To obtain more precise dynamic responses, the tribo-dynamic model integrates the time-varying mesh stiffness, load-sharing ratio and friction parameters. To improve the computational efficiency and guarantee the calculation precision, an improved and updated wear depth methodology is constructed in the wear prediction model. This paper demonstrates the capability of the proposed dynamic wear prediction model in the investigation of the interaction effects between gear dynamics and surface wear, allowing for the development of improved gear wear prediction tools. The obtained results indicate that the surface wear impacts the dynamic characteristics, even with slight wear. In the initial stage of wear, the friction coefficient decreases slightly, largely due to the reduction in surface roughness; but the friction force increases because of the improved dynamic meshing force. Although the initial wear depth distributions of a pinion under dynamic and static conditions are similar, the wear depth distributions under dynamic conditions becomes significantly different compared to the those under static conditions with the wear process. The maximum wear depth of a pinion under dynamic conditions is about 1.6 times as the corresponding static conditions, when the wear cycle comes to 4 × 104. Similarly, the maximum accumulative wear depth of a pinion under dynamic conditions reaches 1.2 times of that under static conditions. Therefore, the proposed dynamic wear prediction model is more appropriate to be applied to the surface wear of gears.

Prediction of fatigue damage and spalling in a multilayered journal bearing shell

A 3D nonlinear approach for predicting the fatigue damage of plain journal bearings is proposed. The criterion selected, among several models, is inspired by Dang Van’s but is modified through an ascending slope in tensile direction. This criterion is consistent with the stresses seen on the bearing shells through hydrodynamic oil pressure and allows to reflect the severity of the compressive multiaxial non-proportional loading. From a fatigue test campaign, a modified Dang Van criterion is calibrated. Then, the simulation on the engine bench structure predicts a lifetime mapping consistent with the imposed loading and the experimental observations.

Study on strip WEA wear damage and fatigue spalling of U71MnG rail material by laser quenching treatment

The wear damage and fatigue spalling behaviors of the martensite strip white etched area (WEA) prepared by subjecting the U71MnG steel to laser quenching were studied. The results showed that the wear mechanism of the strip WEA surface changed from a combination of oxidation wear and adhesive wear to oxidation wear with increasing number of cycles. The uncoordinated deformation of the substrate and strip WEA initiated the formation of cracks at their interface. Moreover, the low thickness of WEA at the initial position and plastic deformation of the substrate in front and below accelerated the WEA spalling. At the middle position, the increase in the WEA bulge made it bear a larger load, leading to a more significant rheological displacement of the strip WEA than that of the substrate. The cracks were preferentially initiated at the interface and then propagated to the surface and depth of WEA to form branch cracks. The main crack propagated through WEA to the underlying substrate, causing severe spalling. At the end position, the plastic flow of the substrate formed the sheet metal on the strip WEA surface.

Tribological behavior of GNPs doped Al2O3 coating fabricated by SHVOF thermal spraying on cemented carbide

AbstractThis paper aims to experimentally investigate the effect of graphene nanoplatelets (GNPs) doped Al2O3 coating deposited on the surface of cemented carbide substrate using suspension high velocity oxy fuel (SHVOF) thermal spraying technique. Scanning electron microscopy was applied to characterize GNPs doped Al2O3 feedstock, the surface morphologies of cemented carbide before and after spraying, and the wear track morphology of cemented carbide after wear tests. The phases of GNPs doped Al2O3 feedstock, uncoated and coated cemented carbide were analyzed by X‐ray diffraction. The existence of GNPs was analyzed by Raman spectroscopy. A mixture of un‐molten and molten splats formed on the surface of cemented carbide substrate after SHVOF thermal spray. The average coefficient of friction (CoF) of coated samples was slightly lower than that of uncoated samples, which might be due to the friction‐reduction effect of GNPs. The wear rate of the samples was one order of magnitude higher than that of the alumina ball, showing that the wear of samples was the main wear between the friction couples. The wear mechanism of uncoated sample was mainly fatigue spalling, and that of cemented carbide substrate coated with GNPs doped Al2O3 coating was mainly plowing and abrasive wear.

Crack path and regularities for ball‐bearing fracture in the very‐high‐cycle fatigue regime

AbstractThe process of fatigue spalling in the rings of ball bearings at durability exceeding 108 cycles under in‐service loading conditions is analyzed on the basis of fractography and the slices prepared in radial planes of rings. The cracks are shown to originate at subsurface from carbides inherent in the bearing steel or inclusions permissible by sizes for the material. Subsequently, the development of cracks perpendicular to the ring raceway surface takes place similarly as in the very‐high‐cycle fatigue (VHCF) regime with the elliptical “fish‐eye” formation. The subsequent crack growth was demonstrated step‐by‐step up to the ring material fragment separation. The total crack path by alternating stops of propagation and new crack nucleation under conditions of mixed‐mode I + II + III mechanisms with the crack branching was discussed. In the final stage, the crack grows towards the ring raceway and either appears on the raceway surface or coalesces with a similar adjacent crack followed by fatigue spalling formation.

Effect of ultrasonic surface rolling process on the impact wear behavior of Inconel 690 alloy at 25 °C and 300 °C

As an important nuclear power material, Inconel 690 alloy always need to suffer various harsh impact wear behaviors during its service period. Therefore, how to further enhance its surface wear resistance and objectively reveal its fretting wear mechanism under various conditions have vital scientific values for improving its service performance. This study first applies specific ultrasonic surface rolling process (USRP) to treat the Inconel 690 alloy surface with two and four times separately. And then a controllable impact kinetic energy wear test rig is used to comparative investigate the impact wear behaviors of as-received and USRP treated samples at 25 °C and 300 °C temperature. Results indicate that USRP can effectively improve the near surface Nano-hardness, residual compressive stress and other mechanical properties of Inconel 690 alloy, thereby increasing its impact wear resistance. The impact wear mechanism at 25 °C is plastic deformation causes fatigue spalling, and some adhesion wear are found at the 300 °C wear condition.

Experimental Analysis of Planet Carrier Bearing Loads under Torque and Bending Moment in a Four-Point-Suspension Drive Train

Bearing failures in wind turbine gearboxes still occur which results in downtimes and hence leads to an increase in the levelized cost of energy. One of these affected bearings are the planet carrier bearings as they are still subject to unexpected fatigue related failure modes, like pitting and spalling, which are mainly influenced by the load distribution in the bearing. Hence it is necessary to determine the influence of torque and bending moment loads onto the planet carrier bearings. In this work the generator sided planet carrier bearing load distribution is investigated. Therefore, strain gauges are applied onto the circumference of that bearing of the gearbox of a 1 MW wind turbine four-point-suspension drive train. The loading is measured while testing at the 4 MW wind turbine test bench at CWD. The relevant loading for the investigated generator sided planet carrier bearing is torque which leads to a tilting of the gearbox leading to two load zones in the bearing. Bending moments at the hub of the drive train do not influence the bearing load distribution as they are absorbed by the main bearing.

Failure Analysis of a Cylindrical Roller Bearing Caused by Excessive Tightening Axial Force

The premature failure of a cylindrical roller bearing took place during service, with a total operation time of 100 h. The failure cause was analyzed by macroscopic and microscopic observation, metallographic analysis, hardness testing, tightening axial force influence analysis, and test verification. The results show that failure modes of the bearing are contact fatigue spalling, wear, and fatigue fracture. The outer ring, inner ring, rollers, and cages all have suffered relatively heavy damage in the sides corresponding to the bearing side with laser marking. Excessive load, induced by the excessive tightening axial force, derived from the lock nut, is the cause of the bearing failure. The failure mechanism is that excessive tightening axial force caused a great deformation and cylindricity increase of the inner ring raceway, which induced high local contact stress between one side of the ring raceways, as well as the corresponding ends of the rollers, resulting in the bearing failure. At last, measures for prevention of this failure are put forward as follows: controlling the tightening axial force within the range of technical requirement, increasing the convexity of the inner ring raceway and rollers, and decreasing the grinding undercut size of the inner ring.

Formation mechanism and influence of white etching area on contact fatigue spalling of M50 bearing steel

Contact fatigue spalling failure ocurred in the M50 steel bearings during test due to the formation of white etching area (WEA). In this paper, characteristics, formation mechanism, influence on contact fatigue spalling failure and control methods of the WEA were obtained by examining loctaions and morphological characteristics, composition analysis, hardness test and microstructure analysis of the WEA in the two failure bearing and the other three bearing which are not failure. The results show that the WEAs origin from the boundary between matrix and primary carbides or inclusions which located in the subsurface of raceway, show irregular block shape morphologies, have length direction of about 30°-50° degrees to the rolling direction and microstructure of body centered cubic ferrite nanocrystalline. There is no obvious difference between the WEA and matrix in chemical compositions, while hardness of the WEA is higher than that of the matrix. Formation mechanism of WEA is phase transformation driven by accumulation of plastic deformation induced by high stress in micro region. The smaller the distance between WEA and the raceway surface, the faster of WEA growth rate are reached. And WEA is more likely to cause contact fatigue spalling of the bearing as the deformation coordination between WEA and matrix is poor. The initiation and propagation of WEA can be controlled by reducing the material defects and avoiding the bearing from high working stress.

Torsion Wear Behavior of PEEK-on-UHMWPE as an All-Polymer Joint Combination in Total Knee Replacement

Polyether ether ketone (PEEK) has been considered as an alternative material to cobalt chrome in the femoral component of a total knee replacement. In this article, the experimental simulation of torsion wear for a PEEK and CoCr femoral head against an ultra-high-molecular-weight polyethylene (UHMWPE) tibial pad was carried out using a two-station knee simulator. The testing results showed that T-θ curves of torsion wear for PEEK-on-UHMWPE bearing couples showed three types of morphological characteristics, such as linear, elliptical, and parallelogram shapes. With an increase in torsion angular displacement, T-θ curves changed from the linear to the parallelogram type, and the relative motion state changed from the partial slip regime coordinated by the elastic deformation to the slip regime with plastic deformation. With an increase in normal load, the T-θ curve changed from the parallelogram to the elliptical type, and the relative motion state changed from the slip regime to the mixed slip regime. Under intermediate torsion wear conditions, the wear factors of UHMWPE were 11.25 ± 2.08 × 10−6 mm3/C and 14.65 ± 2.49 × 10−6 mm3/C against PEEK and CoCr. Under high torsion wear conditions, the wear factors were 20.51 ± 3.23 × 10−6 mm3/C and 23.26 ± 3.01 × 10−6 mm3/C, respectively. The wear surface of UHMWPE against PEEK showed slight adhesive wear and plastic deformation in the center, and abrasive wear with local fatigue spalling was found at the edges. The wear topographies presented characteristics similar to the CoCr bearing combination.

Microstructure, mechanical properties and tribological behaviors of TiAlN-Ag composite coatings by pulsed magnetron sputtering method

TiAlN-Ag composite coating was prepared by pulsed magnetron sputtering method on cemented carbide surface. The effect of silver content on the microstructure, mechanical properties and tribological behaviors of TiAlN-Ag composite coatings was studied. Results show that doping an appropriate amount of Ag into TiAlN coating can significantly refine the grain size of TiN nanocrystalline, reduce the internal stress, and improve hardness, plasticity and toughness, as well as the coating/substrate bond strength and tribological properties of the coating. Under dry friction conditions, the wear forms of TiAlN-Ag coating transfers from severe adhesion wear and brittle spalling of TiAlN coating to slight adhesion wear and abrasive wear, whereas the wear mechanism under oil lubrication changes from the comprehensive form of brittle fracture, fatigue peeling and abrasion to the mainly abrasive wear with slight fatigue spalling. Overall, the TiAlN-Ag composite coating with 2.40 at.% Ag exhibits the best comprehensive mechanical properties and wear resistance.

Fracture Failure Analysis of Gear Teeth

Gears are important transmission components in the field of aviation industry. Failure cases such as fatigue fracture and fatigue spalling often occur due to poor conditions, and the status of teeth surface is usually one of the important elements for the failure cause analysis, but few have analyzed how the machining status of gear end surface affects the fracture failure. In this paper, one engagement failure of two gears was studied, and the failure phenomenon is as follows: all teeth of the driving gear fractured, two adjacent teeth of the driven gear fractured and several locations of teeth bottom cracked. According to the fracture morphology of the gear, it is judged that the driven gear fatigue-cracked firstly, and the fatigue zone is located at the lower end surface rather than the tooth bottom. Material structure, machining status of gear end surface, and the thickness of nitriding layer were inspected. In addition, the difference of the machining status between the lower and the upper end surface was analyzed. The results show that compared to the upper end surface, the lower end surface is smoother and the grinding amount is relatively larger. The residual stress tested by XRD shows that there is a residual compressive stress of about 84 MPa on the upper end surface and a residual tensile stress of about 238 MPa on the lower end surface. The tensile stress and the working stress cause the local stress level of the lower end surface of the gear to be higher than the fatigue strength, causing fatigue cracking from the lower end surface.

Microstructure and tribological performance of boride layers on ductile cast iron under dry sliding conditions

Stamping die is prone to wear failure due to mechanical friction. In this work, high-hardness boride layers were obtained on ductile cast iron as stamping die, by a boronizing process at 800–950 ℃ for 2–6 h with the addition of rare-earth oxide La2O3. A sawtooth-like morphology of the boride layer was observed using scanning electron microscopy (SEM). The greatest boride layer micro-hardness of the boride layers of 1648 HV0.1 was obtained at 900 ℃ and 6 h with 4% La2O3, and X-ray diffraction (XRD) analysis showed that the boride layers were a component of Fe2B as adding La2O3. The tribological tests showed that the wear resistance of the boride layers was enhanced with increasing boronizing temperature and time, where the ductile cast iron substrate corresponding to 900 ℃ and 6 h exhibited the best wear resistance. Compared with that of the boride layer without La2O3, the thickness and wear resistance of the boride layer with 4% La2O3 was increased by 37.2% and 31%, respectively. The thickness of the boride with 6% La2O3 decreased by 27.6%, and the wear rate was highest, indicating that excessive La2O3 inhibited the enhancement effect. The wear mechanism of the boride layers transformed from mild adhesive wear to fatigue spalling as the normal load and sliding speed increased.