Decrease In Wear Rate Research Articles

Mechanically tailored surface of titanium based alloy (Ti6Al4V) by laser surface treatment

In this study, laser surface treatment (LST) of Ti6Al4V carried out by melting within a narrow regime of optimum process parameters for the formation of a surface with improved wear and tribo-corrosion resistance is presented. The effect of applied power and shrouding gas on the microstructure, phase, surface hardness, residual stress, dry wear (against tungsten carbide, WC) and tribocorrosion resistance (against ZrO2 in Hank's solution) is established. LST in argon atmosphere leads to the formation of a composite structure consisting of acicular α’ martensite and α. LST in nitrogen atmosphere causes the formation of titanium nitride (TiN and Ti2N) dispersed in α matrix. Due to LST, there is an increase in surface microhardness both under argon (435–630 VHN) and nitrogen atmosphere (839–1327 VHN) when compared to untreated Ti6Al4V (278 VHN). There is a marginal decrease in wear rate (against WC ball) due to laser surface melting (5.17–5.81 × 10−3 mm3/Nm) under argon and a substantial decrease in wear rate when melting was conducted under nitrogen atmosphere (1.91–4.94 × 10−3 mm3/Nm) as compared to Ti6Al4V (5.93 × 10−3 mm3/Nm). The mechanism of wear is established. On the other hand, the tribo-corrosion rate is found to decrease for laser surface melting (3.5–4.8 × 10−3 mm3/Nm) and nitriding (1.3–3.2 × 10−3 mm3/Nm) as compared to Ti6Al4V (5.7 × 10−3 mm3/Nm). Bioactivity in terms of calcium phosphate deposition followed by dipping in Hank's solution was found to increase due to both melting and nitriding, though nitriding offered a marginally higher bioactivity than only melting.

Enhancing PEO coating on TC6 alloy through in-situ synthesis of MoSe2—Towards more efficient wear-reducing lubrication and wear resistance

Plasma electrolytic oxidation (PEO) has demonstrated significant enhancements in the mechanical properties and corrosion resistance of titanium alloys. Despite these advantages, the presence of micropores and microcracks in the coating can still detrimentally impact tribological properties. This paper introduces a novel approach involving the in-situ growth of a surface structure. The resulting interface structure exhibits outstanding tribological properties under a load of 3 N and a speed of 1.5 cm/s. In contrast to prior studies, improvements are made to the electrical parameters and electrolyte formula of Plasma electrolytic oxidation, facilitating the in-situ growth of MoSe2. This results in the formation of a lubricating layer and a robust TiO2 ceramic coating with excellent adhesion. A systematic analysis of friction, wear characteristics, reveals that MoSe2 in situ grow on the surface of the PEO coating, within micropores, microcracks, and crater structures after hydrothermal treatment. This process significantly enhances the microporous structure of the coating, with the MoSe2 film forming a dense and uniform interlocking layer with the PEO lower layer. Dry friction test experiments demonstrate a 33.7% reduction in friction coefficient and a 29% decrease in wear rate compared to the PEO sample, indicating the synergistic effect between the MoSe2 film and the PEO coating.

Tribological properties of two-dimensional nanochains in water controlled by a magnetic field with various alignment directions

Nanoparticles are extensively utilized as effective lubrication additives. In a novel approach, one-dimensional nanoparticles undergo self-assembly, transforming into two-dimensional nanochains for use as additives, thereby enabling varied lubrication effects. We involved synthesizing Fe3O4 nanoparticles via a solvothermal method, followed by their self-assembly into magnetic Fe3O4@SiO2 nanochains under a magnetic field. These NCs, measuring 57.8 µm in length and 0.2 µm in diameter, were dispersed in deionized water. This study explored the influence of various orientations on the tribological properties of the lubricant through the manipulation of nanochains’ alignment using a magnetic field. The results indicate a 48.51% reduction in coefficient of friction and a 73.56% decrease in wear rate when the NCs were aligned perpendicular to the direction of friction.

Effect of a Substrate’s Preheating Temperature on the Microstructure and Properties of Ni-Based Alloy Coatings

Laser cladding is a new technology to fabricate a coating on the surface of a metal substrate. The properties on copper substrates are usually not very good due to the high thermal conductivity and reflectivity. The appropriate preheating temperature is helpful to fabricate coatings with good quality and properties, especially for copper substrates. In order to investigate the effect of different preheating temperatures, four coatings with different preheating temperatures (100, 200, 300 and 400 °C) were fabricated via a laser on a copper substrate. The microstructures and properties of four coatings were investigated using SEM, XRD, EDS, a Vickers microhardness meter, a wear tester and an electrochemical workstation. The results show that the elements from Ni-based alloy powder were uniformly distributed among the binding region, which obtained a good metallurgical bonding. The microstructure was mainly composited of cellular, dendrite and plane crystals, and the main reinforced phases were γ (Fe, Ni), Cr0.09Fe0.7Ni0.21, WC and Ni3B. The values of average microhardness of the four coatings were 614.3, 941.6, 668.1 and 663.1 HV0.5, respectively. The wear rates of the four coatings were 9.7, 4.9, 12.5 and 13.3 × 10−5 mm3·N−1·m−1, respectively, which were less than that of the copper substrate (4.3 × 10−3 mm3·N−1·m−1). The decrease in wear rate was due to the existence of the reinforced phases, such as WC, Ni3B, M7C3 (M=Fe, Cr) and Cr0.09Fe0.7Ni0.21. The fine crystals in the coating preheated at 200 °C also improved the wear resistance. Additionally, the minimum values of corrosion current density were 3.26 × 10−5, 2.34 × 10−7, 4.02 × 10−6 and 4.21 × 10−6 mA·mm−2, respectively. It can be seen that the coating preheated at 200 °C had higher microhardness, lower wear rates and better corrosion resistance due to the existence of reinforced phases and fine and uniform crystals.

Lithium nitrate salt-assisted CO2 absorption for the formation of corrosion barrier layer on AZ91D magnesium alloy.

Mg alloy corrosion susceptibility is a major issue that limits its wide industrial application in transport, energy and medical sectors. A corrosion-resistant layer containing crystalline MgCO3 was formed on the surface of AZ91D Mg alloy by Li salt loading and thermal CO2 treatment. Compared to the uncoated AZ91D surface, the surface layer exhibited up to a ∼15-fold increase in corrosion resistance according to the electrochemical results in 3.5 wt% NaCl solution and ∼32% decrease in wear rate compared to untreated AZ91D. The improved corrosion resistance is attributed to the formation of a <10 μm thick dense layer containing Mg, O, C and Li with crystalline MgCO3 phases. The initial step was to form a porous MgO layer on the surface of AZ91D Mg alloy, followed by loading an alkali metal salt (i.e., LiNO3) onto the MgO surface. The porous MgO surface was then reconstructed into a dense insulation layer containing Mg carbonate through CO2 absorption facilitated by molten Li salt during thermal CO2 treatment at 350 °C. As a potential method to utilize excessive CO2 for beneficial outcomes, the formation of the carbonate-containing film introduced in this study opens a new pathway for protecting various existing Mg alloys for diverse industrial applications.

Unveiling of grain structure, porosity, phase distributions, microstructural morphology, surface hardness, and tribo-corrosion characteristics of nickel, and titanium dioxide-based SS-304 steel microwave composite coatings cladding

The microstructure, homogeneity, and tribo-corrosion behavior of microwave-developed Nickel as well as titanium dioxide SS-304 cladding surfaces are the primary emphasis of this research. The study includes assessing the hardness enhancement from Ni and TiO2 particles in the cladding surface. The investigation additionally evaluates cladding surface wear rates, friction coefficients, and resistance to corrosion under tribological conditions. The microstructure, homogeneity, and tribo-corrosion behavior of SS-304 cladding surface with Ni and TiO2 developed by microwave cladding energy were investigated in this study. The microstructure was being examined to validate the uniformly homogeneous dispersion of Ni and TiO2 particles, and XRD was employed to determine cladding surface phases. The hardness of the cladding surface was evaluated, and a pin-on-disk tribometer has assessed the wear behavior. Tribo-corrosion was tested in 3.5-percent NaCl solution. To enhance cladding's efficiency, microwave hybrid heating (MHH) utilising charcoal as a susceptor has been employed. Findings exhibited that the microstructure analysis showed that the cladding surface had a uniform distribution of Ni and TiO2 particles and a compact and homogeneous microstructure. The hardness of the cladding surface was significantly improved by about 37.68% due to the incorporation of Ni and 10% TiO2 particles. The FeNi3, NiSi2, Ni3C, NiC, Ni2Si, FeNi, and TiO2 phases were seen by XRD on the cladding surface. The behavior of the cladding surface under tribological conditions was also evaluated using a pin-on-disk tribometer. The outcomes have exhibited that the Ni and 10% TiO2 cladding surface exhibited decreased wear rates and friction coefficients compared to the uncoated SS-304 substrate. Moreover, the tribo-corrosion behavior of the cladding surface was evaluated in a 3.5% NaCl solution. The wear rate and coefficient of friction of Ni and 10% TiO2 cladding surfaces were measured to be 0.00412 mm3/m and 0.297, respectively. The results indicated that the Ni and TiO2 cladding surface had enhanced corrosion resistance compared to the uncoated SS-304 substrate.

Dry tribological behaviour of microwave-assisted sintered AA2024 matrix hybrid composites reinforced by TiC/B4C/nano-graphite particles

Abstract This study aimed to produce hybrid composites with a AA2024 matrix reinforced by TiC/B4C/nano-graphite through a microwave-assisted sintering technique at 560 °C for 60 min. The nano-graphite ratio in the produced composite samples was kept constant as 1 wt.%. TiC and B4C were used in equal ratios at 2, 6 and 10 % by weight total to determine their effects on tribological properties. Wear tests were conducted under three different loads: 3, 5 and 10 N. In the hybrid composites produced, an inverse correlation was observed between the increase in reinforcement ratio and sinterability, while a direct correlation relationship was found in hardness and wear resistance. Compared to the sample containing 2 % TiC/B4C in total by weight, a ∼50 % increase in Brinell hardness and a 52–68 % decrease in wear rate was obtained in the sample containing 10 % TiC/B4C. As the reinforcement ratio increased, tribofilm formation increased, and abrasive wear was replaced by mild-oxidative wear type.

Wear mechanism transforming of ultrafine-grained pure titanium by multi-axial forging and low-temperature annealing

The effect of microstructure and mechanical properties of submicro grained commercial pure titanium (CP–Ti) on the wear mechanism is still unclear. In the present work, CP-Ti samples were subjected to multi-axial forging (MAF) and low-temperature annealing treatment to prepare ultrafine-grained (UFG) material. The mechanical properties, microstructure, and tribological characterization between coarse-grained (CG) sample and UFG samples were comparatively studied. The results showed that the MAF sample could reach a grain size of 165 nm, while its grains coarsened slightly after low-temperature annealing. The MAF sample had the highest strength and hardness and the lowest coefficient of friction, but only a 7.3 % decrease in wear rate compared to the CG sample. The 400 °C annealed MAF sample possessed a good combination of tensile strength (814 MPa) and elongation (18.6 %), resulting in the lowest wear rate of 16.8 × 10−5mm3/(N∙m). The dominated wear mechanisms of the CG sample, MAF sample and 500 °C annealed MAF sample were abrasive wear, adhesive wear and delamination wear, while the primary mechanism of the 400 °C annealed MAF sample was abrasive wear and adhesive wear. It was found that the wear mechanism transforming, higher hardness and sufficient work hardening could be responsible for lower wear rate of the 400 °C annealed MAF sample. The 400 °C annealed MAF sample showed a thinner and more homogeneous deformation layer near the worn surface, and its thickness of deformation layer was about 8 μm.

Enhancing elevated-temperature fretting wear performance of GH4169 by tuning wear mechanism through laser shock peening

Turbine disks and blades made of GH4169 for turbine engines are highly prone to fretting wear damage. In this work, we used laser shock peening (LSP) to improve the elevated-temperature fretting wear performance of GH4169, and the corresponding underlying mechanisms are also systematically investigated. Fretting wear experiments conducted on specimens following LSP treatment reveal that the wear resistance of GH4169 was significantly improved, namely a 12.7% reduction in average friction coefficient and a 67.0% decrease in wear rate. Multiscale electron microscopy characterizations reveal that the gradient microstructures induced by LSP serve as the main contributor, which promotes the transition of mechanisms from adhesive wear to abrasive wear, then leading to an exceptional fretting wear performance.

Evaluation of erosion of AISI 1045 carbon steel due to non-cohesive microparticles

Erosion behavior of AISI 1045 carbon steel was investigated using slurry solutions with different viscosities (1 cP, 3 cP, and 8 cP) containing 5 wt% silica sand as erodent particles. Tests were carried out using a slurry pot apparatus with various rotational velocities and at three mounting angles (30°, 60°, and 90°). The qualitative and quantitative analysis was performed using the Taguchi design method, paint modeling, image processing, and microscopic imaging techniques. The results indicate that the erosion process in the slurry flow is significantly influenced by fluid viscosity. There is a notable decrease in erosion wear rate as fluid viscosity increases. An analysis of variance (ANOVA) test was conducted, concluding that viscosity and rotational speed are the significant factors influencing the weight loss of carbon steel. The results demonstrate that each factor has a major impact on the response; velocity (47.20 %) is the primary factor contributing to R, followed by viscosity (38.20 %). The erosive wear mechanism changed considerably with the variation in fluid viscosity and impact angles. As viscosity increases, the cutting and pitting erosion wear mechanism shift to sliding wear with the development of micro-perforation sites.

ECO-DESIGN And MECHNICAL STRENGTH ANALYSES Of A BRAKE PAD

Brake pads are a crucial component of any vehicle's braking system. It is important to consider both eco design and mechanical strength analyses when developing brake pad materials to ensure they are environmental-friendly and safe to use. When developing brake pad material, it must satisfy certain criteria, among which are supporting high temperature, pressure, tensile stresses, decreased wear rate, and in addition to that its environmental sustainability by using eco-friendly materials. Four types of brake pad materials are analyzed. The eco-design analysis revealed that one material was the most environmentally friendly compared to the others. From a mechanical strength perspective, one material with better performance was selected. By combining the two analyses, one material was identified that meets both environmental and mechanical requirements. These findings can be used to guide future research and development in brake pad design, with the goal of reducing the environmental impact and improving the safety of brake pads for all users.

Tribology Performance of TiO2-SiO2/PVE Nanolubricant at Various Binary Ratios for the Automotive Air-conditioning System

Tribological properties are crucial for air-conditioning system performance. The properties can be improved using nanolubricant. However, the effect of the binary ratio of hybrid nanolubricants on the tribological performance of automotive systems is limited in the literature. Therefore, the present study investigates the tribology performance of TiO2-SiO2 nanolubricants for application in automotive air-conditioning (AAC) systems. The dispersion of TiO2 and SiO2 into PVE lubricant was carried out using a two-step method. Subsequently, the dispersion stability was assessed qualitatively and quantitatively. The samples were characterised by a volume concentration of 0.010%, with variations in the mixture ratio of 20:80, 40:60, 50:50, 60:40, and 80:20. Coefficient of friction (COF) and wear scar diameter (WSD) values were determined using the Koehler Four-ball Tribo Tester and Light Compound Microscopy. The investigation revealed that each sample experienced a reduction in COF, with the 40:60 ratio demonstrating the best ratio with the most significant decrease of 37.09%. At the same time, the COF decreased by 8.34%, 2.12%, 7.37%, and 15.11% for the nanolubricant samples at 20:80, 50:50, 60:40, and 80:20, respectively. The WSD evaluation showed that the 40:60 ratio has the lowest scar diameter of 0.0344 mm and a 37.09% wear rate decrease compared to pure lubricant. Each sample exhibits superior performance when evaluated for tribological characteristics and performance, particularly in the case of nanolubricants with the 40:60 ratio. The TiO2-SiO2/PVE, characterised by a volume concentration of 0.010%, has remarkable efficacy across different binary ratios, making it highly recommended with a 40:60 ratio for lubricating AAC compressor systems.

Simultaneous enhancement of friction and wear resistance for high‐speed braking system with Cr3C2‐NiCr‐coated brake disk

AbstractThe current steel brake disk and Cu‐based powder metallurgy brake pad used in high‐speed trains suffer fading coefficient of friction (COF) and excessive wear, resulting in a shorten lifetime and numerous exhausted brake disks. High‐velocity oxygen fuel (HVOF) spray‐prepared coatings have proven their ability to improve COF and decrease wear rate. In this article, Cr3C2‐NiCr coating was sprayed on a steel brake disk, and a series of emergency braking tests under dry and wet conditions were performed on a subscale brake dynamometer, to comprehensively evaluate the braking performance of coated brake disk. The results showed that the coated brake disk exhibits a higher COF at 380 km/h, which effectively inhibits the COF fade compared to the steel brake disk case. The coated brake system also achieves a lower wear rate of the brake pad at 380 km/h, showing the desired high COF and low wear rate properties of the braking system. Additionally, the coated brake disk maintained surface integrity even after severe braking tests, highlighting its potential in the braking system. Based on the characterizations of wear debris and brake pads, a harder and thinner oxide friction film plays a crucial role in achieving the excellent braking performance in coated brake disk cases.

Study of Surface Modification of NiCrBSi Coating by Electron Beam Cladding on Inconel 625 Alloy

Surface modification of nickel‐based 625 alloy is performed using a vacuum electron beam to improve its surface properties. The development of the microstructure is analyzed through scanning electron microscopy, X‐ray diffraction, and transmission electron microscopy. The tribometer RETC (MFT‐5000) is used to assess the wear resistance of the modified surface. The results demonstrate that the microstructure of the cladding zone exhibits columnar growth of the face‐centered cubic phase. As the scanning speed increases, the Cube texture s gradually weak, surface hardness increases, and both wear volume and wear rate decrease, thereby improving wear resistance. The maximum surface hardness is achieved at a scanning speed of 400 mm min−1, with a value of 489.8 HV, 1.977 times higher than the substrate. The minimum wear volume measures 0.1518 mm3, and the wear rate is likewise at its lowest point, measuring 0.506 × 10−5 mm3 N−1 m. Compared to the substrate, the material demonstrates an 88.44% reduction in wear rate and an 8.65‐fold improvement in wear resistance. These results demonstrate the significant enhancement of surface properties in Inconel 625, through surface modification using a vacuum electron beam.

Influence of Artificially Altered Engine Oil on Tribofilm Formation and Wear Behaviour of Grey Cast Cylinder Liners

This work investigates the influence of altered engine oil on the tribological performance, focusing in particular on wear and interconnected tribofilm formation. For this purpose, Zinc dialkyldithiophosphate (ZDDP) additivated engine oils of different degradation levels, produced in an artificial oil alteration process, were used in tribometer tests with a nitride steel piston ring against a grey cast iron cylinder liner model contact. Parameters were chosen to simulate the boundary and mixed lubrication regime typical for the top dead centre conditions of an internal combustion engine of a passenger car. Wear of the cylinder liner specimens was continuously monitored during the tribometer tests by the radio-isotope concentration (RIC) method, and tribofilms were posteriorly investigated by X-ray photoelectron spectroscopy (XPS). The results clearly show that the steady-state wear rates for experiments with altered lubricants were significantly lower than for the experiments with fresh lubricants. XPS analysis on the formed tribofilms revealed a decrease in sulphide and an increase in sulphate states for altered oils evaluated at 120 °C oil temperature, correlating with a decrease in steady-state wear rate. This finding emphasizes the role of sulphate species in the tribofilm formation process and its anti-wear capabilities, in contrast to the sulphide species and the (poly-)phosphate species, as outlined in most of the ZDDP literature. Moreover, the RIC signal that represents the amount of wear in the engine oil showed a decrease over time for specific altered lubricants and test conditions. These “negative” trends in the wear signal are remarkable and have been identified as an incorporation of wear particles from the lubricant into the tribofilm. This finding is supported by XPS results that detected an iron-oxide layer with a remarkably similar quantity within the tribofilm on the surface. Based on these findings, an assessment of the minimum film formation rate and particle incorporation rate was achieved, which is an important basis for adequate tribofilm formation and wear models.

Understanding the microstructural evolution and fretting wear behaviors of M50 bearing steel heat treated at different temperatures

For M50 bearing steel, which is widely used in aerospace engine main bearings, fretting wear is an important but neglected category of wear failure during engine cold startup. High temperature tempering is crucial in heat treatment to enhance its microstructure and wear resistance. In order to investigate the influence of different tempering conditions on fretting wear performance of M50 steel, it is essential to conduct a comprehensive study. This research explores how heat treatment processes affect the fretting wear properties of M50 steel by varying the tempering temperature (450 °C, 500 °C, 550 °C, 600 °C, and 650 °C). We analyzed the microstructure evolution and fretting wear behavior under different conditions using SEM, EDS, XRD and other characterization methods. The results show that the tempering temperature influences fretting wear through martensite, retained austenite, and carbide transformations. In the 450 °C–600 °C range, wear volume and wear rate decrease with hardness. At 550 °C tempering, M50 achieves the highest hardness (59.71 HRC) and a lower wear rate (9.661 × 10−8 mm3/(N·mm)). M50 steel exhibits optimal fretting wear performance at 550 °C tempering. Overall, wear behavior occurs in the mixed slip regime, shifting towards partial slip with higher tempering temperatures. When the tempering temperature is low, the fretting wear mechanism is predominantly dominated by fatigue wear and abrasive wear, while at higher tempering temperatures, the fretting wear mechanism is primarily governed by oxidative wear and adhesive wear.

Effect of HVOF–sprayed nanostructured WC–10Co–4Cr coating on sliding wear and tensile–tensile fatigue properties of TC6 titanium alloy

Aerospace equipment has been placing greater demands on the wear resistance and fatigue strength of titanium alloys. In light of this, the research objective was to prepare a WC-10Co-4Cr coating with better performance through the utilization of the ultra-short distance high-speed oxygen fuel (HVOF) spraying process. Then the microstructure, microhardness, sliding wear, and fatigue performance of TC6 alloy reinforced with WC–10Co–4Cr coating were further explored and analyzed. The ultra–short distance HVOF spraying process was employed to suppress decarburization, resulting in a minimal amount of W2C phase in the coating. The WC–10Co–4Cr coating exhibited excellent surface characteristics, displaying minimal microcracks and a low porosity rate of 0.15 ± 0.08%. The interface between the coating and the substrate was sharp and clean, while the TC6 alloy retained its dual structural characteristics without any microstructural changes. The microhardness of the WC–10Co–4Cr coating exhibited a remarkable value of 1172.64 HV0.025, which is 3.2 times greater than that of the substrate. The coating exhibited a noteworthy decrease in wear rate, wear depth, and wear area, indicating superior wear resistance. Additionally, a thorough examination was conducted to uncover the underlying wear mechanism of the coating under different loads. The WC-10Co-4Cr coating, which was developed through this study, shows a minimal influence on the fatigue strength of the original base material. Furthermore, a comprehensive analysis was conducted to elucidate the factors contributing to the significant fatigue life of the WC–10Co–4Cr coating.

Improvement of mechanical and wear properties of epoxy/glass fiber/Titanium Carbide+Titanium diborides hybrid composites by adding clay nanoparticles

In previous work, despite the positive effect of the titanium carbide + titanium diboride (TiC+TiB2) on the wear, hardness and erosion properties of the epoxy/glass fiber composites, the particles reduced tensile and flexural strength. This research targets to improve the tensile and flexural properties of the epoxy/glass fiber/TiC+TiB2 composites by adding clay nanoparticles in content of 1, 3, and 5 wt%. The effect of nano-clay content on mechanical (tensile, flexural, and hardness) properties and wear behavior of the hybrid composites was investigated. The field Emission Scanning Electron Microscopy (FE-SEM) images revealed the morphology, the fracture surface and failure mechanisms of the composites. The X-ray diffraction confirmed the formation of TiC+TiB2 particles and the nanocomposites. Tensile and flexural results showed that introducing clay nanoparticles increases tensile strength and flexural strength by 92% (from 116 to 223 MPa) and 67% (from 194 to 324 MPa), respectively. The nano-clay did not have a significant effect on the tensile and flexural modulus. The hardness increased from 35.1 to 79.4 HRP. Wear properties results revealed that clay nanoparticles improve the wear resistance of the composite samples significantly. The addition of 5 wt% of clay nanoparticles decreased wear rate from 3.7 to 0.4 mg/Nm.

Evolution of microscopic characteristics of rolling contact fatigue coexisting with wear of U75V rail

During the damage and defects related to rolling contact fatigue (RCF), together with wear occurring at the rail surface, the microscopic characteristics of the rail material change with the accumulation of wheel cycles. To find the relationship between rail material characteristics and RCF damage under wheel-rail contact situations, a series of twin-disc rolling-sliding tests, based on real wheel-rail contact situations at a radius of 80 mm rail profile, was established for a heavy-haul railway in China. The microscale characteristics of the rail disc contact surface was researched, including crack, wear, roughness, and hardness of the U75V rail with different load cycles. The results show that the damage mechanism of RCF and wear alternately dominates the rail disc surface at the microscale, taking a certain cycle as a boundary which makes the RCF crack number and wear rate have opposite evolutionary trends. The above factors also affect the wear at the surface rail discs, alternating between fatigue and adhesion. Meanwhile, increasing the surface micro-hardness leads to a decrease in the relative wear rate and an increase in the roughness, length and number of RCF cracks. The plastic deformation layers, including the severely deformed layer (SDL) and the transition layer (TL), almost maintain the same thickness and the dynamic equilibrium increases during the cycles. Two kinds of cracks are initiated and propagated at the rail disc surface, one at the SDL and the other at the junction of SDL and TL. The number of each kind of crack depends on the SDL thickness.

Investigation of Machining Characteristics in Electrical Discharge Machining Using a Slotted Electrode with Internal Flushing.

In die-sinking electrical discharge machining (EDM), it is challenging to implement internal flushing, mainly because it is easy to produce residual material columns on the workpiece cavity's bottom surface, affecting the processing quality and efficiency. In order to solve this problem, the internal flushing slotted electrode EDM technology was proposed. The slotted electrode was designed, and its preparation method was described. The influence of pulse width, pulse interval, and flushing pressure on the performance of the internal flushing slotted electrode EDM was studied using single-factor experiments. The experimental results indicate that, with the increase in pulse width, the material removal rate (MRR) increases first and then decreases, while the electrode wear rate (EWR) and the relative electrode wear rate (REWR) decrease gradually; with the increase in pulse interval, the MRR decreases, while the EWR and the REWR increase gradually; with the increase in flushing pressure, the MRR increases first and then decreases, while the EWR and the REWR increase gradually. When the slotted electrode is used for continuous internal flushing EDM, the appropriate pulse width, flushing pressure, and smaller pulse interval can improve the MRR and reduce the EWR and the REWR.