Quasi-nano wear mechanism under repeated impact contact loading

A new quasi-nano wear mechanism (QNWM) has been proposed in this paper based on the facts of wear curve turning under high energy impact contact loading.Its characteristic is that the wear rate of QNWM is only 1/10-1/3 that of delamination mechanism at the same energy density.The diameters of wear debris and pits on the worn surfaces fall into the quasi-nanometer scale (about 50-120 nm).The necessary and sufficient conditions,which bring about the QNWM,are:(i) the nano-structure (nano-crystalline + amorphous phase) in impact contact surface layer has formed by the intensive impact strain;(ii) the delamination wear cracking in sub-surface layer must be restrained;(iii) the microcracks of QNWM are produced in amorphous phase of surface nano-structure layer rather than in nano-crystalline.

Wear mechanism and serious wear position of casing pipe in vertical backfill drill-hole

Vertical backfill drill-hole is usually a key project in an underground mine with backfill method and can be easily damaged by impact of backfill slurry.Observation of the damaged vertical backfill drill-holes in Jinchuan Nonferrous Metal Corporation（JNMC）,Gansu Province,China,given by a digital drill-hole video camera,indicated that there usually exist serious wear zones in casing pipe in vertical backfill drill-hole（CVBH）.It was suggested that serious wear position of CVBH should be located at an interface between air and solid-liquid mixture within CVBH.Backfill slurry falls freely and impacts the wall of CVBH near the interface with great momentum and energy coming from high speed free fall of backfill slurry.The depth of serious wear position of CVBH,i.e.,free fall height of backfill slurry in CVBH,can be estimated by the height of vertical backfill drill-hole,the length of horizontal pipeline,the density of slurry and the hydraulic gradient of pipeline system.A case study indicated that the estimation equation of serious damage depth of CVBH was of enough accuracy and was helpful for daily maintenance and management of vertical backfill drill-hole.

Dry sliding wear behavior and mechanism of AM60B alloy at 25-200 ℃

Dry wear tests under atmospheric conditions at 25-200 °C and loads of 12.5-300 N were performed for AM60B alloy. The wear rate increases with increasing the load; the mild-to-severe wear transitions occur under the loads of 275 N at 25 °C, 150 N at 100 °C and 75 N at 200 °C, respectively. However, as the load is less than 50 N, the wear rate at 200 °C is lower than that at 25 °C or 100 °C. In mild wear regimes, the wear mechanisms can be classified into abrasive wear, oxidation wear and delamination wear. Delamination wear prevailed as the mild-to-severe wear transition starts to occur; the delamination occurs from the inside of matrix. Subsequently, plastic-extrusion wear as severe wear prevails accompanied with the transition. The thick and hard tribo-layer postpones the mild-to-severe wear transition due to restricting the occurrence of massive plastic deformation of worn surfaces.

TOOL WEAR PATTERNS AND MECHANISMS OF SOLID CEMENTED CARBIDE IN HIGH-SPEED MILLING OF ALUMINUM ALLOY

The wear patterns and wear mechanisms of solid cemented carbide are analyzed in high-speed milling of aluminum alloy. Results show that the dominant wear patterns are coating damage, crater wear, micro-chipping, breakage, and so on. The main wear mechanisms are adhesion, diffusion and fatigue. Compared with conventional speed machining, the effect and impact of thermal-dynamical coupling field play an important role in the cutting tool wear in high-speed milling of aluminum alloy.

Wear behavior and mechanism of B_4C reinforced Mg-matrix composites fabricated by metal-assisted pressureless infiltration technique

The B4C/Mg composites fabricated by metal-assisted pressureless infiltration technique were used as experimental material, and the wear behavior and mechanism of this material were studied. A pin-on-disc apparatus was used to evaluate the wear behavior where loads of 20, 40, 60 and 80 N, and a sliding velocity of 250 r/min were exerted. The results show that B4C/Mg composites possess superior wear resistance than pure Mg under various applied loads, and the content of Ti, as infiltration inducer, has an influence on the wear resistance of B4C/Mg composites. The dominant wear mechanism for pure Mg is abrasion, while that for B4C/Mg composites under low loads is adhesion and delamination. Under high loads, the wear mechanism of B4C/Mg composites can be attributed to thermal softening and melting or plastic deformation.

Intelligent Identification of Wear Mechanism via On-line Ferrograph Images

Condition based maintenance（CBM） issues a new challenge of real-time monitoring for machine health maintenance. Wear state monitoring becomes the bottle-neck of CBM due to the lack of on-line information acquiring means. The wear mechanism judgment with characteristic wear debris has been widely adopted in off-line wear analysis; however, on-line wear mechanism characterization remains a big problem. In this paper, the wear mechanism identification via on-line ferrograph images is studied. To obtain isolated wear debris in an on-line ferrograph image, the deposition mechanism of wear debris in on-line ferrograph sensor is studied. The study result shows wear debris chain is the main morphology due to local magnetic field around the deposited wear debris. Accordingly, an improved sampling route for on-line wear debris deposition is designed with focus on the self-adjustment deposition time. As a result, isolated wear debris can be obtained in an on-line image, which facilitates the feature extraction of characteristic wear debris. By referring to the knowledge of analytical ferrograph, four dimensionless morphological features, including equivalent dimension, length-width ratio, shape factor, and contour fractal dimension of characteristic wear debris are extracted for distinguishing four typical wear mechanisms including normal, cutting, fatigue, and severe sliding wear. Furthermore, a feed-forward neural network is adopted to construct an automatic wear mechanism identification model. By training with the samples from analytical ferrograph, the model might identify some typical characteristic wear debris in an on-line ferrograph image. This paper performs a meaningful exploratory for on-line wear mechanism analysis, and the obtained results will provide a feasible way for on-line wear state monitoring.

Wear mechanism for spray deposited Al-Si/SiC_p composites under dry sliding condition

Al-Si/15%SiCp(volume fraction) composites with different silicon contents were fabricated by spray deposition technique, and typical microstructures of these composites were studied by optical microscopy(OM). Dry sliding wear tests were carried out using a block-on-ring wear machine to investigate the effect of applied load range of 10-220 N on the wear and friction behavior of these composites sliding against SAE 52100 grade bearing steel. Scanning electron microscopy(SEM) and energy-dispersive X-ray microanalysis(EDAX) were utilized to examine the morphologies of the worn surfaces in order to observe the wear characteristics and investigate the wear mechanism. The results show that the wear behavior of these composites is dependent on the silicon content in the matrix alloy and the applied load. Al-Si/15%SiCp composites with higher silicon content exhibit better wear resistance in the applied load range. Under lower loads, the major wear mechanisms are oxidation wear and abrasive wear for all tested composites. Under higher loads, severe adhesive wear becomes the main wear mechanisms for Al-7Si/15%SiCp and Al-13Si/15%SiCp composites, while Al-20Si/15%SiCp presents a compound wear mechanism, consisting of oxidation, abrasive wear and adhesion wear.

Erosive Wear and Wear Mechanism of in situ TiC_P/Fe Composites

The base structure of in situ TiCp/Fe composites fabricated under industrial condition was changed by different heat treatments. Erosive wear tests were carried out and the results were compared with that of wear-resistant white cast iron. The results suggest that the wear resistance of the in situ TiCp/Fe composite is higher than that of wear-resistant white cast iron under the sand erosive wear condition. The wear mechanism of the wear-resistant white cast iron was a cycle process that base surface was worn and carbides were exposed, then carbides was broken and wear pits appeared. While the wear mechanism of in situ TiCp/Fe composite was a cycle process that base surface was worn and TiC grains were exposed and dropped. The wear resistance of in situ TiCp/Fe composite was lower than that of wear-resistant white cast iron under the slurry erosive wear condition. Under such circumstance, the material was not only undergone erosive wear but also electrochemistry erosion due to the contact with water in the medium. The wear behaviours can be a combination of two kinds of wear and the sand erosive wear is worse than slurry erosive wear.

Effect of TiC nanoparticle on friction and wear properties of TiC/AA2219 nanocomposites and its strengthening mechanism

TiC nanoparticles reinforced 2219 aluminum matrix composites were successfully prepared by ultrasonic casting, followed by forging and T6 heat treatment. The friction and wear properties of the disc-to-column were studied under four separate normal values of 5, 10, 20 and 30 N. The increasing hardness value of the nanocomposite may be attributed to the large amount of TiC(i.e., 1.3 wt.% and 1.7 wt.%) introduced to the composites. The friction coefficient of the nanocomposite decreased with the increase of TiC nanoparticles(0-1.7 wt.%) under the same load. But the wear resistance of the TiC/AA2219 nanocomposite increased by 30%-90% as compared to the 2219 matrix alloy. And it decreased with the increasing load. The composite with 0.9 wt.% TiC produced the best results in terms of friction and wear because of its relatively higher hardness and perfect ability to retain a transfer layer of a comparatively larger thickness. On the wear surface, some Al2O3particles were found which aided in the development of protective shear regions and improved the wear resistance. The wear mechanism for the TiC/AA2219 nanocomposite was a combination of adhesive and oxidative wear, with the composites containing hard TiC nanoparticles being mainly abrasive.

Formation mechanism and wear behavior of gradient nanostructured Inconel 625 alloy

The formation mechanism and wear behavior of a gradient nanostructured(GNS) Inconel 625 alloy were investigated using SEM, TEM and ball-on-disc sliding wear tester. The results show that surface mechanical grinding treatment(SMGT) induced an approximately 800 μm-deep gradient microstructure, consisting of surface nano-grained,nano-laminated, nano-twined, and severely deformed layers, which resulted in a reduced gradient in micro-hardness from 6.95 GPa(topmost surface) to 2.77 GPa(coarse-grained matrix). The nano-grained layer resulted from the formation of high-density nano-twins and subsequent interaction between nano-twins and dislocations. The width and depth of the wear scar, wear loss volume, and wear rate of the SMGT-treated sample were smaller than those of untreated coarse-grained sample. Moreover, the wear mechanisms for both samples were mainly abrasive wear and adhesive wear, accompanied with mild oxidation wear. The notable wear resistance enhancement of the GNS Inconel 625 alloy was attributed to the high micro-hardness, high residual compressive stress, and high strain capacity of the GNS surface layer.

Dynamic modelling and properties analysis of 3RSR parallel mechanism considering spherical joint clearance and wear

The collision and wear caused by inevitable clearance in kinematic pair have an effect on the dynamic characteristics of the mechanism.Therefore,we established the dynamic model of a 3RSR(R is the revolute joint and S is the spherical joint)parallel mechanism with spherical joint clearance based on the modified Flores contact force model and the modified Coulomb friction model using Newton-Euler method.The standard quaternion was introduced in the constraint equation,and the four-order Runge-Kutta method was adopted to solve the 3RSR dynamic model.The simulation results were compared and analyzed with the numerical results.The geometrical parameters of the worn ball socket were solved based on the Archard wear model,and the geometrical reconstruction of the worn surface was carried out.The geometric reconstruction parameters were substituted into the dynamic model,which was to analyze the dynamic response of the 3RSR parallel mechanism with wear and spherical joint clearance.The simulation results show that the irregular wear occurs in the spherical joint with clearance under the presence of the impact and friction force.The long-term wear will increase the fluctuation of the contact force,thereby decreasing the movement stability of the mechanism.

A Review on Fretting Wear Mechanisms,Models and Numerical Analyses

Fretting wear is a material damage in contact surfaces due to micro relative displacement between them.It causes some general problems in industrial applications,such as loosening of fasteners or sticking in components supposed to move relative to each other.Fretting wear is a complicated problem involving material properties of tribosystem and working conditions of them.Due to these various factors,researchers have studied the process of fretting wear by experiments and numerical modelling methods.This paper reviews recent literature on the numerical modelling method of fretting wear.After a briefly introduction on the mechanism of fretting wear,numerical models,which are critical issues for fretting wear modelling,are reviewed.The paper is concluded by highlighting possible research topics for future work.

Wear Mechanism of Cemented Carbide Tool in High Speed Milling of Stainless Steel

Adhesion of cutting tool and chip often occurs when machining stainless steels with cemented carbide tools. Wear mechanism of cemented carbide tool in high speed milling of stainless steel 0Cr13Ni4 Mo was studied in this work. Machining tests on high speed milling of 0Cr13Ni4 Mo with a cemented carbide tool are conducted. The cutting force and cutting temperature are measured. The wear pattern is recorded and analyzed by high?speed camera, scanning electron microscope(SEM) and energy dispersive X?ray spectroscopy(EDS). It is found that adhesive wear was the dominant wear pattern causing tool failure. The process and microcosmic mechanism of the tool’s adhesive wear are analyzed and discussed based on the experimental results. It is shown that adhesive wear of the tool occurs due to the wear of coating, the a nity of elements Fe and Co, and the grinding of workpiece materials to the tool material. The process of adhesive wear includes both microcosmic elements di usion and macroscopic cyclic process of adhe?sion, tearing and fracture.

WEAR FAILURE MECHANISM AND MULTI-IMPACT PROPERTY OF AUTOMOTIVE ENGINE CHAIN

The multi-impact characteristics and failure mechanism of two kinds of automotive engine chain made in China are studied through engine assembly and road-drive tests. The worn surface morphologies of rubbing area between pin, bush and roller are also analyzed based on scanning electron microscope. The results show that the main wear mechanism of automotive engine chain is fatigue wear, and its failure mechanism is the forming, extending and flaking of cracks on top layer of pin and bush. In addition, the material, hot-treatment method and shaping technique for roller have a great influence upon the resistance to multi-impact. Ensuring sufficient strength and plasticity of roller, as well as adopting suitable shaping technique are the effective method to increase its resistance to multi-impact.

Influence of carbon content on wear resistance and wear mechanism of Mn13Cr2 and Mn18Cr2 cast steels

By means of impact abrasion tests, micro-hardness tests, and worn surface morphology observation via SEM, a comparison research based upon different impact abrasive wear conditions was conducted in this research to study the influence of different carbon contents(1.25 wt.%, 1.35 wt.%, and 1.45 wt.%) on the wear resistance and wear mechanism of water-quenched Mn13Cr2 and Mn18Cr2 cast steels. The research results show that the wear resistance of the Mn18Cr2 cast steel is superior to that of the Mn13Cr2 cast steel under the condition of the same carbon content and different impact abrasive wear conditions because the Mn18Cr2 cast steel possesses higher worn work hardening capacity as well as a more desirable combination of high hardness and impact toughness than that of the Mn13Cr2 cast steel. When a 4.5 J impact abrasive load is applied, the wear mechanism of both steels is that plastic deformation fatigue spalling and micro-cutting coexist, and the former dominates. When the carbon content is increased, the worn work hardening effect becomes increasingly dramatic, while the wear resistance of both steels decreases, which implies that an increase in impact toughness is beneficial to improving the wear resistance under severe impact abrasive wear conditions. Under the condition of a 1.0 J impact abrasive load, the wear mechanism of both steels is that plastic deformation fatigue spalling and micro-cutting coexist, and the latter plays a leading role. The worn work hardening effect and wear resistance intensify when the carbon content is increased, which implies that a higher hardness can be conducive to better wear resistance under low impact abrasive condition.

THE WEAR MODES AND MECHANISMS OFDIAMONDS IN SAWING HARD STONE

Four wear modes and four wear mechanisms of diamonds in sawblades are identified in a study of varied segments damaged in field operation of sawing hard stone. The four wear mechanisms are impactshearing, fatiguing, pullingout and thermal effects. Surface erosion is the result of thermal effects, while impactshearing and fatiguing lead to macro and microfracture, and pullingout results in wholesale dislodgement of diamonds provided the inequality Fn>M/(μλδ) is satisfied.

Abrasive Wear Mechanisms of Sand Particles Intruding into ATM Roller-scraper Tribosystem

The roller-scraper tribosystem of automatic teller machine（ATM） plays an important role in reliable cash requests.However,the abrasive wear of the polymer tribosystem becomes a prominent problem when operating in sandy environment.The wear behavior of the tribosystem in a simulated sandy environment has been experimentally studied previously.However the abrasive wear mechanism of roller-scraper tribosystems is still unknown to new design.The wear rates of polymer rollers were examined comprehensively and several jumping variations were found in the full data extent.Three wear stages were classified by the magnitude of wear rates,and different dominant wear mechanisms corresponding with different particle diameter were found by examining the worn surfaces.Accordingly a presumption was proposed that wear mechanisms in different stages were correlated with sand particles of different diameter.In a verification experiment,three typical wear mechanisms including cutting,ploughing,and wedging were found corresponding with different wear stages by scanning electron microscope（SEM） examination.A theoretical analysis was carried out with a simplified sphere particle intrusion model and the transfer conditions for different wear mechanisms were studied referring to the slip-field theory.As a main result,three typical wear models versus friction coefficient of particle/roller,and particle radius were mapped with variant hardness of the polymer roller and ratio of contact shear stress to bulk shear stress.The result illuminated the abrasive wear mechanism during particle intrusion.Particularly,the critical transition conditions gave the basis for improving the wear performance of roller-scraper tribosystems in a sandy environment.

Wear Mechanism of WC-Co Cemented Carbide Tool in Cutting Ti-6Al-4V Based on Thermodynamics

In order to optimize the tool coating material and reduce the tool wear rate,the coating material and wear mechanism for carbide tools are proposed and analyzed based on thermodynamics theory.We deduced the Gibbs free energy function method and analyzed the enthalpy value of the coating material of cemented carbide tools.The rules of diffusion wear and oxidation wear for WC-Co-based carbide tools were analyzed based on the diffusion dissolution theory and the calculation method of the thermal effect of chemical reaction.The diffusion wear and oxidation wear of WC-Co-based carbide tools when machining Ti-6Al-4V were studied with SEM-EDS.The results indicate that a good prediction accuracy of both diffusion wear and oxidation wear can be achieved by the method of thermodynamic theory analysis method.The conclusion will provide useful references for the optimization of cutting parameters and the improvement of the tool life.

Wear Mechanisms of Ceramic Inserts in Machining Nickel-Based Superalloy

The performances of ceramic inserts in cutting nickel-based alloy were investigated. A new cutting test-bed was devised and used to deburr. The burr height on the working surface with notch wear in deburring cutting was compared with that in normal cutting. The impact force, impact pressure, and impact frequency of the saw-tooth-shaped chip edge on rake face and cutting edge at different speeds were calculated, and the influence of chip edge on notch wear formation was analyzed. A new tool design for reducing notch wear was presented, which is flexible and can deburr effectively.

Tribological behavior and wear mechanism of resin-matrix contact strip against copper with electrical current

The resin-matrix pantograph contact strip (RMPCS),which has excellent abrasion resistance with electrical current and friction-reducing function,was developed in view of the traditional contact strips with high maintenance cost,high wear rate with electrical current and severe damage to the copper conducting wire.The characteristics of worn surfaces,cross-section and typical elemental distributions of RMPCS were studied by scanning electron microscopy (SEM) and energy dispersion spectrometry (EDS).The wear behavior and arc discharge of RMPCS against copper were investigated with self-made electrical wear tester.The results show that the electrical current plays a critical role in determining the wear behavior,and the wear rate of the RMPCS against copper with electrical current is 2.7-5.8 times higher than the value without electrical current.The wear rate of the contact strip increases with the increase of the sliding speed and electrical current density.The main wear mechanism of RMPCS against copper without electrical current is low stress grain abrasive and slightly adhesive wear,while arc erosion wear and oxidation wear are the dominate mechanism with electrical current,which is accompanied by adhesive wear during the process of wear.