Research on material design and high-temperature friction and wear properties of new graphitic steel

To solve the problem of the severe mismatch between the product and roll materials in the preliminary rolling line,a new graphitic steel material was designed,its microstructure and high-temperature friction and wear properties were investigated.Moreover,the feasibility of replacing semi-steel with this new material in the V1 stand roll was studied herein.The results show that the graphitic steel matrix is strengthened by silicon and nickel elements.The presence of spherical graphite also provides self-lubrication and heat conduction and prevents the propagation of cracks.Carbides in the appropriate amount and size strengthen the matrix,reduce the cracking effect of the matrix,and are not easily broken,thereby reducing high-temperature abrasive wear.Under the same hightemperature friction and wear conditions,compared with semi-steel,the wear-scar surface of graphitic steel exhibits less wear-scar depth and wear volume,a smaller friction coefficient,reduced oxide layer thickness,and fewer instances of peeling and microcracks.Therefore,the newly designed graphitic steel has higher wear resistance and hot-crack resistance than semi-steel,which makes it feasible for use in replacing semi-steel as a new V1 frame roll material in the blooming mill.

Research on microstructure and high-temperature friction and wear properties of a cobalt-based alloy for hot extrusion die

The hot extrusion die is a key tool for determining the surface quality and dimensional accuracy of extruded products.Because its service process is subject to high temperature,high pressure,and wear,it must be resistant to these conditions.In this paper,the high-temperature friction and wear properties of a cobalt(Co)-based alloy were investigated and compared with those of a titanium carbide(TiC)cemented material.The results show that the high-temperature wear performance of the Co-based alloy is better than that of the TiC cemented material,and that Co-based materials have the potential for replacing TiC cemented materials as hot-extrusion-die materials.Due to the high density and good combination of the matrix and carbide,the carbides do not easily peel off from the matrix during the wear process.Due to the higher impact toughness of the Co-based alloys,microcracks that can cause worn-surface peeling are not easily generated.As a result,the high-temperature wear performance of Co-based alloys is found to be better than that of TiC cemented materials.

Exploring the Friction and Wear Properties of Silver Coatings on 718 Alloy

Fasteners of 718 alloys are used to set up connection between each support and other components for ITER system, metal-based Ag solid lubricant coating is widely used as an anti-seizure lubricant coating due to its strong low-temperature shear resistance. But the poor adhesion to the steel surfaces has been a critical restriction for applying the silver coatings to the practical machine elements. In this work, an 8-μm silver self-lubricating coating was deposited on the surface of 718 alloy by the method of magnetron sputtering. The coating was uniform, dense and consistent. The wear mechanism was investigated by analyzing the friction and wear properties of the coating. Stress is one of the important impacts on the friction coefficient, the results showed that it first increased and then decreased with the increase of pressure at room temperature and under vacuum. Temperature exerted an effect on the silver self-lubricating coating. A study was conducted under vacuum on the friction and wear performance of the coating at 300 K, 225 K, 155 K, and 77 K, respectively. The results showed that the wear mechanism and wear state varied under various low-temperature conditions, with the severity of wear reaching the maximum only at 225 K. Through the same silver coating process, the washer of superbolt was improved by silver coating treatment.

Effect of Al2O3sf addition on the friction and wear properties of (SiCp+Al2O3sf)/Al2024 composites fabricated by pressure infiltration

Aluminum(Al) 2024 matrix composites reinforced with alumina short fibers(Al_2O_(3sf)) and silicon carbide particles(SiC_p) as wear-resistant materials were prepared by pressure infiltration in this study. Further, the effect of Al_2O_(3sf) on the friction and wear properties of the as-synthesized composites was systematically investigated, and the relationship between volume fraction and wear mechanism was discussed. The results showed that the addition of Al_2O_(3sf), characterized by the ratio of Al_2O_(3sf) to SiC_p, significantly affected the properties of the composites and resulted in changes in wear mechanisms. When the volume ratio of Al_2O_(3sf) to SiC_p was increased from 0 to 1, the rate of wear mass loss(K_m) and coefficients of friction(COFs) of the composites decreased, and the wear mechanisms were abrasive wear and furrow wear. When the volume ratio was increased from 1 to 3, the COF decreased continuously; however, the K_m increased rapidly and the wear mechanism became adhesive wear.

Friction and Wear Properties of TiAl and Ti_2AlN/TiAl Composites at High Temperature

The high-temperature friction and wear properties of TiAl alloys and Ti2AlN/TiAl composites （TTC） in contact with nickel-based superalloy were studied. The results showed that, at 800 and 1 000 ℃, the coefficient of the friction （COF） decreased with the increase of sliding velocity and the wear loss of the TTC decreased with the increase of volume fraction of Ti2AlN. The wear mechanisms of the pairs are adhesive wear and the wear debris mainly comes from the contacting nickel-based superalloy. The intergranular fracture and the cracking of the phase boundary in the lamellar structure are the wear mode of TiAl alloy. The wear mode of TTC is phase boundary fracture and adhesive spalling. The abrasive resistance of TTC is slightly higher than that of TiAl alloy.

The Friction Wear Properties and Application of Thermoplastic Polyester Elastomer and Polyoxymethylene

The experiment of injection molding, Dais-simulating test, morphological structure investigation(Scanning Electron Microscopy, SEM),X-ray photoelectron spectroscopy(XPS)were performed on mini-automobile spherical seat which was made of thermoplastic polyester elastomer(TPEE)and oiled polyoxymethylene(POM),respectively. The friction-wear properties between the frictionl pair of polymer spherical seat and metallic(iron)spherical pin were studied. The test results indicate that the antifriction property of TPEE is superior to that of POM, while its surface chemical effect is inferior to that of POM.

Dry Sliding Friction and Wear Properties and Wear Mechanism of SiC_P/Al Composites

Dry sliding friction and wear properties of A356/SiC composites against AISI D2 were analyzed by means of SEM,XRD and EDS.Results indicated that the wear rate of A356/SiC increased with increase of the applied load.Mild wear took place under lower load,transferring to severe wear at the load heavier than 400 N.Mechanical mixed layer(MML) formed on worn surface during dry sliding friction process,whose thickness became deeper with increasing load.Cracks formed easily in MML and spread transversely,resulting in peeling wear.The wear mechanism of the composite is that oxidation wear mechanism was dominant under low load,with the formation of tiny powdery debris.As the load enhanced,peeling wear was primary due to laminar debris detached from the MML,including oxidation and adhesive wear at the same time,with the load at 350-450 N,adhesive wear with irregular debris and peeling wear were predominant.

Friction and wear properties of ultra-high molecular mass polyethylene reinforced with Al2O3 nano-particle

The ultra-high molecular mass polyethylene (UHMMPE) as an artificial joint acetabular material was filled with nano-powder of Al2O3 of various mass fractions. The effect of Al2O3 mass fraction on the hardness, wetting property and tribological properties of the Al2O3-UHMMPE composites under dry friction sliding against both stainless steel and Ti-6Al-4V alloy was investigated. The morphologies of the worn surfaces of composites were observed with optical microscope. The results show that, wetting property and wear resistance of the composites are improved by filling Al2O3, while the friction coefficient is decreased largely under dry friction as compared with that of the unfilled UHMMPE. This is attributed to the reinforcing function of the nano-powder of Al2O3 in the composites. The wear of UHMMPE is dominated by plowing, plastic deformation and fatigue wear; while the Al2O3-UHMMPE composites are characterized by the mild fatigue wear.

Microstructure, mechanical properties and wear behaviour of Zn-Al-Cu-TiB_2 in situ composites

Zn-Al-Cu-TiB2（ZA27-TiB2） in situ composites were fabricated via reactions between molten aluminum and mixed halide salts（K2TiF6 and KBF4） at temperature of 875 °C. The microstructure, mechanical properties and wear behavior of the composites were investigated. Microstructure analysis shows that fine and clean TiB2 particles distribute uniformly through the matrix. The mechanical properties of the composites increase with the increase in TiB2 content. As TiB2 content increases to 5%（mass fraction）, an improvement of HB 18 in hardness and 49 MPa in ultimate tensile strength（UTS） is achieved. The overall results reveal that the composites possess low friction coefficients and the wear rate is reduced from 5.9×10-3 to 1.3×10-3 mm3/m after incorporating 5% TiB2. Friction coefficient and worn surface analysis indicate that there is a change in the wear mechanism in the initial stage of wear test after introducing in situ TiB2 particles into the matrix.

Impact Wear Properties of Metal-Plastic Multilayer Composites Filled with Glass Fiber Treated with Rare Earth Element Surface Modifier

The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigated. Experimental results show that the metal-plastic multilayer composite filled with glass fiber exhibits excellent friction and impact wear properties when using rare earth elements as surface modifier for the surface treatment of glass fiber.

Effect of heat treatment on mechanical and wear properties of Zn−40Al−2Cu−2Si alloy

In order to determine the effect of heat treatment on the mechanical and wear properties of Zn−40Al−2Cu−2Si alloy,different heat treatments including homogenization followed by air-cooling(H1),homogenization followed by furnace-cooling(H2),stabilization(T5)and quench−aging(T6 and T7)were applied.The effects of these heat treatments on the mechanical and tribological properties of the alloy were studied by metallography and,mechanical and wear tests in comparison with SAE 65 bronze.The wear tests were performed using a block on cylinder type test apparatus.The hardness,tensile strength and compressive strength of the alloy increase by the application of H1 and T6 heat treatments,and all the heat treatments except T6,increase its elongation to fracture.H1,T5 and T6 heat treatments cause a reduction in friction coefficient and wear volume of the alloy.However,this alloy exhibits the lowest friction coefficient and wear volume after T6 heat treatment.Therefore,T6 heat treatment appears to be the best process for the lubricated tribological applications of this alloy at a pressure of 14 MPa.However,Zn−40Al−2Cu−2Si alloy in the as-cast and heat-treated conditions shows lower wear loss or higher wear resistance than the bronze.

Microstructures and wear-resistant properties of in-situ TiC_p/ZA-12 composites

TiC_p/ZA-12 composites were fabricated by exothermic disposition method process and stirring-casting techniques. The microstructure and wear-resistant properties were investigated . The results show that TiC particles are formed in-situ and distributed uniformly in matrix. No particles aggregation and macro or micro precipitation are observed. The wear-resistant properties of composites increase with the increase of TiC_p content, but will not increase when the TiC_p content reaches constant value. Finally, the friction and wear mechanism were also discussed.

Analysis on Tribological Properties of Potentially New Friction Material with Response Surface Method

The tribological properties of newly developed friction material were evaluated by statistical analysis of the major affecting factors.The material for investigation was non-metallic friction material synergistically reinforced with aramid fibre and CaSO 4 whisker,which was developed for hoisting applications in coal mine.The response surface method（RSM）was employed to analyze the material performances affected by the independent and interactive effect of the factors under the normal working condition and severe working condition,respectively.Results showed that under the normal working condition,the newly developed material exhibited stable tribological properties which were insensitive to the test conditions.While under the severe working condition,the sliding velocity was the most dominant factor affecting the friction coefficient.Additionally,compared to the commercially available material,the modified material showed superior wear resistance and thermal stability.

Friction and Wear Behaviors of Nanostructured Metals

Nanostructured （ns） materials, i.e., polycrystalline materials with grain sizes in the nanometer regime （typically below 100 nm）, have drawn considerable attention in the past decades due to their unique properties such as high strength and hardness. Wear resistance of ns materials, one of the most important properties for engineering materials, has been extensively investigated in the past decades. Obvious differences have been identified in friction and wear behaviors Between the ns materials and their corresponding coarse-grained （cg） counterparts, consistently correlating with their unique structure characteristics and mechanical properties. On the other hand, the superior tribological properties of ns materials illustrate their potential applications under contact loads. The present overview will summarize the important progresses achieved on friction and wear behaviors of ns metallic materials, including ultrafine-grained （ufg） materials in recent years. Tribological properties and effects on friction and wear behaviors of ns materials will be discussed under different wear conditions including abrasive wear, sliding wear, and fretting wear. Their correlations with mechanical properties will be analyzed. Perspectives on development of this field will be highlighted as well.

Friction and wear behaviors of TiCN coating based on electrical discharge coating

Titanium carbonitride (TiCN) coating was prepared on 45# carbon steel by electrical discharge coating (EDC), and the compositions, morphology and microstructure of the coating were studied. In addition, its friction and wear behaviors relative to the physical vapor deposition (PVD) TiN coating were investigated. The results show that the TiCN coating features a thickness of 15μm with a primary phase of TiC 0.3 N 0.7 . The wear rates of the two coatings have no clear distinction at low applied loads. However, severe abrasive wear appears in the PVD TiN coating when the applied load exceeds 30 N, while the TiCN coating features better wear resistance. The abrasive wear with coating peelings is found to be the predominant wear mechanism at high applied loads.

Tribology properties of composite layer of CrMoCu alloy cast iron by combined treatment of ion nitrocarburizing and sulphurizing

Composite layer with nitrocarbonide and sulfide was made on the surface of CrMoCu alloy cast iron by combined treatment of ion nitrocarburizing and sulphurizing. The composite layer is composed of sulfide layer, nitrocarbonide hypo-surface layer and its diffusing layer, the size of sulfide globular grains distributing equably on the surface is in nano-micron-scale, and the phase structure of the composite layer is composed of FeS, FeS1-x, Fe2C and Fe3N. Under oil lubrication, sulphurized surface shows good scuffing-resistance only under low velocity, and nitrocarburized and sulphurized surface greatly improves the scuffing-resistance and wear-resistance of CrMoCu alloy cast iron, its integrated friction and wear properties are better than those of the plain and sulphurized surfaces under all the velocities.

Effect of Graphite Content and Granularity on Mechanical and Tribological Properties of Bronze Alloyed Powder Composite

The bronze alloyed powder composite containing nanoparticles was developed by hot pressing.The effects of the content and granularity of graphite on hardness,machinability,bending strength,compression strength,and friction and wear behavior of the composites were studied.The microstructures of the specimens were analyzed by SEM.The results showed that the graphites are distributed in net when nanographites are added,resulting in the decrease of mechanical properties and abrasive resistance.When the content of nanographite is 10%,the composite is brittle.The graphite is distributed in the form of block when micrographite is added,improving the mechanical properties and abrasive resistance.Wear track was studied by SEM.

The Friction and Wear of Sleeve-ring Pair Lubricated by Active Lubricants in the Presence of Magnetic Field

The effect of magnetic field on the tribological process of sleeve-ring pair lubricated by WRL lubricants was investigated by means of a NG-x wear tester and a PS5013 video microscope. The friction coefficient(f) and the wear weight(W) in lubricating test with WRL lubricant were decreased with the increase in the magnetic field vertical to the rubbing surface, and an almost zero wear lubricating situation was gained in a magnetic field of 1000A/m. The captured wear micro particles on the rubbing surface were observed in the testing process, and the theoretical analysis of magnetic effects was completed. It is indicated that the magnetic field has not only a capturing action of wear micro particles on the worn surface, but also a inducing polarization of magnetic anisotropy of lubricant molecular. The actions promote the absorption of WRL lubricant into the wear surface as well as wear micro-particles, so that a good tribological effect is obtained when both magnetic field and WRL present.

Tribological properties of Fe(Cr)-B alloys at high temperature

This work is aimed to study the effect of boron on wear resistance of Fe-Cr-B alloys containing different boron contents(0 wt%,5 wt%,7 wt%and 9 wt%)from room temperature(RT)to 800°C in order to explore their applications as high-temperature wear resistant mechanical parts.Additionally,the wear mechanism of alloys is evaluated.The tribological properties of alloys are systematically studied by using a ball-on-disc tribometer at 10 N and 0.20 m/s from RT to 800°C sliding against Si3N4 ceramic ball.The boron element greatly improves the wear resistance of specimens as compared with that of unreinforced specimen.The friction coefficients of specimens decrease with increasing of testing temperature.The wear rates of Fe-Cr-B alloys decrease firstly and then raise with the increase of boron content.The specific wear rates of specimens with boron are 1/10 of the unreinforced specimen.Fe-21wt%Cr-7wt%B keeps the best tribological properties at high temperature.

Effects of titanium addition on structural, mechanical, tribological, and corrosion properties of Al-25Zn-3Cu and Al-25Zn-3Cu-3Si alloys

To investigate the effect of grain refinement on the material properties of recently developed Al-25 Zn-3 Cu based alloys,Al-25 Zn-3 Cu,Al-25 Zn-3 Cu-0.01 Ti,Al-25 Zn-3 Cu-3 Si and Al-25 Zn-3 Cu-3 Si-0.01 Ti alloys were produced by permanent mold casting method.Microstructures of the alloys were examined by SEM.Hardness and mechanical properties of the alloys were determined by Brinell method and tensile tests,respectively.Tribological characteristics of the alloys were investigated by a ball-on-disc type test machine.Corrosion properties of the alloys were examined by an electrochemical corrosion experimental setup.It was observed that microstructure of the ternary A1-25 Zn-3 Cu alloy consisted ofα,α+ηandθ(Al2Cu)phases.It was also observed that the addition of 3 wt.%Si to A1-25Zn-3Cu alloy resulted in the formation of silicon particles in its microstructure.The addition of 0.01 wt.%Ti to the Al-25Zn-3Cu and Al-25 Zn-3 Cu-3 Si alloys caused a decrement in grain size by approximately 20%and 39%and an increment in hardness from HRB 130 to 137 and from HRB 141 to 156,respectively.Yield strengths of these alloys increased from 278 to 297 MPa and from 320 to 336 MPa while their tensile strengths increased from 317 to 340 MPa and from 334 to 352 MPa.Wear resistance of the alloys increased,but corrosion resistance decreased with titanium addition.