Thermal fatigue and wear of compacted graphite iron brake discs with various thermomechanical properties

The increase in payload capacity of trucks has heightened the demand for cost-effective yet high performance brake discs.In this work,the thermal fatigue and wear of compacted graphite iron brake discs were investigated,aiming to provide an experimental foundation for achieving a balance between their thermal and mechanical properties.Compacted graphite iron brake discs with different tensile strengths,macrohardnesses,specific heat capacities and thermal diffusion coefficients were produced by changing the proportion and strength of ferrite.The peak temperature,pressure load and friction coefficient of compacted graphite iron brake discs were analyzed through inertia friction tests.The morphology of thermal cracks and 3D profiles of the worn surfaces were also discussed.It is found that the thermal fatigue of compacted graphite iron discs is determined by their thermal properties.A compacted graphite iron with the highest specific heat capacity and thermal diffusion coefficient exhibits optimal thermal fatigue resistance.Oxidization of the matrix at low temperatures significantly weakens the function of alloy strengthening in hindering the propagation of thermal cracks.Despite the reduced hardness,increasing the ferrite proportion can mitigate wear loss resulting from low disc temperatures and the absence of abrasive wear.

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 Mn content on microstructure and properties of AlCrCuFeMnx high-entropy alloy

AlCrCuFeMnx(x=0,0.5,1,1.5,and 2)high-entropy alloys were prepared using the vacuum arc melting technology.The microstructure and mechanical properties of AlCrCuFeMnxwere analyzed and tested by XRD,SEM,TEM,nanoindentation,and electronic universal testing.The results indicate that the AlCrCuFeMnxhigh-entropy alloy exhibits a dendritic structure,consisting of dendrites with a BCC structure,interdendrite regions with an FCC structure,and precipitates with an ordered BCC structure that form within the dendrite.Manganese(Mn)has a strong affinity for dendritic,interdendritic,and precipitate structures,allowing it to easily enter these areas.With an increase in Mn content,the size of the precipitated nanoparticles in the dendritic region initially increases and then decreases.Similarly,the area fraction initially decreases and then increases.Additionally,the alloy’s strength and wear resistance decrease,while its plasticity increases.The Al Cr Cu Fe Mn1.5alloy boasts excellent mechanical properties,including a hardness of 360 HV and a wear rate of 2.4×10^(-5)mm^(3)·N^(-1)·mm^(-1).It also exhibits impressive yield strength,compressive strength,and deformation rates of 960 MPa,1,700 MPa,and 27.5%,respectively.

Effect of RE Modification and Heat Treatment on Impact Fatigue Property of a Wear Resistant White Cast Iron

The morphology of carbides, as well as the generation and propagation of fatigue cracks in a wear resistant white cast iron after impact fatigue test were observed by means of optical microscope and SEM, and the relationship among the content of RE (rare earths) in the wear resistant white cast iron and the heating temperature as well as the length and propagation speed of the fatigue cracks were determined. Based on the obtained results, the effect of RE modification and heat treatment on the impact fatigue property was further studied. Experimental results show that addition of RE can defer the time required for the generation of fatigue cracks, reduce their propagation speed and increase the impact fatigue resistance. The aforesaid effect is more noticeable in case of combined RE modification with heat treatment, which can be attributed to the variation in morphology and the distribution of the eutectic carbide network.

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 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.

Cu-Zn-Al2O3 nanocomposites: study of microstructure, corrosion, and wear properties

Alumina nanoparticles were added to a Cu-Zn alloy to investigate their effect on the microstructural,tribological,and corrosion properties of the prepared alloys. Alloying was performed using a mixture of copper and zinc powders with 0vol% and 5vol% of α-Al nanopowder in a satellite ball mill. The results showed that the Cu-Zn solid solution formed after 18 h of mechanical alloying. The mechanically alloyed powder was compacted followed by sintering of the obtained green compacts at 750°C for 30 min. Alumina nanoparticles were uniformly distributed in the matrix of the Cu-Zn alloy. The tribological properties were evaluated by pin-on-disk wear tests,which revealed that,upon the addition of alumina nanoparticles,the coefficient of friction and the wear rate were reduced to 20% and 40%,respectively. The corrosion properties of the samples exposed to a 3.5wt% Na Cl solution were studied using the immersion and potentiodynamic polarization methods,which revealed that the addition of alumina nanoparticles reduced the corrosion current of the nanocomposite by 90%.

Effects of Si alloying and T6 treatment on mechanical properties and wear resistance of ZA27 alloys

To improve the mechanical properties and wear resistance of ZA27 alloy, Si was introduced to the alloy, and the effect of Si alloying and T6 heat treatment on the microstructure, mechanical properties and wear resistance was investigated. The results show that with 0.55% Si, the microstructure of the alloy can be refined effectively, which leads to the increase of hardness. But the tensile strength and elongation decrease because Si undermines the integrity of the matrix. On the other hand, the dendrites are transformed into a desired α+η+(α+η)mixture with T6 heat treatment, which introduces a remarkable increase to the elongation and hardness of the alloy. The wear resistance of the ZA27 alloy with Si alloying is significantly better than that of the ZA27 alloy without Si. With the increase of Si addition, the wear resistance of the alloy firstly increases and then decreases.In the alloy without Si alloying, severe plastic deformation and large delamination were observed on the worn surface of the alloy. However, with the increase of Si, the main wear mechanism transformed to abrasive wear gradually. In addition, the T6 treatment can further improve the wear resistance of the alloy with Si alloying.

Effects of Mo and Zr on Microstructure,Mechanical Properties and Wear Resistance of Fe-Al Based Alloys

In this work the microstructure, mechanical properties and wear resistance of Fe-Al based alloys with various alloying elements were studied. The microstructures were examined by optical and scanning electron microscopy （SEM） equipped with an energy dispersive X-ray spectroscope （EDS）. Two types of alloys were prepared by vacuum arc melting. One is Fe-28Al based alloys （D03 structured） with and without alloying elements such as Mo and Zr. The other one is Fe-35Al based alloys （B2 structured） produced with the same manner. For both types of alloys, Mo addition had found to exhibit an equiaxed microstructure, while dendritic structure was observed to show the effect of Zr addition. These microstructural features were more evinced with increasing content of alloying element. Concerning the mechanical properties and wear resistance, Fe-35Al based alloys were superior to Fe-28Al based alloys over the whole temperature range investigated.

Microstructure and wear property of hardfacing alloy with nitrogen strengthening

The nitrogen-alloying hardfacing alloy of the martensitic stainless steel was deposited on a low carbon steel substrate using hardfacing flux-cored wire. Microstructure and surface hardness of hardfacing alloy were investigated and measured by optical microscope and microhardness tester. Carbonitrides of the hardfacing alloy were observed by electron probe. The wear behaviour of the hardfacing alloy was studied using the belt abrasion test apparatus and the worn surface was analyzed by scanning electron microscopy. The results showed that carbonitride particles in the hardfacing alloy are complex MX （ M： alloy elements ; X： C, N） precipitate with fine size. These carbonitride particles distributed homogeneously in the hardfacing alloy and had a good strengthening effect on the wear property. The wear property of the hardfacing alloy with nitrogen was better than the one without nitrogen.

Effect of Rare Earths on Microstructure and Properties of TiC-based Cermet/Cu Alloy Composite Wear Resistant Materials

The effect of rare earth (RE) oxide on the microstructure and properties of TiC based cermet/Cu alloy composite hardfacing materials was investigated by using scanning electron microscope (SEM), transmission electron microscope (TEM), impact test and wear test. The mechanism of RE oxide for improving the phase structure and the impact toughness was also discussed. The experimental results indicate that the microstructure of the matrix can be refined, and the micro-porous defects can be eliminated by adding RE oxide into the composite materials. The polycrystalline and amorphous phase structure is formed at the interface of cermet and matrix metal. The formed structure enhances the conjoint strength of interface. The frictional wear resistance can be improved obviously, although the microhardness of the matrix metal can not be effectively increased by adding RE oxide.

Microstructure and wear properties of the electroslag remelting layer reinforced by TiC particles

The electroslag remelting （ESR） layer reinforced by TiC particles was obtained by electroslag remelting. The microstructure and wear properties of the ESR layer were studied by means of scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and wear test. The results indicate that TiC particles are synthesized by self-propagating high-temperature synthesis （SHS） reaction during the electroslag remelting process. The size of TiC particles is in the range of 1-10 μm, and the distribution of TiC particles is uniform, from outside to inside of the ESR layer, and the volume fraction and the size of TiC particles decrease gradually. Molten iron and slag flow into porosity due to the SHS process leading to rapid densification and the elimination of porosity in the ESR layer during the ESR process. TiC particles enhance the wear resistance of the ESR layer, whereas CaF2 can improve the high temperature lubricating property of the ESR layer.

Mechanical properties and wear resistance of ultrafine bainitic steel under low austempering temperature

The mechanical properties and wear resistance of the ultrafine bainitic steel austempered at various temperatures were investigated.Scanning electron microscopy(SEM)and X-ray diffraction were used to analyze the microstructure.The worn surfaces were observed via laser scanning confocal microscopy and SEM.Results indicated that,under low austempering temperatures,the mechanical properties differed,and the wear resistance remained basically unchanged.The tensile strength of the samples was above 1800 MPa,but only one sample austempered at 230°C had an elongation of more than 10%.The weight loss of samples was approximately linear with the cycles of wear and nonlinear with the loads.The samples showed little difference in wear resistance at different isothermal temperatures,whereas the thickness of their deformed layers varied greatly.The results are related to the initial hardness of the sample and the stability of the retained austenite.Meanwhile,the experimental results showed that the effect of austempering temperature on the wear resistance of ultrafine bainitic steel can be neglected under low applied loads and low austempering temperature.

Influence of carbon-partitioning treatment on the microstructure, mechanical properties and wear resistance of in situ VCp-reinforced Fe-matrix composite

The wear resistance of iron(Fe)-matrix materials could be improved through the in situ formation of vanadium carbide particles(VCp)with high hardness.However,brittleness and low impact toughness limit their application in several industries due to addition of higher carbon content.Carbon-partitioning treatment plays an important role in tuning the microstructure and mechanical properties of in situ VCp-reinforced Fe-matrix composite.In this study,the influences of carbon-partitioning temperatures and times on the microstructure,mechanical properties,and wear resistance of in situ VCp-reinforced Fe-matrix composite were investigated.The experimental results indicated that a certain amount of retained austenite could be stabilized at room temperature through the carbon-partitioning treatment.Microhardness of in situ VCp-reinforced Fematrix composite under carbon-partitioning treatment could be decreased,but impact toughness was improved accordingly when wear resistance was enhanced.In addition,the enhancement of wear resistance could be attributed to transformation-induced plasticity(TRIP)effect,and phase transformation was caused fromγ-Fe(face-centered cubic structure,fcc)toα-Fe(body-centered cubic structure,bcc)under a certain load.

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.

Microstructure and properties of a wear resistant Al-25Si-4Cu-1Mg coating prepared by supersonic plasma spraying

A high content silicon aluminum alloy(Al-25Si-4Cu-1Mg)coating was prepared on a 2A12 aluminum alloy by supersonic plasma spraying.The morphology and microstructure of the coating were observed and analyzed.The hardness,elastic modulus,and bonding strength of the coating were measured.The wear resistance of the coating and 2A12 aluminum alloy was studied by friction and wear test.The results indicated that the coating was compact and the porosity was only 1.5%.The phase of the coating was mainly composed ofα-Al andβ-Si as well as some hard particles(Al9Si,Al3.21Si0.47,and CuAl2).The average microhardness of the coating was HV 242,which was greater than that of 2A12 aluminum alloy(HV 110).The wear resistance of the coating was superior to 2A12 aluminum alloy.The wear mechanism of the 2A12 aluminum alloy was primarily adhesive wear,while that of the coating was primarily abrasive wear.Therefore,it is possible to prepare a high content silicon aluminum alloy coating with good wear resistance on an aluminum alloy by supersonic plasma spraying.

Microstructure,mechanical properties and wear resistance of Ti particles reinforced AZ31 magnesium matrix composites

The compromise between strength and plasticity has greatly limited the potential application of particles reinforced magnesium matrix composites(MMCs).In this work,the Ti particles reinforced AZ31 magnesium(Mg)matrix composites achieved simultaneous improvement in strength,elongation and wear resistance.The Ti particles reinforced AZ31 composites were fabricated by ultrasonic-assisted stir casting with hot extrusion.The results showed that a strong interfacial bonding was obtained at Ti/Mg interface because of the formation of semicoherent orientation relationship of Ti Al/Mg,Ti Al/Al_(2)Ti and Al_(2)Ti/Mg interfaces.The as-extruded 6 wt.%Ti/AZ31 composite presented the best compressive mechanical properties and wear resistance with ultimate tensile strength,elongation and wear rate of 327 MPa,20.4%and 9.026×10^(-3)mm^(3)/m,obviously higher than those of AZ31 alloys.The enhanced mechanical properties were attributed to the grain refinement and strong interfacial bonding.The improved wear resistance was closely related to the increased hardness of composites and the formation of protective oxidation films.

Wear properties of potassium titanate whiskers-reinforced Al-12Si alloy composites

Potassium titanate(K2O·6TiO2) whiskers-reinforced Al-12Si alloy composites were prepared by the squeeze casting technique.Wear properties of the composites were investigated by pin-on-disc tests under dry conditions.The experimental results showed that K2O·6TiO2 whiskers can effectively reinforce the matrix alloy and improve the wear resistance of the composite when the volume fraction of whiskers is low at 10 vol%.However,the composites with a high volume fraction of whiskers showed lower wear resistance than the Al-12Si alloy.The main wear mechanism of the composites is clarified as de-lamination and abrasive wear.

Grain refinement impact on the mechanical properties and wear behavior of Mg-9Gd-3Y-2Zn-0.5Zr alloy after decreasing temperature reciprocating upsetting-extrusion

Based on the deforming technique of severe plastic deformation(SPD), the grain refinement of a Mg-9Gd-3Y-2Zn-0.5Zr alloy treated with decreasing temperature reciprocating upsetting-extrusion(RUE) and its influence on the mechanical properties and wear behavior of the alloy were studied. The RUE process was carried out for 4 passes in total, starting at 0 ℃ and decreasing by 10 ℃ for each pass. The results showed that as the number of RUE passes increased, the grain refinement effect was obvious, and the second phase in the alloy was evenly distributed. Room temperature tensile properties of the alloy and the deepening of the RUE degree showed a positive correlation trend, which was due to the grain refinement, uniform distribution of the second phase and texture weakening. And the microhardness of the alloy showed that the microhardness of RUE is the largest in 2 passes. The change in microhardness was the result of dynamic competition between the softening effect of DRX and the work hardening effect. In addition, the wear resistance of the alloy showed a positive correlation with the degree of RUE under low load conditions. When the applied load was higher, the wear resistance of the alloy treated with RUE decreased compared to the initial state alloy. This phenomenon was mainly due to the presence of oxidative wear on the surface of the alloy, which could balance the positive contribution of severe plastic deformation to wear resistance to a certain extent.

Preparation, mechanical properties and wear behaviors of novel aluminum bronze for dies

A modified single melt technique involving joint charging was developed for preparation of aluminum bronze, Cu-14%Al-X(mass fraction) alloy, which could be used as die materials. The mechanical properties and wear behavior of the developed alloy under boundary-lubrication conditions was investigated. The results demonstrate that all the phases disperse homogeneously in the bronze matrix with a significant amount of discrete and spherical brittle and hard γ2 phase, moreover, the dispersed κ phase are the dominant factor that improves the anti-deformation properties of the soft matrix, after a solution treatment at 920 ℃ for 2 h and followed by aging at 580 ℃ for 3 h, thus remarkably improves the mechanical properties and wear resistance of the developed alloy. The Cu-14%Al-X alloy can be used as materials for static precise stretching and squeezing dies.