Investigations on Microstructures and Two-body Abrasive Wear Behavior of Fe–B Cast Alloy

The microstructures of Fe–B alloys containing different carbon and boron concentrations have been investigated. The solidification microstructures of Fe–B alloy consist of the eutectic boride, pearlite, and ferrite. Borides precipitate along the grain boundary during the formation of eutectic. After heat treatment, the phases in Fe–B alloy are composed of the boride and martensite. With increase of carbon and boron concentrations, the Rockwell hardness of Fe–B alloy becomes larger. Meanwhile, by using a pin-on-disk abrasion tester, the effects of carbon and boron concentrations on the wear behaviors including ploughing depth, roughness, and wear weight loss under different loads have been studied. The results show that the wear resistance of Fe–B alloy with higher carbon and boron concentrations is comparable with the high chromium white cast iron.     

Three-Body Abrasive Wear Behavior of Low Carbon Fe–B Cast Alloy and Its Microstructures Under Different Casting Process

This study investigates the effect of semi-solid processing on the microstructures, mechanical properties of low carbon Fe–B cast alloy. The as-cast microstructure of Fe–B cast alloy consists of the eutectic boride, pearlite, and ferrite. Compared with the coarse eutectic borides in the ordinary alloy, the eutectic boride structures in the semi-solid alloy are greatly refined. Moreover, the boride area fraction, Rockwell hardness, impact toughness, etc., before and after heat treatment under different casting methods are also investigated systemically. The wear behaviors of low carbon Fe–B cast alloy are studied by three-body abrasive wear tester. The wear weight loss of semi-solid Fe–B cast alloy is lower than that of the ordinary Fe–B cast alloy because of the lower average boride area for semi-solid specimen. Meanwhile, the wear mechanism of the low carbon Fe–B cast alloy under different casting process is depicted and analyzed by using the physical models.     

Effects of Chromium Addition on Microstructure and Abrasion Resistance of Fe–B Cast Alloy

This research work studies the effects of chromium on microstructure and abrasion resistance of Fe–B cast alloy. The results show that eutectic boride changes from continuous network to less continuous and matrix changes from pearlite to martensite with the increase in chromium content in the alloy. Meanwhile, an increase in chromium addition in the alloy leads to an increase in the chromium content in M₂B-type boride because chromium can enter boride by substituting for iron in Fe₂B. Under two-body wear, Fe–B cast alloy exhibits excellent wear resistance. When alloys are tested against soft abrasive, chromium can markedly improve the wear resistance of Fe–B cast alloy, whereas excessive chromium can reduce the wear resistance. The wear resistance of Fe–B cast alloy increases first and then decreases with the increase in chromium. But when tested against hard abrasive, since the hardness of SiC is much higher than that of M₂B boride, an increase in chromium content marginally increases the wear resistance. Weight losses of Fe–B cast alloy increase with the increase in the load and exhibit the linear relationship.     

The Influence of the Matrix Microstructure on Abrasive Wear Resistance of Heat-Treated Fe–32Cr–4.5C wt% Hardfacing Alloy

The abrasion wear resistance of Fe–32Cr–4.5C wt% hardfacing alloy was investigated as a function of matrix microstructure. In this study, the alloy was deposited on ASTM A36 carbon steel plates by the shielded metal arc welding (SMAW) process and the as-welded matrix microstructure was changed into ferrite, martensite, and tempered martensite by heat treatment processes. The Pin-on-disk test results show that under low (5 N) and high (20 N) load conditions, the wear resistance behavior of the as-welded matrix sample is 20 and 15% higher, respectively, than the martensitic matrix sample, although the bulk hardness of the as-welded matrix is 5% lower. The ferritic matrix sample has the poorest wear resistance behavior which is less than half of that of the as-welded matrix one. Micro-ploughing, micro-cutting, and micro-cracking are recognized as the micro-mechanisms in the material removal in which the proportion of micro-ploughing mechanism increased by increasing matrix toughness.     

Effect of Aramid Pulp and Lapinas Fiber on the Friction and Wear Behavior of NBR Powder–Modified Phenolic Resin Composite

Short fiber reinforcement plays a definite role in governing the performance of a composite through the improvement of different material properties. The present investigation deals with the effect of aramid pulp and lapinas fiber on the friction and wear characteristics of a composite made from phenolic resin modified by powdered acrylonitrile butadiene rubber (NBR) on a pin-on-disc tribometer. Four composites, containing 10, 20, 30, and 40 wt% of aramid pulp with respect to phenolic resin content, were prepared. Another four composites, containing 50, 100, 200, and 300 wt% of lapinas fiber with respect to phenolic resin content, were also made. It was found that the two different fibers have distinctly different contributions to the friction and wear properties of the composites. It was also found that the incorporation of aramid pulp enhances friction stability of the composites much better than that of lapinas fiber. The change in surface morphology of these composites was studied by scanning electron microscopy (SEM) before and after the friction test. SEM images of friction samples containing aramid pulp corroborated the occurrence of wear through an adhesive wear mechanism, whereas the lapinas fiber–containing composites showed an abrasive wear mechanism.     

Corrosion-Wear Resistance and Interfacial Morphologies of Novel Fe–Cr–B Cast Steels in Molten Aluminum

In order to improve the corrosion–wear resistance properties of steels in molten aluminum, novel Fe–Cr–B cast steels with different boron concentrations were prepared. The steels were investigated at 750 °C for 0.5 h using a ring-block corrosion–wear test, and the interfacial morphologies were examined. Results showed that the corrosion–wear resistance of the Fe–Cr–B cast steel was three times that of H13, and benefited greatly from the effects of the primary Cr-rich Fe₂B, which bore the main load during the corrosion–wear test. The corrosion–wear behavior of the coarse primary Cr-rich Fe₂B in molten aluminum was clearly different from that in static molten aluminum.     

Effects of Silicon Content on the Mechanical Properties and Lubricated Wear Behaviour of Al–40Zn–3Cu–(0–5)Si Alloys

In this work, one ternary Al–40Zn–3Cu and seven quaternary Al–40Zn–3Cu–(0.25–5)Si alloys were synthesized by permanent mould casting. Their microstructure, mechanical and lubricated wear properties were investigated using appropriate test apparatus and techniques. As the silicon content increased the hardness of the alloys increased, but their elongation to fracture decreased. Tensile strength of the alloys decreased with increasing silicon content following a sharp decrease and a slight increase. Among the silicon-containing quaternary alloys the highest and the lowest tensile strength values (348 and 305 MPa) were obtained with the Al–40Zn–3Cu–2Si and Al–40Zn–3Cu–5Si alloys, respectively, while the base alloy (Al–40Zn–3Cu) exhibited a tensile strength of 390 MPa. However, the volume loss due to wear of the alloys increased with increasing silicon content after showing an initial increase and a sharp decrease. The lowest wear loss was obtained with the alloy containing approximately 2% Si which has the highest tensile strength among the quaternary alloys containing more than 0.25% Si. Wear surfaces of the alloys were characterized mainly by smearing indicating that adhesion is the dominant wear mechanism for the experimental alloys.     

The Effect of “Hot-Spot” Temperatures on the Unlubricated Wear of Steel

Experiments are described in which pins of low-alloy, medium-carbon steel are worn against disks of the same material under unlubricated sliding conditions. The friction and wear characteristics of this system are measured as functions of load and speed. The choice of loads and speeds was made in such a way as to obtain the entire range of “hot-spot” temperatures possible for the system. The results are then compared with those to be expected from a model of the wear process in which the wear at the contacting regions between the pin and the disk is closely associated with the oxidation of the metal in these regions. The temperature of oxidation is assumed to be the calculated “hot-spot” temperature. In order to make the results compatible with the proposed model, it is necessary to introduce a new parameter (having the dimensions of length) which is shown to increase steeply with increasing “hot-spot” temperature up to about 700 C. It then levels off, at about 10^?6 cm, for all hot-spot temperatures in excess of about 700 C. In this way, the hot-spot temperature is shown to be a very important variable in the wear of steel.     

Effect of 10 wt% VC on the Friction and Sliding Wear of Spark Plasma–Sintered WC–12 wt% Co Cemented Carbides

The effect of 10 wt% VC addition on the friction and sliding wear response of WC–12 wt% Co cemented carbides produced by spark plasma sintering (SPS) was studied. The SPS of WC–12 wt% Co alloys with and without 10 wt% VC, at 1100 and 1130°C, respectively, yielded dense materials with minimal porosity. No eta phase was found in any of the alloys. The WC–12 wt% Co–10 wt% VC alloy showed the formation of a hard WV₄C₅ phase, which improved the alloy's hardness. Friction and dry sliding wear tests were done using a ball-on-disk configuration under an applied load of 10 N and sliding speed of 0.26 m.s^?1, and a 100Cr-steel ball was used as the counterface. A significant improvement in the sliding wear response of the harder and more fracture tough WC–12 wt% Co–10 wt% VC alloy compared to the WC–12 wt% Co alloy was found. Analysis of the worn surfaces by scanning electron microscopy showed that the wear mechanisms included plastic deformation, preferential binder removal, adhesion, and carbide grain cracking and fragmentation.     

Effect of Carbides on Wear Characterization of High-Alloy Steels under High-Stress Rolling–Sliding Condition

This article describes the wear characterizations of high-speed steel composed of vanadium carbide and high-chromium cast iron composed of chromium carbide. These metals were studied under rolling–sliding conditions with a sliding ratio of 10% using a self-made ring–ring wear testing machine. The fine microstructure of carbides and failure behaviors were analyzed by scanning electron microscopy and high-resolution electron microscopy. The results showed that carbide significantly affected the wear properties and failure behaviors of metals. The relative wear resistance of high-speed steel reinforced by vanadium carbides was twice that of high chromium cast iron composed of chromium carbides. Chromium carbide was characterized by a stacking fault substructure, and slips occurred in chromium carbide under high-stress contact, resulting in crack formation. Vanadium carbide was reinforced and pinned by large amounts of nanoparticles, which prevented its dislocation under high-stress rolling–sliding conditions, thereby effectively resisting crack initiation. Furthermore, the (200) lattice plane of vanadium carbide is coherent with the (111) lattice plane of austenite, preventing cracks from forming at the interface of the vanadium–carbide matrix. The morphology and hardness of vanadium carbide also contributed to the excellent wear property of high-speed steel.     

Effects of Strain-Induced Martensitic Transformation on the Solid Particle Erosion Behavior of Fe–Cr–C–Ni/Mn Austenitic Alloys

The effects of Ni and Mn concentrations and also the impact velocity on the solid particle erosion behavior of Fe?C12Cr?C0.4C?CxNi/Mn (x?=?5 and 10) alloys were investigated with respect to strain-induced martensitic transformation. The critical strain energy (CSE), which is defined as the energy required to initiate the martensitic transformation increased with increasing Ni and Mn concentrations. As the impact velocity decreased, the solid particle erosion resistance of the low CSE alloy improved compared to that of the high CSE alloy under the given ranges of impingement angles and impact velocities. This result was most likely due to an increase in the volume fraction of martensite that formed during the solid particle erosion test in the low CSE alloy when the impact velocity was decreased.     

Effect of Air and Helium on the Head–Disk Interface During Load–Unload

The tribological characteristics of the head–disk interface are investigated during load–unload for air and helium-filled drives as a function of the pitch static angle and the roll static angle between slider and disk. A custom-made experimental tester inside a sealed environmental chamber was used to determine the regions of “safe” pitch static angle and “safe” roll static angle in air and helium environment during the load–unload process. The presence of head–disk contacts during load–unload were evaluated by measuring the acoustic emission signal and the decrease in rotational speed of the spindle. Scanning electron microscopy and optical surface analysis were used to investigate wear of the slider and the redistribution of lubricant on the disk surface after 10,000 load–unload cycles. The results indicate that the tribological performance of the head–disk interface is improved in helium environment compared to air environment.     

Dry Sliding Friction and Wear Properties of Al–25Zn–3Cu–(0–5)Si Alloys in the As-Cast and Heat-Treated Conditions

Dry sliding friction and wear properties of ternary Al–25Zn–3Cu and quaternary Al–25Zn–3Cu–(1–5)Si alloys were investigated using a pin-on-disc test machine after examining their microstructures and mechanical properties. An alloy (Al–25Zn–3Cu–3Si), which exhibited the highest tensile and compressive strengths, was subjected to T7 heat treatment. Surface and subsurface of the wear samples were investigated using scanning electron microscopy (SEM). The hardness and both tensile and compressive strengths of the alloys increased with increasing silicon content, but the trend reversed for the latter ones above 3% Si. It was observed that T7 heat treatment reduced the hardness and both tensile and compressive strengths of the Al–25Zn–3Cu–3Si alloy, but increased its elongation to fracture greatly. Three distinct regions were observed underneath the surface of the wear samples of the Al–25Zn–3Cu–3Si alloy. The formation of these regions was related to the heavy deformation of surface material and mixing, oxidation and smearing of wear material. Al–25Zn-based ternary and quaternary alloys in both as-cast and heat-treated conditions were found to be superior to SAE 660 bronze as far as their mechanical and dry sliding wear properties are concerned.     

Influence of High-Pressure Coolant Assistance on the Machinability of the Titanium Alloy Ti555–3

The origin of this article is the quantification of productivity gains and the improvement in surface integrity seen for a recent titanium alloy that is seeing increasing use in the aeronautical industry. The Ti555–3 titanium alloy, which is starting to find greater application in the aeronautical field, exhibits certain difficulties in terms of machining. High Pressure Coolant (HPC) assisted turning consists of projecting a high pressure coolant jet between the chip and the tool. Comparisons are made between assisted turning using variable jet pressure and conventional turning (dry and classical lubrication). It is shown that it is possible to improve productivity by using HPC-assisted machining. The results highlight good chip fragmentation and a great improvement of tool life with HPC assistance. Surface integrity is also shown to be improved, through surface roughness parameters that decrease, and surface residual stresses that become more compressive. These effects have been attributed to the thermo-mechanical action of the coolant jet resulting in lower cutting forces, lower coefficient of friction and lower temperature in the cutting zone.     

The Microstructure and Wear Characteristics of Cu–Fe Matrix Friction Material with Addition of SiC

The Cu–Fe matrix continuous braking friction materials using SiC as abrasive were fabricated by powder metallurgy technique, and the effect of content and size of SiC were investigated. The tribological properties of friction materials sliding against AISI 1045 steel ring were carried out on a block-on-ring tester at different loads and sliding speeds. The strengthening effect of nano-SiC (55 nm) was superior to that of micro-SiC (70 μm) of the tribological properties for friction materials. The friction coefficients of friction materials increased with increasing nano-SiC content. However, the wear rates decreased with increasing nano-SiC content and then increased when the content of nano-SiC particle exceeded 10 wt%. The specimen contained 10% nano-SiC had the best tribological properties at different testing conditions.     

The effects of nickel and carbon concentrations on the wear resistance of Fe–Ni–C austenitic alloys

The effects of nickel and carbon concentrations on the wear resistance of Fe–xNi–yC (x = 14–20 wt.%, y = 0.6–1.0 wt.%) were investigated with respect to strain energy initiation of the martensitic transformation and hardness. The strain energy needed to initiate the martensitic transformation increased with increasing carbon and nickel concentrations, except in 1.0 wt.% C alloys. The wear resistance of the material decreased with increasing carbon concentration up to 0.9 wt.% C. This effect is most likely due to decrement of the martensite volume fraction with increasing carbon concentration induced by the incremental strain energy required to begin the martensitic transformation. In the case of 1.0 wt.% C, the improved wear resistance may be due to carbide precipitation.     

Effect of Extrusion on the Microstructure and Tribological Behavior of Copper–Tin Composites Containing MoS2

This article deals with the effect of extrusion on the microstructures and tribological properties of powder metallurgy–fabricated copper–tin composites containing MoS₂ by optical microscopy, scanning electron microscopy (SEM), and tribotesting. The extrusion decreases the number of pores and increases the density and hardness and thus improves the tribological properties of the composites. Results demonstrated that abrasion is the dominant wear mechanism in all extruded composites, whereas a combination of adhesion and delamination appears to be the governing mechanism for prepared composites. The developed hot-extruded composites exhibited lower coefficient of friction and wear rates compared to prepared composites. Design Expert software was used to develop contour map.     

Effect of deformation martensite on the electrical and magnetic properties of plastically deformed chromium–nickel steel

Connection between the structural and phase changes in specimens of chromium–nickel austenitic steel and their magnetic and electrical properties has been studied. It has been established that electric resistivity can be used as an additional testing parameter for the phase composition of plastically deformed articles made of austenitic-ferritic steel. It has been shown that the emergence of an additional phase of strain-induced martensite leads to a significant increase in electric resistivity.     

Effect of the cut-off frequency on rough-point and flat-surface contacts?

In the past years, contact between two bodies has been studied from various ways that do not consider the cut-off frequency effect on the contact mechanism. This paper reports the correlation between rough point contact and flat surface contact at different cut-off frequencies of filter. The similarity and difference between the two types of contact mechanisms are presented for materials with linear or elasticperfectly plastic deformation. The conjugate gradient method (CGM) is used for analysing the rough point contact, while the rough flat surface contact is studied with an improved CGM in which the influence coefficient for the elastic deformation of the rough flat surface is obtained with finite element method. Numerical results show that for the above two types of contacts, their von Mises stress and maximum shear stress are greatly affected by the cut-off frequency of a high-pass filter. Moreover, a decrease in the cut-off frequency leads to an increase in the contact area and a decrease in the approach for the rough flat surface contact, while the opposite variations is for the point contact between rough bodies with the small radii.     

Influence of Polyfluo-Wax on the Friction and Wear Behavior of Polyimide/Epoxy Resin–Molybdenum Disulfide Bonded Solid Lubricant Coating

Polyimide/Epoxy resin–molybdenum disulfide bonded solid lubricant coatings (denoted as PI/EP-MoS₂) were prepared. The influence of polyfluo-wax (denoted as PFW) on the microhardness and friction and wear behavior of as-prepared PI/EP-MoS₂ lubricant coating was measured using a microhardness tester and a reciprocating ball-on-disc tribometer, respectively. The worn surfaces of the lubricant coatings were observed with a scanning electron microscope, and their wear rate was determined with a Micro XAM surface mapping microscope. Moreover, the transfer films formed on the counterpart steel ball surfaces were analyzed by X-ray photoelectron spectroscopy. Results indicate that the incorporation of a proper content of PFW filler is effective at improving the antifriction performance of the PI/EP-MoS₂ lubricant coating while maintaining better wear resistance. Moreover, the friction coefficient of the lubricant coating decreases with increasing content of PFW from 2 to 10%, and the one with a filler content over 6% PFW has a steady friction coefficient of 0.07. The improvement in the antifriction performance of the lubricant coating with the incorporation of the PFW filler is attributed to the excellent lubricity of homogeneously distributed PFW.