High temperature wear of cermet particle reinforced NiCrBSi hardfacings

The aim of the current study was to investigate erosive and impact/abrasive wear behaviour of TiC–NiMo and Cr₃C₂–Ni reinforced NiCrBSi hardfacings at temperatures up to 700 °C.Coatings were produced using plasma transferred arc cladding process. It was shown that the high temperature wear behaviour of TiC–NiMo and Cr₃C₂–Ni NiCrBSi hardfacings is influenced by oxidation. The formation of mechanical mixed layers and oxide films was observed for both investigated coatings. TiC–NiMo and Cr₃C₂–Ni reinforced hardfacings show high wear resistance at all testing temperatures for both impact/abrasion and erosion conditions.     

Wear properties of cemented carbides/Cu-based alloy composite strengthening materials for milling shoes

The microstructure and wear behavior of WC–8TiC–3TaC–8Co cemented carbide and Cu–Zn–Ni alloy composite strengthening materials have been investigated by means of scanning electron microscopy (SEM), electron dispersion X-ray analysis (EDAX) and wear test. Effect of applied load and sliding distance on the wear behavior of the strengthening materials are also studied in this paper. The results show that the cemented carbide particles are surrounded by the α-Cu + β-Zn phases in the hardfacing layers. There exists an inter-diffusion zone at the interface of the cemented carbides and Cu-based matrix due to the mutual diffusion of elements. The wear volume of both the WC–8TiC–3TaC–8Co/CuZnNi and WC–8Co/CuZnNi composite strengthening layers increased with the increasing of applied load. The WC–8TiC–3TaC–8Co/CuZnNi hardfacing layers exhibited lower wear volume loss than that of WC–8Co/CuZnNi. According to the results of engineering application, the working efficiency and employing life of the milling shoes, which were strengthened by WC–8TiC–3TaC–8Co/CuZnNi composite materials, is by approximately two to three times the milling tools strengthened by WC–8Co/CuZnNi.     

Wear properties of cemented carbides/Cu-based alloy composite strengthening materials for milling shoes

The microstructure and wear behavior of WC–8TiC–3TaC–8Co cemented carbide and CuZnNi alloy composite strengthening materials have been investigated by means of scanning electron microscopy (SEM), electron dispersion X-ray analysis (EDAX) and wear test. Effect of applied load and sliding distance on the wear behavior of the strengthening materials are also studied in this paper. The results show that the cemented carbide particles are surrounded by the α + β phases in the hardfacing layers. There exists an inter-diffusion zone at the interface of the cemented carbides and Cu-based matrix due to the mutual diffusion of elements. The wear volume of both the WC–8TiC–3TaC–8Co/CuZnNi and WC–8Co/CuZnNi composite strengthening layers increased with the increasing of applied load. The WC–8TiC–3TaC–8Co/CuZnNi hardfacing layers exhibited lower wear volume loss than that of WC–8Co/CuZnNi. According to the results of engineering application, the working efficiency and employing life of the milling shoes, which were strengthened by WC–8TiC–3TaC–8Co/CuZnNi composite materials, is by approximately two to three times the milling tools strengthened by WC–8Co/CuZnNi.     

Wear characteristics of Cr3C2–NiCr and WC–Co coatings deposited by LPG fueled HVOF

Wear behavior of the HVOF deposited Cr₃C₂–NiCr and WC–Co coatings on Fe-base steels were evaluated by the pin-on-disc mechanism. The constant normal load applied to the pin was 49 N and sliding distance was 4500 m with velocity of 1 m/s, at ambient temperature and humidity. The specific wear rate of WC–Co coating was 3 mm³/N m and Cr₃C₂–NiCr coating was 5.3 mm³/N m. SEM/EDAX and XRD techniques were used to analyze the worn out surface and wear debris. The Fe₂O₃ was identified as the major phase in the wear debris. The wear mechanism is mild adhesive wear in nature.     

Two-body dry abrasive wear of cermets

The present paper concerns the two-body dry abrasive wear phenomenon of a series of cermets on the base of titanium and chromium carbides with different composition, using a “block on abrasive grinding wheel” test machine. WC–Co hardmetals were used as reference material. Abrasive wear resistance of WC-base hardmetals is superior to that of TiC- and Cr₃C₂-base cermets. The wear coefficient of the cermets reduces with the increase of carbide content in the composites. The volume wear decreases with the increase in bulk hardness. At the first period volume wear of cermets increases linearly with the sliding distance up to the first 100 m; after that the alumina grits become blunt. Scanning electron microscopy examination of the wear tracks in the worn blocks suggests that abrasive wear mechanisms of different cermets are similar and occur through surface elastic-plastic and plastic deformation (grooving). The fracturing of bigger carbide grains and carbide framework the formation of sub-surface cracks by a fatigue process under repeated abrasion is followed by loss of small volumes of the material.     

Three-body abrasive wear of TiC–NiMo cermets

The mechanism of three-body abrasive wear of TiC-base cermets was studied. The wear rate of a series of cermets with different percentage of NiMo binder phase (20–60 wt%) was studied. Silica sand was used as an abrasive. The wear rate of the cermets decreases with the increase of TiC and Mo content, which corresponds to the increase in the bulk hardness. The post-run wear tracks of the worn blocks were analyzed with SEM. The material is removed by several processes such as extrusion and removal of the binder and also fractures of the carbide grains and the carbide network.     

Mechanical and tribological behavior of nanostructured copper–alumina cermets obtained by Pulsed Electric Current Sintering

Nanostructured Cu–Al₂O₃ powders obtained by the reduction of CuO with Al in a high energy ball mill were successfully consolidated by Pulsed Electric Current Sintering (PECS). The effect of the composition and microstructure of these PECS Cu–Al₂O₃ cermets on their strength was investigated. The friction and wear behavior of these cermets were studied under reciprocating sliding against corundum at 23 °C and 50% RH, and compared to the behavior of coarse grained PECS sintered pure copper. The effect of grain size on the coefficient of friction was masked by the formation of a surface tribolayer. The wear depth recorded on Cu–Al₂O₃ is lesser than half the one on coarse grained copper. Surface and subsurface deformation studied through FIB cross-sections showed that delamination and oxidative wear were active on Cu and Cu–Al₂O₃ cermets respectively under the current sliding test conditions. PECS Cu–Al₂O₃ cermets showed a good thermal stability even at 600 °C.     

Surface finishing: Impact on tribological characteristics of WC–Co hardmetals

Flat samples of WC–Co hardmetals with 6–12 wt%Co were surface finished by grinding, polishing and wire-electro-discharge machining (EDM). Comparative dry reciprocating sliding experiments against WC–6 wt%Co pins were performed using a Plint TE77 tribometer. Tribological characteristics were recorded online. Wear surfaces were characterized by surface scanning topography and scanning electron microscopy. Wire-EDM’ed samples exhibited higher friction and wear compared to ground and polished equivalents. This trend was correlated to X-ray diffraction measurements revealing tensile residual surface stresses in WC after wire-EDM contrary to compressive surface stresses after grinding and polishing. However, finer executed EDM reduces friction and wear significantly.     

On data dispersion in pin-on-disk wear tests

Ten pin-on-disk sliding wear tests for each experimental condition were carried out with a commercial tungsten carbide (WC) pin on silicon carbide (SiC) disks in order to determine the wear and friction data dispersion. The tests were repeated using two sliding speeds (v), 0.1 and 1.0 m/s, and two applied loads (P), 5 and 50 N. The wear data showed a dispersion in the range of 28–47 and 32–56%, for disk and pin, respectively. For the disk, the dispersion decreased when increasing both sliding speed and applied load; for the pin, no clear relationship was found. The friction values spread in the range of 5–15%, with a lower dispersion at high applied load, independent of the sliding speed. From a statistical point of view, it was found that, in all the experimental conditions adopted, about 20% of the wear and friction values can be considered outliers.     

Two body dry abrasive wear of TiC–NiMo cermets

Abstract

The present paper covers the two body dry abrasive wear of a series of titanium carbide base cermets with different amounts of NiMo binder phases (20–60 wt-%) using a 'block on abrasive grinding wheel' test machine. The wear coefficient of the cermets decreases with increasing TiC and Mo contents in the composite, which corresponds to an increase in bulk hardness. The volume loss increases with the increases in the sliding distance and the applied normal load, as predicted by the Rabinowitcz equation. The post-run wear tracks of the worn blocks were analysed by SEM to determine the wear mechanisms. The material is actually removed by several processes which scale the process of groove formation, including the formation of subsurface cracks by a fatigue process under repeated abrasion.     

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.     

Wear behavior of electroless Ni–P–B4C composite coatings

In this research, the wear of electroless Ni–P and Ni–P–B₄C composite coatings was reviewed. Auto catalytic reduction of Ni in nickel sulfate and sodium hypophosphate bath including suspended B₄C particles with different concentration was used to create composite coatings with 12, 18, 25 and 33 vol.% of B₄C particles. Coatings 35 μm thick were heat treated at 400 °C for one hour in an argon atmosphere and the wear resistance and friction coefficient of heat-treated samples were determined by block-on-ring tests. All wear tests were carried out at 24 °C, 35% moisture, 0.164 m/s sliding speed and about 1000 m sliding distance. Graphs show that an electroless Ni–P–B₄C composite coating with 25 vol.% of B₄C had the best wear resistance against a CK45 steel counterface.     

Preparation,microstructure and tribological behavior of laser cladding NiAl intermetallic compound coatings

Nickel aluminide (NiAl) intermetallic compound coatings were in situ synthesized from pre-placed mixed powders of Ni and Al by laser cladding. The phase composition and microstructure of the NiAl coatings were studied by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The effects of laser cladding parameters on the microstructure and friction and wear behavior of the NiAl coatings were investigated. It has been found that laser power density had a crucial influence on the microstructure and friction and wear behavior of NiAl coatings. Namely, the NiAl coatings synthesized under a lower power density have more dense and fine microstructure, and lower friction coefficient and wear rate. Besides, the friction and wear behavior of the laser cladding NiAl coatings is highly dependent on applied normal load and sliding speed; and the resulting coatings sliding against Si₃N₄ in a ball-on-disc contact mode is more suitable for tribological application at a moderate normal load of 3–7 N and sliding speed of 0.16–0.21 m/s.     

WC–ZrO2 composites: processing and unlubricated tribological properties

In the present work, we report the processing and properties of WC–6 wt.% ZrO₂ composites, densified using the pressureless sintering route. The densification of the WC–ZrO₂ composites was carried out in the temperature range of 1500–1700 °C with varying time (1–3 h) in vacuum. The experimental results indicate that significantly high hardness of 22–23 GPa and moderate fracture toughness of ∼5 MPa m^1/2 can be obtained with 2 mol% Y-stabilized ZrO₂ sinter-additive, sintered at 1600 °C for 3 h. Furthermore, the friction and wear behavior of optimized WC–ZrO₂ composite is investigated on a fretting mode I wear tester. The tribological results reveal that a moderate coefficient of friction in the range from 0.15 to 0.5 can be achieved with the optimised composite. An important observation is that a transition in friction and wear with load is noted. The dominant mechanisms of material removal appear to be tribochemical wear and spalling of tribolayer.     

Carbide tool wear mechanism in turning of Inconel 718 superalloy

Wear surfaces of the cutting tools are analyzed to study the wear mechanism of cemented carbide tools in turning in Inconel 718 superalloys. SEM and EPMA analyses indicated that the wear of carbide tools during high speed turning condition (V = 35 m min⁻¹) was caused by diffusion of elements (Ni or Fe) in workpiece into tool's binder (Co) by a grain boundary diffusion mechanism. This action weakened the bonding strength between carbide particles (WC, TiC, TaC) and the binder (Co). The carbide particles were then detached out of the cemented carbide tool by high flow stresses. The proposed grain boundary diffusion mechanism is also confirmed by theoretical analysis.     

A comparison of the reciprocating sliding wear behaviour of steel based metal matrix composites processed from self-propagating high-temperature synthesised Fe–TiC and Fe–TiB2 masteralloys

Steel matrix particulate composites were processed by direct addition of various powders to molten medium carbon steel. Fe–TiC and Fe–TiB₂ powders were produced using a self-propagating high-temperature synthesis (SHS) reaction and consisted of a dispersion of fine TiC (5–10 μm) and TiB₂ particles (2–5 μm), respectively in an iron binder.Addition of the Fe–TiC powder to the steel resulted in the formation of a metal matrix composite containing a homogeneous dispersion of TiC particles. However, addition of the Fe–TiB₂ powder resulted in the formation of a parasitic Fe₂B phase and TiC within the steel microstructure. In response to this an SHS masteralloy composed of Fe–(50% TiB₂+50%Ti) was manufactured which, when added to steel, prevented the formation of Fe₂B and resulted in a composite containing a mixture of TiB₂ and TiC particles.Dry reciprocating sliding wear behaviour of the three composite materials and their unreinforced counterpart was investigated at room temperature against a white cast iron counterface. Relative wear behaviour of the materials varied as a function of load. In all cases, the composite manufactured by addition of Fe–TiB₂ (yielding Fe₂B and TiC phases in the steel) exhibited wear rates greater than three times that of the unreinforced alloy. However, improvements in wear resistance over the base steel of up to two and a half times were observed with the other composites where the desired TiC and/or TiB₂ phases were retained in the steel. Scanning electron microscopy has been used to interpret wear behaviour in relation to both the as-cast microstructures of the composites and the wear scar microstructures observed.     

Sliding wear of TiC–NiMo cermets

The friction and wear properties of TiC–NiMo/steel rubbing pairs were investigated under dry condition. The sliding wear tests were carried out on the testing device at a velocity of 2.2 m/s and a load of 40 N. The volume wear increases with increase of the sliding distance as predicted by Archard’s equation. The wear coefficient of the cermets reduces with the increase of TiC and Mo content in the composite. The study has shown that the coefficient of friction was approximately the same for all the samples. The main wear mechanism in the TiC–NiMo cermets was micro-abrasion (polishing) and adhesive wear. At the initial stages of wear, adhesive wear characteristics featured by mild scratching and plastic smearing were observed on the worn surface, but at the later stages, contact fatigue failure of a relatively thick surface layer takes place.     

Friction and wear behaviors of C/C-SiC composites containing Ti3SiC2

In the present paper, friction and wear behaviors of a carbon fiber reinforced carbon–silicon carbide–titanium silicon carbide (C-SiC–Ti₃SiC₂) hybrid matrix composites fabricated by slurry infiltration and liquid silicon infiltration were studied for potential application as brake materials. The properties were compared with those of C/C-SiC composites. The composites containing Ti₃SiC₂ had not only higher friction stability coefficient but also much higher wear resistance than C/C-SiC composites. At an initial braking speed of 28 m/s under 0.8 MPa pressure, the weight wear rate of the composites containing 5 vol% Ti₃SiC₂ was 5.55 mg/cycle, which was only one-third of C/C-SiC composites. Self-lubricious film-like debris was formed on the composites containing Ti₃SiC₂, leading to the improvement of friction and wear properties. The effect of braking speed and braking pressure on the tribological properties of modified composites were investigated. The average friction coefficient was significantly affected by braking speed and braking pressure, but the wear rate was less affected by braking pressure.     

Microstructure and tribological properties of laser clad γ/Cr7C3/TiC composite coatings on γ-TiAl intermetallic alloy

In order to improve the wear resistance of the γ-TiAl intermetallic alloy, microstructure, room- and high-temperature (600 °C) wear behaviors of laser clad γ/Cr₇C₃/TiC composite coatings with different constitution of NiCr–Cr₃C₂ precursor-mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS), block-on-ring (room-temperature) and pin-on-disk (high-temperature) wear tests. The responding wear mechanisms are discussed in detail. Results show that microstructures of the laser clad composite coatings have non-equilibrium solidified microstructures consisting of primary hard Cr₇C₃ and TiC carbides and the inter-primary γ/Cr₇C₃ eutectic matrix, about three to five times higher average microhardness compared with the TiAl alloy substrate. Higher wear resistance than the original TiAl alloy is achieved in the clad composite coatings under dry sliding wear conditions, which is closely related to the formation of non-equilibrium solidified reinforced Cr₇C₃ and TiC carbides and the positive contribution of the relatively ductile and tough γ/Cr₇C₃ eutectics matrix and their stability under high-temperature exposure.     

Tribological properties of a Fe3Al material in sulfuric acid corrosive environment

The tribological properties of a Fe₃Al material in an aqueous solution of 1 mol/l H₂SO₄ corrosive environment sliding against a Si₃N₄ ceramic ball are studied using an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. We investigate the effects of load and sliding speed on tribological properties of the Fe₃Al material. The worn surfaces of the Fe₃Al material are examined by a scanning electron microscope (SEM) and an X-ray photoelectron spectroscope (XPS). It is found that the Fe₃Al material exhibits better wear resistance than 1Cr18Ni9Ti stainless steel in the sulfuric acid corrosive environment. The wear rate of the Fe₃Al material is on the order of 10^?13 m³/m and increases with increasing load, but does not vary below the sliding speed of 0.08 m/s then dramatically increases with increasing sliding speed. The friction coefficient of the Fe₃Al material is in the range of 0.1–0.28, and slightly increases with increasing load, and does not vary with the increase of sliding speed. The Fe₃Al material occurs tribochemical reaction with the H₂SO₄ aqueous solution in the friction process. Wear mechanism of the Fe₃Al material is dominated by microploughing and corrosive wear.