Lowest Specific Wear Rate Research Articles

Investigation of Tribological Behavior of PTFE Composites Reinforced with Bronze Particles by Taguchi Method

Reinforced PTFE materials can be designed to show high mechanical stability against harder materials under sliding wear conditions. Especially bearing metal-reinforced PTFE is of high practical interest. In this class of materials, bronze-filled PTFE was reported to obtain high wear resistance, a low coefficient of friction (COF), and excellent self-lubrication properties in sliding conditions. In the statistical approach of this work, PTFE composites reinforced with 25 vol%, 40 vol%, and 60 vol% bronze particles were evaluated against pure PTFE regarding wear behavior under varied wear test parameters, i.e., material, normal load, and sliding speed. Wear tests were planned to use a standard orthogonal array based on the Taguchi design method. An analysis of variance test was utilized to quantify the effects of test parameters on the wear behavior of the bronze/PTFE composites and pure PTFE. According to the variance analysis, the material type has the largest influence on the COF and the specific wear rate (SWR) under test conditions of this work. Both COF and SWR were found to be influenced by the material type (29.83% and 96.16%), the normal load (33.34% and 0.95%), and sliding speed (9.14% and 1.28%). The lowest SWR and COF values were achieved at the optimum wear test conditions where the wear test parameters were 1 m/s sliding speed (A4B2C2) at PTFE + 60 vol.% bronze reinforced composite 50 N application load and 0.32 m/s sliding speed (A4B3C1) at PTFE + 60 vol.% bronze reinforced composite 100 N application load, respectively.

Tribology of Ti2/Cr2 and (TiCr)2AlCx MAX Phase Ceramics

The MAX phase ceramics namely Ti2AlCx, Cr2AlCx, and (TiCr)2AlCx were examined under dry sliding conditions against stainless steel ball at room temperature and 5 N applied normal load using a Ball-on-disk tribometer. At 5 N, 100 m sliding distance and 20 cm/s sliding velocity, Cr2AlCx, and (TiCr)2AlCx ceramic samples exhibited low specific wear rate (3.2 × 10-7 cm3/Nm and 4.2 × 10-7 cm3/Nm), while the coefficients of friction were 0.31 and 0.10, respectively. At 5 N, 100 m and increasing velocity from 5 cm/s to 20 cm/s, Ti2AlCx sample the coefficients of friction decreases from 0.25 to 0.14. The specific wear rate of Ti2AlCx sample was 6.7 × 10-7 cm3/N m at 5 N, 100 m and 5 m/s, and decreases with increasing velocity (3.3 × 10-7 cm3/N m at 20 m/s). The correlations between observed tribological properties and tribo-film characteristics were discussed.

Impact of Relative Humidity on the Formation of Low-Frictional Interface and its Continuity in Tribological Systems with Hydrogenated Carbon Nitride Coatings

The impact of relative humidity on the formation of low-frictional interface in hydrogenated carbon nitride (CNx:H) coatings sliding against Si3N4 balls and the formation continuity was elucidated through friction tests conducted in both air and nitrogen atmospheres with controlled relative humidity levels. In air atmosphere, a carbonaceous tribolayer with a transformed structure from the initial CNx:H was formed on Si3N4 at less than the critical humidity that existed in 1.0–3.0% RH, resulting in low friction (μ < 0.05) and a low specific wear rate of the balls (< 2 × 10–9 mm3/N·m). In contrast, this tribolayer failed to form above 3.0% RH. In nitrogen atmosphere, within the 0.25–1.0% RH range, the tribolayer continued to form concurrently with wear progression, maintaining low friction for over 50,000 cycles. However, in less than this humidity range, the lifetime of low friction was limited owing to the tribolayer’s structural alteration. Thus, relative humidity influences not only the formation of the low-frictional interface but also the formation continuity. On the CNx:H friction surface, hydrogen, hydroxyl, and oxygen groups from environmental water and oxygen molecules continued to chemisorb owing to tribochemical reactions on the uppermost few nanometers during continuous low friction in a nitrogen atmosphere, while hydrogen content of CNx:H desorbed. This study experimentally confirmed the critical role of controlling relative humidity in tribological systems using CNx:H coatings to achieve low friction and improve its durability of low friction through the continuous formation of the low-frictional interface.

A novel plasma-facing NdB6 particulate reinforced W1Ni matrix composite: Powder metallurgical fabrication, microstructural and mechanical characterization

Tungsten (W) is one of best candidate metal for plasma-facing materials (PFM), especially due to its high melting temperature and neutron absorption capability. However, converting W into bulk PFM is hard because of its high melting point. This problem can be solved by adding metallic sintering aids with low melting points. In this study, W matrix with 1 wt% Ni aid was reinforced by adding NdB6 particles (1, 5, and 10 wt%). It can be introduced as a novel potential PFM, thanks to its low volatility and high neutron absorbability. The ceramic and composite powders produced via mechanochemical synthesis and mechanical alloying were examined in terms of composition, particle size, crystallite size, and lattice strain. Samples sintered via pressureless sintering (PS) and spark plasma sintering (SPS) were microstructurally analyzed by using an X-ray diffractometer (XRD), a scanning electron microscope (SEM) attached with an energy dispersive spectroscope (EDS), and mechanically analyzed in terms of microhardness and wear behavior. Based on the results, W2B and WB phases emerged in the SPS'ed W1Ni-5NdB6 and PS'ed./SPS'ed W1Ni-10NdB6 composites. SPS'ed W1Ni-10NdB6 composite had the highest hardness value and the lowest specific wear rate. The SPS'ed W1Ni-5NdB6 composite showed fewer surface damages and higher irradiation resistance as compared with other samples after exposure of He+ irradiation.

A comparative investigation on the surface characteristics of AISI 304 and AISI 1045 steel influenced by turning combined with ball burnishing

Burnishing is a popular superfinishing procedure in the manufacturing industry that induces plastic deformation to the finished product by the application of a highly polished and hardened deforming element known as a burnishing tool. Research work on the burnishing process is numerous. However, the reports containing the comparative investigations are lacking. In this work, the effect of ball burnishing parameters namely penetration depth, burnishing spindle speed, and number of passes has been compared and analyzed on AISI 1045 and AISI 304 steels with respect to surface roughness, hardness, wear resistance, and corrosion resistance. Results indicate that the combination of a feed rate of 0.12 mm/rev, spindle speed of 160 rpm, and penetration depth of 0.025 mm with four passes generated minimum surface roughness (AISI 1045). However, maximum surface hardness is obtained with a feed rate of 0.12 mm/rev, spindle speed of 160 rpm, and at 0.085 mm penetration depth under one pass (AISI 304). The lowest specific wear rate is achieved with a feed rate of 0.12 mm/rev at a spindle speed of 160 rpm and a penetration depth of 0.085 mm in one pass (AISI 304). The burnishing process influenced both materials, AISI 304 and AISI 1045, under varying parametric conditions. The maximum reduction in surface roughness is 68.1% for AISI 304 and 79.3% for AISI 1045, while surface hardness improves by 27% for AISI 304 and 22% for AISI 1045. Additionally, the burnishing process reduces the specific wear rate by 49.3% for AISI 304 and 45.4% for AISI 1045. The refinement of grains during the burnishing process enhances corrosion resistance compared to the unburnished surface.

Enhancing mechanical properties and tribological performance through boron carbide hybridization in Novolac matrix graphite composites under dry sliding condition

This study extensively investigates the effects of 10 wt% graphite reinforcement and varying B4C content (1 wt%, 2 wt%, 4 wt%) on the properties of Novolac matrix polymer composites prepared by mechanical milling-assisted hot pressing. The microstructures, wear surfaces, wear debris, and fracture surfaces of the produced polymer composites were examined using SEM and EDS. The density measurements were conducted according to the Archimed’s principle. Their tribological behavior was evaluated with a reciprocating ball-on-flat sliding wear test at 50 N, 75 N, and 100 N loads. After the wear tests, surface topography was analyzed in 3D with an optical profilometer. The results indicated that composites with 2 wt% B4C had the lowest specific wear rate and the highest wear resistance.

The development of B/Cr co-doped DLC coating by FCVA deposition system and its tribological properties at 300 °C

The diamond-like carbon (DLC) coating prepared using filtered cathodic arc deposition (FCVA) lost its promising wear resistance under high temperatures. Element-doped DLC coatings have been investigated to suppress carbon oxidation reaction and subsequently enhance the wear resistance in high-temperature environments. Previous research clarified the excellent tribological properties of boron-doped DLC (B-DLC) but identified challenge such as arc discharge extinguishment and coating declamation (under high-temperature friction test). In this study, the introduction of Argon gas (10 sccm) during the deposition process stabilized stable arc discharge, resulting in high hardness and deposition rate. Moreover, a chromium interlayer and varying concentration of Cr dopant (0.5 %, 1.0 %, 3.0 % at.) were added to B-DLC to develop a stable, co-doped DLC with low friction and high wear resistance. Raman spectroscopy and nano-indentation revealed an increase in the disordered carbon structure and reduction in hardness and Young's Modulus with Cr doping. Macroscopic ball-on-disk friction test, showed 1 % Cr-doped B-DLC (a-C:B:Cr1) coating exhibited super low friction (avg. coefficient 0.02) and a low specific wear rate (<5.0 × 10−6 mm3/Nm). Raman spectroscopy indicated that the transferred graphite-like tribo-film onto the surface of Si3N4 counterparts contributed to stable low friction. Additionally, XPS analysis on the DLC coatings' wear track suggested the rich BB bond might contribute to its high wear resistance. This successful improvement on element-doped DLC prepared by FCVA provided valuable insights for further exploration of DLC coating applied to various working situations.

Effect of Sn addition on mechanical, wear, and electrochemical properties of Ti-Al-Sn alloys

This study aims to investigate the effect of Sn content on the structural, mechanical, wear, and electrochemical properties of Ti-6Al-xSn (x = 3.5–17.5, wt%) alloys fabricated by powder metallurgy method. The results showed that the microhardness generally decreased with increasing Sn content, although there was an unusual increase in microhardness in the alloy with 10.5 wt% Sn. Depending on the Sn content, various phases such as α-Ti, Ti3Sn, and Ti3Al indicated complex phase formations. The flexural and tensile strengths increased up to 10.5 wt% Sn content, but the strengths reduced above this level. The maximum values for flexural and tensile strengths were obtained as 270 MPa and 125.8 MPa, respectively. With increasing Sn content, the fracture surfaces shifted from cleavage mode to mixed brittle and ductile failure modes. The wear tests were conducted in two different environments: dry and wet conditions. Considering dry sliding conditions, the lowest specific wear rate was obtained as 0.85 × 10−6 mm3/N·m in the alloy coded 3.5Sn at a sliding distance of 1500 m. On the other hand, the highest wear was measured as 2.89 × 10−6 mm3/N·m in the 17.5Sn coded sample at a sliding distance of 6000 m in wet conditions. The wear results demonstrated a relationship between mechanical properties and wear resistance, which was influenced by the existence of porosity. The Ti-6Al-7Sn alloy exhibited the best corrosion resistance with a 2.22 × 10−7 icorr value, while the one with Ti-6Al-17.5Sn alloy showed the worst performance with a 9.71 × 10−6 icorr value.

A synergetic effect of ternary refractory nitride reinforcements on densification, mechanical, tribological and thermal stability characteristics of spark plasma sintering-developed Ti6Al4V matrix composites

This paper reports the possibility of developing advanced Ti6Al4V matrix composites (TMCs) with enhanced mechanical properties and highly improved resistance to wear and thermal degradation for structural and high-temperature aerospace applications. The synergetic effect of different weight compositions (1, 1.5 and 2 wt%) of ternary reinforcements consisting of h-BN, TiN and AlN nanoparticles on the characteristics of the microstructure, phase constitution, densification, mechanical, tribological and thermal stability of Ti6Al4V matrix composites developed by spark plasma sintering (SPS) is investigated. The unreinforced Ti6Al4V exhibited a two-phase microstructure made up of α/β phases, however the simultaneous reinforcements resulted in notable microstructural changes and emergence of nitride-rich secondary phases. The relative densities of the composites decrease with increasing reinforcement addition, whereas the nanohardness and elastic modulus values of the composites continue to improve with increasing reinforcement from 1 wt% (28.319 ± 0.525 GPa and 219.43 ± 6.77 GPa) to 2 wt% (55.642 ± 0.693 GPa and 314.59 ± 7.58 GPa) compared to the unreinforced Ti6Al4V (5.838 ± 0.323 GPa and 115.07 ± 3.63 GPa). The unreinforced alloy yields higher average COF values, while the composites at equivalent applied normal loads yield lower average COF values. Thus, in comparison to the unreinforced alloy, the produced composites exhibit considerably lower specific wear rates (with increasing applied normal load). Based on thermogravimetric analysis, the oxidized composite reinforced with 1 wt% of ternary reinforcements exhibits the highest thermal stability in the high-temperature oxidizing environment, as evidenced by its greatest resistance to oxidation and its smallest weight gain of 1.55%.

A comparative analysis of compressive and wear failure of laser-powder bed fused Stainless Steel 316L produced with different hatch spacing in stripe and contour patterns

The selection of hatch spacing is crucial in additive manufacturing processes to produce a defect free Stainless Steel 316L (SS) components, especially in laser powder bed fusion (LPBF) process. Improper selection of hatch spacing could lead to various failure regimes (like vertical cracking, porosity, and un-melted particles) in Stainless Steel 316L (SS) component produced through laser powder bed fusion (LPBF). Further, the failure regimes have a direct impact on the hardness, compression strength, friction, and wear properties of LPBF SS components. The present study has taken substantial efforts to analyse the impact of various hatch spacing (0.08 mm, 0.10 mm. and 0.12 mm) in stripe and contour patterns, in terms of morphology, mechanical, and tribological properties of LPBF SS components. Also, the present study elucidates how variations in hatch spacing influences the features like particle fusion, crack formation, density, hardness, surface roughness, compression, and wear properties. The stripe pattern with low hatch spacing of 0.08 mm showed better particle fusion and high surface roughness; whereas the high hatch spacing has produced voids, un-melted powder particles, and cracks in the stripe and contour pattern. High densities and hardness values were attributed to the stripe patterns with more effective melting and fusing of powder particles. XRD analysis revealed the stable phase compositions across various hatch spacing with a predominant FCC crystal structure. Residual stress distribution was significantly influenced by the hatch spacing for both stripe and contour patterns. Importantly, the low hatch space leads has promoted the tensile residual stress formation and vice versa for the higher hatch spacing. Stripe patterns showed higher compression strengths with buckling and shear mode as a compression failure. The stripe pattern demonstrated a low specific wear rate (SWR) and coefficient of friction (COF) compared to the contour pattern, with respect to the various hatch spacing. Furthermore, the simulated body fluid (SBF) lubrication regime played a significant role in reducing the COF. Patches, groves, furrows, and craters demonstrated the abrasive and adhesive failure for both stripe and contour pattern, which is further detailed in the article.

Investigation of the Nitriding Effect on the Adhesion and Wear Behavior of CrN-, AlTiN-, and CrN/AlTiN-Coated X45CrMoV5-3-1 Tool Steel Formed Via Cathodic Arc Physical Vapor Deposition

Monolayer (CrN, AlTiN) and bilayer (CrN/AlTiN) coatings are formed on the surface of conventional heat-treated and gas-nitrided X45CrMoV5-3-1 tool steel via Cathodic Arc Physical Vapor Deposition (CAPVD), and the adhesion characteristics and room- and high-temperature wear behavior of the coatings are compared with those of the un-nitrided ones. Scratch tests on the coatings show that the bilayer coating exhibits better adhesion behavior compared to monolayer ones, and the adhesion is further increased in all coatings due to the high load carrying capacity of the diffusion layer formed by the nitriding process. Dry friction tests performed at room temperature reveal that, among ceramic-based coatings, the coating system with a high adhesion has the lowest specific wear rate (0.06 × 10−6 mm3/N·m), and not only the surface hardness but also the nitriding process is important for reducing this rate. Studies on wear surfaces indicate that the bilayer coating structure has a tendency to remove the surface over a longer period of time. Hot wear tests performed at a temperature (450 °C) corresponding to aluminum extrusion conditions show that high friction coefficient values (&gt;1) are reached due to aluminum transfer from the counterpart material to the surface and failure develops through droplet delamination. Adhesion and tribological tests indicate that the best performance among the systems studied belongs to the steel–CrN/AlTiN system and this performance can be further increased via the nitriding process.

Composite Materials with Nanoscale Multilayer Architecture Based on Cathodic-Arc Evaporated WN/NbN Coatings.

Hard nitride coatings are commonly employed to protect components subjected to friction, whereby such coatings should possess excellent tribomechanical properties in order to endure high stresses and temperatures. In this study, WN/NbN coatings are synthesized by using the cathodic-arc evaporation (CA-PVD) technique at various negative bias voltages in the 50-200 V range. The phase composition, microstructural features, and tribomechanical properties of the multilayers are comprehensively studied. Fabricated coatings have a complex structure of three nanocrystalline phases: β-W2N, δ-NbN, and ε-NbN. They demonstrate a tendency for (111)-oriented grains to overgrow (200)-oriented grains with increasing coating thickness. All of the data show that a decrease in the fraction of ε-NbN phase and formation of the (111)-textured grains positively impact mechanical properties and wear behavior. Investigation of the room-temperature tribological properties reveals that with an increase in bias voltage from -50 to -200 V, the wear mechanisms change as follows: oxidative → fatigue and oxidative → adhesive and oxidative. Furthermore, WN/NbN coatings demonstrate a high hardness of 33.6-36.6 GPa and a low specific wear rate of (1.9-4.1) × 10-6 mm3/Nm. These results indicate that synthesized multilayers hold promise for tribological applications as wear-resistant coatings.

Tribological behaviors and mechanical properties of novel Al-5Cu hybrid composites under dry sliding conditions

This study aims to develop aluminum composites, which are widely used in the automotive and aerospace industries. For this purpose, novel Al-5Cu/Al2O3-SiC hybrid composites were produced, and their mechanical and tribological performances were investigated. Hardness, density, and three-point bending analyses of hybrid composites were performed. In addition, wear and friction analyses were carried out under dry sliding conditions and applying different loads (5-10-15 N). In addition, the morphological properties of the produced hybrid composites were determined by microstructural analysis (SEM/EDS). High density, hardness, and strength values were obtained in hybrid composites produced using powder metallurgy and hot pressing methods. As a result of the wear test, it was determined that the hybrid reinforcements showed positive effects on the wear resistance. The lowest specific wear rate (SWR) value was 2.09 × 10−6 mm3/N.m. It was determined that the SWR values of the hybrid composites decreased with the increase of the applied load. In addition, plastic deformation and adhesion wear were observed as a result of SEM/EDS analyses taken from the worn surfaces.

The effect of nanocarbon inclusion on mechanical, tribological, and thermal properties of phenolic resin‐based composites: An overview

AbstractNanocarbons including carbon nanotubes, graphene oxide, reduced graphene oxide and particularly graphene have unique properties such as high mechanical strength, thermally stable, highly conducting, high friction stability and lower specific wear rates, which can potentially provide synergically improved performance of advanced engineering materials and technologies for various fields of applications such as automotive, aerospace, and other industrial components. Development of phenolic resin‐based nanocomposites comprised of nanocarbon material remained as a research focus to outperform different properties of conventional material based components. In application, phenolic resin is the most popular binder in frictional components development such as brake pads, brake linings, and clutch facings, particularly used in many of light and medium automotive brake pad applications. Specifically, the present review study aims to provide thorough discussion on the mechanical, tribological, and thermal performances of phenolic resin‐based nanocomposites containing nanocarbon as a property modifier by comparing with the neat phenolic resin or with the composite containing other micro ingredients. As per presented overview, the analysis shows the significant improvement in some required application‐based properties of phenolic resin‐based nanocomposites such as tensile strength, young's modulus, impact strength, specific wear rate reduction, residue yield, and thermal conductivity due to the inclusion of nanocarbon, where the content of nanocarbons ranges about 0.5 wt% to 5 wt%. Hence nanocomposites synthesized using phenolic resin matrix with nanocarbons fillers found to have better mechanical strength, better wear resistance, and thermal stabilities when compared to pure phenolic resin and other composites.

Characterization of annealed‐silane modified barley husk biosilica and garment waste cotton microfiber vinyl ester composite

AbstractThis study investigates the effect of adding annealed‐silane modified biosilica and waste cotton microfiber into the vinyl‐based composite on load‐bearing properties. The primary objective of this study was to unveil the significance of annealing treatment on the biosilica and its effect on composite's properties. The biosilica was prepared from waste barely husk ash and the waste cotton microfiber was used as received. The composites were fabricated using mold casting method and their properties were assessed in accordance with ASTM standards. Among the composites examined, the VCB2 displays improved mechanical properties with a highest tensile strength of 120 MPa. In contrast, the VCB3 composite exhibited enhanced hardness with a low specific wear rate of 0.22 mm3/N m and a coefficient of friction of 0.19. Furthermore, the composite VCB3 demonstrated an elevated dielectric constant of 3.85 and a low dielectric loss of 0.136 with a high thermal stability up to 388°C. This study underscores the potential of annealing process on biosilica and its stress free grain structure in property improvement made as valuable reinforcement in waste cotton microfiber‐vinyl ester composites, opening up new avenues for diverse engineering applications with advanced material performance.Highlights Vinyl ester composites are prepared from waste biomass biosilica and cotton microfiber. Addition of biosilica improved the void filling effect of matrix. Addition of biosilica improved the mechanical properties. Addition of biosilica up to 3 vol.% improved the wear properties. Addition of biosilica up to 3 vol.% improved the thermal stability.

Role of process control agent in the production of Al2O3-reinforced titanium matrix composites

Metal Matrix Composites (MMCs) have recently been preferred over traditional materials in many engineering applications. Titanium matrix composites (TMCs) are used in the automotive, aerospace and defence industries thanks to their exceptional strength, high fatigue strength, good corrosion resistance and high elastic modulus. Some of the most used reinforcement materials for TMCs are SiC, Zr2O3, Al2O3, graphene, carbon nanotube (CNT) and TiC. In this study, TMCs reinforced Al2O3 were produced via conventional powder metallurgy (PM) and ultrasonic-assisted mixing. An Al2O3 in varying amounts (5 and 10 wt%) was incorporated into the TMCs via mechanical alloying (MA) for 5 h in a high-energy ball mill and using different process control agents (PCA, Stearic acid (SA), Polyvinyl Alcohol (PVA), Ethanol). The mechanically alloyed (MA'ed) powders were compacted by a hydraulic press under uniaxial pressure of 450 MPa and sintered at 1200 °C for 2 h in an argon atmosphere. The microstructural, mechanical and tribological properties of Ti-xAl2O3 powders and bulk samples were investigated. The highest hardness and the lowest specific wear rate were found in specimens reinforced with 5 wt% Al2O3, using ethanol as PCA, and produced by ultrasonic-assisted mixing, but the same specimen had the lowest compressive strength.

Enhancing the Tribological Performance of Additively Manufactured Aluminium Alloy ER 5356 via the Cold Deformation Process

Typically, in handling worn parts, to avoid extra expenditure, car manufacturers will send them to the scrap yard. Reconstruction of the worn area via additive manufacturing is now an option. Unfortunately, heat will reduce the deposited material’s properties, like wear resistance. In this study, the effect of a cold deformation via cold forging on the tribological performance of aluminium alloy wire ER 5356 fabricated by wire arc additive manufacturing (WAAM) will be investigated. The cold forging process was conducted at room temperature on an open die transverse to the direction of the deposited weld. Comparisons were made between unforged and forged specimens at dry and wet sliding conditions at varied speeds and loads applied. Based on the results, it was observed that forged specimens exhibit a lower specific wear rate than unforged specimens for both conditions. The coefficient of friction (COF) in dry sliding decreases as the specific wear rate increases. However, comparatively, COF at wet sliding is lower for both unforged and forged samples. As a conclusion, the cold forging enhances the tribological performance by lowering the specific wear rate and COF.

Studies on Al-Si based hybrid aluminium metal matrix nanocomposites

A lightweight Hybrid Aluminium Metal Matrix Nanocomposite (HAMNC) is proposed for brake rotor application in this work. Hypereutectic Aluminium-Silicon (Al-Si) grade LM30 alloy is opted as the matrix with Boron Carbide (nB4C) and Rutile (nTiO2) nanoparticles as reinforcements. The brake rotor samples are produced using ultrasonic squeeze-assisted stir-casting, which is cost-effective and feasible for mass production. The hybrid nanocomposite specimens are fabricated by maintaining 1 wt% of nB4C and by varying TiO2 nanoparticles from 0 wt% to 1.00 wt% in steps of 0.25 wt%. The formulations are subjected to microstructure study and dry sliding wear test. The Field Emission Scanning Electron Micrographs (FESEM) reveal that the stir-casting method combining ultrasonic and squeeze effects aids in the uniform distribution of nano reinforcements. The tribological findings show that the hybrid nanocomposite containing 0.75 wt%. of nTiO2 has an 82.76% lower specific wear rate compared to the parent LM30 alloy. Further, the HAMNC brake rotor is 60% lighter than the brake rotors made of Grey Cast Iron making it a potential replacement material.

Nano-Scratch and Micro-Scratch Properties of CrN/DLC and DLC-W Coatings

Abstract Diamond-like carbon (DLC) coatings are well known for their excellent adhesion to silicon wafers. However, they often exhibit poor adhesion properties on metallic substrates. Interlayers and metallic doping help improve the adhesion properties of DLC coatings on metallic substrates. In this study, both nano-scratch and micro-scratch were performed on chromium nitride (CrN)/DLC and tungsten doped DLC coating (DLC-W) coatings deposited on 920 HV DIN 16CrMn martensitic valve tappets. Nano-scratch was performed at 300 mN in a Hysitron nano-indenter, whereas micro-scratch was performed at 1–50 N using a CETR-UMT tribometer. The 3-D images and 2-D longitudinal and transversal profiles of the nano-scratch and micro-scratch were obtained using atomic force microscopy and 3-D optical profilometry, respectively. The scratch hardness equation was used to estimate the scratch hardness of the coatings. Experimental and theoretical values for the volume removed and the specific wear rates for the micro-scratch and nano-scratch of CrN/DLC and DLC-W coatings were estimated. The coefficients of friction (COF) obtained during the micro-scratch tests were very similar for both coatings. The same happened with the COF measured during the nano-scratch. The maximum COF in both cases reached 0.14. The wider and deeper penetration of the indenter for the DLC-W coating was mainly due to the lower hardness of the multilayered coating, composed of alternating nanometric thick amorphous carbon and tungsten carbide (WC) layers. The greater wear observed for the DLC-W coating system could also be attributed to the abrasive effect of detached WC nanoparticles abrasively acting during the contact of the diamond tip with the DLC coating. The experimental and theoretical values for the volume removed and the specific wear rates indicate a lower volume removal and specific wear rate for CrN/DLC because of higher hardness and better load-carrying capacity, contrary to DLC-W, which presents higher volume removal and specific wear rate because of its lower hardness.

Microstructural Modification of Cold-Sprayed Ti-Cr3C2 Composite Coating by Laser Remelting

Laser processing is an effective post-treatment method for modifying the structure and improving the properties of cold-sprayed coatings. In the present work, the possibility of fabricating a hard and wear-resistant Ti-based cermet coating by cold spray followed by laser remelting was studied. A mixture of titanium and chromium carbide powders in a ratio of 60/40 wt.% was deposited by cold spray onto a titanium alloy substrate, which ensured the formation of a composite coating with a residual chromium carbide content of about 12–13 wt.%. The optimal values of laser beam power (2 kW) and scanning speed (75 mm/s) leading to the qualitative fusion of the coating with the substrate with minimal porosity and absence of defects were revealed. The microstructure and phase composition of as-sprayed and remelted coatings were examined with SEM, EDS and XRD analysis. It was shown that the phase composition of the as-sprayed coating did not change compared to the feedstock mixture, while the remelted coating was transformed into a β-Ti(Cr) solid solution with uniformly distributed nonstoichiometric TiCx particles. Due to the change in microstructure and phase composition, the remelted coating was characterized by an attractive combination of higher microhardness (437 HV0.1) and lower specific wear rate (0.25 × 10−3 mm3/N × m) under dry sliding wear conditions compared to the as-sprayed coating and substrate. Laser remelting of the coating resulted in a change in the dominant wear mechanism from oxidative–abrasive to oxidative–adhesive with delamination.