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This study focused on chromium addition (0 wt%, 3 wt%, 6 wt%, 9 wt% and 12 wt%) on the boride layer formation, microhardness, fracture toughness and elevated temperature friction and wear behaviour of alloys formed by powder metallurgy (P/M). The boride layers obtained on P/M alloys were characterized by examining density, porosity, surface roughness, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray difraction, surface proflometry, microhardness, and fracture toughness. The addition of Cr has a signifcant efect on both boride layer formation and friction-wear behaviour of P/M alloys. Increasing the Cr addition up to 6 wt% has an improving efect on the microhardness, fracture toughness and wear resistance of the P/M alloys, whereas in the case of 9–12 wt% Cr addition causes exfoliation in the boride layer and low fracture toughness, thus reducing wear resistance. Coefcients of friction and wear volume losses at elevated temperatures are higher than room temperature. The best wear resistance at room temperature was obtained in the sample containing 3 wt% Cr with the highest fracture toughness, while the best wear resistance at 250 °C and 500 °C was obtained in the sample containing 6 wt% Cr, where the highest hardness value was obtained.

Electroless nickel-based coatings are frequently used in the field of coatings to improve the surface properties of materials such as wear, hardness, and corrosion. In this study, Ni-W-P alloy and Ni-W-P/Al2O3 composites were coated on the aluminum substrate by electroless technique. Composite coatings were carried out after suspending process of alumina (Al2O3) particles at different concentrations in the electroless bath. The characterizations of the coatings were studied to be able to reach optimum particle concentration. Aluminum oxide particles (average particle size 300 nm) with different concentrations (5, 10, 15, 20 g/L) were added to the bath to determine the concentration effect. Scanning electron microscope (SEM) and field emission scanning electron microscopy (FESEM) analyses were performed to examine the microstructure images of the composite coatings. x-ray diffraction (XRD) analysis was performed to determine the coating layers' phase structures. The hardness of the coatings was determined by applying the hardness test on a microscopic scale. CSM tribometer was used to establish the wear and friction properties of the coatings. Galvanometer was used to determine corrosion resistance. After the studies, hardness values of coatings were successfully increased from 552 to 700 HV depending on the amount of particles in the coating layer. The friction coefficient was also improved by decreasing that from 0.45 to 0.1 µ grades with the contribution of Al2O3 particle reinforcement to Ni-W-P coating. The wear rate of the coatings decreased from 5.96 × 10 −5 to 3.16 × 10−5 mm3/Nm) with the increase of Al2O3 particles in the composite coating which indicates approximately two times improvement in the wear resistance. The corrosion resistance of composite coatings also increased, and an improvement in corrosion rate was achieved from 392 value to 063µm/year value with increasing particle concentration. © 2023, ASM International.

In the present study, the effect of an La alloying element with different quantities (1, 3 and 5 wt.-%) on the microstructure, mechanical and dry sliding wear properties of Mg- 3Al-3Sn-3Sb alloy was investigated. The wear tests were done on the alloys using pin on-disk equipment against a 4140 steel disc as counterpart under three different sliding velocities of 0.3, 0.6 and 1.2 ms-1 and four different loads of 5, 10, 20 and 40 N. The microstructural results showed that the new intermetallic phases (La5Sn3 and LaSnSb2) were formed with addition of La to the main alloy. Also, it was observed that the hardness of the Mg-3Al-3Sn-3Sb alloy was raised with increasing La addition. Furthermore, the tensile properties of the Mg-3Al-3Sn-3Sb alloy improved with rising La content at room and elevated temperature. The wear rates of the alloys increase with increasing of the sliding speed and load. In addition to this, the wear rate of the Mg-3Al-3Sn-3Sb alloy was found to be higher than that of the La content alloys for all test conditions.

Distaloy SA is a sponge iron powder (nominal composition: Fe-1.75Ni-1.5Cu-0.5Mo) widely used in the production of powder metallurgy (P/M) parts in the automotive industry. In this study, Distaloy SA powders were sintered in two different atmospheres, one consisting of pure Ar gas (traditional sintering) and the other consisting of a mixture of 90 wt.% B4C and 10 wt.% NaBF(4)powders (borosintering). To investigate the effects of the different sintering atmospheres, the P/M samples were characterized using density measurements, surface roughness tests, scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, microhardness measurements, nanoindentation experiments, wear tests and corrosion tests. On the surface of the borosintered samples, a 160-325 mu m thick double-phase FeB + Fe2B boride layer was formed. The hardness (1405-1688 HV) and elastic modulus (122.21-162.42 GPa) of the surface were significantly improved with the borosintering treatment compared to conventional sintering (215-250 HV, 63.28-94.86 GPa). Borosintering also provided low friction coefficient values and an increased wear resistance compared to conventional sintering. A significant increase in corrosion resistance was also observed with the borosintering treatment in three different solutions. The corrosion rates of both sintered and borosintered samples were ranked as NaCl < HCl < H2SO4. The borosintered samples displayed superior corrosion resistance compared to the sintered samples, especially in the acid solutions. The results of this study show that significant cost savings can be achieved by combining the boriding and sintering treatments in a single borosintering process.

Laser-clad AlCrFeCoNi high entropy alloy (HEA) coatings, produced on the surface of AISI 316 L stainless steel, were pack-borided at 1000 °C for 4 h in open air, high-purity Ar and vacuum environments. The HEA, which had an initial hardness of 6.14 ± 2.06 GPa, formed a complex boride layer consisting of (CoFe)B2, (CrFe)B2 and Cr2Ni3B6 phases on its surface, with hardness ranging from 15.95 ± 0.7 to 20.15 ± 4.50 GPa as a result of the boriding process. While the greatest boride layer thickness was obtained in the sample borided in vacuum, the highest surface hardness was obtained in the sample borided in air. The borided coatings showed improved wear resistance and lower friction values compared to the untreated control samples, both at 25 °C and 650 °C. The borided coatings also showed reduced coefficients of friction at 650 °C. The wear losses at 650 °C significantly exceeded those at 25 °C.

The effects of diferent heat and cryogenic (sub-zero) treatment parameters such as temperature and holding time on the microstructure (amount of retained austenite) and hardness of extrusion molds produced from the 21NiCrMo2 and 100Cr6 steels were investigated. The 21NiCrMo2 grade extrusion die was carburized for 22.5 h in an endogas (25% CO, 35% N-2 40% H2) atmosphere at 920 degrees C. At the end of the carburization process, the temperature was kept at 850 degrees C, which is the austenitization temperature, for 2 h, followed by cooling in oil at 80 degrees C and remaining in oil for 45 minutes. The carburizing process was not performed for the extrusion molds made of 100Cr6 steel grade. Only the austenitizing heat treatment at 850 degrees C (holding for 2 h) was carried out in this steel. The steel molds which were produced with 21NiCrMo2 and 100Cr6 steels were cryogenically treated at -120 degrees C for 2 h and subsequently tempered at 150 degrees C for 1.5 h. As a result of the cryogenic treatment, the hardness of 21NiCrMo2 steel increased to 840 Hv and the wear resistance of the extrusion die surface was improved. The amount of residual austenite decreased from 20% to 6% after the cryogenic treatment. Due to the effect of the cryogenic process, the surface hardness of the 100Cr6 steel sample increased to similar to 870 Hv, which implies an increase of 4.5%, due to the transformation of residual austenite to martensite. The mass loss, during the wear tests, of the hardened extrusion dies was reduced from 0.1420 mg to 0.0221 mg. The notch impact strength value measured in this condition was 20 J. The 100Cr6 steel after the cryogenic treatment was used to extrude 12 tons of Al alloy in an industrial press. This amount of material is 30% lower than for hot work tool steel. On the other hand, the 100Cr6 steel is more economical and heat treatment is more practical. The extrusion performance of 21NiCrMo2 steel was 50% lower than the hot work tool steel.

This study is dedicated to the detailed investigation of boronization kinetic, microstructural, mechanical, and wear properties of high entropy alloys (HEAs) considering their sluggish diffusion effect properties. A CoCrFeNiAl0.5Nb0.5 HEA was powder-pack boronized in the interval of 850–1050 °C for 2, 4, and 6 h in the boronizing medium containing 90 wt% of boron carbide and 10 wt% of sodium tetrafluoroborate. Boronizing of CoCrFeNiAl0.5Nb0.5 HEA was successfully produced. The obtained multi-phase boronized layers were characterized by compactness and flatness showing up inside its typical dendritic zones. The X-Ray Diffraction (XRD) studies showed the presence of ternary phases inside the boronized layers having a thickness of 4.38–92.16 µm. The nano and microhardness values were also determined and the adhesion force was analyzed through the Rockwell indentation tests. In addition, the Vickers fracture toughness values (0.46–1.83 MPa m−1/2) of the treated samples were found to be very dependent on the boronizing temperature. The wear losses have decreased due to the increase in hardness and an improvement of up to 99% has been achieved. The average diffusion coefficient model was implemented to deduce the boron activation energy in the CoCrFeNiAl0.5Nb0.5 HEAs. Finally, the predicted layers’ thicknesses were coincident with the experimental data.

High velocity air fuel (HVAF) spraying is an emergent thermal spray process, which is used in this work to realize high-performance large area tribological coatings of nickel-phosphorus cladded cubic-boron nitride (c-BN) particles. To the best of authors’ knowledge, this is the first time that HVAF has been utilized for developing Ni–P coatings reinforced with c-BN (NBN). The importance of appropriate processing was highlighted by utilizing two different nozzle configurations, for which microstructure, phase analysis and hardness results demonstrates considerable differences. Furthermore, the coatings were subjected to sliding wear tests to assess their friction and wear characteristics. Post-wear SEM analysis reveals the associated wear mechanisms. Effect of annealing on tribological performance of NBN coatings was also examined, and it is shown that optimal processing can preclude the need for post-treatment. Results ensuing from this work lay the foundation for new generation of HVAF-sprayed wear resistant metal/c-BN composite coatings for diverse applications. © 2022 The Author(s) The authors thank NUCoP project (Energimyndigheten, Sweden, Dnr. 2018e003191, Project nr. P46393-1 and the knowledge foundation, Sweden, for its financial support to projectHiPerCOAT (Dnr. 20180197) for their financial support. Theauthors also thank Mr. Magnus Sandberg, University West, forassisting in spraying the coatings and Mr. Mats Hogstr € om, €University West, for performing heat treatment.

Simulation of erosion wear and design optimization have been performed for a convective gas cooler with a helical coil. Based on the results of simulation of the standard gas cooler design with a flat baffle used in Shell gasification-based combined cycle unit, it is concluded that the particle impact angle is the main factor determining the erosion maximum. To reduce erosion, it is necessary to install a structural element instead of the flat baffle to align the flow path of ash particles at the inlet to the gas cooler. The results of simulation for various baffle shapes show that a hemispherical baffle is optimal. The use of a hemispherical baffle plate made it possible to align the ash particle flow path at the inlet to the gas cooler channels and reduce the maximum level of erosion by a factor of almost 4 compared to the standard geometry of the baffle plate.

Austempered ductile irons (ADIs) are used in applications commonly exposed to severe contact conditions, and as a consequence wear damage frequently followed by failure of components. Hence, wear resistance of the material governs the final life time of a component. In the present work, the sliding wear resistance of two ausferritic spheroidal graphite ductile irons ADI1 and ADI2 used commonly in mining and construction equipment was investigated. ADI1 and ADI2 were heat treated to a similar strength, the volume fraction of the carbon-rich austenite in ADI1 and ADI2 was around 30% and 16%, respectively, and they both contained 10 – 13% nodular graphite. The wear tests were performed using a slider-on-flat-surface (SOFS) tribometer. Case-hardened steel plates made of a high strength steel, 22NiCrMo12–F, were used as the counterface. The wear tests were conducted under lubricated sliding contact at normal loads of 50, 100, 200 and 300 N, and at each load level sliding at 100, 200 and 300 m. The friction force between contacting surfaces was continuously monitored during sliding. The lubrication used in the present investigation was a mineral-oil-based paste commonly used in applications where high frictional heating is generated. Wear mechanisms of the tested specimens were investigated by means of optical and scanning electron microscopy and X-ray diffraction, and the wear damage was quantified using a 3D-profile optical interferometer. The main wear mechanisms, severe plastic deformation and surface delamination, were discussed concerning test conditions and material properties. The ADI1 grade with the higher volume of carbon-rich austenite displayed better resistance to sliding wear at high normal loads. The higher normal loads promoted larger deformation at and beneath the contact surface and initiated austenite transformation into hard martensite. Thus, it was concluded that the increase of wear resistance in ADI1 was due to the formation of marteniste. On the other hand, the ADI2 grade with higher silicon content showed lower wear resistance at high normal loads. This was associated with cracking of the proeutectoid ferrite presented in ADI2.

Iron-based superalloys are alloys produced for use in corrosive environments as an alternative to high-cost nickel-based superalloys. However, their average strength and hardness, attributed to their austenitic structures, limit their use in tribological applications. In an attempt to counter these drawbacks, boriding was applied to an iron-based A286 superalloy having an initial surface hardness of 320 HV. Boriding kinetics, some mechanical properties, and tribo-wear (ambient air and 3.5 NaCl environment) behaviors of the formed boride layers were investigated. Multicomponent boride layers (consist of FeB, Fe2B, CrB, NiB, Ni4B3) were formed on the surface of the alloy, with hardness and thickness values of 1498-1961 HV and 20-130 mu m, respectively, depending on the boriding temperature and the treatment time. The integral diffusion model was adopted to deal with the kinetics of monoboride and hemiboride layers formed on the surface. The boron activation energies of FeB, Fe2B, and DZ layer were estimated as equal to 175.86, 198.7, and 205.73 kJ mol- 1, respectively. As a result of increased surface hardness, all of the borided samples displayed reduced friction coefficients and higher wear resistance compared to the untreated alloy, in both ambient air and 3.5% NaCl. However, the increase in wear resistance was not proportional to the increase in hardness; while the best wear resistance was obtained in samples borided at 850-950 degrees C for 6 h, the lowest wear resistance was obtained in samples borided for 4-6 h at 1050 degrees C. This situation was caused by the Kirkendall effect and residual stresses in the structure of alloying elements with different diffusion rates due to the high-temperature effect of the boriding process.

Electrolytic Plasma Technology has been used to improve the surface properties of AISI-316L Steel. Electrolytes were selected from water-soluble inorganic salts containing interstitial elements such as N and C. High energy cathodic plasma was created by applying from 300V to 600V at the electrolyte/316L interface. N and C elements ionized in high energy plasma diffused to 316L surface. Diffusion time was between 5 seconds and 30 minutes. As a result, it was observed that the surfaces consist of phases containing N, C and O, and the diffusion distance and hardness increased depending on the increasing time. Using H2N-CO-NH2 electrolyte, magnetite in the chemical form of Fe3O4 and non-cytochiometric ironnitride and chromiumnitride were formed on the surface. The hardness increased from 187 HV to 536 HV. Using NH4NO3 electrolyte, the highest hardness increased up to 550 HV. As a result of XRD analysis, thin film magnetite in the chemical form of Fe3O4 and non-cytochiometric ironnitride (FeN0.076), chromiumnitride phases were formed on the surface. There is diffusion of oxygen and nitrogen elements on the surface, and the nitrogen concentration has reached 1% by weight. After electrolytic plasma diffusion process, wear loss decreased significantly. Wear resistance increased up to 6 times after plasma diffusion., AISI 316L Çeliğinin yüzey özelliklerinin iyileştirilmesi için Elektrolitik Plazma Teknolojisi kullanılmıştır. Elektrolitler suda çözünebilen N (azot) ve C (karbon) gibi ara-yer elementi içeren inorganik tuzlardan seçilmiştir. Elektrolit/316 L ara yüzeyinde 300 V ve 600 V arağındaki gerilimler uygulanarak yüksek enerjili katodik plazma oluşturulmuştur. Yüksek enerjili plazma içinde iyonize olan N ve C elementleri 316 L yüzeyine difüze olmuştur. Elektrolitik Plazma difüzyon süresi katodik olarak 5 saniye ile 30 dakika arasında farklı sürelerde uygulanmıştır. İşlemler sonucunda katot yüzeyinin N, C ve O içeren fazlardan oluştuğu, artan süreye bağlı olarak difüzyon derinliğinin ve ara-yer elementi ile doplanan yüzeyin sertliğinin arttığı gözlenmiştir. H2N-CO-NH2 elektrolit ile yapılan deneylerde, yüzeyde Fe3O4 kimyasal formunda magnetit yapıda demiroksit ve sitokiometrik olmayan demir nitrür ve krom nitrür gibi fazlar oluşmuştur. Sertlik değeri 187 HV den 536 HV ye yükselmiştir. NH4NO3 elektrolit ile yapılan deneylerde, en yüksek sertlik 550 HV değerine kadar yükselmiştir. XRD analizleri neticesinde yüzeyde Fe3O4 kimyasal formunda ince film magnetit ve sitokiometrik olmayan demir nitrür (FeN0,076), krom nitrür fazları oluşmuştur. Yüzeyde oksijen ve azot elementlerinin difüzyonu söz konusu olup, azot konsantrasyonu ağırlıkça %1 seviyesine ulaşmıştır. Elektrolitik plazma difüzyon işlemi sonrası aşınma kaybı önemli ölçüde azalmıştır Difüzyon sonrası aşınma dayanımı 6 kata kadar artış göstermiştir.

In this study, Ni-based Inconel 718 coatings were additively manufactured on the surface of AISI H13 work tool steel by electro-spark deposition (ESD). Some of the electro-spark deposited samples were boronized at 1000 ? for 5 h to evaluate the effects of boronizing on microstructure, high-temperature wear, and corrosion resistance. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), 2D pro-filometry, wear and electrochemical corrosion testing was used to characterize the surfaces, microstructures, microhardness, some mechanical properties, high-temperature wear, and corrosion resistance of the applied coatings. Wear tests were performed at room temperature and 650 ?, and corrosion tests were performed in 3.5% NaCl at room temperature, considering the applications of AISI H13 and Inconel 718 alloys. The characterization studies showed evidence of microcracking and oxidation in the as-deposited Inconel 178 coatings. In the boronized Inconel 718 coatings, the oxides and microcracks were slightly reduced. The hardness of the boronized Inconel 718 coating was increased to about four times the hardness of the as-deposited Inconel 718 coating, and this significantly improved its wear resistance. The highest wear resistance was achieved with the boronized coating, while the best corrosion resistance was obtained with the as-deposited coating. The improvements in wear resistance provided by boronizing have the potential for expanding the applications of Inconel 718 coatings in machine components.

WOS: 000520134000010, Remelted NiCrBSi coatings were examined using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction analysis, microhardness and wear testing. After wear tests, the surfaces of the worn samples were examined by 3D profilometry and scanning electron microscopy to investigate the effects of load and temperature on the coefficient of friction and wear resistance. In all the wear experiments, there was a momentary increase in the wear volume and a momentary decrease in the average coefficient of friction values at the elevated test temperatures. This behavior was caused by the stable oxide layer formed on the surface as a consequence of the elevated test temperature. Three dominant wear mechanisms were observed with the NiCrBSi coatings: delamination at room temperature, spalling and adhesion at 250 degrees C, and oxidation at 450 degrees C, whereas in the uncoated samples there was delamination at room temperature, and micro-cracking and oxidation, both at 250 degrees C and 450 degrees C. Remelted NiCrBSi coatings provided better wear resistance and lower coefficient of friction than uncoated STKM-13A steel, especially at higher temperatures.

Variety thermal spray coatings are used to improve wear performance and life span of part in many industrial applications. The solid particle erosive wear mechanisms of the lamellar structured thermal spraying coatings are not still clearly understood. In this study, the wear behavior of different oxide based coatings produced using the flexicord flame spray gun developed in recent years has been investigated on many aspects. The wear rates of flame spray coatings in different composition (alumina, chromia, spinel, zirconate) and thicknesses were compared. In order to determine the effect of heat treatment on the wear performance, heat treatment was performed at 700?C for 60 h and the wear rate of the coatings were measured. As a result, coating quality, thickness and composition have been found to play an important role in erosive wear behavior. It has been observed that the wear rates vary depending on the different angle of impact. Discontinuities in the coating structure, splat thickness and porosity seem to affect the wear resistance of the coating. As a result of the work, it is understood that oxide based flame spray coatings increase the wear resistance of the metallic part. Among these coatings, the best wear performance has been demonstrated by chromium oxide coatings. © 2019 Polish Academy of Sciences. All rights reserved.

The present study aims to examine the effects of operational parameters on the surface topography and wear mechanisms of monolithic and conventional yttria-stabilized zirconia (Y-TZP) ceramics in the micro blasting process, performed under various acceleration pressures (1.5–3 bar), particle impact angles (30°–90°), and erodent particle sizes (50–460 ?m). Three-dimensional (3D) surface topography, surface roughness, and surface morphology of micro-blasted specimens were analyzed by using non-contact optical profilometry and SEM-EDS. The micro blasting characteristics of both Y-TZP were similar that increased blasting pressure and erodent particle size increased surface roughness. Erosion rate increased with increasing blasting pressure, whereas it decreased with increasing erodent particle size. Particle size was the most effective parameter on changing surface topography, while the particle impact angle had no distinct effect on the erosion rate, surface roughness, and surface topography of Y-TZP ceramics. SEM-EDS analyses showed that the primary wear mechanism during micro blasting was micro-cutting with a substantial amount of embedded particles on the material's surface. © 2020 The Authors. Engineering Reports published by John Wiley & Sons, Ltd. information Kocaeli Üniversitesi, Research Projects Coordination Unit / 2015/084 HDThis research was funded by Kocaeli Üniversitesi Scientific Research Projects Coordination Unit grant number 2015/084 HD. The authors thank Research Assistant Dr. Fatih Erdem Baştan and Prof. Dr. Fatih Üstel for their support on SEM studies.

The grain refining effect of Zirconium (Zr) is known, nevertheless the effect of Zr amount and its effect on solidification and wear behavior of modified Mg-Zn alloys has not been adequately studied. Mg-4Zn-(x)Zr alloys alloyed with the addition of 0.5 wt.% to 4 wt.% Zr element are melted and poured into two different casting molds and thermal analyzes were performed. Casting microstructure, solidification behavior, phase transformations, grain size, thermal analysis curves and wear properties were examined. The microstructure was modified by the addition of Zr and the grain size was reduced for both graphite and ceramic mold materials. Maximum tensile strength was obtained by adding 1% Zr (170 MPa) and 4Zr (105-110 HRB) using graphite mold, respectively. The maximum room temperature tensile strength was achieved on the Mg-4Zn-1Zr alloy the elongation was 4.9 percent and the tensile strength was 138 MPa. The max hot tensile value was achieved on the 2 wt% Zr added alloys. The wear rate of Mg-4Zn alloy decreased with increasing Zr element up to 2 wt% Zr. Addition of more than 2% by weight of Zr caused an increase in microporosity in the microstructure. Due to the microporosity caused by the Zr addition, the wear rate was slightly reduced.

In situ TiC-NiCr cermet was manufactured through the selective laser melting (SLM) of an elemental powder mixture prepared using high energy milling for 15 hours. Effects of the applied laser energy densities (138.7, 218.9, 346.7, 378.2 and 416 J.mm-3) on the microstructure, densification, hardness and wear properties of the samples were investigated. Microstructural evaluation of the SLM processed samples using scanning electron microscopy showed that energy densities of lower than 346.7 J.mm-3 result in a relatively non-uniform distribution of TiC and more defects in the cermets. It was also found that by increasing the energy density to 416 J.mm-3; densification is affected due to increased defects. Vickers microhardness test was used for hardness measurement, which showed the highest average hardness value of 1369.5 HV1 at a laser energy density of 378.2 J.mm-3. However, hardness decreased at energy densities of higher than 378.2 J.mm-3. Pin-on-disk dry sliding wear tests were conducted at room (for SLM processed samples) and elevated temperatures (for the specimen manufactured at 378.2 J.mm-3 energy density). The results showed that increasing the input energy density causes a slight improvement in wear resistance at room temperature. At elevated temperatures, the wear rate showed fluctuations, and the lowest wear rate and friction coefficient were achieved at 600 °C.

Nickel-based superalloy Nimonic 80A was pack-borided in a solid medium at temperatures of 850 degrees C and 950 degrees C for 2 h and 4 h using silicon-free boriding powders. To investigate the effects of the boriding treatments on mechanical properties (hardness, modulus of elasticity, fracture toughness) and high temperature oxidation resistance, the layers grown on the surfaces were characterized using optical and scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry, and evaluated using microhardness, nanoindentation, wear and oxidation tests. Wear tests were performed on untreated and borided Nimonic 80A alloys using a ball-on-disc tribometer at room temperature and at 500 degrees C under dry sliding conditions. Oxidation tests were carried out in air at 1000 degrees C for 5 h, 25 h and 75 h. Characterization studies revealed a smooth, 22 to 86 mu m thick crack-free boride layer consisting mainly of Ni2B and minor quantities of CrB, Cr2B and Cr5B3 in the borided samples. The hardness and elastic modulus of the boride layer was measured as 15.57-18.95 GPa and 142-217 GPa, respectively. Increasing the boriding temperature and time increased the concentrations of chromium in the boride layer. The hardness and elastic modulus of the boride layer increased with chromium content while its fracture toughness decreased. The boriding treatments improved the dry sliding wear resistance. Increasing boriding time and temperature generally led to a higher wear resistance values. However, the treatments had no significant effect on oxidation resistance. The results of this study show that boriding can significantly improve the wear resistance of Nimonic 80A without compromising its oxidation resistance.

Coatings used in tribological applications often exhibit high hardness and stiffness to achieve high wear resistance. One coating characterization method frequently used is nanoindentation which allows the determination of indentation hardness and indentation modulus among other material properties. The indentation modulus describes the elastic surface behavior during indentation and is, among hardness, a direct indicator for wear resistance. To obtain the true indentation modulus of a coating, it must be measured with varying loads and then extrapolated to zero load. Current recommendation of the standard ISO 14577-4:2016 is a linear extrapolation which fits poorly for nonlinear curves. Such nonlinear curves are commonly found for high hardness mismatches between coating and substrate, for example, superhard tetrahedral amorphous carbon coatings (ta-C) on a steel substrate. In this study, we present a new empirical fit model, henceforth named sigmoid. This fit model is compared to several existing fit models described in the literature using a large number of nanoindentation measurements on ta-C coatings with wide ranges of indentation modulus and coating thickness. This is done by employing a user-independent and model agnostic fitting methodology. It is shown that the sigmoid model outperforms all other models in the combination of goodness of fit and stability of fit. Furthermore, we demonstrate that the sigmoid model's fit parameter directly correlates with coating thickness and thus allows for a new approach of determining ta-C coating thickness from nanoindentation.

High-entropy alloys (HEAs) with face-centered cubic (FCC) structures exhibit high toughness and corrosion resistance, but their average strengths and relatively low wear resistance can limit their engineering ap-plications. In this study, FCC Al0.07Co1.26Cr1.80Fe1.42Mn1.35Ni1.10 HEAs were boronized for 4 h at temperatures of 900, 950, and 1000 degrees C to form hard, protective metal borides on their surfaces. The microstructural characteristics of the borides formed were examined using X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The mechanical properties of the boride layers were studied by nanoindentation measurements, and the tribological performances of the layers were evaluated by ball-on -disk type wear tests in air, 3.5% NaCl and 5% H2SO4. Irrespective of the boronizing temperature, (Fe0.4Mn0.6) B, (Cr0.4Mn0.6)B, (CoFe)B2 and Cr2Ni3B6 phases were detected in the surfaces of the boronized samples. The surface hardnesses of the boronized samples reached nearly ten times the hardness of the as-cast HEA. The borides were effective in reducing friction as well as wear. Increasing the boronizing temperature increased the thicknesses of the coatings and further improved wear characteristics. Wear rates in 5% H2SO4 were generally higher than the wear rates in 3.5% NaCl, but the highest wear rates were observed in air. (c) 2021 Elsevier B.V. All rights reserved.

During metal cutting, high temperatures of several hundred-degree Celsius occur locally at the cutting edge, which greatly impacts tool wear and life. Not only the cutting parameters, but also the tool material&rsquo, s properties influence the arising cutting temperature which in turn alters the mechanical properties of the tool. In this study, the hardness and thermal conductivity of cemented tungsten carbides were investigated in the range between room temperature and 1000 &deg, C. The occurring temperatures close to the cutting edge were measured with two color pyrometry. The interactions between cemented carbide tool properties and cutting process parameters, including cutting edge rounding, are discussed. The results show that cemented carbides with higher thermal conductivities lead to lower temperatures during cutting. As a result, the effective hardness at the cutting edge can be strongly influenced by the thermal conductivity. The differences in hardness measured at room temperature can be equalized or evened out depending on the combination of hardness and thermal conductivity. This in turn has a direct influence on tool wear. Wear is also influenced by the softening of the workpiece, so that higher cutting temperatures can lead to less wear despite the same effective hardness.

Ti6Al4V alloy is the most widely used titanium alloy due to its attractive properties such as heat resistance, strength, plasticity, toughness, formability, weld-ability, corrosion resistance and biocompatibility. However, the main problem with titanium and its alloys is that they have poor tribological performance. Boriding seems to be the effective way to improve the tribological performance of titanium alloys. Titanium borides have an attractive combination of low density, high hardness, excellent wear, and corrosion resistance. In this study, Ti6Al4V alloy was borided in a solid media at 1100°C for 20 h. The microhardness profile was studied by a Vickers indenter. The hardness value of surface increases from 330 HV to 2789 HV. Wear experiments were performed in Ringer's solution that simulates human body environment. It was observed that boriding process improved tribological performance of Ti6Al4V alloy under all test conditions. © 2018 Polish Academy of Sciences Institute of Physics. All rights reserved.

Graphene possesses high fracture toughness and excellent lubrication properties, which can be exploited to enhance tribological performance of coating systems utilized to combat wear. In this work, suspension plasma spray (SPS) process was employed to deposit a composite, graphene nano-platelets (GNP) incorporated alumina coating. For comparison, monolithic alumina was also deposited utilizing identical spray conditions. The as-deposited coatings were characterized in detail for their microstructure, porosity content, hardness, fracture toughness and phase composition. Raman analysis of the as-deposited composite coating confirmed retention of GNP. The composite coating also showed good microstructural integrity, comparable porosity, higher fracture toughness and similar alumina phase composition as the monolithic alumina coating. The as-deposited coatings were subjected to dry sliding wear tests. The GNP incorporated composite coating showed lower CoF and lower specific wear rate than the pure alumina coating. Additionally, the counter surface also showed a lower wear rate in case of the composite coating. Post-wear analysis performed by SEM/EDS showed differences in the coating wear track and in the ball wear track of monolithic and composite coatings. Furthermore, Raman analysis in the wear track of composite coating confirmed the presence of GNP. The micro-indentation and wear test results indicate that the presence of GNP in the composite coating aided in improving fracture toughness, lowering CoF and specific wear rate compared to the monolithic coating. Results from this work demonstrated retention of GNP in an SPS processed coating, which can be further exploited to design superior wear-resistant coatings. The authors gratefully acknowledge financial support received from the national Strategic Innovation Programme for graphene, SIO Grafen, supporting the industrial graphene development in Sweden. The programme is supported by the Swedish government agencies Vinnova (Sweden’s Innovation Agency), the Swedish Energy Agency and the Swedish Research Council Formas. The project grant nr. is Dnr 2018-03315. We also thank Mr. Sven Forsberg, 2DFab AB, Sweden, for providing the water-based GNP suspension.