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Abrasive wear at high temperature (HT) applications is a serious issue in industry, limiting the lifetime of core components, e.g. in steel- or cement production. In literature abrasive wear is commonly linked to material's hardness, but it is known that microstructure and temperature show also major influence. Current studies also found wear protecting effects by the in-situ formation of mechanically mixed layers (MML) with the abrasive, which can be especially beneficial at HT. To investigate the temperature and load influence of this MML formation at high-stress abrasive conditions a modified ASTM G65 test, allowing for temperatures up to 700 °C, was utilised. Two metal matrix composite (MMC) materials prone to MML formation were chosen: a Ni-based and Fe-based cast alloy with carbide content of ~15%. Thereby the MMC matrix influence on MML formation was studied. Load was varied from 10 to 45 and 80 N, and temperature from room temperature to 500 °C and 700 °C. Abrasive is collected during tests in order to determine the severity of the contact during the wear process. Post-test analysis investigate the MML coverage and depth in order to estimate the wear protecting effect. Further micro-hardness investigations and nano-scratch experiments identified fundamental wear mechanisms and load bearing capacity of the hard phase network. It was found that increasing load leads to higher severity of the contact (more abrasive breakage). MML coverage was strongly dependent on load and temperature at the Fe-based material. Despite a pronounced drop of the hardness at 500 °C this material features efficient wear protection by MML formation at HT. On the other hand the Ni-based MMC shows minor temperature and load influence on MML formation, which can be put down to its relative temperature stable fcc matrix. Wear rates of the Ni-based MMC are superior to the Fe-based material at highest testing temperature. Strain hardening and dynamic recrystallisation were found to be beneficial especially at 500 °C for the Ni-based MMC. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, TiC–NiMo composites were remilled to particle size of 250–315μm and used as reinforcements for NiCrBSi alloy by plasma transferred arc hardfacing process. The manufactured hardfacing alloy was characterised in terms of microstructure, mechanical properties and abrasive wear resistance. Deposition results indicate good quality thick coating with uniform distribution of hard cermet (TiC–NiMo) particles in the matrix, minimum level of hard particle dissolution and low porosity of the hardfacing. Cermet particles remain in initial form and consist of agglomerates (TiC and (Ti,Mo)C grains) embedded into Ni-based matrix. The mechanical properties of the TiC and (Ti,Mo)C phases measured by nanoindentation are very similar exhibiting a narrow distribution. The nano-scratching test reveals excellent bonding between the matrix and cermets in the hardfacing. No crack propagation was found in the interface matrix/hard phase region. The abrasive wear results ensure the promising features of TiC–NiMo reinforcements for Ni-based alloys. Produced coatings showed excellent performance under high-stress abrasion with wear values lower than for industrially used WC/W2C reinforced coatings. [Copyright &y& Elsevier]

Abstract: Wear caused by abrasion is the predominant factor in mining industry. Abrasive wear is a rapid and severe process due to the contact between abrasives and solid material surfaces. This type of wear is usually classified into two categories: (i) 2-body abrasive wear and (ii) 3-body abrasive wear according to the type of contact that occurs between the abrasives and the material. The tribological system formed in mining environment embraces both abrasive wear categories. The focus of this paper is to bring in detailed focus the 2-body and 3-body wear behaviour based on correlations which point out some physical and mechanical rock properties having a significant influence. The study was based on three different rock types wearing a typical martensitic steel 42CrMo4 (DIN 1.7225) under 2-body conditions using a Cycling Impact Abrasion Test (CIAT) and 3-body conditions using a Slurry Steel Wheel Abrasion Test (SSWAT). Results showed that tested rocks perform totally different when the testing conditions are changed. Furthermore, the specific wear energy under 3-body conditions was calculated in order to gain understanding regarding energy needed to produce wear. [Copyright &y& Elsevier]

Abstract: Within this work, the effect of carbide degradation in a WC/W2C reinforced Ni-based hardfacing was assessed under abrasive and combined impact/abrasive conditions. In view of the above, a WC/W2C reinforced Ni-based hardfacing was deposited by plasma transferred arc (PTA) welding using different welding currents. Microstructure was characterised by quantitative metallography to determine specific structural parameters: mean carbide diameter and carbide area fraction. Scanning electron microscopy (SEM, EDS) and X-ray diffraction (XRD) were also used to characterise carbide dissolution mechanism. Tribological behaviour was determined with a 3-body abrasion test according to ASTM G65 and with a cyclic impact/abrasion test (CIAT). Results showed significant carbide degradation with increasing welding current, resulting in a significant reduced primary carbide content and carbide diameter. Reduced carbide content indicated a significantly wear rate increase under pure 3-body abrasion conditions. Specific wear energy was determined under pure abrasive condition and showed significant dependence on the primary carbide content. However, wear rates under combined impact/abrasion were at constant level due to the reduction of the brittle primary carbide content. [Copyright &y& Elsevier]

Abstract: Fe-based hardfacing alloys are widely used to protect machinery equipment exposed to different loading situations where abrasives play a dominant role in restricting lifetime of tools. Wear at elevated temperatures is superposed by the effect of oxidation of the wearing surface. In view of the above, two hardfacing alloys based on Fe-Cr-C incorporating Nb, Mo and B to ensure improved performances at elevated temperature were deposited onto mild steel under optimised gas metal arc welding (GMAW) condition. 2-body erosive wear behaviour was evaluated from room temperature up to 650°C under 30° and 90° impact angle. For 3-body impact/abrasion conditions tests were done with a specially designed cyclic impact abrasion tester (CIAT) at room temperature and 600°C. The wear behaviour of the hardfacings was compared with austenitic stainless steel. Results indicate that 2-body erosive wear rate of the hardfacing increases with test temperature and with increase in impact angle, whereas wear behaviour of the austenitic stainless steel is non-sensitive to the testing temperature at normal impact. In 3-body impact abrasion testing similar behaviour can be seen; cyclic tests in CIAT at enhanced temperatures result in breaking of coarse carbides, whereas wear mechanisms of the austenitic steel result in massive abrasion and formation of a mechanically mixed layer (MML). [Copyright &y& Elsevier]

Abstract: Metal matrix composites (MMCs) are used to increase lifetime of parts of machines in environments where they undergo severe conditions, for instance abrasive wear or impact. When a metal matrix composite is manufactured, reactions between matrix and carbides take place and a reaction zone between matrix and carbides, the interface, is formed. It is shown in the literature, that the interface has an influence on the mechanical properties of MMC. Therefore, it is important to understand, how the interface develops, whose influences on the development exist and how the interface affects the mechanical properties of the MMC. Also the composition of the interface needs to be observed. The aim of this work is to give a qualitative description of the mechanical behaviour of carbide/matrix interface in relation with the interfacial reactivity at this interface. Furthermore, a selected MMC hardfacing alloy based on 60wt.% WC/W2C and Ni matrix was manufactured by plasma transferred arc (PTA) process at variation of welding current to estimate the composition of the interface and mechanical properties of the whole composite material. A special designed single impact test (SIT) enabled investigation of impact wear behaviour at high single loads. The evaluation of interface properties was supported by optical microscopy, SEM, XRD investigations and hardness tests. In the literature damage mechanisms under impact are pointed out to decohesion and cracking of hard phases based on interface properties. In the SIT investigations of MMC hardfacing alloy based on 60wt.% WC/W2C and Ni matrix it can be shown that welding current is controlling the formation of the carbide/matrix interface and furthermore the dominating wear mechanisms under high single loads in SIT. [Copyright &y& Elsevier]

Abstract: Transition metal dichalcogenides films are well known for their self-lubricating properties. These films are having lamellar structure – whereby weak “van der Walls” forces act between the layers – commonly believed to be responsible for their excellent self-lubricating properties. Among these films, diselenoids have shown less sensitivity to humidity and they are more oxidation resistant in humid environment than sulphides. In view of the above, a comprehensive work is undertaken to study friction properties in macro- and micro-scale. The present work deals with preliminary study and critical examination of friction due to scratching of WSe2 film. WSe2 film is deposited using sputtering technique. The composition of the film is determined by means of energy dispersive spectrometry (EDS) and X-ray photoelectron spectrometry (XPS). The micro-structural features, topography and mechanical properties of the film are evaluated using transmission electron microscopy (TEM), atomic force microscopy (AFM) and nano-indenter. The film is scratched at different constant loads and also with increasing load using a scratch tester with a spherical indenter in macro-loading regime. A 3D confocal microscope is used to study the scratched portion. In micro-loading regime the film is scratched with an angular indenter. The results show that even though self-lubricating effect comes into play in macro-loading regime, this effect cannot be seen in micro-loading regime. Further coefficient of friction in different loading regime is independent of applied load. [Copyright &y& Elsevier]

Abstract: Many engineering components are subjected to erosive wear at elevated temperature. As erosive wear at elevated temperature is governed by the synergistic effect of erosive wear and oxidation, it is possible to modify surfaces of the components in order to achieve improved performances. In view of the above, two different types of hardfacing alloys of Fe–Cr–C were designed incorporating Nb, Mo and B to ensure improved performances at elevated temperature. In order to achieve the above objective, mild steel was hardfaced with these alloys under optimised gas metal arc welding (GMAW) condition. The microstructures of the hardfaced coating was characterised with the help of optical microscopy (OM) and scanning electron microscopy (SEM). The mechanical properties of these coatings were obtained by means of micro indenter. Erosive wear of these coatings was evaluated for four different temperatures, for two different impact angles and at one impact velocity. The morphologies and the transverse sections of the worn surfaces are examined with SEM. The erosive wear of these coatings were compared with conventional M2 tool steel. Results indicate that erosion rate of these coatings increases with increase of test temperature and impact angles. Among various coatings, Fe–Cr–C coating containing higher amount of Nb, Mo and B exhibits best erosion resistance particularly at elevated temperature. [Copyright &y& Elsevier]

Abstract: Iron-based hardfacing alloys are widely used to protect machinery equipment exposed either to pure abrasion or to a combination of abrasion and impact. The specific wear behaviour of a welding alloy under these conditions depends on its chemical composition, the microstructure obtained after welding and finally the welding technology used to apply them respectively the parameter settings which strongly influence, for example, dilution with the base material or formation of metallurgically precipitated hard phases. The main objective of this study was to evaluate the wear behaviour for pure abrasion and for combined wear of iron-based alloys which are typically applied by gas metal arc welding (GMAW). A new complex Fe–Cr–W–Mo–Nb alloy with high boron content was set into comparison with lower alloyed materials on basis Fe–Cr–B–C, a synthetic multiphase alloy on iron base with around 50wt.% tungsten carbides and a crack free martensitic Fe–Cr–C alloy containing finely precipitated Niobium carbides. Besides these a conventional hypereutectic Fe–Cr–Nb–C alloy was integrated in the program serving as standard which is already well described in literature. In order to simulate real field conditions on a lab scale, tests were performed with a standard ASTM G65 dry-sand rubber-wheel tester (3-body abrasion). A specially designed impeller-tumbler apparatus enabled investigation of impact abrasion wear tests (combined impact and abrasion wear). The evaluation of wear behaviour was supported by micro- and macrostructural investigations and by hardness tests. [Copyright &y& Elsevier]

Abstract: Wear parts which are exposed to severe abrasive conditions must withstand high wear demands. Abrasive loading superposed with impact due to abrasive particles are a dominating wear mechanism restricting lifetime in many different industries, for example mining and farming. In practical application, different welding technologies such as plasma transfer arc (PTA), metal active gas (MAG) and laser are used to form wear resistant materials. The aim of this study is to evaluate the influence of welding parameters on the microstructure and wear behaviour of these wear resistant materials using MAG welding technology. To simulate real field conditions on a lab-scale, tests were performed with a standard ASTM G65 dry-sand rubber-wheel tester (3-body abrasion). In order to investigate impact abrasion, a special impeller-tumbler apparatus was designed and used for wear tests (combined impact and abrasion wear). Wear tests were performed on Ni-based alloys containing large amounts of hard phase. Within this work it was shown that welding parameters such as current intensity and number of layers strongly influence dilution with the base material and furthermore the formation of transition zones between welding layers and overlap zones. Concerning wear behaviour it was found that high content of uniformly distributed tungsten carbides in a metallic matrix show the best behaviour under a condition of pure abrasion, whereas under cyclic impact loading (high energy level) massive breaking of the tungsten carbides results in a high wear regime, compared to martensitic materials which perform best. [Copyright &y& Elsevier]

Recently, several new solid lubricants and modern lubrication concepts have been developed to achieve lower friction and wear and thus longer lifetime in severe tribological applications. The aim of this study is to characterize tribo-layers formed during ball-on-disc testing on low-friction, Cl-containing TiN coatings deposited by plasma assisted chemical vapor deposition and to clarify their formation mechanism. Characterization of the transfer layers was done by optical microscopy, optical profilometry, Raman spectroscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy. Differential scanning calorimetry was used to provide information on the chlorine-influenced chemical reactions of the coatings in ambient air. Iron oxide layers of a thickness in the nm-range have been found on low-chlorine containing TiN coatings (<3 at.% Cl) showing friction coefficients of approximately 0.8, whereas on TiN coatings with higher chlorine contents (>3 at.% Cl) rutile layers were preferably formed, resulting in friction coefficients below 0.2. This self-lubrication mechanism can be explained by the in-situ formation of easy-shearable titanium oxides in the contact zone in the presence of humidity and oxygen. [Copyright &y& Elsevier]

Recently, a low-friction effect with friction coefficients of below 0.2 against ball-bearing steel has been reported for chlorine-containing TiN coatings grown by plasma-assisted chemical vapor deposition (PACVD). This low-friction effect has been attributed to the formation of a chlorine-containing lubricant layer on top of the coating in humid air which can be regarded as a self-adaptation process of the coating to the given tribological situation. Within this study we show that in dry sliding ball-on-disc experiments against different counterparts, the response of the coating to the tribological conditions is determined by the hardness of the counterpart material. For the softest ball material used, i.e. austenitic stainless steel, the friction coefficient drops to the low-friction regime after a running-in distance which is more than 35 times longer compared to that of the hardest counterpart material, i.e. alumina. [Copyright &y& Elsevier]

A ball cratering test has been used to investigate the abrasive wear of high speed steels with different volume fraction and size of primary carbides. Three different abrasives, SiC, Al2O3 and ZrO2 were used. Wear mechanisms were investigated by scanning electron microscopy (SEM). A good correlation between the hardness of the abrasives and the abrasive wear coefficient was found. Higher abrasive wear resistance was determined for steels containing coarser primary carbides compared to those without or with smaller carbides. The most pronounced difference in abrasive wear resistance was found for Al2O3 abrasives. This indicates that in ball cratering the abrasive medium has to be chosen properly, i.e. with a hardness adjusted to those of both primary carbides and martensitic matrix, to obtain results suitable to rank high speed steels with respect to abrasion resistance. [Copyright &y& Elsevier]

It has been reported in our earlier paper, that TiN coatings deposited by plasma-assisted chemical vapour deposition (PACVD), showing a low chlorine content are well suited to reduce the friction coefficient against steel to low values of approximately 0.2. The aim of this study was to use the PACVD technique to deposit different TiN coatings with defined chlorine contents and to investigate the tribological properties of these coatings in the temperature range from 25 to 150 °C. Dry sliding experiments were conducted in ambient air and dry nitrogen. The coatings were worn against ball-bearing steel using a ball-on-disc configuration. An optical 3d profiler was used to investigate the geometry of the wear tracks after ball-on-disc testing. Coating characterisation was done using electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). The abrasion resistance of the coatings investigated was evaluated using a small-scale abrasive wear test. Hardness measurements were performed with a nanoindenter. Low friction coefficients of approximately 0.14–0.17 have been obtained during ball-on-disc testing at room temperature in ambient air for coatings containing more than 3 at.% chlorine. The friction coefficient against ball-bearing steel increases to values of approximately 0.7–0.8 at enhanced temperatures. For testing in dry nitrogen atmosphere, the friction coefficient increases to the same range. [Copyright &y& Elsevier]

Titanium nitride (TiN), is still the standard coating for cutting as well as forming applications. The aim of this study is to investigate the tribological behavior of low-friction plasma-assisted chemical vapor deposition (PACVD) TiN coatings with low chlorine content as well as the thermal stability of the low-friction effect. Dry sliding experiments at temperatures ranging from room temperature to 500 °C were conducted on PACVD TiN coatings, deposited onto high speed steel substrates. The coatings were worn against ball-bearing steel and Al2O3 balls using a ball-on-disc configuration. Characterization of the wear tracks was done by scanning electron microscopy, electron-probe microanalysis and an optical 3d profiling system. Extremely low-friction coefficients against ball-bearing steel and Al2O3 balls of 0.14–0.17 have been obtained at room temperature for coatings with chlorine contents between 3.2 and 3.7 at.%. The friction coefficient against Al2O3 increases to values of approximately 0.6–0.8 for temperatures above 70 °C. The lowest coating wear coefficient with 1.93×10−16 m2/N was obtained for Al2O3 balls at room temperature, whereas for temperatures exceeding 200 °C increased abrasion of the coating takes place, resulting in higher wear rates. [Copyright &y& Elsevier]

Hard coatings like TiN are widely used to protect cutting and forming tools against wear and corrosion. The aim of this study was to develop TiN coatings deposited by PACVD (plasma-assisted chemical vapor deposition) with different chlorine contents to optimize their friction and wear properties. Coating structure and chemical composition were characterized using scanning electron microscopy (SEM), wavelength-dispersive electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The tribological properties of the coatings were evaluated using a ball-on-disc tribometer. Hardness measurements with a nanoindenter gave values of 17.9 … 24.8 GPa for TiN according to the chlorine content. Extremely low friction coefficients against ball-bearing steel of 0.17 … 0.22 have been obtained for those TiN coatings showing a chlorine content in the range of 3.2 … 6.3 at.%. For lower chlorine contents, the friction coefficient increases to 0.75. The wear tracks were investigated with an optical profiler where mainly material transfer was found for low chlorine contents whereas for higher chlorine concentrations the dominant wear mechanism was mild abrasion. The addition of low chlorine impurity levels by PACVD allows one to tailor friction and wear properties of TiN coatings. [Copyright &y& Elsevier]

The main purpose of this work is to identify and describe complex wear mechanisms that usually occur in the mining environment. Abrasive conditions can differ a lot, especially in the mining industry. Therefore, the need to study the influence of abrasion conditions on the material wear is crucial in order to improve the lifetime and the cost efficiency of the machinery used in such environments. To study various abrasion mechanisms, a cyclic impact abrasion test was used to simulate two-body impact/abrasion. The tests were performed using two martensitic steels, and three different standard rock types of the mining environment were chosen as abrasives, respectively. The wear was indicated as mass loss by measuring the samples before and after the tests. On the other hand, the particle breakage index, which indicates the potential of a rock to wear, was observed by sieving the abrasives before and after the test. The wear results were correlated with different mechanical rock properties. Wear mechanisms were observed using microscopic investigations. The results indicate that different abrasive rock types have a significant influence on the wear rate of the tested martensitic steels. It was observed that by combining different rocks as abrasives, a simulation of the real field was achieved. [ABSTRACT FROM AUTHOR]

Tribological systems in forming applications often work under severe conditions as high contact pressure, sliding velocities and temperature resulting in different wear phenomena and changes in microstructural and mechanical properties. In this work, the material response of austenitic and martensitic tribo-partners was investigated after severe loading condition in a forming tribometer. Main focus was laid on the understanding of the microstructure modification in near-surface zone on a mesoscopic range and the changes of mechanical properties due to friction energy transformation within the tribomaterials. Tribotests were performed using 1.4301 (304) workpiece and 1.2343 (H11) tool material under constant contact pressure of 390MPa under varying sliding velocity of 0.025m/s and 0.125m/s, respectively. Investigation of near-surface zones was done by optical microscopy and HV0.05 micro-hardness depth profiles combined with detailed High Resolution Scanning Electron Microscopy (HRSEM) analysis and Electron Back Scatter Diffraction (EBSD) measurements in depths from contact surface of 30µm, 70µm, 130µm and 220µm. The results showed that sub-surface zones correspond to refinement partly due to dynamic recrystallization and/or to phase transformation; whereas the final properties depend on the dominating mechanism. New grains and a strong increase of large angle grain boundaries (LAGB) were observed which may increase plasticity and reduce failure by fracture. Finally, for the applied variation of testing conditions, no formation of friction martensite on the tribologically stressed materials was observed. [ABSTRACT FROM AUTHOR]

Abstract: Machinery and equipment used in abrasive environments, such as the mining industry, suffer from severe wear. In order to understand wear and to prolong the life time of the machinery, it is important to understand how materials respond to wear depending on the environmental and tribological conditions imposed. This paper exposes a comparative study between the influence of two abrasive environments (dry and slurry) on hard particle coatings and steels. To study this, the 3-body wear behaviour was evaluated in a dry environment using a continuous abrasion test (CAT) and in a slurry environment using a slurry steel wheel abrasion test (SSWAT) method. Both tests are capable of experimentally modelling the high stress wear at 45N and 216N, using quartz sand as an abrasive. The tests were performed on two types of coatings processed by sintering and hardfacing and martensitic steel was used as a reference. The wear was indicated as volume loss by measuring the samples before and after the tests. Furthermore, the specific wear energy was calculated in order to have a fundamental understanding about the material's response to wear. A correlation between the wear rate and the particle brakeage index (PBI) was done for the dry conditions using different loads, in order to explain the interdependence between the two parameters and the change in the wear mechanism between the two loads. The influence of load on the wear of the materials showed different wear mechanisms on coatings compared to the steel in the same environmental conditions. However, a change in wear mechanism at different load levels was observed, which might be directly dependent on the change of the particle's motion from sliding to rolling combined with the change in their shape and size. The results showed that the need to study the influence of different abrasive conditions on the material wear is crucial in order to improve the lifetime and the cost efficiency of the machinery used in such environments. The hard-particle coatings showed comparatively low wear rates promising a great potential in improving the lifetime of industrial equipments in different environments. [Copyright &y& Elsevier]

Abstract: A tools lifetime absolutely depends on the material properties and lubrication. By a lubricant absence, the direct contact between the materials might cause an increase of friction and wear, which might lead to a tool''s failure. That is why wear prediction and control are important requirements in industry. The wear prediction experiments in this study were performed for an unlubricated (dry) bushing/shaft system of relatively high load and low sliding speed. Two different commercially available tool steels were used for tribological investigations. Normal load and temperature were considered as independent variable in the wear testing. The results showed that the extensive oxidation of metals have a positive factor on wear. When the temperature raises formation of the protective oxide layers consequently change the wear transition to the mild oxidative wear. Based on the classical wear equations and on the chemical oxidation kinetics concepts a wear prediction model was developed and statistically evaluated in the case when metallic contact wear as the predominant wear mechanism was combined with the oxidation of metals. [Copyright &y& Elsevier]

Reinforcing a temperature resistant matrix with carbides (MMC, metal matrix composite) is expected to improve the abrasion resistance at high temperatures. Experiments show that carbides brought in during a plasma transferred arc (PTA) welding process get partly dissolved in the martensitic matrix and secondary carbide structures precipitate. Further analyses with nano-indentation and XRD show that these secondary precipitations strongly influence the properties of the originally homogeneous ductile martensitic matrix. Although hot hardness is increased, wear resistance is diminished due to changed nano-microstructural material properties. [ABSTRACT FROM AUTHOR]

Abstract: Metal matrix composite (MMC) coatings composed of nickel-based matrices and tungsten carbides (WC/W2C) are frequently used to solve problems of reduced life time under severe abrasive and corrosive conditions. The influence of processing conditions on the carbide/matrix interface was studied in the liquid-sintering process with a well defined temperature/time profile. Evaluation of the sintered samples by optical microscopy (OM) showed formation of an interface layer between matrix and carbides. SEM/EDS analysis indicated the formation of mixed Ni- and W-rich carbides on the interface microstructures. XRD measurements revealed the formation of Ni3B. The layer thicknesses were determined quantitatively by OM-image analysis. The hardness profiles across the interface were examined by nanoindentation. Furthermore, scratch tests were performed for the characterisation of carbide bonding in the matrix and evaluation of the influence of the interface layer on the single abrasion behaviour of the MMC samples. Results show that the carbide/matrix bonding and the single abrasion behaviour were dependent on the gradient of the micro-mechanical properties. Increasing processing temperature or time increased the hardness gradient and consequently decreased the bonding between carbide and matrix. Additions of chromium and iron in the matrix powder caused an improvement of the bonding and the abrasion behaviour under 2-body-condition of the MMC samples. [Copyright &y& Elsevier]

Abstract: Hard-particle metal–matrix composites (MMC) are generally used to increase the lifetime of machinery equipment exposed to severe wear conditions. Depending on the manufacturing technology, dissolution reactions of hard phases undergo different temperature/time profiles during processing affecting the microstructure and mechanical properties of the MMCs. Therefore, quantification of the carbide dissolution effects on the microstructure and micro-mechanical properties is the key to success in the development and optimisation of MMCs. Dissolution kinetics of WC/W2C in Ni-based matrices were determined in the liquid-sintering with a well-defined temperature/time profile. Microscopic evaluation of the samples showed two intermediate layers between matrix and carbides. The layer thicknesses were quantitatively determined using image analysis. A kinetics relationship was used for modelling the interface layer growth as a function of processing time, temperature and Cr-addition. Furthermore, the micro-mechanical properties of the intermediate layers were examined using nanoindentation. Based on the chemical composition and the hardness of the intermediate layers, formation of mixed Ni- and W-carbides and/or borides on the interface microstructures was indicated. Results showed that the chemical composition and the micro-mechanical properties were almost constant within all the detected layers in the interface zone between matrix and carbides, indicating that the microstructure gradients were most dependent on the intensity of the MMC processing. [ABSTRACT FROM AUTHOR]

Physical vapor deposited WC based coatings strongly vary in their microstructure ranging from multi-phased columnar-crystalline up to nanocomposite coatings in relation to the usage of reactive or non-reactive carbon sources. Within this study, we investigated in detail the influence of additional carbon implemented into WC based target mmaterials as well as bias potential on the structure-mechanical properties of non-reactively sputtered WC coatings. Providing additional graphitic carbon within WC targets promotes the formation of nanocrystalline morphologies. Increasing bias potentials dominate the transition from a nanocrystalline to a columnar-crystalline morphology obtaining also a mixed state in between. The change in morphology is accompanied by a large modification in mechanical properties with hardness values ranging from 27 to 39 GPa, respectively. In addition, high adatom mobility – caused by bias potentials up to −200 V – predominates the phase formation of crystalline WC coatings changing from face-centered cubic (fcc)-WC x to competing W 2 C based structures. The W—C phase formation is furthermore examined using DFT calculations. • Influence of WC/C target composition on sputter deposited WC x coatings • Different morphologies accessible by varying the bias potential • Large variation of mechanical properties with altered morphology • Increased adatom mobility favors formation of W 2 C phases [ABSTRACT FROM AUTHOR]

Highly loaded wear components in applications such as crushers or sieves suffer from combined impact and abrasive wear, in the worst case exaggerated by high operation temperatures. Hardfacings based on the system FeCrC with high hardphase contents are promising candidates for such applications. Understanding of the influence of precipitated carbides or carbo-borides on the impact-abrasive wear resistance is therefore of high importance to increase the lifetime, decrease downtime as well as maintenance costs. In this study, two different FeCrC-based hardfacings were chosen for investigation, an FeCrC-alloy and a complex alloyed FeCrNbMoBC type. A thorough microstructural analysis was performed via scanning electron microscopy. Here, present hardphases, namely chromium carbides, chromium carbo-borides as well as niobium carbides were found. To evaluate the hardness H and Young's modulus E nanoindentation measurements were performed and the plasticity indicating ratios H/E and H³/E 2 were derived. Scratch tests at elevated temperatures were performed identifying critical loads for carbide displacement and fracture. Those critical loads as well as the plasticity indexing parameters were correlated with the impact-abrasion behaviour of the two hardfacings via high-temperature cyclic impact abrasion tests up to 500 °C. Results showed higher impact-abrasion resistance of the complex-alloyed FeCrC-based hardfacing due to better stability of the carbides as well as optimal ratios H/E and H³/E 2 indicating increased plasticity and thereby better impact resistance. • High-temperature impact-abrasion resistance of FeCrC-based hardfacings. • Influence of Mo, Nb and B on microstructure & micromechanical properties. • Micromechanical evaluations on H/E, H³/E2 of hardphases present. • Effect of phase properties on the scratch-behaviour and phases critical loads. • High impact of phases micromechanical behaviour on impact-abrasive wear found. [ABSTRACT FROM AUTHOR]

The aim of this study was to characterise TiC-Ni and ZrC-Ni cermet reinforced NiCrBSi hardfacings in a 40:60 vol.% ratio respectively and to investigate their respective wear behaviour at temperatures up to 700 °C. Coatings were produced using plasma transferred arc welding; optimised methods and parameters were meant to ensure a uniform distribution of the cermet across the metal matrix composite. High-temperature testing included macro hot-hardness, cyclic impact abrasion, and cyclic abrasion, all featuring temperatures between room temperature and 700 °C. During cyclic abrasion, both TiC-Ni and ZrC-Ni reinforced hardfacing show decreasing wear rate with increasing temperatures. During impact abrasion testing, it was shown that TiC-Ni and ZrC-Ni reinforced hardfacings possess superior wear properties in comparison to conventional WC reinforced ones. The role of TiO 2 oxide, and in the case of ZrC-Ni, the role of a complex mixed carbide phase, M 23 C 6 , played an important role in stabilising the kinetics of oxidative wear at temperatures beyond 500 °C. [ABSTRACT FROM AUTHOR]

Sieves for high temperature (HT) environment are necessary for screening of iron oxide sinter in steel industry. Sinter is produced at temperatures of ~ 1000 °C, crushed and screened for usage as raw material in blast furnaces. To determine the critical cause that leads to sieve cavity widening and subsequent productivity loss of the steel plant, a comprehensive damage analysis was undertaken. Sieves are equipped with plates covered by a hypereutectic hardfacing for wear protection. Cavities are cut by oxygen plasma cutting. Long-term wear investigation was done using replica samples taken from cavities after defined time intervals during the sieve's lifetime. Thereby differences in wear progress due to asymmetric material flow, position and alignment of cavities were studied. Additional temperature measurements were conducted via thermography of the sieve while in operation to identify service temperatures. Furthermore cross-sectional and microscopic analyses were carried out after end-of-life of the sieve to investigate wear mechanisms and microstructural changes. It was found that plasma cutting of the sieve cavities leads to a wide range of cavity widths. Continuous investigation of wear progress showed that the first interval resulted in significant blunting of edges. After this period of running-in, the ongoing wear loss at the edges became less pronounced. Significant wear was found descending up to 1.5 mm in depth along the cavity sidewalls. Furthermore, large break-outs could occur at any time due to cracks in the microstructure and fatigue. Nevertheless, blunting and cavity widening limited the lifetime of the sieve. Wear losses were more distinct on top of the sieve at the beginning of the sinter flow. No significant influence of the angle of the cavity positions in respect to the material flow was found. Cross-sections showed microstructural changes due to the thermal cutting process. Microstructure changed from hard hypereutectic structure to softer hypoeutectic microstructure, which is less wear resistant. [ABSTRACT FROM AUTHOR]

In the early-damage regime of rails subjected to rolling contact fatigue, the material undergoes severe plastic deformation forming a modified sub-surface microstructure. This zone close to the surface determines subsequent fatigue properties of the whole component and can differ considerably from an initial microstructure of the same material. Therefore, a fundamental understanding of early damage phenomena (<4000 cycles) is the focus of this work by comparing exemplary as a rolled standard R260 steel with a surface finished R260 pearlitic steel regarding their response to the rolling stresses by plastic deformation. Thus, electron backscatter diffraction technique based results were used to describe the material modification and set up a model for early-damage response of a pearlitic rail steel. Thereby, increased plastic deformation was found in the decarburized zone already after 100 cycles while the surface finished R260 remains almost undeformed. After 4000 cycles, both specimens have undergone high plastic deformation with work hardening concentrated directly below the surface for the decarburized steel and up to higher depths in the surface finished one. [ABSTRACT FROM AUTHOR]

Corrosion phenomena play an important role in limiting the lifetime of tribological systems. It is well known out of different studies that synergistic effects between mechanical sliding and corrosion often lead to increased volume losses when compared to their individual contributions. The aim of this work is to describe the tribological performance of low-alloyed C-steel under sliding/corrosion conditions at specific oxygen-free environments using CO 2 atmosphere and brine. Low-alloyed C-steel was used as base material and was tribologically loaded in a novel close-to-reality test rig under reciprocating sliding contact against spray Ni-based coating counterpart. Additionally, pure sliding tests were carried out under N 2 atmosphere with distilled water for comparison. Different microscopic methods were applied (e.g., SEM-FIB) for understanding the sliding/corrosion phenomena in addition to quantitative wear measurements by mass loss. The results show a significant influence of the microstructure on the tribological performance under sliding/corrosion conditions, where the formation of corrosion siderite layers (FeCO 3 ) and their tribological properties plays a crucial role. [ABSTRACT FROM AUTHOR]

Predicting the lifetime of a conveyor belt from lab-scale tests has become increasingly important, as the cost for the belt represents up to 70% of the acquisition and maintenance costs of a transport system. In practice, belt selection relies strongly on the well-established ISO 4649 abrasion test, where fixed corundum paper is utilised as the abrasive medium, resulting in 2-body abrasion. In the present article, this is compared to the ASTM G65 test with rolling, round abrasive particles, leading to 3-body abrasion. To evaluate the lab-scale results, they were compared to a conveyor belt that had been used to transport sintered charge for eight years. The comparability and reproducibility of wear patterns encountered on this particular belt was matched with the lab test and then correlated with mechanical properties of the rubber materials. It was found that the ISO 4649 tests, where abrasive wear is dominant, rarely reflect wear patterns and wear mechanisms occurring in real applications. In contrast, the ASTM G65 3-body abrasion test entails fatigue dominated wear, which is found in real applications. The ISO 4649 test results showed a strong dependence on tensile strength and Shore A hardness, while tear strength was the most influential factor for the ASTM G65 test. [ABSTRACT FROM AUTHOR]

Abstract: Tribological research concerning sliding contacts at temperatures of 500–1000°C has received limited attention. Industrial systems operating under high temperatures can be readily found in sheet metal forming processes. The control of friction during the tool–workpiece interaction and minimisation of tool wear are both crucial in maintaining the products quality. The application of solid lubricants can be a possible approach in accomplishing these goals. The objective of this work is to investigate the reliability of combined model and component tests under solid lubricating conditions. The laboratory tests showed that both methodologies provide consistent results in exploring potential of the solid lubricants. [Copyright &y& Elsevier]

Highlights: [•] High temperature gaseous hydrochloric corrosion analysis of different boiler steels. [•] Influence on the corrosion of the presence of oil shale ashes and cyclic removing. [•] Empiric kinetic coherence equation and diagram for corrosion depth versus time. [•] Additional oxidation tests of all materials investigated. [•] Qualitative analysis of the present corrosion mechanisms. [Copyright &y& Elsevier]

Highlights: [•] Point contact sliding produces tensile stresses in the material. [•] Highest stresses are measured transversal to the sliding direction. [•] Crack propagation is correlated with the direction of highest stress longitudinal to the sliding direction. [ABSTRACT FROM AUTHOR]

Highly loaded wear components in manifold applications such as sieves, crushers, etc. suffer from combined impact and abrasive wear. To gain deeper understanding of different ongoing mechanisms, four different Fe-based materials, two martensitic steels Hardox 450 and Hardox 600, and two gas metal arc welded (GMAW) hardfacings - a Fe–Cr–C based hardfacing and a complex-alloyed Fe–Cr–Nb–C–B alloy were investigated with a novel modification of a cyclic impact and abrasion test. This test rig uses quartz sand as abrasive and a plunger simulating industrial sieving applications. Pre- and post-test materials analyses were performed utilising 3D microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), microhardness and nanoindentation tests for a thorough materials analysis and the clarification of the main occurring damaging mechanisms. Results indicate a very beneficial performance of a complex-alloyed Fe–Cr–Nb–C–B alloy due to its fine-dispersed hard phases and their homogenous distribution throughout the material, which does not change much with varying deposition parameters. In comparison, higher wear rates of a hypereutectic Fe–Cr–C alloy are attributed to coarse precipitated Cr-carbides within the microstructure. At martensitic steels, mechanically mixed layer were formed in the impact-abrasion region, which decreases the wear attack to a certain extent. However, massive materials displacement and abrasive wear occurs due to the lack of hard phases and high ductility, which obstruct increased abrasive attack. • Novel test method simulating impact-abrasive wear in sieve applications established. • Martensitic steels, Fe–Cr–Cr- and complex-alloyed Fe–Cr–C–B-based hardfacings tested. • Materials microstructure, toughness and hardness ratios correlated with wear behaviour. • Influence of hardfacing parameter and materials processing not negligible for wear behaviour. • Wear ranking: martensitic steels < Fe–Cr–C hardfacings < complex-alloyed hardfacings. [ABSTRACT FROM AUTHOR]

Certain materials show a tribolayer formation especially at enhanced temperatures in abrasive environment, building a wear protection layer with the abrasive on the surface. Three materials with different microstructures were tested in three-body abrasive and impact/abrasive environments at temperatures up to 700°C to investigate tribolayer formation. Optical and electron microscopical methods were used for wear qualification. Furthermore, hot hardness tests were performed up to 700°C to investigate the influence of hardness drop on tribolayer formation. It was shown that no significant tribolayer formation occurs on grey cast iron, whereas other materials form tribolayers. Generally, tribolayer formation increases with increasing testing temperature, especially for austenitic and ferritic materials. This entails a self-protecting effect and thus superior wear resistance in abrasive environment. [ABSTRACT FROM AUTHOR]

Abstract: Metal matrix composite hardfacings provide various types of heat and wear resistant products. They are widely used in high temperature aggressive environments due to their excellent high temperature corrosion and wear resistance. In this study, Cr3C2–Ni and TiC–NiMo particles were used to reinforce a NiCrBSi matrix in plasma transferred arc welding process. These cermet particle reinforced hardfacings were examined on their oxidation behaviour and high temperature corrosion in different solid salts to optimise the field of application under high temperature conditions. Corrosion behaviour in solid salts is strongly dependent on the corroding anion. Cr3C2–Ni reinforced hardfacings behave better in oxidative and sulphate/phosphate environment, while TiC–NiMo hardfacings show better resistance against chlorine and carbonate ions up to 700°C. Additionally, oxidation is no critical exposure for these types of hardfacings. [Copyright &y& Elsevier]

Abstract: Ceramic metal composite powders are widely used in thermal spray technologies; however, application of such hardphases in cladding systems has not been strongly developed yet. In the present study, two different hardfacings produced by the plasma transferred arc (PTA) process were analysed and compared to reveal differences between NiCrBSi coatings reinforced with standard chromium carbide and chromium-based cermet powders. The coatings were produced from a mixture of hardphases (Cr3C2 or Cr3C2–Ni) and nickel based powder with a ratio of 40/60vol.%. The coatings'' thickness was set to 2–2.5mm on an austenite substrate. Hardfacings were characterised in terms of their microstructures, mechanical properties and impact–abrasion wear resistance at room and elevated temperatures. The manufactured Cr3C2–Ni reinforced hardfacing alloy has shown promising microstructural features with a low level of carbide dissolution and high temperature wear performance. [Copyright &y& Elsevier]

Transition metal nitride based hard coatings are widely applied in metal cutting, however, there are still drawbacks in metal forming processes limiting their implementation. The aim of this study is thus to discuss deposition processes suitable for coating of the often large and three-dimensional molds and dies used in metal forming. Furthermore, results obtained using different hard coatings in industrial applications for several case studies like aluminum pressure die-casting, plastics injection molding and sheet metal forming are presented and discussed. For best coating performance, a careful optimization of both substrate pre-treatment and coating deposition is necessary. The plasma-assisted chemical vapor deposition (PACVD) technique shows advantages for these applications because of the high flexibility in pre-treatment using chemical etching and plasma-nitriding, because of its ability to coat large complexly shaped tools and because of the possibility of deposition of low-chlorine containing low-friction coatings. Typical factors for the increase in lifetime in aluminum pressure die-casting are between 2 and 4, in plastics injection molding more than 10 and in deep drawing of 13 with respect to uncoated tools. [Copyright &y& Elsevier]

The aim of this research work was to investigate the influence of surface roughness and presence of phosphate coating on the galling resistance of medium-grade carbon steel. Galling resistance was evaluated in terms of coefficient of friction level and stability, critical loads for galling initiation, surface quality, and volume of adhered material, analysed by load-scanner test rig as a function of load. Results of the investigation show that best galling resistance is not provided by very smooth surfaces but with semi rough ones (Ra = 0.21–0.28 μm), obtained by fine turning. Furthermore, by phosphating and formation of low-friction Mn–P coating superior galling resistance for medium-grade carbon steel is provided, at the same time diminishing effect of surface roughness. • Effect of surface roughness and presence of phosphate coating on galling resistance of carbon steel has been investigated. • Very smooth surfaces do not provide the best galling resistance of the medium grade carbon steel. • The best performance is obtained by semi rough machined surfaces. • Machining grooves lead to contact area redistribution and trapping of wear particles. • Phosphating successfully protects medium grade carbon steel against galling and diminishes roughness effect. [ABSTRACT FROM AUTHOR]