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Wear of materials at high temperatures (HT) is a very challenging issue, implying many different mechanisms. Individual wear phenomena occurring during abrasive contact at HT can be investigated by scratch testing. To study the influence of temperature and load on scratch behaviour a novel scratch test was utilised, allowing for scratch investigations up to 1000 °C. Three materials for HT usage were chosen for investigation: an austenitic steel, a cast steel with carbide network and a Ni-based material with carbide network. Test load was varied from 10 to 100 N and temperature steps were room temperature, 500 °C and 800 °C. Additionally hot hardness tests were performed to measure the hardness-temperature dependency of the materials. The three materials show very diverging wear behaviour at the investigated temperatures. While at low temperatures the wear scars are relatively smooth, wear behaviour became instable with temperature induced material softening. Especially inhomogeneous materials show pronounced stick-slip phenomena at highest testing temperatures. To understand the wear behaviour in a greater detail, numerical simulations of the scratch process were undertaken using smooth particle hydrodynamics. First results show a good correlation with wear scars of the austenite and allow a deep insight in the stress distribution and deformation process during scratching. [ABSTRACT FROM AUTHOR]

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]

Abrasive wear at high temperatures (HT) is a serious issue that limits the lifetime of many industrial components, e.g. in steel production, the cement or the chemical industry. Various forms of abrasion like three-body abrasion, gouging, impact-abrasion or solid particle erosion degrade surfaces. In order to study abrasive wear behaviour, three different abrasion modes were investigated experimentally up to 700 °C using prospective HT alloys. The wear modes were high-stress three-body abrasion, impact-abrasion and solid particle erosion to investigate the material response to these very different forms of abrasion and to further identify the critical temperatures for the materials. Various temperature- and wear-resistant metallic alloys were compared: materials with low hard phase content (~15%) and Fe-, Ni- and Co-based matrix against a high-alloyed Fe-based hardfacing with a hard phase content >50%. It was found that the in-situ formation of mechanically mixed layers (MML) with the abrasive provides excellent HT wear protection in many abrasion modes. Hence the mechanisms of MML formation were studied in greater detail, in order to predict the effectiveness of this MML formation in abrasive applications. [ABSTRACT FROM AUTHOR]

In order to gain a fundamental understanding of material behaviour at elevated temperatures a unique tribometer was designed which can operate at temperatures up to 1000°C. The test takes place in vacuum in order to avoid oxidation and the normal load range varies from 10 to 500 N. It is thus possible to describe the evolution of hardness over a broad range of temperatures and loads. This can give indications of possible microstructural modifications, which can be investigated afterwards on cross sections. For the characterisation of single abrasive phenomena on a very fundamental level, scratch tests at variable loads are proposed. The interaction of sliding surfaces can be simulated by adhesion testing. To this end an application specific counter body, e.g. taken from a field specimen, can be slid over the specimen surface at variable loads. Finally, it can be stated that this newly designed tribometer offers an enormous potential for deeper understanding of fundamental wear phenomena like ploughing, micro-breaking or adhesion occurring at high temperature. The possibilities of high temperature scratch and hardness testing with the new measurement system are shown on the common austenitic stainless steel 1.4301 (AISI 304). [ABSTRACT FROM AUTHOR]

The role of contact pressures in high temperature, high speed sliding wear has been studied in the context of alignment plates for the hot rolling of steel. To this end, a lab-scale simulation of the process was performed under varying normal loads, using several iron-based materials to be implemented in the real field application. The resulting wear rates and friction coefficients were compared, and it turned out that applied loads exerted no discernible effect on wear rates at room temperature, while leading in some cases to significant wear decrease at temperatures equal or higher than 500 °C. This was attributed to a tribolayer formation influenced not only by sample temperature but also by applied load. Running-in stage duration was also observed to be related to decreased wear rates for several of the materials. [ABSTRACT FROM AUTHOR]

Hot hardness, related to the mechanical strength and wear resistance of materials at high temperatures, has been measured from room temperature up to 800 °C for a comprehensive set of iron-based alloys having different microstructures and chemical compositions. The results obtained suggest the existence of several softening regimes with increasing temperatures, also with a massive hardness drop observed to begin at temperatures close to 0.5 times the melting temperature for most of the chosen alloys. Austenitic steel grades were also observed to show a significant softening behaviour at moderate temperatures compared to ferritic and martensitic alloys, attributed to the dislocation dynamics of face cubic centred alloys. The exact nature of the temperature dependence shown by hardness has been proposed to adopt the form of an exponential Arrhenius equation. Another model suggested in the available literature is also discussed within this context. Additionally, the role of alloying elements has been correlated to the softening behaviour. Molybdenum or boron were found to slow down the softening behaviour, while carbide-forming elements such as vanadium and tungsten were found to be beneficial for room temperature hardness. [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]

Wear plates are used for the alignment of sheet metal during hot rolling of steel. Conditions found during the process, such as the high temperature contact with sheet metal and high sliding speeds are responsible for severe plate wear. Damage characterisation of worn alignment plates showed in particular the onset of microstructure changes beneath the wear grooves and the formation of a mechanically mixed layer in the contact region.The aim of this work is the development of a material selection map for cost-efficient steel grades by means of a new high temperature sliding wear testing. As a result, significant differences in wear behaviour were found between the investigated material classes. [ABSTRACT FROM AUTHOR]

Highlights: [•] MMC using cemented carbide scrap, which is a cost efficient hard phase alternative, can be produced by casting. [•] Using optimised casting parameters dissolution of cemented carbide scrap is low and bonding with the matrix is good. [•] Optimised parameters involve that cemented carbide scrap is as short as possible in the liquid melt, still good flux of the melt must be guaranteed. [•] Abrasive wear tests show excellent performance of MMCs with cemented carbide scrap. [•] The investigated MMCs are competitive to expensive wear protection solutions in abrasive environment also at 500°C testing temperature. [ABSTRACT FROM AUTHOR]

Iron aluminides are promising candidates for high-temperature corrosion- and wear resistant materials. Their intermetallic nature provides good mechanical stability at comparatively low density in contrast to commonly used iron- and nickel-based wear resistant alloys such as white cast irons or Inconel alloys. The objective of this study is to measure the influence of different alloy compositions on the high-temperature abrasion resistance of iron aluminides. Alloys of 25–30 wt% Al, Ti, B and Si were characterized and compared to a high-temperature resistant white cast iron. Microstructural analysis via scanning electron microscopy as well as electron backscatter diffraction were performed to elucidate the materials' microstructures and the different phases present. Hot hardness up to 700 °C and nanoindentation were determined to quantify differences in mechanical properties between compositions. Wear resistance was quantified with high-temperature abrasion tests performed in a modified ASTM G65 test at 20, 500 and 700 °C, with standard quartz sand as abrasive and a high-temperature resistant steel wheel as counterbody. Wear results point out a significantly better behaviour of the iron aluminides at 500 °C and 700 °C at a quarter of the wear rates of the white cast iron, which can be attributed to beneficial mechanical properties enabling the formation of protective mechanically mixed layer under incorporation of abrasives. Finally, a life cycle assessment (LCA) was performed to assess the environmental impact of the iron aluminides compared to the steel reference during production, accounting for the lifetime as indicated by the wear rates obtained. Results show significantly reduced environmental impacts in the evaluated impact categories, making iron aluminides promising candidates for future high-temperature wear components. • High-temperature abrasion resistance of iron aluminides and white cast iron tested. • Influence of alloying of Cr, Si, Ti & B on mechanical properties and wear analysed. • Iron aluminides show increased wear resistance up to 700 °C. • Lifetime increase evaluated and life cycle assessment calculations performed. • Iron aluminides show lower ecological impact than the white cast iron. [ABSTRACT FROM AUTHOR]

Structural steels provide a broad spectrum of heat, creep and wear resistance at different microstructures and hardness levels. Two different steel grades were chosen for investigation and simulated repair welds with different parameters were performed, aiming on the influence of heat input during welding and the resulting microstructure on the high temperature abrasion resistance. The impact on the wear resistance and its temperature dependence was evaluated within a high temperature three-body abrasion test and a hot hardness test rig. Results indicate a strong dependence of present microstructural phases and hardness on the wear resistance entailed by different welding parameters. Optimised parameters and low energy input during welding leads to stable hot hardness progress and wear conditions for the investigated materials. [ABSTRACT FROM AUTHOR]

Self-lubricating coatings extend the efficient dry-operational life of cutting and forming tools. In the current work, millimeter-thick NiCrBSi coatings with 10 wt% metal sulfide i.e. Ni 3 S 2 , CuS, or Bi 2 S 3 were fabricated on a stainless steel substrate by laser cladding (in-situ alloying). Thermodynamic modelling utilizing the calculation of phase diagrams method (CALPHAD) was performed to predict the phase evolution during laser melting. Electron microscopy methods combined with X-ray diffraction and Raman spectroscopy were used to elucidate the developed microstructure. The coatings were further subjected to reciprocating dry sliding wear against a martensitic steel ball counterbody using a ball-on-plate configuration at 0.1 m/s and 50 N (Hertz contact pressure 1.7 GPa). The tests were conducted at room temperature (20), 400, and 600 °C. The results demonstrate a self-lubricating behavior of the sulfide coatings resulting in friction reduction by ⁓60 % at room temperature and ⁓40 % at 400 °C sliding, particularly for Bi 2 S 3 -added cladding, due to the prevalent existence of lubricious phases of chromium sulfide (Cr x S y) along with others (NiBi, Bi) and leading to 'self-healing' phenomena. The results are reported in comparison to the unmodified NiCrBSi alloy. • Self-lubricating NiCrBSi alloy containing Ni 3 S 2 , CuS, or Bi 2 S 3 produced by laser cladding. • Bi 2 S 3 addition results in the encapsulation of pure Bi within Cr x S y phase. • Friction reduction by 60 % and 40 % for sulfide claddings at RT and 400 °C. • Tribolayer self-healing was observed for sulfide claddings at RT and 400 °C. • At 600 °C, oxidation (3rd body) causes high friction and wear of sulfide claddings. [ABSTRACT FROM AUTHOR]

It is a well-established fact, that the tribological performance of titanium and its alloys at high temperatures is poor, especially for self-mated titanium‑titanium pairs. Previous work has shown a significant improvement in mechanical and high temperature tribological behaviour (700–900 °C) for pure Ti sintered with TiB 2 ceramic, occasioned by the in-situ formed boric acid lubricant. The current work explores the possibility to extend the lubrication temperature range (below 700 °C) of Ti-TiB 2 composites through the incorporation of a nickel‑bismuth mixture (Ni Bi) as a solid lubricant using laser melting. To this end, phase equilibrium diagrams have been calculated for the Ti-B-Ni Bi quaternary system using the CALPHAD method to evaluate the possibility of the formation of different phases due to dilution between the substrate and deposit, as well as their possible interactions. The self-lubricating Ni Bi samples feature a formation of Bi-Ni-Ti-TiB x functional surface. The functional surface demonstrates a compact and unique microstructure of a hard B-rich phase encapsulated inside a lubricous Bi-rich phase. A two-fold increase in hardness of the surface in comparison to the underlying substrate was noted for Ni Bi laser-melted samples. Further, the Ni Bi samples were studied under a reciprocating sliding configuration against a Ti-alloy flat-pin counterbody at temperatures including RT, 400 and 600 °C. The resulting wear scars were analysed utilizing SEM, XRD and 3D profilometry to understand the prevalent wear mechanisms. A significant decrease in coefficient of friction and wear rate was observed for the Ni Bi laser-melted samples sliding at 400 °C and 600 °C due to the formation of a self-lubricating tribo-oxide layer rich in Bi-compounds. The results are reported in comparison to the unmodified reference Ti-TiB 2 composite. • Laser incorporation of nickel-bismuth (Ni Bi) mixture into Ti-TiB x composite to serve as a solid lubricant. • Thermodynamic modelling of quaternary Ti-B-Ni Bi system. • Formation of a hard, self-lubricating Bi-Ni-Ti-TiB x functional surface featuring a hard B-rich phase encapsulated inside a lubricous Bi-rich phase. • Significant increase in sliding wear resistance for Ni Bi incorporated Ti-TiB x at 400 and 600 °C. • Room and high-temperature CoF reduction due to the presence of Bi-rich compounds in the generated tribolayer. [ABSTRACT FROM AUTHOR]

Strain hardening is commonly used to reach the full potential of materials and can be beneficial in tribological contacts. 2-body abrasive wear was simulated in a scratch test, aimed at strain hardening effects in various steels. Different working conditions were examined at various temperatures and velocities. Strain hardening effects and microstructural changes were analysed with high resolution scanning electron microscopy (HRSEM), electron backscatter diffraction (EBSD), micro hardness measurements and nanoindentation. Statistical analysing was performed quantifying the influence of different parameters on microstructures. Results show a crucial influence of temperature and velocity on the strain hardening in tribological contacts. Increased velocity leads to higher deformed microstructures and higher increased surface hardness at a lower depth of the deformed zones at all materials investigated. An optimised surface hardness can be achieved knowing the influence of velocity (strain rate) and temperature for a “tailor-made” surface hardening in tribological systems aimed at increased wear resistance. [ABSTRACT FROM AUTHOR]

Slag pots are commonly used for the transportation of liquid slag from steel mills to slag dumps. A detailed failure analysis of slag pots is required to determine effects limiting their lifetime. Temperature measurements were implemented throughout an ongoing operation to quantify thermal loading. Different microscopy methods, cross sectional analyses and hardness measurements were performed on a slag pot after prolonged usage. Material degradation mechanisms, wear and deformations found during and after slag pot operation were compared to performed finite element simulations of the transport cycle. Special focus was placed on weaknesses of the current design. This study addresses thermal effects on wear, failure and degradation mechanisms present at slag pots. Additionally, attempts for specific solutions will be proposed. Results indicate that thermal shocks and oxidation lead to material degradation, which alongside the thermally induced deformation of the pot shape reduce the overall lifetime. Layers of solidified slag inside the pots further cause severe abrasive wear on the inner pot walls during the discharging procedure. [ABSTRACT FROM AUTHOR]