Wear Micromechanisms Research Articles

Temperature-induced wear micro-mechanism transition in additively deposited nickel alloys with different solid lubricants

Additive manufacturing of self-lubricating alloys plays a crucial role in the production of complex wear-resistant components and in expanding repair capabilities, especially for intricate wear parts with low tolerances (e.g. with cooling channels). Herein, we report a novel approach providing nickel-based alloy with an excellent tribological performance in dry sliding contacts. Laser-deposited self-lubricating nickel alloys, infused with anti-wear additives of molybdenum disulfide, nickel sulfide, copper sulfide, or bismuth sulfide, were subjected to dry sliding wear tests against an alumina ball counterbody at a temperature range of up to 800 °C. The self-lubricating alloys exhibited a significant decline in friction (43 %) and wear (45 %) at room temperature, 400 °C (friction 40 %, wear rate 55 %), and 600 °C (MoS2-based, friction 58 %, wear rate 75 %). The MoS2-based alloy coating demonstrated excellent performance characteristics up to 800 °C (friction coefficient ⁓0.25, wear rate 11 × 10−6 mm3 N−1 m−1) due to the formation of a ‘glazed’ tribolayer. Wear mapping allowed to identification of a critical condition for self-lubricating alloys where positive transitions in wear mechanisms led to a synergistic lubrication mode involving the formation of tribologically induced new lubricious phases such as silver molybdate or nickel-bismuth intermetallic. This work provides a comparative evaluation of the micromechanisms, surface transitions, and tribochemistry of solid lubricants at a wide temperature range and a variety of applications.

Microstructural effects on impact-sliding wear mechanisms in D2 steels: The roles of matrix hardness and carbide characteristics

This study investigates the wear micromechanisms of D2 steels under impact-sliding conditions, offering insights into their performance when used in applications such as trimming dies for high-strength steel sheets where they undergo plastic deformation and chipping. Two D2 steel samples, both with a bulk hardness of 59.7 HRC but different matrix hardnesses and carbide distributions, are tested by using an impact-sliding wear test rig at Hertzian contact pressures exceeding 2 GPa. The sample with a softer matrix exhibits wear primarily through delamination caused by plastic deformation. This initiates cracks at the matrix/primary carbide interface, leading to material loss in the form of large chips. In contrast, the steel with a harder matrix shows reduced wear due to its resistance to plastic deformation. Initially, wear occurs through the fracture of primary carbides. However, with prolonged loading, the matrix begins to soften, adopting a wear mechanism similar to the D2 steel with softer matrix. Notably, smaller primary carbides are associated with improved wear resistance by limiting the initiation sites for cracks, especially at the matrix/primary carbide interface. This understanding enables the selection and design of heat treatments to optimize D2 steel microstructure, thus improving resistance to impact-sliding wear damages observed in processes like trimming.

Influence of grit particles characteristics on the abrasive wear micro-mechanisms of NbC-Ni and WC-Co hard materials

Knowledge of wear and associated damage mechanism that is prevalent during abrasive wear conditions using NbC-based cermets is lacking. In the current investigation, the abrasive wear response and associated damage mechanisms of cermets due to characteristics effect of grit particles such as size and hardness have been explored. The present study evaluates the abrasive wear response of NbC-12Ni-10Mo2C (NbC-Ni) cermet during two-body abrasive wear, which was experimentally simulated by a pin abrasion tester following the ASTM G132 standard. The WC-Co cemented carbide (WC-15.6Co) with similar hardness was used as a reference material in this study for a comprehensive comparison of materials. The investigated test parameters included different applied loads (4–16 N) and abrasive particle sizes (22–200 μm) for a 30 m sliding distance at 0.15 m/s sliding velocity. Silicon carbide (SiC) and aluminium oxide (Al2O3) were used as abrasive counter bodies. Test results clearly show the particle size effect and the critical abrasive particle size (CPS) for the cermet lies between 82 μm and 125 μm for both abrasives (SiC, Al2O3). It is noticed that the wear rate shows three different trends as the particle size increases, initial increase then a steady state during critical particle size and becomes unpredictable. This effect reflects the transition of wear micro-mechanisms dominated from binder removal (below CPS) to fracture and fragmentations (beyond CPS). The wear mode transition map from plastic grooving to fracture-dominated failure (fragmentation and granular cracks) was created by correlating factors such as the severity of contact and specific wear rate with microscopic observations. The wear produced by SiC abrasives was about an order of magnitude higher (≈18×) than with Al2O3 abrasives. In addition, the material comparison highlight that the abrasive wear rate of NbC-Ni cermet was about 37–86% (SiC) to 66–83% (Al2O3) higher than for the WC-Co cemented carbide, despite both cermets having similar micro-hardness. In addition, the present study illustrates that the abrasion of cermets is not only related to mechanical properties such as hardness and fracture toughness but is inherently related to composite chemical properties such as wettability and interfacial strength. This work provides new insight into the wear response of NbC-Ni cermets and WC-Co cemented carbides regarding different abrasive counterfaces, abrasive particle sizes and transition of abrasive wear mechanisms.

Selective oxidation induced wear degradation in cemented carbides

Understanding the wear micro-mechanisms of metallic binders is a prerequisite to designing durable cemented carbides for drilling applications. Here we studied the oxidational wear behaviors of WC-based composites encompassing particularly the CoAl binder (α phase, comprised of 5.7 wt% Al and bal. Co) and the CoFeAl binder (B2 phase) with same Al content. Unlike the oxidation of Co in the CoAl, selective oxidation of Al occurred unexpectedly in the CoFeAl, which weakened the binder integrity and aggravated the wear losses. Such unique behavior was rationalized computationally, where the Al2O3 formation was attributed to the low energy barrier to Al diffusion in the B2 structure. These findings could lay a useful basis for future development of robust cemented carbides.

Influence of abrasive characteristics on the wear micro-mechanisms of NbC and WC cermets during three-body abrasion

The present study has developed new insights into the wear transition mode of cermets and provides a better understanding of the role of abrasive characteristics in three-body abrasive wear. Two sintered and fully densified cermets, NbC–Ni (NbC–12Ni–10Mo2C) and WC-Co (WC-9.5Co) with similar micro-hardness (HV30 ≈ 13.5 GPa) were selected in this study. The abrasion response of cermets against different abrasive characteristics namely size (67–245 μm), hardness (silica, alumina and SiC), and shape (round and angular) was experimentally investigated according to the ASTM G65 standard. The test results showed that the specific wear rate (SWR) of the cermets increased significantly with increasing abrasive size and hardness. The size effect shows that the dominant wear micro-mechanisms shift from binder removal (rolling) to mixed binder-carbide extrusion (sliding) as the abrasives particle size changes from smaller (67 μm) to larger (245 μm). The hardness ratio between the abrasives and cermets (Ha/Hs) highlights that silica and alumina abrasives provide mild wear (Ha/Hs < 1.5), while SiC abrasives cause severe wear (Ha/Hs > 1.5). Both cermets exhibited similar SWR during mild wear, but NbC–Ni showed 7 times higher SWR than WC-Co during severe wear. The abrasives shape effect does not show a significant difference on the wear rate of the cermets.

Effect of heat treatment on microstructure and tribological performance of PH 13-8Mo stainless steel fabricated via wire arc additive manufacturing

The scratch and reciprocating sliding wear response of a PH 13-8Mo stainless steel fabricated by wire arc additive manufacturing (WAAM) are investigated after different cycles of post-printing heat treatments and correlated with the microstructure and mechanical properties. The performed heat treatment cycles comprised of solutionizing for 1 h at 1050 °C followed by an aging cycle for 4 h at 400 °C, 500 °C, and 600 °C. The optimum aging temperature was found to be at 500 °C under which hardness, scratch, and wear resistance were maximum and the coefficient of friction was minimum due to removal of determinantal δ-ferrite phase from the as-printed microstructure and the attained precipitation hardening through the formation of coherent nano-scale β-NiAl precipitates. The employed heat treatment was effective in eliminating the anisotropic scratch and wear response in the as-printed part arising from its anisotropic microstructure. The overall wear micro-mechanisms were similar for as-printed and heat-treated conditions with ploughing during scratch test, and adhesive, oxidative, and three body abrasive wear mechanism during the reciprocating sliding wear test. The results showed that WAAM-produced PH 13-8Mo parts have great potential to be an alternative to their wrought counterparts for wear resistance demanding applications.

Microabrasive wear behavior of different stellites obtained by laser cladding and casting processes

Cobalt superalloys are used in several applications, mainly involving corrosive environments and high temperatures, in which wear and corrosion resistance are key factors in their performance. These alloys can be produced by a variety of manufacturing processes. Among these, the technology of laser cladding coatings has emerged as a promising and economically viable alternative to produce coatings from cobalt-based alloys. One of the applications of these alloys is in the production of components to obtain second-generation ethanol. In this application, about 8% of the processed material is composed of micrometric abrasive particles, mainly silica, among others, which cause wear of components. In order to better understand the tribological behavior of these alloys in microabrasion, three coatings of commercial cobalt-based superalloys, Stellite 1, 6 and 12, were produced by laser cladding. Additionally, two cast alloys, Stellite 250 and an experimental Stellite alloy, were also evaluated. Microabrasion tests using a statistical design of experiments were performed with SiO2, Al2O3 and SiC abrasives in a suspension of distilled water. Statistical analysis revealed that the wear coefficients of these alloys are influenced by both the abrasives and the alloy. The as-cast Stellite 250 alloy showed the highest wear coefficients, while the coated Stellite 1 and the as-cast experimental Stellite showed the lowest wear coefficients. The predominant wear micromechanism was scratching, except for Stellite 6 and 12 coated alloys in SiC tests, in which predominant mechanism were mixed and rolling, respectively. The presence of secondary micromechanism of rolling wear was also observed and associated with the granulometric distribution of the abrasives. The analysis of wear severity allowed the comprehension of the granulometric distribution influence of abrasive particles on wear.

Tribological performance under abrasive wear of Fe-Cr-C+Nb coating deposited by FCAW process

This paper aims to investigate the abrasion resistance performance of Iron-Crhomium-Carbon + Niobium (Fe-Cr-C + Nb) coatings deposited by Flux-Cored Arc Welding (FCAW) process. Two coatings conditions were prepared in a 1-layer setup, with a selfshielded tubular wire over SAE 1020 carbon steel substrate, varying the FCAW parameterization levels, searching to reproduce different conditions of welding energy and their respective effects on the coatings' properties. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were employed in the microstructure and wear micromechanism analysis. X-ray Energy Dispersive Spectroscopy (EDS) was used for chemical composition assessment and Vickers microdurometer for hardness evaluation. In the tribological attempt, it was used the dry/sand rubber wheel apparatus according to ASTM G65. From the results, in neither sample of the two coating conditions, deleterious defects were observed on the surfaces, as well as in the cross-sections, such as lack of fusion and process interruptions. Dilutions were sufficient to ensure metallurgical bond without compromising layer geometry. Cold cracking characteristics of the process and material were observed, which did not significantly influence the performance of the coatings. The microstructure of both coatings showed CrC and NbC carbides dispersed in the Fe-matrix, whose volume fraction and mean free path between them varied as a function of dilution. The greater Nb-content and less intense heat input in the lower dilution coating provided greater refining of the CrC, NbC, and Fe-matrix strength, which was reflected in higher hardness, lower wear rate, and less severe abrasive wear micromechanism.

Effect of carbide orientation during single scratch test in directionally solidified and heat-treated high chromium cast irons

In this work, a billet of eutectic high chromium cast iron, material commonly used in highly abrasive environments, such as in grinding and milling, was unidirectionally solidified. The resulting microstructure was composed of oriented M7C3 carbides and eutectic matrix. Specimens were cut parallel and transversally to the billet axis and split into two groups. Both were heat treated with different austenitization temperatures. The temperature for the first group was 1100 °C, and the value for the second was 950 °C, providing matrix instrumented indentation hardness values of 8.0 and 6.3 GPa, respectively. This procedure resulted in specimens with three carbide directions dispersed in two different matrices. Samples were evaluated by means of single scratch test with a cono-spherical diamond stylus under progressive and constant normal load conditions. To support the analysis, a non-contact 3D surface profiler and scanning electron microscopy (SEM) were used to characterize the scratched surfaces. Progressive load tests indicated a transition in wear micro-mechanisms which was mainly observed in the samples with the long axes of the carbides parallel to the wear surface and oriented orthogonal to the scratch direction and with matrix hardness of 6.3 GPa. On the other hand, constant load tests showed that carbides with the long axes parallel to the wear surface and oriented parallel to the scratch direction tend to produce deeper scratchers with higher ridges than in the other directions. Results also indicate that the hardness, despite being an important variable, does not entirely explain the behavior of the material under single scratch, since the orientation of the carbides with respect to the scratch direction must also be considered.

Abrasive wear resistance of idler roll polymeric materials

Idler rolls are an integral part of belt conveyors. Recently, steel idler rolls have been replaced with polymeric ones in low to middle load applications, bringing several advantages due to the polymer’s lightweight and low abrasiveness in the conveyor belt. However, using polymeric material for high load application brings challenges, particularly presenting similar structural and abrasion resistance to steel. This work puts forwards a methodology using a rubber-wheel tribometer to evaluate the abrasion resistance of polymeric idler rolls in their most severe operating condition (halted idler roll) and defines a threshold limit based on the results obtained with steel idler rolls. The methodology was applied to 07 different polymeric materials. To further understand materials abrasions resistance, scratching tests were performed, and the main wear mechanisms, verified by scanning electron microscopy (SEM) and abrasion factor (FAB), were discussed along with the material properties. The main conclusions are: i) some polymeric materials present abrasion resistance similar to steel rolls; ii) the wear micromechanisms, verified by SEM and FAB, are good indicators of abrasion resistance of the materials but insufficient because they do not include temperature and fatigue effects resulting from multi abrasive events; iii) the additive fillers significantly altered the abrasive resistance of materials, although they do not change the material properties significantly.

Performance testing of supercoarse sintered carbides with alternative nickel-based matrices in the context of mechanical, tribological, thermal and metallographic investigations

The recent advances in rock, coal, gas and oil drilling under continuously increasing loads and increased cutting speeds motivate the interest in and development of coarse and supercoarse sintered carbides. Complex drilling conditions are best simulated during in-service tests but their objectiveness and reliability are often problematic. Therefore, performance testing of real cutting tools in controlled conditions is of great importance. New grades of supercoarse hardmetals with nickel-based binders and relevant mining tools were designed and manufactured. Performance tests consisting in controlled rotary mining of a homogeneous artificial mineral block showed significantly lower wear of the experimental sinters (24–69%) in comparison with the classical cobalt matrix counterpart. The performed mechanical, tribological, thermal, fractographic and substructural investigations revealed the wear micromechanism, the correlations between the results obtained as well as the factors of the increased tool performance.

Sub-surface microstructural investigation for establishing micro-mechanisms of wear in sliding of SiC and SiC-WC ceramics

Dual-beam FIB/FEG-SEM and TEM/HRTEM observations of sub-surfaces of SiC and SiC-50 wt% WC composite disks worn against SiC ball have provided important insights into the micro-mechanisms of material removal and the role of WC towards suppressing the same. Sub-surface analysis reveals the silicon oxide rich tribochemical layer just underneath the worn surfaces of monolithic SiC. Further below this tribochemical layer, dislocations and twins in SiC grains, as well as micro-cracks, are identified. Micro-cracks get extended up to ∼2 μm depth below the layer, eventually leading to material removal in SiC ceramics. In case of the SiC-WC composite, neither is the tribochemical layer dominant, nor is twin/dislocation networks seen to extend beyond the SiC/WC interfaces. Overall, the present study highlights that WC particulate reinforcements in SiC-WC composite minimize the wear damage by suppressing oxidative wear and restricting the generation of micro-cracks, which otherwise form extensively due to stress build-up at the tips of dislocations or twins in SiC grains.

High temperature wear micromechanisms in Al–17Si–5Cu alloy after an isothermal heat treatment

ABSTRACT The present investigation deals with the wear micromechanisms in hypereutectic Al–Si alloy containing Cu (AR alloy) after an isothermal heat treatment developed by the present authors. The heat-treated alloy (HT alloy) is subjected to a dry sliding wear test in a rotary tribometer under various loads against a hardened steel disk. Tests are conducted at higher temperatures, viz., at 200°C and 300°C. Worn surfaces and wear debris are characterised in the scanning electron microscope and X-ray diffractometer to find out wear mechanisms. The study reveals that severe wear occurs in the case of AR alloy at higher temperatures due to accelerated wear processes. On the other hand, HT alloy exhibits less wear due to resistance to wear in HT alloy. This improvement in wear behaviour in HT alloy is explained by the micromechanisms of wear.

Tribological investigation of abrasion resistant steels with martensitic and retained austenitic microstructure in single- and multi–asperity contact

Steel making companies are developing new steels with complex microstructure to satisfy abrasion resistance issues. Three newly developed steels (fresh martensitic, tempered martensitic and a TRIP steel) were investigated under single and multi-asperity abrasion test conditions. Abrasive performance was linked to material properties. In the multi-asperity test, increasing the normal load and abrasive particle size resulted in increasing mass loss and in transition in micro-mechanisms from ploughing to micro-cutting. Martensitic materials showed better wear performance due to their higher hardness. As a result of the abrasive action a newly formed tribo-layer was observed in the contact zone of all steel specimen. In the single asperity testing a diamond spherical indenter was used with different normal loads. Wear micro-mechanisms were analysed during the scratching using optical microscopy and 3D-profilometry. The fresh and tempered martensitic steels showed a transition in micro-mechanism from micro-ploughing to micro-cutting at higher loads and smaller tip radius. For the multiphase steel with retained austenite, despite its TRansformation Induced Plasticity effect, micro-cutting was reached already at lower loads. The tempered martensitic material outperformed the fresh martensitic material despite the similar hardness and microstructure. For all materials single-asperity test data showed similar ranking in abrasion wear resistance as in the multi-asperity test.

The Sclerometrical, Mechanical, and Wear Behavior of Mg-Y-Nd Magnesium Alloy after Deep Cryogenic Treatment Combined with Heat Treatment.

The paper investigates changes in the structure, microhardness, and sclerometrical and tribological properties of a Mg-Y-Nd alloy under the influence of deep cryogenic treatment (DCT) in combination with heat treatment. The solution treatment was carried out at 545 °C for 8 h, aging was carried out at 250 °C for 24 h, and the deep cryogenic treatment applied at different treatment stages was performed at −196 °C. Tests showed a significant increase in the number of β-phase precipitates identified as Mg46.1Y6.25RE3.45 in the alloy subjected to DCT after solution treatment followed by aging. In addition, an approximately 20% reduction of the grain size was observed. Changes in the structure in the precipitation process strengthened the alloy and resulted in an increase of its hardness. At the same time, sclerometric tests allowed the micromechanism of wear and the coefficient of resistance to abrasive wear to be determined. Tribological tests showed a three-fold reduction in the volumetric wear and a considerable reduction of the friction coefficient, with the main mechanism observed during friction being abrasive wear. The most favorable properties of the alloy were obtained after precipitation hardening combined with DCT, resulting in a large increase in resistance to abrasive wear. Additionally, the formation of deep scratches in the examined material was reduced. The introduction of sub-zero treatment reduces the precipitation hardening time, and the results obtained indicate that the service life of the Mg-Y-Nd alloy can be extended.

Abrasion wear of austenitic manganese steels via jaw crusher test

The abrasion wear of the austenitic manganese steels with 12% Mn and 20% Mn was evaluated via jaw crusher tests. The abrasive mass (i.e. gravel) used per test was 100 kg and 14.3 mm of mean sized particles. The wear characterization was carried out with the evaluation of mass loss, hardness profile, worn surface roughness, and wear micromechanisms. Additionally, the subsurface's microstructure was analysed by a Focused Ion Beam (FIB). The stationary and movable jaws presented differences in mass loss and wear micromechanisms. The stationary jaw has higher wear than the movable one. These results are related to the micromechanism of microcutting and microploughing to the stationary jaw and the micro-indentation to the movable jaw. For the relative wear of the jaws' materials, there was a significant difference for the values of stationary jaw conditions, resulting in higher wear resistance for the high manganese alloy applied in this condition. FIB results show that the wear promotes the formation of ultrafine grains and deformation twins in the subsurface layer.

Single-point scratch testing for understanding particle engagement in abrasion of multiphase materials

The current research explores the influence of multi-asperity abrasive particles engagement on multiphase materials. WC-Co (WC-15.6% Co) and NbC-cermet (NbC-12% Ni–10% Mo2C) hard materials were tested using a scale down single point scratch tester. Multi-asperity scratch patterns were produced by implying multiple scratches on hardmetal surface by parallel and repeated sliding. Superimposition of interactions has been implemented to study the damage evaluation of close-up parallel scratches. The abrasive particle characteristics such as size and apex angle were replicated by the diamond indenter and their influence with different applied loads [1–20 N] and sliding speeds [0.2–5 mm/s] were studied. NbC-cermet and WC-Co show a decrease in friction coefficient by 20–46% and 11–30% respectively, while the indenter tip radius changes from 200 μm to 25 μm under the same operating conditions. The wear micro-mechanism mainly changes from plastic deformation to fracture when the load and tip radius is increased. An extensive comparative study shows NbC-cermet prematurely experiences fracture dominated failure than its reference WC-Co. Moreover, tip size defect from indenter curvature geometry greatly affects the mean apex angle.

Size Effects and Mechanisms in the Friction and Wear Processes of Ceramics Based on Zirconium Dioxide

This paper presents a study of the tribological properties of ceramics based on ZrO2 stabilized with CaO in a ceramic-ceramic friction pair. The influence of the scale factor on the coefficient of friction in the micro- and nanoscale is established. A qualitative correlation of the theoretical and experimental curves is shown for friction coefficient dependence on the body-counterbody contact force. Friction and wear micromechanisms at a micro- and nanoscale are proposed for the investigated TZP ceramics.

Tribological and Mechanical Behavior of Graphite Composites of Polytetrafluoroethylene (PTFE) Irradiated by the Electron Beam.

This research investigated the effect of irradiation with an electron beam energy of 10 MeV in doses of 26–156 kGy on polytetrafluoroethylene (PTFE) with a 15% and 20% graphite additive. The research has shown that mechanical (compression strength, hardness, and Young’s modulus) and sclerometric (coefficient of wear micromechanism and coefficient of resistance to wear) properties improve and tribological wear decreases as graphite content increases. Electron beam irradiation increases the degree of crystallinity of both materials to a similar extent. However significant differences in the improvement of all examined properties have been demonstrated for PTFE with higher (20%) graphite content subjected to the electron beam irradiation. This polymer is characterized by higher hardness and Young’s modulus, reduced susceptibility to permanent deformation, higher elasticity, compression strength, and above all, a nearly 30% reduction in tribological wear compared to PTFE with a 15% graphite additive. The most advantageous properties can be obtained for both of the examined composites after absorbing a dose of 104 kGy. The obtained results hold promise for the improvement of the operational life of friction couples which do not require lubrication, used for example in air compressors and engines, and for the possibility of application of these modified polymers. In particular PTFE with 20% graphite content, in the nuclear and space industry.

Running-in period for the abrasive wear of austenitic steels

The initial transient, or running-in, period during abrasive wear has been largely overlooked in the literature, with the focus instead being on steady-state conditions. However, the running-in period of abrasion might determine the evolution to steady-state wear behaviour, as is known to occur in sliding wear conditions. To this end, the running-in period during the abrasive wear of the austenitic stainless steel AISI 316L and Hadfield (15%Mn-1.5%C) steel was analysed through the testing pin (flat-ended)-abrasive paper wear configuration. The effects of the normal load, the size of the abrasive, and the type of material were evaluated, and the wear rate and the strain hardening of the matrix were recorded. The steady-state wear might be influenced by the phenomena occurring during the running-in period. Thus, the hardening, roughness, friction coefficient and wear micromechanisms were correlated with the wear rate to elucidate these possible relationships.