Worn Surface Features Research Articles

Effect of austempering treatment on lubricated sliding contact of compacted graphite iron

Significant research has been done to improve the wear properties of the components used in internal combustion engines. Excessive wear is observed in components such as cylinder liners and rings, which can lead to lower volumetric efficiency of the engine, increase oil consumption, polluting emissions, and scuffing related issues. Since tribological systems in internal combustion engines are complex, the different wear mechanisms involved need to be investigated to improve the life of components. Cast irons are commonly used for engine components, especially compacted graphite irons (CGI) for piston rings and gray cast irons (GCI) for cylinder liners. This work aims to evaluate the tribological behavior of two different microstructures of CGI (pearlitic and ausferritic), sliding on pearlitic GCI. The samples of CGI with different microstructures and hardness were evaluated in a short-stroke reciprocating sliding tester, using Petronas Urania SAE 30 API CF lubricant oil at 100 °C for four hours. The characterization of worn surfaces was made using a scanning electron microscope (SEM) and 3D roughness measurements. The coefficient of friction (COF) comparison between the two CGI microstructures showed very similar results with COF = 0.11. The pearlitic CGI showed more severe wear than the austempered one, confirmed by SEM images and the difference in topography parameters before and after the tests. Phosphorus, sulfur, and zinc were detected by EDS analyses in the samples' worn-out regions, indicating the formation of tribo-films, which was further confirmed by the friction tests.

Role of metal composite alloys in non-asbestos brake friction materials-A solution for copper replacement

Copper plays a vital role in the performance of brake friction materials due to its better thermal conductivity and fade resistance. But owing to the negative impact towards to the aquatic life, the usage of copper in brake material formulations is reduced considerably in developed nations. Research is being carried out globally to reduce the copper with single ingredient or combination in brake materials. Thus the present study dealt with the development of brake pads using a commercially available alloy of aluminum and iron (Mechanomade) in the formulation with other ingredients. To compare the performance, three other brake pads were also developed by replacing mechanomade with copper, aluminum, and iron in the formulation. The developed brake pads were analysed for the physical, chemical, mechanical and thermal properties as per standard industrial practice. The tribological characteristics were analysed using Chase test following SAE J661. It was evident from the test results that Iron aluminum alloy based brake pads showed good fade and recovery characteristics. To study in detail regarding the worn surface characteristics, Scanning Electron Microscope with Elemental mapping was used.

Tribological Performance of Al Alloys Dispersed with Carbon Nanotubes or Ni-Coated Carbon Nanotubes Produced by Mechanical Milling and Extrusion

The microstructure, mechanical and tribological behaviors of Al alloy (AA), Al alloy-carbon nanotubes (AC) and Al alloy-Ni-coated carbon nanotubes composites (ANC) fabricated by mechanical milling of elemental powders and subsequent hot extrusion were investigated. Dry sliding wear tests conducted at three different normal loads reveal that the wear rate increases monotonously with the load. The formation and subsequent delamination of the mechanically mixed layer indicate that the general wear mechanism is a combination of sliding and adhesion, while ripple-like worn surface features correspond to wear mode transition. The higher wear resistance exhibited by AC and ANC samples correlates well with the corresponding mechanical properties achieved through the dispersion of carbon nanotubes (CNT) and Ni-coated CNT, following the traditional Archard’s wear relationship.

Two-Body Abrasive Wear Behaviour of In-Situ Al-TiC Particle Composites: Influence of TiC Reinforcement and Content in the Alloy Matrix and Experimental Parameters

This study pertains to observations made on the abrasive wear response of Al-TiC composites under varying applied load and traversal distance conditions. The influence of TiC particle reinforcement and its content in the matrix on the abrasion characteristics of the samples was investigated. The composites were prepared by generating the reinforcement phase (TiC particles) from within the matrix employing a hybrid in-situ technique consisting of a combination of steps involved in powder and liquid metallurgy routes of synthesizing metal matrix composites. The unreinforced matrix alloy (AA2014) was also tested under identical experimental conditions for comparison purposes. Properties characterized were wear rate, frictional heating and friction coefficient. Microstructural features of the samples and characteristics of wear surfaces, subsurface regions and abrasive medium have also been examined.
 
 The TiC reinforcement led to improved abrasion resistance (inverse of wear rate), the degree of improvement increasing further with the rising concentration of the TiC particles in the alloy matrix. Increasing applied load led to deterioration in the wear behaviour of the samples while a reverse trend was followed as the traversal distance was raised. The severity of frictional heating was noted to increase with load. On the contrary, friction coefficient tended to decrease with increasing load except for the composite containing the highest concentration of TiC wherein a reverse trend was noticed. Both frictional heating and friction coefficient increased sharply with traversal distance initially. This was followed by a reduction in the rate of temperature increase at longer traversal distances whereas friction coefficient was observed to attain steady state condition after showing a decrease in some cases. The presence of TiC reinforcement in the alloy matrix and its increasing content led to a decrease in the friction coefficient and the severity of frictional heating. The observed wear behaviour has been substantiated through the characteristics of abraded surfaces and subsurface regions of the samples and degradation of the abrasive medium. Operating material removal mechanisms have also been examined.

Wear resistance of 3D-printed denture tooth resin opposing zirconia and metal antagonists

Statement of problemAdditive manufacturing technology can be used for denture bases and also denture teeth. Therefore, the mechanical properties of 3D-printed resin denture teeth should be evaluated. PurposeThe purpose of this in vitro study was to compare the wear resistance of 3D-printed denture tooth resin with that of conventionally prefabricated denture teeth. Material and methodsEighty substrate specimens were prepared with 5 kinds of resin denture teeth: 3D-printed denture tooth resin (DENTCA denture tooth resin; DENTCA, Inc), Artic 6 (Kulzer GmbH), Preference (Candulor AG), Premium 6 (Kulzer GmbH), and Surpass (GC Corp). The 3D-printed denture tooth specimens were made of methacrylate-based photopolymerized resin by stereolithography 3D printing. Antagonistic surfaces were made from zirconia by milling and from cobalt-chromium (Co-Cr) alloy by 3D printing and casting. The specimens were loaded at 49 N for 30 000 cycles under thermocycling conditions in a mastication simulator. Wear resistance was measured by calculating the volume of substance lost. Wear surface characteristics were observed by using a scanning electron microscope (SEM). Two-way ANOVA was used to analyze the data (α=.05). ResultsThe influence of the resin denture teeth and the type of antagonist were both statistically significant. The wear volume loss of the 3D-printed denture tooth resin was higher than that of Artic 6 and Preference when opposing the zirconia and the metal antagonists (P<.05). The 3D-printed denture tooth resin did not show a significant difference from Premium 6 with the zirconia and the metal antagonists or Surpass with the zirconia antagonist. From the SEM images, the specimens of the 3D-printed denture tooth resin showed a relatively smooth surface with the zirconia antagonist and exhibited cracks when opposed by the metal antagonist. ConclusionsThe results suggest that 3D-printing by using resin materials provides adequate wear resistance for denture tooth use.

Evolution of ultrafine precipitates and its influence on wear mechanism in cryoprocessed high nitrogen martensitic steel

ABSTRACTDevelopment of the space engines with liquid propellants necessitates the use of bearings of high quality. During recent years, a new family of high strength corrosion resistant steels, with partial replacement of carbon by nitrogen, known as high nitrogen steels were developed having higher impact strength and fracture toughness coupled with high hardness for antifriction bearing of cryopumps in rocket. In this research work, wear characteristics of cryogenically treated high nitrogen martensitic stainless steels were investigated by Pin-on-disc wear testing machine. After conventional hardening treatment, specimens were subjected to cryogenic treatment at −196°C with cryosoaking period varying from 8 to 32 h in the interval of 8 h followed by soft tempering. These specimens were analysed for hardness, wear resistance, subsurface and worn surface features by SEM. It is established that there is a profound influence of nucleation and growth of precipitates on the wear behaviour and the underlying wear mechanisms.

Tribological Behavior of Ni-based Self-lubricating Composites with the Addition of Ti3SiC2 and Ag2W2O7

The tribological properties of Nickel-based composites containing Ti3SiC2 and Ag2W2O7 fabricated by spark plasma sintering against Si3N4 balls were investigated using a ball-on-disk tribometer from room temperature to 600 °C. The tribolayers formed on the friction surface and their effects on the tribological properties of composites at different temperatures were discussed based on the worn surface characterization. The results show that Ag2W2O7 is decomposed into metallic silver and CrWO4 during the high-temperature fabrication process. The composite with the addition of 20 wt% Ti3SiC2 and 5 wt% Ag2W2O7 exhibits a friction coefficient of 0.33–0.49 and a wear rate of 7.07×10−5–9.89×10−5 mm3/(Nm) over a wide temperature range from room temperature to 600 °C. The excellent tribological properties at a wide temperature range are attributed to the formation of a glaze layer at low temperature and a tribooxide layer at high temperature, which can provide a low shearing strength for the synergistic effects of Ag and tribooxides.

Wear Behaviour of ZA27-Based Composite Reinforced with 5 wt% of SiC Particles and Processed by Multi-directional Forging

Zinc aluminium-based alloys (ZA/27) are widely used in bearing application, but due to its density and higher level of porosity of cast component, it limits the usage of these alloys in automobile industries. Stir casting technique followed by squeeze process was adopted. ZA27-based silicon carbide particles (SiCP)-reinforced composite was subjected to multi-directional forging (MDF) at 100 °C and 200 °C up to three and six numbers of passes to a total strain of 0.54 and 1.09, respectively. Wear behaviour of ZA27/SiCP was investigated using pin-on-disc test rig. Distributions of SiCP were fairly uniform. Average grain size of 200–250 nm and 1–2 µm was achieved for three passes at 100 °C and six passes at 200 °C of MDF processed samples. Vickers hardness value increased by incorporation of SiCP. Better wear resistance was observed for MDF processed sample at 100 °C up to three passes. Wear mechanisms of the samples were validated through characteristics of worn surfaces.

Tribological Response of PEEK to Temperature Induced by Frictional and External Heating

Frictional heating is common during the dry sliding of polymers against steel, which further makes it complex to understand the friction and wear performance of polymers at high temperature. Towards the goal of addressing the tribological response of polymers to such combined temperatures, the counter steel was heated crossing the glass transition (150 °C) of polyetheretherketone (PEEK), and tribological tests were conducted during temperature ramping or at constant counterbody temperatures. With increasing temperature, different friction responses were revealed depending on the variation manner of temperature (sliding during ramping or at controlled counterbody temperature). Even so, counterbody temperature around PEEK’s glass transition defined a transition, from which distinct friction and wear of PEEK was exhibited. Based on real-time analysis of temperature in the counterbody and PEEK near to the sliding interface, the completion between frictional and external heating is discussed. In combination with worn surface characterization, this also helped understand the mechanisms behind such kind of tribological response to temperatures.

Spur gear wear analysis as applied for tribological based predictive maintenance diagnostics

This paper describes an experimental investigation on a pair of spur gears in which wear and pitting were intentionally allowed to occur, namely, moisture corrosion pitting, acid-induced corrosion pitting, hard contaminant-related pitting and mechanical induced wear. A back to back spur gear test rig was used throughout 32 test series. The tests samples of wear debris were collected and assessed through the utilization of an optical microscope in order to correlate and compare the debris morphology to pitting and wear degradation of the worn gears. In addition, weight loss from all test gear pairs were assessed with utilization of statistical design. It was observed that there were significant distinctions between both weight losses, wear debris morphology generated from each induced pitting conditions and worn surface characteristics. It can be deduced that wear debris characteristics exhibited a direct relationship with different pitting and wear modes. Thus, it should be possible to detect and diagnose gear pitting and wear utilization of worn surfaces, generated wear debris and quantitative measurement such as weight loss.

Tribological performance evaluation of fused mullite-reinforced hybrid composite brake pad for defence application

The current study deals with the replacement of existing sintered bronze brake pad using hybrid composite brake pads for armour vehicle application. In the present work, fused mullite was added in three different weight percentages which was compensated by synthetic barites. The pads were produced by conventional manufacturing procedure. The physical and mechanical properties were measured as per industrial standards. The tribological performance was evaluated using Chase test following IS2742 Part-4 standards. The test results showed that 3 wt% of mullite abrasive in hybrid brake pad formulation produced reduced density, less squeal, less frictional undulations with the minimum wear of 0.887 g for 100 brake applications. Worn surface characteristics were analysed using scanning electron microscopy.

Influence of Surface Groove Width on Tribological Performance for Cylinder Liner–Piston Ring Components

Surface groove width is of great significance to the performance of the cylinder liner–piston ring (CLPR) with the different surface textures in marine diesel. However, little is understood about the specific application (e.g., the geometric parameters of surface textures and operating conditions) of surface texture in actual marine diesel engines. To address this issue, different surface groove textures including grooves structures with 1-, 2-, 3-, and 4-mm widths were designed based on previous results related to marine diesel engine applications. A series of experimental tests was conducted in a reciprocation tester, and data on the friction characteristics were obtained under different operating conditions. Comparative studies on the friction coefficients, worn surface features, and oil film characteristics were performed. Results showed that the 2-mm groove structure of the cylinder liner was more favorable for improving the wear performances at low speed, whereas a 3-mm groove structure of the cylinder liner was more suitable for improving the wear performance at higher speeds, though its wear performance needs to be improved under high load. These results help to understand the specific application of surface texture on the wear performance of the CLPR pair.

Room and elevated temperature sliding wear behavior of cold sprayed Ni-WC composite coatings

The tribological properties of cold sprayed Ni-WC metal matrix composite (MMC) coatings were investigated under dry sliding conditions from room temperature (RT) up to 400°C, and during thermal cycling to explore their temperature adaptive friction and wear behavior. Characterization of worn surfaces was conducted using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy to determine the chemical and microstructural evolution during friction testing. Data provided insights into tribo-oxide formation mechanisms controlling friction and wear. It was determined that the steady-state coefficient of friction (CoF) decreased from 0.41 at RT to 0.32 at 400°C, while the wear rate increased from 0.5×10−4mm3/N·m at RT to 3.7×10−4mm3/N·m at 400°C. The friction reduction is attributed primarily to the tribochemical formation of lubricious NiO on both the wear track and transfer film adhered to the counterface. The increase in wear is due to a combination of thermal softening of the coating and a change in the wear mechanism from adhesive to more abrasive. In addition, the coating exhibited low friction behavior during thermal cycling by restoring the lubricious NiO phase inside the wear track at high temperature intervals. Therefore, cold sprayed Ni-WC coatings are potential candidates for elevated temperature and thermally self-adaptive sliding wear applications.

Effect of magnesium content on the microstructure and dry sliding wear behavior of centrifugally cast functionally graded A356-Mg2Si in situ composites

Functionally graded A356 alloy (Al–7.2Si–0.3Mg) –Mg2Si in situ composites have been synthesized via centrifugal casting route. Mg2Si particles tend to migrate towards the core of the tubular product by centrifugal force. The in situ formed Mg2Si particles in composites are characterized by x-ray diffraction (XRD) analysis, Energy dispersive spectrometry (EDS), Optical, Scanning Electron and Transmission Electron Microscopy. Apart from primary blocky Mg2Si particles the matrix contains other phases viz. Al-Si eutectic, pseudo-binary Al-Mg2Si eutectic and Al-Fe-Si intermetallics. Density is found to decrease and %porosity is increased with increase in volume fraction of Mg2Si. Maximum hardness was observed at the inner core region due to maximum segregation of Mg2Si particles and gradually decreases towards the outer periphery region. The dry sliding wear was evaluated with varying parameters such as normal loads (N) and sliding distances (m). A substantial increase in wear resistance at the inner core region is observed. From the worn surface characterization, the wear mechanisms have been explained.

Mechanical and Tribological Characteristics of Aluminium Powder filled Glass Epoxy Composites

Mechanical and tribological characteristics of glass epoxy composites with aluminium particulate (5-15 wt%) filler are experimentally investigated. Mechanical test is conducted on INSTRON 8801 whereas tribological characterization is done using a pin on disc type friction and wear monitor as per ASTM standards. With a fixed wt% of fiber reinforcement, and different wt% aluminium powder filler, glass epoxy composites are fabricated in conventional hand lay up technique followed by light compression moulding process. Tribological experiments are conducted for fixed speed, load and sliding distance. Worn surface features are examined by a scanning electron microscope (SEM). Results show steady decrease of tensile strength with aluminium powder addition. Friction and wear of 5 and 10 wt% aluminium content composites are less than unfilled glass epoxy composite. Glass epoxy composite with 5 wt% aluminium has the lowest frictional and wear characteristics whereas composite having 15 wt% aluminium shows the highest friction and wear.

Wear performance of bulk oriented nanocomposites UHMWPE/FMWCNT and metal-polymer composite sliding bearings

Traditional metal-polymer sliding bearings have low cost and may operate under conditions of dry sliding friction; however, the wear rate of such bearings can be unacceptably high. This work tests the hypothesis that applying a layer of bulk oriented, polymer-based nanocomposites can reduce both the friction coefficient and wear rate. Bulk oriented nanocomposites based on ultra-high molecular weight polyethylene (UHMWPE) and fluorinated carbon nanotubes were prepared and their wear performance against AISI 304 stainless steel was compared using a rotating ring-in-bushing arrangement. The effects of supramolecular structure, surface roughness, mechanical properties, and carbon nanotubes additions on the COF and energetic wear rate of the materials were studied. The wear surface features were studied using scanning electron microscopy. The coefficient of dry friction (COF) was investigated over a range of loadings from 9.64 to 16N. An average COF of bulk oriented nanocomposites decreased by 70% (at a load of 9.64N) in contrast to the UHMWPE matrix material. Localized fatigue wear of polymer layers on the UHMWPE having an isotropic structure were observed. Additions of carbon nanotubes and the formation of nanofibrillar structure facilitated the development of a smooth wear surface. There was a significant effect of nanotubes on the sliding COF and energetic wear rate. An extremely low COF (0.046) was obtained at a load of 57.3kPa for the metal-polymer composite bearing surface against stainless steel. Finally, a new technology to manufacture metal-polymer composite sliding bearings using a layer of oriented nanocomposites was proposed

Self-lubricating mechanisms via the in situ formed tribo-film of sintered ceramics with hBN addition in a high humidity environment

Sliding wear tests against monolithic Si3N4 and austenitic stainless steel, respectively, were performed on Si3N4 ceramic with the addition of hBN solid lubricants. The friction coefficients and wear rates were measured. The wear surface features were examined by scanning electron microscopy (SEM) and laser scanning microscopy (LSM), and the chemical characterization of worn surface was made by Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Results showed that the friction coefficient and the wear rate decreased with the increase of hBN up to 20vol% at high relative humidity (RH95%). When Si3N4-hBN ceramic composites sliding against stainless steel, with further increases in hBN content, the wear rate increased rapidly. The mechanism responsible were determined to be an in-situ formed tribo-chemical film composed of B-O and Si-O compounds between the pin-disc sliding couple. SEM observations showed that a black surface film is formed on the wear surface depending on the hBN content. The surface film associated with small friction coefficient of 0.03 and low wear rate with the magnitude of 10−6mm3/Nm was formed by the releasing and smearing of the tribo-chemical reaction products of hBN and moisture on the wear surface when with 20vol%hBN content. This tribo-chemical film acted as solid lubricant film between the sliding couple, and thus the couple entered to a state of boundary lubrication. Hence, the friction coefficient and the wear rate were significantly reduced. For Si3N4-hBN/stainless steel sliding pair, even at high relative humidity, no tribo-chemical film was observed on samples with 30vol%hBN content, just because of a large degradation of mechanical properties of the composite with higher hBN content. At low relative humidity (RH25%), the wear mechanism for Si3N4-hBN sliding couple was mainly dominated by mechanical wear (abrasive or adhesive wear) due to the absence of tribo-chemical film on the wear surfaces, and higher friction coefficient and wear rate were obtained.

Tensile, compressive and wear behaviour of self-lubricating sintered magnesium based composites

The graphite (Gr)/MoS2 reinforced Mg self-lubricating composites were prepared through powder metallurgy. The composites were characterized for microstructure, physical, mechanical and wear properties. Gr/MoS2 phase in the composites was identified by XRD analysis. Microstructural observation showed that the Gr/MoS2 particles were homogeneously dispersed within the magnesium matrix. Micro-hardness was measured using an applied load of 5 g with a dwell time of 15 s at room temperature. Hardness of all the composites was measured to be in the range of VHN 29–34. The mechanical properties were studied using micro-hardness, tensile and compression tests. A fractographic analysis was performed using scanning electron microscope. The highest values of hardness, compressive strength and tensile strength were attained using Mg–10MoS2 composite. A pin-on-disk tribometer was used to measure the friction coefficient and the wear loss of the sintered composites. In addition to that, the friction and wear mechanism of the composites were systematically studied by worn surface characterization and wear debris studies using SEM analysis. The reduced friction coefficient and wear loss were achieved in MoS2 rather than Gr.

Vacuum pressure dependence of the tribological behaviors of sintered polycrystalline diamond sliding against silicon nitride

The friction and wear behaviors of sintered polycrystalline diamond (PCD) were investigated under various vacuum pressures using a ball-on-disk space tribometer. The wear surface features of PCD and Si3N4 mating balls were examined by scanning electron microscope (SEM). Energy dispersive X-ray spectrum (EDS), X-ray diffraction (XRD) and Raman spectroscopy were performed to detect the chemical composition of the worn surfaces formed on PCD discs and mating balls. The results proposed that the tribological behaviors of PCD are significantly affected by the vacuum pressure. The coefficient of friction (COF) presented low stable values under high pressures, while COFs were much higher and fluctuated in lower pressures. It might be contributed to different degrees of passivation of σ bonding on the surface of PCD. In high pressure, the occurrence of mild abrasive results in slight wear for both PCD and Si3N4 mating balls. Inversely, much more severe adhesive wear takes place in lower pressure. It demonstrated that a high friction-induced graphitization and strong adhesive force lead to the shedding of diamond grains, resulting in the serious wear of PCD in low pressures. These results proposed that the tribological behaviors of PCD were significantly affected by vacuum pressure.

Wear and tribocorrosion behaviour of 304L stainless steel welds

The influence of the microstructures of the base metal and weld metals on the wear and tribocorrosion properties of 304L stainless steel (SS) welds prepared by Manual Gas Tungsten Arc Welding (M-GTAW) and Activated Flux Gas Tungsten Arc Welding (A-GTAW) processes are reported. Increase in sliding speed increased both friction forces as well as wear rate. Higher hardness in M-GTAW weld metal resulted in increased wear resistance than A-GTAW weld metal and base metal. The inferior wear resistance of the base metal was due to the strain hardening behaviour under sliding condition. The polarization curves showed increase in passive current density under sliding condition. The applied potential was found to influence the tribocorrosion resistance of the material. Under tribocorrosion condition, the total material loss was higher in base metal followed by A-GTAW weld metal and M-GTAW weld metal. Characterization of worn surface by SEM indicated a mixed wear mechanism of abrasive and adhesive wear. The worn surface appeared relatively smoother in nitric acid medium than in dry condition. The influence of microstructure affecting the hardness, wear and tribocorrosion resistance of the base metal and weld metals of 304L SS is discussed.