The tribological behavior of a commercial brake pad material, wear tested under dry sliding conditions against a cast iron counterface disc with a pin-on-disc apparatus, was investigated. Wear tests ...were conducted at the following disc temperatures: 25°C, 170°C, 200°C, 250°C, 300°C and 350°C. Above 170°C a transition from mild to severe wear was observed. At 25°C and 170°C, the friction layer on the pin surface consists of primary and compacted secondary plateaus. At 200°C and above, a progressive reduction of the pin surface coverage by the secondary plateaus, that are barely present after the 350°C test, is observed. Wear tracks on the discs derive from wear fragments due to the tribo-oxidation of the disc itself and from the wearing out of the pin material. The observed tribological behavior is very much influenced by the thermal degradation of the phenolic binder of the friction material, confirmed by thermogravimetric analyses, conducted on purpose on the pin material. Raman spectroscopy indicated the presence of carbonaceous products on the high temperature worn out pin surface. Although referring to rather extreme and simplified sliding conditions, the results obtained in this study provide useful indications on the role of the thermal stability of the organic component.
•High temperature pin-on-disc wear tests.•Brake friction material against cast iron disc.•Main tribological phenomena identified.•Decompostion of the phenolic resin paramount above 200°C.•Nearly complete lack of friction layer above 350°C.
The tribological phenomena that occur in brake systems are interesting even in other respects than just the braking action. One important issue, that is gaining increasing importance over the last ...years, concerns the environmental impact of wear debris produced by the braking action. In this context, the present study is focussed on the tribological behaviour of a commercial friction pad material dry sliding against a cast iron disc. Pin-on-disc tests were conducted at room temperature under mild wear conditions, as concerns load and rotating speed. The effect of some components of pad material, in particular of copper, on the dynamic of formation of tribological layer and wear debris is presented. The results obtained so, although referring to quite a simpler system that real brake systems, still may provide interesting indications, for instance in view of the development of novel brake pad materials and braking control systems.
•Wear of the cast iron counterface is by tribo-oxidation.•Different pad constituents form the primary plateaus.•Pad wear is controlled by the secondary plateaus.•Copper plays an important role for a better quality of the secondary plateaus.
In commercial automotive braking systems, consisting of a friction pad dry sliding against a pearlitic cast iron disc, the wear of the disc contributes significantly to the overall wear. In the ...present work, pin-on-disc sliding tests were carried out for determining the role of conventional heat-treatment conducted on cast iron discs on the friction and wear behavior of the above coupling. Wear rates of both disc and friction materials were reduced by almost one order of magnitude when the disc is preliminarily heat-treated and then ground to remove the surface decarburized layer that forms during the thermal cycle. Heat-treatment and heat-treatment plus grinding resulted also in the decrease of the friction coefficient, which was comparatively lower for the ground samples. The friction and wear behavior along with the contact temperature evolutions were rationalized according to the actual materials characteristics, as resulting from the different treatments.
•Heat treatment reduces wear sliding materials.•Surface grinding is necessary to remove the decarburized layer.•Friction coefficient is slightly reduced by heat-treatment plus grinding.•Contact temperature is affected by friction and cast iron microstructure.
In this work a streamline characterization protocol for debris coming from wear tests on materials used for disc brake assemblies is presented. An important aspect of the methodology concerns powder ...collection involving aluminum foil, for a gravitational collection, and polycarbonate filters of an impactor, on which particles are selectively trapped, according to their size. The protocol is based on the application of scanning and transmission electron microscopy, X-ray spectroscopy, X-ray and selected area electron diffraction. The aim of the study was to identify selection parameters, like specimen availability and average particle size, for an effective and smart application of the techniques.
•Debris from brake assemblies are becoming an important environmental issue.•Debris particle size range from nanometric up to micrometric interval.•Phase and chemical compositions are generally rather complex.•We developed a characterization protocol for debris involving several techniques.•We suggest criteria to adopt suitable test strategies for this sort of specimens.
In this paper, an investigation of the load-dependent wear behavior of copper-free semi-metallic brake material is presented. The experiments were conducted in ambient thermal settings with varying ...sliding velocities (3.141 m/s, 2.09 m/s, and 1.047 m/s), normal load (60 N, 50 N, and 40 N), and sliding distance (4500 m, 3000 m, and 1500 m). Taguchi’s method was used in designing experiments to examine the output through an L9 orthogonal array. ANOVA was used to identify the consequence of interactions among different constraints. It also established the significant contribution of each process factor. The objective was set as the ‘smaller is better’ criterion to find minimum wear conditions. The impact of the normal load on the wear process was found to be maximum (71.02%), followed by sliding velocity (27.84%) and sliding distance (1.14%). The optimum condition for the minimum wear rate was found at 40 N normal load, 1500 m sliding distance, and 3.14 m/s sliding velocity. The results were confirmed with validatory friction experiment runs. The resulting error was within 10% error, which verified the experiment methods. The SEM investigation of worn surfaces of pin and disc confirmed abrasive wear and adhesive wear at 60 N and 40 N, respectively.
Dental implants play an important role in the reconstruction of the lost tooth. The implant materials and manufacturing techniques are of significant importance in the performance of the implants. ...Conventional dental implant materials such as titanium and zirconia exhibit many limitations such as allergies, peri-implant bone loss, and implant fractures. Implant fractures are caused due to stress shielding arising from the significant difference in mechanical properties between the implant and jawbone. However, polymeric materials can overcome the limitations of metallic implant materials. In this work, Polyether ether ketone (PEEK) specimens are manufactured using the fused deposition molding (FDM) technique, and the effect of printing parameters on its mechanical properties are investigated for dental implant applications. Three different raster angles, (0°/0°), (45°/−45°), and (90°/90°), were considered, and an array of mechanical characterizations are performed on the printed specimens to find tensile, compression, flexural, hardness, and saliva absorption properties for as-printed and saliva soaked conditions. 3D-printed PEEK specimens with a (45°/−45°) raster angle displayed a superior mechanical properties compared to other raster angle specimens. Results showed that 3D printed PEEK exhibits similar properties to natural human tooth enamel, while extruded PEEK exhibits characteristics similar to natural dentin and cortical bone. The 3D printed PEEK crown's potential to withstand compressive loads during biting (∼50 N) was also evaluated and found that the PEEK has adequate mechanical properties to be a better low-cost implant material than titanium and zirconium.
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•Conventional dental implant materials such as titanium and zirconia cause stress shielding, leading to implant failures.•PEEK specimens were manufactured using 3D printing and mechanical properties are investigated for dental implant applications.•3D printed specimens with (45o/-45o) raster angle showed better mechanical properties compared to other raster angles.•3D printed PEEK samples have enamel-like properties; extruded PEEK samples have dentine and cortical bone properties.•The total cost of 3D printed PEEK dental implant can be well over 10 times lower than the conventional dental implants.
The MoS
2
nanoflakes can be a novel candidate as a solid lubricant in fabricating friction material for automotive brake-pad disc systems. In this paper, an investigation has been made to analyze the ...effect of MoS
2
nanoflakes on the mechanical and tribological behavior of the formulated copper-free low-metallic composite friction material. Three samples, namely S
1
, S
2,
and S
3,
have been fabricated containing different types of solid lubricant. Sample S
1
had a solid lubricant as graphite, while samples S
2
and S
3
had graphite mixed with solid lubricant MoS
2
with average flake sizes of 2 µm and 50 nm, respectively. Other components included steel, PAN, and aramid as reinforcing fibers; walnut powder, barium sulphate (BaSO
4
), and nitrile-butadiene rubber as fillers; phenolic resin as a binder; and FeO, Quartz, and MgO as abrasives. A pin-on-disc tribometer test (ASTM G-99) was conducted to carry out the wear test at a load of 60 N, sliding velocity of 2.09 m/s, and sliding distance of 6283 m at room temperature. A scanning electron microscope was used to study the micro-structural evolution of worn composite friction pin material. The results show that the nano-sized MoS
2
solid lubricant influences the structural integrity of the formulated composites, which governs the friction and wear behavior. The graphite and MoS
2
-based friction composites S
2
and S
3
perform better than the conventional friction material (S
1
) containing graphite in terms of physical–mechanical, thermal, and tribological properties. The specific wear rate of the S
1
sample is the highest (2.72 × 10
–5
mm
3
/Nm) followed by S
2
(1.84 × 10
–5
mm
3
/Nm) and S
3
(0.98 × 10
–5
mm
3
/Nm) respectively. The graphite and MoS
2
-based friction specimens S
2
and S
3
showed adequate coverage of friction plateaus, reducing wear and abrasion of the counter disc.
Graphical Abstract
Purpose: This study explored the bio-mechanical properties of polyether ether ketone (PEEK) and carbon fiber reinforced-PEEK (CFR-PEEK) as potential alternatives to traditional dental implant ...materials, such as titanium (Ti) and zirconia (ZrO2). Conventional implant materials often exhibit stress shielding leading to peri-implant bone loss and implant failure.Study selection: Finite element analysis using a three-dimensional computer-aided-design (3D CAD) model of the jawbone with various implant materials (titanium, zirconia, PEEK, and CFR-PEEK) incorporated was implemented to assess the effectiveness of PEEK and CFR-PEEK. Two loading conditions (50 and 100 N) were applied in centric (case-1) and eccentric (case-2) to mimic the oral loading conditions.Results: Titanium and zirconia implants were found to exhibit higher levels of stress shielding and therefore pose greater risks of bone loss and implant failure. Conversely, CFR-PEEK implants demonstrated more-uniform stress distributions that reduce the likelihood of stress shielding compared to their conventional counterparts; consequently, CFR-PEEK implants are particularly suitable for load-bearing applications. Furthermore, maximum strain values on PEEK-implanted cortical bone reached a state of adaptation, referred to as the “lazy zone” in which bone growth and bone loss rates are equal, indicating PEEK’s potential for a long-term implant utilization.Conclusions: PEEK and CFR-PEEK implants are promising alternatives to conventional dental implants because they provide stress shielding and promote bone health. Improved stress distribution enhances long-term success and durability while mitigating complications, and highlights their applicability to dental implant procedures.
In this study, magnetron sputtered carbothermic reduced iron boride (FeB) coatings were developed on grey cast iron (GCI) substrates at different substrate temperatures. The impact of substrate ...temperature on structural, mechanical, and corrosion behavior was examined for two FeB deposition scenarios: FeB coatings deposited at room temperature (RT) and at 500 °C substrate temperature. The evolution of phases and microstructure was studied using XRD and FESEM, respectively. The mechanical properties, creep, deformation behavior, and adhesion strength (scratch test) of the deposited coatings were investigated using nanoindentation at ambient temperature. The highest hardness and Young’s modulus of 16 GPa and 231 GPa respectively, were achieved at 500 °C due to microstructural enhancement. Potentiodynamic polarization and electrochemical impedance spectroscopy were used to evaluate the corrosion behavior of the coatings. The results show that substrate temperature strongly influences the surface morphology of the coatings, which in turn governs the mechanical and corrosion behavior of the FeB coating. The FeB-coated GCI at 500 °C substrate temperature showed higher resistance to scratching, better mechanical properties, and improved corrosion resistance which is attributed to the enhanced adhesive strength, refined microstructure, and formation of protective oxide layers of FeB on the surface of the coatings.
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•FeB coatings have a hardness of 11.8 GPa, an elastic modulus of 165 GPa at RT, and 15.6 GPa and 231 GPa at 500 °C.•The FeB coating showed conformal cracking at RT and tensile cracking at 500 °C, indicating better adherence at 500 °C.•At 500 °C, the FeB coating displayed improved corrosion resistance and reduced corrosion current density.•EIS data revealed higher charge transfer resistance and a larger semicircle arc for the FeB coating at 500 °C compared to RT.
In this research, Laser Cladding (LC) of three different alloys powders, two iron-based (AISI 4140 and SS420) and a Cobalt-based (Stellite 6) was performed on a Grey Cast Iron (GCI) substrate. The ...Stellite 6, SS420, and AISI 4140 cladding samples were tested against a semi-metallic composite brake pin for friction and wear study using a pin-on-disc friction test rig (under dry-sliding conditions). The surface wettability tests were performed on GCI, and cladding discs showed Stellite 6 and AISI 4140 were hydrophobic while SS420 and GCI were hydrophilic. Stellite 6, SS420, and AISI 4140 had surface hardness values of 542.16 HV1, 689.56 HV1, and 719.50 HV1, respectively. The friction test indicated that AISI 4140 and Stellite 6 cladding discs could produce a stable Coefficient of Friction (CoF) and friction layer coverage. SS420 could not maintain a constant CoF for the entire test duration as the plowing effect of the wear particles damaged the friction layer created on its surface. Stellite 6's average CoF value was closest to that of the GCI disc, whereas AISI 4140 and SS420 were found to have a higher average CoF. The LC on grey cast iron reduced its wear rate, with AISI 4140 being the most wear-resistant cladding, followed by SS420 and Stellite 6, respectively. All three cladding layers exhibited three-body abrasive wear, with the rolling mechanism dominating the AISI 4140 surface and sliding on the remaining two.
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•Stellite 6 and AISI 4140 cladding disc shows hydrophobicity, whereas hydrophilicity in SS 420 and GCI.•AISI 4140 was the hardest wear-resistant laser cladding layer, followed by SS420 and Stellite 6.•Plowing and detached layer transfer cause the continuous rising of SS420's CoF value.•Abrasive wear mechanism dominates in cladding surfaces and tribo-oxidation in GCI substrate.•All cladding surfaces had significant friction layer coverage, while SS420 had the least and Stellite 6 the most.
