Friction Stability Research Articles

Microstructure and friction properties of NiTi2-based composite layer prepared by ultrasonic assisted underwater wet laser deposition

An in situ TiC-enhanced NiTi2-based composite deposition layer was prepared by ultrasonic assisted underwater wet laser deposition. The evolution of the microstructure and interface state, and the friction properties in the air and brine solution environments of the deposition layer were analyzed and researched. The results demonstrated that the thermal and steady-state cavitation from ultrasound effects increase the total energy of the melt pool and promote mixing. The dilution rate of the ultrasonic assisted underwater laser deposition layer increases to 86.72 % compared with that of the underwater laser deposition layer (78.75 %). Ultrasonic reduced underwater laser deposition defects such as lack of fusion and weld slag, and enhanced the wettability between the deposition layer and substrate. The contact angle of the UWNT layer (24.40°, in average) is smaller than the WNT layer (29.80°, in average). Ultrasonic shortened the contact time between the deposition layer surface and the solution, which reduced the reaction of the Ni element with the brine solution. It also transformed the deposition layer from hypereutectoid microstructure to hypoeutectic microstructure and from planar interface to cellular interface. With the effect of the ultrasonic field, the elements in the deposition layer become more uniformly distributed and the secondary phases undergo spheroidization. In the ultrasonic assisted deposition layer, stress-induced FCC-Ti was discovered. Ultrasonic field also reduced the dispersion of the microhardness and increased the average microhardness to 863.3 ± 45.1 HV0.3. Tribology properties show that ultrasonic field effectively improved the wear resistance and friction stability of the ultrasonic assisted deposition layer. The COF of the ultrasonic assisted deposition layer was less affected by the environment, with values of 0.25 and 0.24 observed in air and brine solution, respectively. Overall, the research results in this paper can provide a new insight to improve the surface properties of NiTi2-based alloy underwater laser deposition.

Sustainable Grease Lubrication Induced by Graphene Oxide and LiFePO4

This study investigates the possibility of modifying lubricating greases by 2D graphene oxide (GO) and lithium iron phosphate (LiFePO4) to enhance their tribological performance. GO's layered structure plays a crucial role in reducing friction by facilitating easy sliding between rubbing surfaces, making it an effective solid lubricant. The impact of these additives on friction reduction, wear resistance, and the tribolayer formation ability is evaluated by ball‐on‐disc tribometry with an emphasis on durability and sustainability. Comparative results reveal that unmodified greases exhibit a high susceptibility to wear, including oxide formation and severe plastic deformation. In contrast, greases with GO show a notable reduction in friction, while the addition of LiFePO4 contributes to the formation of a continuous protective layer that substantially reduces abrasive wear. The combination of GO and LiFePO4 results in a homogeneous, durable tribofilm that effectively protects surfaces against severe wear providing long‐term friction stability. Although lab‐scale LiFePO4 is used, the findings suggest a great potential for extending the useful life of recycled LiFePO4 from lithium‐ion batteries, similar to commercial LiFePO4 thus confirming significant improvements in the grease performance but also highlighting the potential to advance toward more sustainable solutions in industrial applications and electric vehicles.

Alternatives to Friction Coefficient: Fine Touch Perception Relies on Frictional Instabilities.

Fine touch perception is often correlated to material properties and friction coefficients, but the inherent variability of human motion has led to low correlations and contradictory findings. Instead, we hypothesized that humans use frictional instabilities to discriminate between objects. We constructed a set of coated surfaces with physical differences which were imperceptible by touch but created different types of instabilities based on how quickly a finger is slid and how hard a human finger is pressed during sliding. We found that participant accuracy in tactile discrimination most strongly correlated with formations of steady sliding, and response times negatively correlated with stiction spikes. Conversely, traditional metrics like surface roughness or average friction coefficient did not predict tactile discriminability. Identifying the central role of frictional instabilities as an alternative to using friction coefficients should accelerate the design of tactile interfaces for psychophysics and haptics.

Using lubricant composition to control friction-induced-vibration in an elastomer-steel contact representing a hydraulic seal

Hydraulic seals are key industrial components that can suffer from unwanted friction induced vibration (FIV). The types of FIV mechanism that occur in these components, and how they may be controlled, are not well known. We conducted sliding friction tests on contacts between seal materials, lubricated by hydraulic fluids, under speeds and contact pressures typical of hydraulic machines. FIV that occurred under certain conditions was captured and analysed. Results suggest 1) two FIV mechanisms are occurring: classic stick-slip and speed dependant friction instability, the 2) occurrence and severity of these mechanisms are correlated with the ratio of static to dynamic friction and the gradient of the friction vs. speed (Stribeck) curve, respectively, 3) these parameters can be controlled by including an appropriate additive package in the lubricant and this significantly reduces FIV, 4) most FIV occurs at low temperature and high load since these both lead to low kinetic friction (due to thicker hydrodynamic films and smoother surfaces) and thus promote stick-slip. This may explain instances of noise known in practice as the “Monday-morning effect” and suggests how this too may be alleviated through lubricant formulation.

Effects of Chemical Alteration on Frictional Properties in a Deep, Granitic, Geothermal System in Cornwall: Direct Shear Experiments at Near In Situ Conditions

AbstractThe geochemical alteration of host rocks might affect the productivity and the potential for induced seismicity of geothermal systems. In addition to natural alteration, following production and heat extraction, re‐injected fluids at lower temperatures and different pressures may be in chemical disequilibrium with the rock, impacting mineral solubility and dissolution/precipitation processes. In this study, we investigate the effect of geochemical alteration on the frictional behavior of granites, and their seismogenic potential, by conducting direct shear experiments using samples with varying degrees of alteration. The samples originate from the Carnmenellis granite in Cornwall, SW England, and represent the formation used in the United Downs Deep Geothermal Power Project for heat extraction. Experiments were conducted on granite powders (referred to as gouges) at room temperature and 180°C, at simulated in situ confining and pore pressures of 130 and 50 MPa, respectively (∼5 km depth). With increasing degree of alteration, the frictional strength of the gouges decreases while frictional stability increases. At high temperature, frictional stability is reduced for all samples while maintaining the trend with alteration stage. Microstructural investigation of the sheared gouges shows alteration delocalizes shear by reducing grain size and increasing clay fraction, which promotes the formation of pervasive shear fabrics. Our work suggests that, within the range of tested pressures, more alteration of granite initially causes more stable shearing in a fault. This behavior with alteration is sustained at high temperatures, but the overall frictional stability is reduced which increases the potential for induced seismicity at higher temperatures.

Frictional Strength and Frictional Instability of Glaucophane Gouges at Blueschist Temperatures Support Diverse Modes of Fault Slip From Slow Slip Events to Moderate‐Sized Earthquakes

AbstractFluid overpressure from the water released by subducted sediments and oceanic crust is an important mechanism for generating earthquakes via brittle failure and frictional instability. If unstable, such fault materials may also host diverse fault reactivation mechanisms from slow slip events to moderate‐sized earthquakes in cold subduction zones. We examine this hypothesis for glaucophane gouge ‐ a key index minerals for blueschist facies ‐ at lower confining stresses where behavior is poorly understood. We measure friction and stability at temperatures of 100°C–500°C and effective normal stresses of 50–200 MPa, to explore the controls of temperature, stresses and excess pore fluid pressures on fault friction. The frictional coefficient of glaucophane at representative temperatures and stresses is ∼0.70, insensitive to temperature but with a slight increase at lower effective stresses. Elevating temperature promotes a transition from velocity‐strengthening to weak velocity‐weakening behavior, indicating the destabilizing effect of high temperature downdip in subduction zones. Reducing effective normal stress or concomitantly elevating pore fluid pressure further strengthens the velocity‐weakening response and would be manifest as moderate‐sized earthquakes. Our results support the potential for enhanced unstable sliding of glaucophane gouges at lower effective stresses and blueschist facies temperatures ‐ with weak to moderate velocity‐weakening responses upon fluid pressurization vital for understanding the abundance of slow slip to moderate‐sized earthquakes apparent in cold subduction zones.

Hydrothermal preparation of magnesium alloy surface composite coatings and its performance research

Magnesium alloys have great potential for industrial and aerospace applications due to their low density and high strength. Aiming at its defects of poor corrosion resistance and susceptibility to galvanic coupling corrosion in metal coatings, a composite coating was prepared on the surface of AZ91D magnesium alloy by the hydrothermal method. Scanning electron microscope, x-ray diffraction, and x-ray photoelectron spectroscopy were used to characterize the surface micromorphology, phase composition, and elemental valence and evaluate the adhesion of the coating to the substrate by the ASTM D3359-09 test standard. Electrochemical experiments were done in a 3.5% NaCl solution. The results show that there are nanoscale dense granular structures on the surface of the samples, and the main components of the coatings are Mg(OH)2, Al2O3, and MgSiO3. ASTM grade 4B is between coating and substrate. The corrosion rate of the best sample was reduced by a factor of 238.96 compared to the substrate, and the corrosion current density was reduced by two orders of magnitude. The corrosion rate and corrosion current of the samples after repeated friction did not change much compared with those before friction, which proved that the composite coating had better corrosion resistance and friction stability.

Heterogeneous mineralogical composition and fault behaviour: A systematic study in ternary fault rock compositions

The heterogeneous mineralogical compositions of fault gouges, formed during fault evolution, influence frictional properties and slip behaviour. While the influence of individual mineral phases on friction has been extensively studied, the impact of varying systematically mineral phases in gouge mixtures on macroscopic frictional behaviour remains unclear. Thus, we performed 34 frictional experiments on fault gouges composed of three representative mineral phases: muscovite (platy phyllosilicate), quartz (granular silicate) and calcite (granular carbonate), known for their markedly distinct frictional properties. Using a biaxial rock deformation apparatus (BRAVA), we performed tests on fault gouges with grain sizes <125 μm under normal stresses of 50–100 MPa, at room temperature and water-saturated conditions. Our data indicate that the mineralogical composition of fault gouges significantly affects frictional strength, healing, and stability with a non-trivial pattern. Increasing the muscovite content leads to a decrease in frictional strength, from 0.62 for pure calcite and 0.56 for pure quartz to 0.33 of pure muscovite, along with reduced frictional healing and a velocity-strengthening behaviour. This weakening is promoted by a transition from localized deformation along discrete shear planes in granular-rich fault gouges to distributed deformation within the entire gouge layer with increasing muscovite content. At fixed muscovite content, frictional properties depend on the dominant granular phase. Calcite-dominated mixtures exhibit more marked frictional weakening rather than quartz-dominated ones, suggesting a non-linear mixing law between friction coefficient and muscovite content. This different trend is likely due to favourable conditions for fluid-assisted pressure-solution of calcite and foliation development, unlike quartz. When only the granular phases are mixed, we observe complex behaviour with the indentation of quartz into calcite, resulting in higher values of healing rates than those of pure end-member mixtures.Our findings provide robust insights into microphysical processes strongly dependent on the complex mineralogical compositions usually observed along natural faults.

TRIBOINFORMATICS: MACHINE LEARNING METHODS FOR FRICTIONAL INSTABILITIES

The study of friction is traditionally a data-driven area with many experimental data and phenomenological models governing structure-property relationships. Triboinformatics is a new area combining Tribology with Machine Learning (ML) and Artificial Intelligence (AI) methods, which can help to establish correlations in data on friction and wear. This is particularly relevant to unstable motion, where deterministic models are difficult to build. There are several types of friction-induced instabilities including those caused by the velocity dependency of dry friction, coupling of friction with another process (wear, heat generation, etc.), the elastic Adams instabilities, and others. The onset of sliding is also an unstable process. ML/AI methods, such as Topological Data Analysis and various ML algorithms, which have been already used for various aspects of data analysis on friction, can be applied also to the frictional instabilities.

Synergistic reinforcement mechanisms of Cu/graphite composites with MAX phase Ti2AlN and ZrO2-B4C ceramics: Enhancements in mechanical, thermal, and tribological properties

In braking materials field, MAX phase has been introduced into Cu-based composite materials to address issues such as inadequate wetting between ceramic particles and the metal matrix. This study focuses on preparing Ti2AlN-ZrO2-B4C reinforced Cu-based materials via the powder metallurgy method, and investigates the effects and mechanisms of different Ti2AlN/ZrO2 ratios on the mechanical, thermal, and tribological properties of these materials. The addition of an appropriate amount of Ti2AlN (3 wt%) can enhance the densification and mechanical properties of Cu-based materials, as the diffusion of Al atoms promotes the sintering process. Similarly, the diffusion of Al also improves the thermal conductivity at grain boundaries, resulting in samples with higher Ti2AlN content exhibiting superior thermal diffusivity. When the Ti2AlN content reached 7 wt%, the material exhibited optimal hardness (43.35 ± 1.05 HBW), moderate shear strength (19.84 ± 1.86 MPa), as well as excellent high initial braking speed friction coefficient and stability. The reinforcement primarily arises from the diffusion bonding between Ti2AlN and Cu, leading to the formation of Cu-Ti compounds at the interface, which facilitates Ti2AlN in providing frictional force during the friction process and promotes the formation of a friction film due to the “pinning effect”. Additionally, the layered structure of Ti2AlN and the subsequent formation of amorphous Al2O3 after oxidation contributed to the enhancement of friction stability.

Effects of Particle Size and Normal Stress on the Frictional Stability and Healing of Simulated Basalt Gouges: Implications for Lunar Seismicity

Effects of Particle Size and Normal Stress on the Frictional Stability and Healing of Simulated Basalt Gouges: Implications for Lunar Seismicity

Structure and tribological behavior of a polyetherimide/polytetrafluoroethylene matrix filled with negative thermal expansion zirconium tungstate particles

Thermal expansion mismatch stresses may be a reason for premature failure of sealing and bearing components made of polymer composites that are rubbed against metallic surfaces at elevated temperatures. It is of particular importance for polymer matrix composites loaded with anti-friction inclusions of polytetrafluoroethylene (PTFE) that possesses high coefficient of thermal expansion. In this regard, a study was undertaken to elucidate the effect of the thermal mismatch on wear and friction of amorphous polyetherimide (PEI) matrix loaded with either polytetrafluoroethylene (PTFE) particles (i) or PTFE particles covered with negative thermal expansion zirconium tungstate (ZT) α-ZrW2O8 (ii) at temperatures 23 °C, 120 °C and 180 °C. The ball-on-disk testing scheme was used according to standard with AISI 52100 steel balls rubbed against a polymer composite disks at normal force P = 5 N and sliding velocity V = 0.3 m/s. The PEI/PTFE/ZT composite demonstrated a tendency for wear rate (WR) reduction in sliding at 120 °C and 180 °C as compared to corresponding WR enhancement on the PEI/PTFE. The rationale is provided that the ZT additive effectively reduced thermal expansion of the PTFE in the PEI matrix and thus improved wear resistance of the composite. New thermal expansion-controlled wear and friction instability mechanism has been proposed and discussed.

Micro-arc driven porous ZrO2 coating for tailoring surface properties of titanium for dental implants application

Titanium (Ti) is an ideal material for dental implants due to its excellent properties. However, corrosion and mechanical wear lead to Ti ions and particles release, triggering inflammatory responses and bone resorption. To overcome these challenges, surface modification techniques are used, including micro-arc oxidation (MAO). MAO creates adherent, porous coatings on Ti implants with diverse chemical compositions. In this context, zirconia element stands out in its wear and corrosion properties associated with low friction and chemical stability. Therefore, we investigated the impact of adding zirconium oxide (ZrO2) to Ti surfaces through MAO, aiming for improved electrochemical and mechanical properties. Additionally, the antimicrobial and modulatory potentials, cytocompatibility, and proteomic profile of surfaces were investigated. Ti discs were divided into four groups: machined – control (cpTi), treated by MAO with 0.04 M KOH – control (KOH), and two experimental groups incorporating ZrO2 at concentrations of 0.04 M and 0.08 M, composing the KOH@Zr4 and KOH@Zr8 groups. KOH@Zr8 showed higher surface porosity and roughness, even distribution of zirconia, formation of crystalline phases like ZrTiO4, and hydrophilicity. ZrO2 groups showed better mechanical performance including higher hardness values, lower wear area and mass loss, and higher friction coefficient under tribological conditions. The formation of a more compact oxide layer was observed, which favors the electrochemical stability of ZrO2 surfaces. Besides not inducing greater biofilm formation, ZrO2 surfaces reduced the load of pathogenic bacteria evidenced by the DNA-DNA checkerboard analysis. ZrO2 surfaces were cytocompatible with pre-osteoblastic cells. The saliva proteomic profile, evaluated by liquid chromatography coupled with tandem mass spectrometry, was slightly changed by zirconia, with more proteins adsorbed. KOH@Zr8 group notably absorbed proteins crucial for implant biological responses, like albumin and fibronectin. Incorporating ZrO2 improved the mechanical and electrochemical behavior of Ti surfaces, as well as modulated biofilm composition and provided suitable biological responses.

Rate-and-state friction of epidote gouge under hydrothermal conditions and implications for the stability of subducting faults under greenschist metamorphic conditions

Epidote is a common hydrous mineral present in subduction zones subject to greenschist metamorphic conditions – and potentially an important control on the fault stability-instability transition observed under greenschist facies. We explore controls on this transition through shear experiments on simulated epidote gouge at temperatures of 100–500 °C, effective normal stresses of 100–300 MPa and pore fluid pressures of 30–75 MPa. We use rate-and-state friction to define these controls of temperature, effective stress and pore fluid pressure on gouge stability. Experimental results indicate that the epidote gouge is frictionally strong (μ ∼ 0.73) and the frictional strength is insensitive to variations in temperature or pressure. With increasing temperature, the epidote gouge exhibits a first transition from velocity-strengthening to velocity-weakening at sub-greenschist conditions (T < 100 °C) before transitioning to velocity-strengthening under greenschist metamorphic conditions (T > 300 °C). Elevating the pore fluid pressure or decreasing the effective stress promotes unstable sliding. The transition in gouge rheology at varied temperatures and pressures is explained by the competition between granular flow-induced gouge dilation and pressure solution-induced gouge compaction. Our results demonstrate that the rate-and-state frictional stability of epidote gouges support the potential for a fault stability-instability-stability transition for subduction under greenschist metamorphic conditions.

Mechanical Energy Dissipation During Seismic Dynamic Weakening in Calcite‐Bearing Faults

AbstractEarthquakes are frictional instabilities caused by the shear stress decrease, that is, dynamic weakening, of faults with slip and slip rate. During dynamic weakening, shear stress depends on slip, slip rate, and temperature, according to constitutive laws governing the earthquake rupture process. In the laboratory, technical limitations in measuring temperature during frictional instabilities inhibit the investigation and interpretation of shear stress evolution. Here we conduct high velocity friction experiments on calcite‐bearing simulated faults, both on bare‐rock and on gouge samples, at 20–30 MPa normal stress, 1–6 m/s slip rate and 1–20 m total slip. Seismic slip pulses are reproduced by imposing boxcar and regularized Yoffe slip rate functions. We measured, together with shear stress, slip, and slip rate, the temperature evolution on the fault by employing an innovative two‐color fiber optic pyrometer. The comparison between modeled and measured temperature reveals that for calcite‐bearing faults the heat sink caused by decarbonation reaction controls the temperature evolution. In bare‐rocks, energy is dissipated as frictional heat, and temperature increase is buffered by the heat sink of the calcite decarbonation reaction. In gouges, energy is dissipated as frictional heat and for plastic deformation processes, balanced by the heat sink caused by the decarbonation reaction enhanced by the mechanochemical effect. Our results suggest that in calcite‐bearing rocks, a common fault zone material for earthquake sources in the continental crust at shallow depth, the type of fault materials (bare‐rocks vs. gouges) controls the energy dissipation during seismic slip.

Frictional stability of pumice-reinforced lightweight magnesium composite in ambient and elevated temperature environments

Lightweight materials with better resistance to sliding wear are prominent candidates for automobile brake drums, clutch pads and cylinder block applications to facilitate fuel economy. This attempt is reserved to cater to materials with higher tribological quality needs. Less dense foamy pumice stone particles were involved in three different percentages (5, 10, and 15 wt%) to reinforce lightweight AZ31 Mg alloy. A stir-assisted squeeze casting technique was pursued to process the composite and refine the grain structure. A phase detection, elemental mapping and microstructure study were done through X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM), respectively. An experimental dry sliding wear scrutiny was administered using a pin-on-disc apparatus by considering: (i) ambient and elevated temperature environments and (ii) three different levels of loads. The results reveal a significant drop in wear loss and a frictional coefficient for 15% pumice-loaded composite than the base alloy. Post-wear examination acknowledges the fact that the ambient temperature wear is governed by adhesive-abrasive wear and high temperature is by abrasive wear mechanisms. Worn-out scrutiny authenticates the presence of oxide layers and their role in lubrication. A comparative study with previous works upholds the novel magnesium composite is the right candidate for the mentioned automobile applications.

Self-Lubrication Mechanism of Surface-Textured Polymer-Matrix Composites under the Induction of Frictional Stress.

Polymer-matrix composites have been widely used in the manufacture of seals, bearings, electrical insulators, and self-lubricating films as engineering applications move toward lighter weight, higher strength, and corrosion resistance. However, the high-speed shear effect of the friction pairs in relative motion leads to localized heating of the polymer surface, resulting in deformation or softening of the device. Herein, acer mono maple and canna leaves were used as templates to construct polymer-matrix sulfonated polyether-etherketone/polytetrafluoro-wax (SPEEK/PFW) composites with a surface-textured structure. As the bionic texture reduces the level of direct contact between the friction pairs, the frictional thermosoftening of SPEEK occurs in the localized areas of the bumps and leads to the release of PFW stored in textures, resulting in the formation of a soft polymer sliding layer in the worn area and greatly enhancing the frictional stability. By investigation of the tribological properties of textured SPEEK/PFW composites under different loads and sliding speeds, the mechanisms from surface wear to matrix softening and spontaneous construction of a slipping layer are summarized. The results of scanning electron microscopy and three-dimensional profilometer characterization of the wear scars show the surface state of SPEEK/PFW after friction, revealing the friction-thermotropic deformation of the surface texture. The results of this study not only improve our understanding of the frictional heat-induced surface self-lubrication mechanism of textured polymer composites but also provide a reference for the development of multiphase hybrid polymer-matrix composites with excellent self-lubrication properties.

Effect of mullite on the friction stability of carbon fiber-reinforced friction material

PurposeThe purpose of this paper is to investigate the effect of mullite on the mechanical properties and friction of carbon fiber (CF)-reinforced friction material.Design/methodology/approachCF-reinforced friction materials with varying content of mullite were fabricated by hot press molding, and then the tribological properties were tested on the MRH-3-type tribometer under ambient conditions with the ring-on-block configuration.FindingsThe experimental results indicated that the addition of mullite increased the density and compressive strength of friction material. However, the flexural strength of friction material decreased by 16% with the addition of 15 Wt.% mullite. The friction coefficient was proportional to the mullite content. Friction material with 12.5 Wt.% mullite showed the highest friction stability under different loads, whereas friction material with 10 Wt.% mullite exhibited the highest friction stability under different sliding speeds.Originality/valueBy boosting the resistance to deformation under load and increasing the specific heat capacity, mullite contributed significantly to the friction stability of the friction material.

The Role of Ceramic Materials in Surface Modification of Cutting Tools - A Review Paper

A modification cutting tool is a type of cutting tool that can be altered or adjusted to change its cutting properties. This can include changing the angle or shape of the cutting edge, adjusting the depth of cut, or modifying the material or coating used on the tool. These modifications allow for greater precision and efficiency in cutting operations, particularly in industries for manufacturing and construction different products. Ceramic materials can be used in coatings to provide a variety of benefits, such as corrosion, wear resistance , and thermal insulation. They also offer high hardness, low friction, and chemical stability. Ceramic coatings can be applied to various substrates including metals and ceramic. Modification of cutting tools using nanomaterial deposition is a promising approach to enhance their performance and durability. The process involves depositing one or more layer of nanosized particles onto the surface of the cutting tool, which can improve its mechanical, thermal, and tribological properties. Keywords: Ceramic materials ; coating ;cutting tools; coating process.

Microstructural transformation impact on mechanical and tribological performance of different temperature heat-treated carbon/carbon composites

Due to the harsher application environments of C/C composites, optimizing the internal structure of C/C materials through high-temperature treatments (HTT), specifically above 2300 °C, has become an effective method to enhance their properties. The current study investigates the influence of microstructural evolution on the mechanical and tribological behavior of carbon/carbon composites after heat treatments at 2300 °C and 2700 °C. The C/C composites experience a reduction in mechanical properties as the heat treatment temperature is raised. This may be due to the rearrangement of carbon atomic layers at high temperatures, resulting in increased orientation in pyrolytic carbon. However, fibers parallel to the friction surface are relatively less affected, while fibers perpendicular to the friction surface and PyC are more significantly affected. The average coefficient of friction increases from 0.19 to 0.42 as heat treatment temperature from 2300 °C to 2700 °C under the brake pressure of 1 MPa with 25 m/s brake speeds. This phenomenon is attributed to the samples with high graphitization degree (2700 °C) producing a large number of flaky chips under shear stress during friction, which can be easily ground and compacted to form a complete friction film. Additionally, the more easily deformable z-axis fiber asperities increase the contact area, resulting in an increase in the coefficient of friction and friction stability.