Cast Iron Disc Research Articles

Enhanced tribological performance of MoS2 and hBN-based composite friction materials: Design of tribo-pair for automotive brake pad-disc systems

This research comprehensively analyzes the friction and wear behavior of composite friction materials when dry sliding against grey cast iron and laser-clad nickel-based (LC1) and iron-based (LC2) alloy discs. The composite friction materials (P1, P2, P3, P4, P5, and P6) under investigation contain graphite, MoS2, and hBN-based solid lubricant synthesized through the powder metallurgy technique. Tribological tests were conducted using a pin-on-disc configuration to simulate the dynamic interaction between the composite materials and the laser-clad grey cast iron discs. The tests were performed at a 60 N load, 6283.19 m sliding distance, and 2.094 m/s sliding velocity under dry sliding conditions. The results provide valuable insights into the effectiveness of MoS2 and hBN-based solid lubricant composites in reducing friction and wear when in contact with iron and nickel alloy-based laser-clad grey cast iron surfaces. The study elucidates the mechanisms governing tribological behavior, including the formation of friction plateaus and the role of laser-clad counter-discs in reducing wear. The specific wear rate of the nickel-based laser-clad counter disc (LC1) and iron-based laser-clad (LC2) system improved by 63.76 % and 48.32 %, respectively, compared to the conventional grey cast iron disc system when using the hBN-based pin (P6). Additionally, the specific wear rate of the hBN-based pin was 38.49 % lower than the conventional graphite-based pin when sliding against the grey cast iron counter-disc. Artificial Neural Network (ANN) was used to validate the wear rate of the best-performing tribological pair, namely the hBN-based pin (P6) and LC2 counter discs, through supervised learning.

Design and Control of the Natural Frequency of Brake Discs in the Aspect of the Gray Cast Iron Production Process.

The results of research on the influence of the chemical composition of cast iron and its potential changes in the production cycle on the elastic properties and the correctness of numerical simulations of the natural frequency of ventilated brake discs are presented. The tests were carried out for three grades of gray cast iron with flake graphite with a eutectic saturation coefficient ranging from 0.88 to 1.01. A quantitative metallographic assessment of the pearlitic cast iron matrix and graphite precipitates was carried out, and the hardness and compressive/tensile strength of individual cast iron grades were determined, taking into account the limit contents of the alloying elements. Next, ultrasonic tests were performed, and the elastic properties of cast iron were determined. Based on the obtained data, a numerical modal analysis of brake discs was performed, the results of which were compared with the actual values of an FRF frequency analysis. The error of the computer simulations was estimated at approx. 1%, and it was found that the accuracy of the calculations of the first natural frequency did not depend on the dimensions (size) of the discs and the chemical composition of the cast iron from which they were cast. The functional relationships between the chemical composition of cast iron, its strength and elasticity and the first natural frequency of the disc vibrations were determined, and a database of the material parameters of the produced cast iron grades was developed. An implementation example showed the validation of the brake disc design with natural frequency prediction and demonstrated a high convergence of the experimental results with the simulated values. Using I-MR control cards, both the effectiveness of designing and predicting the natural vibrations of brake discs based on the implemented material database as well as the stability of the gray cast iron production and disc casting processes were confirmed.

Properties of Laser-Alloyed Stainless Steel Coatings on the Surface of Gray Cast Iron Discs

The influence of laser-alloyed stainless steel coatings on the properties of the surfaces of cast iron discs, such as friction-induced vibration and noise, friction coefficient, residual stress, hardness, and corrosion resistance, was investigated in this study. The experimental results show that after laser alloying, the surface hardness of the cast iron discs increased significantly. The residual stresses on the surfaces of the laser-alloyed discs changed from tensile to compressive residual stresses, while any compressive residual stresses increased by more than six times. Most of the laser-alloyed discs demonstrated better performance in friction-induced vibration and noise damping and friction reduction. Metallographic observation and XRD (X-ray diffraction) analysis results show that the laser-alloyed layer is mainly a mixture of acicular martensite and dendritic material, while the phase composition of laser-treated discs is mainly martensitic, [Fe, Ni], Fe3Si, Cr23C6, and austenite, which plays a significant role in the improvement of the properties of the laser-alloyed cast iron in physics, tribology and corrosion resistance. This research has significance for the laser surface treatment of various cast irons and steels, which is an increasingly important manufacturing technology in the vehicle friction brake industry.

Effect of cast-iron disc thickness on the reliability of tribological data from pin-on-disc test: Case study of brake friction materials

For braking system, rubbing between disc and brake pad generates heat, physical transformation on the contact, and activates many complex solicitations. Therefore, researchers used reduced scale testing to evaluate tribological and thermomechanical performance of friction composite. The pin-on-disc configuration of the tribometer is considered the better solution to reproduce these generated transformation and friction evolution. However, if the pin geometry is chospaden based on representative elementary volume (REV) approach, no research has investigated and justified the choice of the disc geometry and thickness. In this research work, an examination of the critical disc thickness is discussed, highlighting its substantial impact on the friction-wear behavior during brake application. For that, four disc thicknesses were tested, varying on thickness values (10, 15, 20, and 22 mm). Through this experiment, the friction coefficient evolution as function of braking numbers and sliding duration was studied while maintaining pressure and sliding velocity constant. Wear and temperature rise are identified for each disc thickness situation. A 3D thermal model is employed also to simulate the heat conduction and dissipation in brake system for various disc thickness. The temperature predictions are carried out using Ansys software. Experimental investigation presented the effect of the thickness on the friction stability, particularly at high temperature. Numerical results highlight the effect of reducing the thickness of the disc on the kinetic temperature rise through a rapid increase in disc temperature. The thickness modification used for the brake disc enhances the resulted thermal response and tribological brake pad performance, and consequently enhance the reliability of tribometer outcomes.

Microstructure and Wear Resistance of Fe3Al Coating on Grey Cast Iron Prepared via Direct Energy Deposition

In this study, the potential of Fe3Al coating material as an environmentally friendly alternative to coatings containing critical elements for brake discs was investigated. A buffer layer of Cr–Mo steel (Ferro 55) that was about 500 µm thick was applied on a gray cast iron disc to enhance the coating quality and prevent the formation of hot cracks during solidification. The microstructural analysis of the cross-section of the coating showed that the buffer layer diffused into the Fe3Al coating, forming a combination of Fe3Al, Fe, and Fe3AlC0.5 phases. The tribological properties of the Fe3Al-coated disc were evaluated using pin-on-disc tests against two different copper-free friction materials extracted from commercial brake pads. The wear results show a coefficient of friction comparable to that of an uncoated disc (≈0.55), but with a reduction in particulate matter (PM) emissions, which decreased from 600 to 476 #/cm3. The last issue is an interesting aspect that is gaining increasing importance in view of the upcoming international standards.

Corrosion of food grinding discs in gastro-intestinal environment

The need for food size reduction before consumption has led to the use of motorized grinding machine which operates on energized rubbing of two grooved cast-iron discs, and this unintentionally results in tribological degradation and corrosion of grinding discs into the ground food. The objective of this study was to carry out an assessment of corrosion susceptibility of grinding discs from different manufacturing methods in simulated gastro-intestinal environment. Six grinding discs from three states in Nigeria were selected for this study, based on manufacturing methods namely: rotary, cupola, and pit furnaces. Experimental techniques used for the study included: X-Ray Fluorescence spectroscope for determination of chemical composition and X-Ray Diffractometer was used for phase identification. Corrosion susceptibility of grinding discs on interaction with pseudo-body fluid was studied using potentiodynamic polarization scan and product analysis (gasometric) methods in simulated gastro-intestinal environment, typical of human stomach, as electrolyte. The electrolyte contained 2 g/L NaCl acidified to pH of 1.7 with HCl and regulated at 37 °C. Optical microscopy of the electrochemical samples was done for corrosion damage assessment. The key finding from the study was that all the grinding discs contain iron and silicon as dominant alloy elements, which existed predominantly as iron carbide and ferrosilicon phases. Corrosion of the discs in simulated gastric solution was well profound irrespective of the manufacturing method, though, with varying degree among the discs. The outcome of this study is applicable to food industries where cognitive measures may have to be taken on materials selection to minimise the risk of food contamination from materials corrosion.

Influence of Functionally Graded Protective Coating on the Temperature in a Braking System.

A mathematical model of heat generation due to friction in a disc-pad braking system was developed with consideration of a thermal barrier coating (TBC) on the friction surface of the disc. The coating was made of functionally graded material (FGM). The three-element geometrical scheme of the system consisted of two homogeneous half-spaces (pad and disc) and a functionally graded coating (FGC) deposited on the friction surface of the disc. It was assumed that the frictional heat generated on the coating-pad contact surface was absorbed to the insides of friction elements along the normal to this surface. Thermal contact of friction between the coating and the pad as well as the heat contact between the coating and the substrate were perfect. On the basis of such assumptions, the thermal friction problem was formulated, and its exact solution was obtained for constant and linearly descending specific friction power over time. For the first case, the asymptotic solutions for small and large values of time were also found. A numerical analysis was performed on an example of the system containing a metal ceramic (FMC-11) pad, sliding on the surface of a FGC (ZrO2-Ti-6Al-4V) applied on a cast iron (ChNMKh) disc. It was established that the application of a TBC made of FGM on the surface of a disc could effectively reduce the level of temperature achieved during braking.

Friction, wear, and characterization of magnesium composite for automotive brake pad material

Magnesium metal matrix composites for lightweight brake pad applications are developed in this study. The composites are fabricated by using the powder metallurgy process. The addition of 0.5 wt.% to 2 wt.% Y2O3 (Rare Earth Oxide) used as a reinforcement to the AZ31 Mg composite is investigated. Density, hardness, and tribometer tests are carried out according to the ASTM standards. The friction and wear test of magnesium composites is tested against the grey cast iron disc. FESEM analysis shows the microstructure and morphology of worn surfaces. The elemental mapping result depicts that the elements of Mg, Al, Zn, Y, and O are uniformly distributed in the composite. X-ray diffraction analysis shows the compounds of Y2O3, MgO, ZnO, and Al2O4 are present on the worn surface of AZ31 + 2 wt.% Y2O3 composite. The outcome of the experiment reveals that increasing the proportion of yttrium oxide increases the magnesium composite's density and decreases the porosity. AZ31 + 2 wt.% Y2O3 composite exhibits the highest hardness of 122HV, a stable coefficient of friction, and a lower wear rate compared to AZ31 + 0 wt.% Y2O3 composite.

Life cycle assessment of carbon ceramic matrix composite brake discs containing reclaimed prepreg scraps

In the last years, carbon ceramic brakes are preferred to traditional cast iron ones for their lightweight, high temperature resistance, and long service life, even though their manufacturing involves the use of high temperature processes and energy-intensive materials such as carbon fibers. Within the European Life Project “CIRCE”, a novel recovery system for carbon fiber prepreg scraps was developed to reclaim high-quality carbon fibers to use as a substitute of virgin carbon fibers in different application, such as in Ceramic Matrix Composite (CMC) brakes. In order to overcome the lack of scientific literature regarding the environmental sustainability of steel and CMC brakes, in the present paper, the Life Cycle Assessment (LCA) methodology was applied to carry out a detailed analysis of the environmental impacts associated with carbon ceramic brakes realized using the reclaimed prepreg scraps. The functional unit was defined as production, use and disposal of a rear brake disc used for the deceleration of a sport car during its lifetime. Different impact indicators were considered, such as Global Warming Potential, Cumulative Energy Deman and ReCiPe midpoint categories. The results were compared to those given by the sustainability assessment of cast iron disc brakes and traditional carbon ceramic brakes. The proposed LCA is a cradle to grave analysis, as it considers all the relevant inputs and outputs of the manufacturing processes, from the raw material extraction to the materials disposal. The surface of ceramic brakes was observed using Scanning Electron Microscopy to assess the different material structures. The results show that, as far as the production is concerned, cast iron brakes are the most sustainable alternative, with impacts lower than 21% of the composite component ones. However, if a long use phase more than 200,000 km is evaluated, carbon ceramic brakes obtained by reclaimed prepreg scraps are characterized by lower environmental impacts, with impacts that are about 8% lower than those obtained by traditional carbon ceramic brakes.

Corrosion Stiction in Automotive Braking Systems.

This review paper targets the corrosion-stiction phenomenon that can occur in automotive braking systems under static conditions in aggressive environments. The corrosion of gray cast iron discs can lead to a strong adhesion of the brake pad at the pad/disc interface that can impair the reliability and performance of the braking system. The main constituents of friction materials are initially reviewed in order to highlight the complexity of a brake pad. Corrosion-related phenomena, including stiction and stick-slip, are considered in detail to discuss the complex effect of the chemical and physical properties of friction materials on these phenomena. In addition, testing methods to evaluate the susceptibility to corrosion stiction are reviewed in this work. Electrochemical methods, including potentiodynamic polarization and electrochemical impedance spectroscopy, are useful tools for a better understanding of corrosion stiction. The development of friction materials with low susceptibility to stiction should follow a complementary approach targeting an accurate selection of the constituents, control of local conditions at the pad-disc interface, and the use of specific additives or surface treatments to reduce the corrosion susceptibility of gray cast-iron rotors.

Interlaboratory Study on Brake Particle Emissions Part II: Particle Number Emissions

The Particle Measurement Programme (PMP) informal working group co-ordinated a global interlaboratory study (ILS) on brake wear particle emissions with the participation of 16 laboratories in 2021. Two articles present the results of the ILS: (I) particulate matter mass (PM) and (II) particle number (PN) emissions. The test matrix covered different brake systems, including ECE and NAO pad materials with grey cast iron discs and a drum brake. Regarding PN, the study measured the total particle number from approximately 10 nm to 2.5 µm (TPN). Some testing facilities measured solid particle number emissions (SPN) in parallel. The mean TPN concentrations ranged from 9.1 × 108 #/km/brake to 1.1 × 1010 #/km/brake. TPN and SPN emission levels were comparable, except for one lab that measured very high volatile particle emissions for one brake system. The minimum and maximum SPN emissions for a given brake differed by a factor of 2.5 ± 0.5, comparable to data from exhaust SPN ILS measurements. This article provides an overview of lessons learned and subsequent measures incorporated in an upcoming global technical regulation to reduce measurement variability when sampling and measuring brake particle emissions for light-duty vehicles up to 3.5 t.

Comparative Study on the Friction Behaviour and the Particle Formation Process between a Laser Cladded Brake Disc and a Conventional Grey Cast Iron Disc

Brake-wear particle emissions are the result of the components of a friction brake being in tribological contact, and they are classified as non-exhaust emissions. Since most of the emitted particles belong to the size classes of particulate matter (≤10 μm) and differ significantly in terms of their physico-chemical properties from automotive exhaust emissions, this source is of particular relevance to human health and, therefore, the focus of scientific studies. Previous studies have shown that coated brake discs offer significant wear and emission reduction potential. Nevertheless, no studies are available that describe the specific particle formation process, the contact conditions, the structure of the friction layer and the differences compared to conventional grey cast iron discs. The aim of this study is to describe those differences. For this purpose, the tribological behaviour, the structure of the friction layer and the associated particle dynamics within the friction contact between a laser cladding coated disc and a conventional grey cast iron disc are compared. The required investigations are carried out both ex situ (stationary) and in situ (dynamic). Parallel to the tribological investigations, the particle emission behaviour is determined on an inertia dynamometer using a constant volume sampling system (CVS) and equipment for particle number and particle size distribution measurement. The results show that, for two different brake pads, the laser cladding brake disc has lower wear and less particulate emissions than the grey cast iron brake disc. The wear behaviour of the coating varies significantly for the two brake pads. By contrast, the grey cast iron brake disc shows a significantly lower influence.

Study of the Influence of the Copper Component's Shape on the Properties of the Friction Material Used in Brakes-Part One, Tribological Properties.

Brakes play an extremely important role in any vehicle. In today's automotive industry, friction brakes are most often used, in which the composite material of the brake pad cooperates with a cast iron disc. While little can be modified in the case of discs, in the case of pads, the composition of the material used for its production can have an almost unlimited number of possibilities. Both scientists and manufacturers invent and test new combinations to achieve the desired end result. A similar task was undertaken in this work. Bearing in mind the fact that materials commonly used as reinforcing materials generate undesirable threats in the production process, it was decided to check whether this role could be taken over by another substance that is already present in brake pads; this substance is copper. A number of samples containing copper, in the form of powder and fibers, were made, and then the samples were subjected to tribological tests in order to determine the coefficient of friction and abrasive wear rate. The ball-cratering research method was used, and the Taguchi process optimization method was used to plan the experiment. As a result of the tests, it was found that the replacement of aramid fibers with copper fibers does not significantly affect the value of COF and the abrasive wear rate.

Modeling and Simulation of Brake Disc Using Lightweight Materials

Conventionally, Cast iron discs are used for brake discs. In the recent past, lightweight materials replace conventional materials in many vehicles to make them more fuel efficient. This work reports the results of the modelling and simulation of brake discs using five different materials. AISI6150, Cast Iron, Ti–6Al–4V, LM13 and Al SiC MMC were considered as brake disc materials. The temperature distribution, heat flux and thermal gradient of these materials were analysed and the results are reported. Al SiC MMC is found to have the lowest weight, distributes heat to a larger area for enhancing the heat dissipation, has a higher heat flux and a low thermal gradient.

Influence of contact pressure and velocity on the brake behaviour and particulate matter emissions

In this work, the braking performance and the emission behavior of airborne wear particles of a low-metallic and NAO friction material have been investigated using a reduced-scale dynamometer, adapted for emission measurements. A specific braking cycle has been developed to assess the influence of velocity and pressure on the tribological performance of friction materials sliding against a cast iron disc. The adopted brake cycle consists of a factorial design of blocks of repeated brake stops, where each block was intercalated with a so-called reference block, meant to recover the initial characteristics of the sliding surfaces. A progressive stabilization of the tribological parameters was observed during the blocks featuring a higher initial velocity. The relevant values of these parameters would depend on the extension of the secondary plateaus in the friction layer. At high pressure and velocity, the low-metallic friction material exhibited a higher wear rate and lower friction coefficient than the NAO material, although the NAO material displayed a weaker recovery behavior regarding the friction coefficient. The emissions of the NAO material were found to be lower and more stable than the low-metallic material. In general, the emissions were found to be correlated with the initial brake velocity mainly, through a cubic relationship, whereas the emissions did not show a clear dependence on contact pressure.

Mechanical and tribological properties of a WC-based HVOF spray coated brake disc

Abstract Thermally sprayed WC-based coating systems are generally used to increase engineering components’ wear resistance. This research presents the results of a comparative study conducted to examine the tribological characteristics of a new brake disc created with thermal sprayed WC-10Co4Cr coating. This study implemented braking tests on the WC-10Co4Cr coated brake disc against commercial friction material on a laboratory scale disc-pad tester and compared the findings with the reference disc. The coating system was created with a high velocity oxygen-fuel spraying on a cast iron disc. The braking tests followed the sections of the SAE-J2430 test procedure. The microstructure, phase composition and properties of the coating were characterized by SEM/EDS, XRD and Vickers microstructure. The effect of carbide coating on the friction and wear behaviour of the tribological system was examined. The WC-10Co4Cr coating has increased the hardness by 3 times with a thickness of 300 μm compared to the cast iron surface. The amount of wear in the coated disc (CD) was reduced by about 85% compared to the reference disc (BD). The coefficient of frictions of BD and CD was found to be in the range of 0.43–0.61 and 0.47–0.62, respectively. The inclusion of hard phases (WC and W2C) in the disc coating played an important role in improving the sliding wear resistance by maintaining the coefficient of friction of the brake disc at an acceptable level. In brief, carbide coating could be claimed to be promising for challenging braking implementations.

Characterization, wear and emission properties of MnS containing laser cladded brake disc

In this study, the laser cladding of gray cast iron brake discs using a Fe-based coating material was investigated. A 5 wt% MnS was added as a solid lubricant to the coating formulation to track the improvement of wear and emissions. Microstructural and tribological characteristics of the coated discs (with and without MnS) were studied comparatively. Three different friction materials, that are typically used for commercial brake pads, were adopted to evaluate the performance of the coatings. The pin on disc results indicated that, with the addition of MnS, both friction coefficient and wear rate have been reduced to levels comparable with those obtained in case of uncoated gray cast iron discs. The tribological behavior of MnS containing coating showed the best results when sliding against a Cu full friction material.

A novel study on the reduction of non-exhaust particulate matter emissions through system vibration control.

The need to reduce non-exhaust particulate matter emissions is of paramount importance as they pose repercussions on human lives and the environment. In this study, a novel way to limit emissions is proposed based on the minimization of the vibration of the mating bodies. Two model friction material formulations were tested in the form of pins and paired with a pearlitic grey cast iron disc counterface in a laboratory pin on disc apparatus. To reduce the vibrations, a damping tape was wrapped around the pins. With the damping of vibration, a significant drop in the emissions was recorded, and this was correlated with the friction layer establishment during sliding, which observed low disruption. It is believed that the use of this method for reducing emissions can accompany the optimization phase of the brake squeal noise of friction materials, thereby, providing new design perspectives.

Study on the effects of laser quenching power and scanning speed on the property of cast iron

The laser surface quenching power, scanning speed, and spot area have significant effect on the properties of the laser quenched materials. The effects of laser quenching power and scanning speed on the tribological, vibration, and noise performance of gray cast iron (HT250) are studied in this paper. Keeping the laser quenching spot constant, 12 cast iron discs are laser quenched by changing the laser quenching power and scanning speed. Various mechanical, tribological, and dynamical testing equipment are used to characterize the properties of the laser quenched cast iron discs, in terms of the surface hardness, residual stress, friction coefficient, and frictional vibrations and noise of the cast iron discs. The experimental results show that after laser surface quenching, the surface hardness of the cast iron disc has been increased more than 4 times, the residual stress on the disc surface is changed from tensile stress to compressive stress, the friction coefficients of the laser quenched cast iron discs have been significantly increased, and the vibration and noise generated from the laser quenched cast iron discs have been significantly changed. This research has significance to the improvement of the surface performance of automotive brake discs and the control of braking frictional vibrations and noise.

Tribological behavior of graphene-based friction composite tested on cryogenically treated cast iron

Enhancement of friction and wear performance is the basic requirement of a friction composite material, which primarily relies on the properties of ingredients and the type of counter disc. To meet the superior requirements of the tribological system, a new tribopair between graphene-based friction composite and cryogenic treated grey cast iron disc was designed in this work. Friction composites in the shape of a pin were made from solid lubricants—20 wt.% of molybdenum disulfide, 20 wt.% of graphite, and 10 wt.%, 15 wt.%, and 20 wt.% of graphene nanopowder. The prepared five friction composites are tested on the cryogenic treated grey cast iron disc and untreated disc in a pin-on-disc tribometer under dry state conditions, resulting in 10 different tribopairs. The tribological efficacy of the tribopairs was assessed and finally compared with the tribopair formed from a commercial brake pad. Results proved that the tribological performance of the tribopairs, namely 20 wt. % of graphene nanopowder—cryogenic treated grey cast iron disc and 15 wt.% of graphene nanopowder—cryogenic treated grey cast iron disc was superior compared to the other tribopairs. Thus, the addition of graphene nanopowder in the friction composite and cryogenic treatment of the grey cast iron disc significantly affects the overall friction and wear properties of the tribopairs. Scanning electron microscopy micrographs were used to characterize the friction composites surface and counter disc.