A. Sinatora

Wear resistance of cast irons used in brake disc rotors

The wear resistance of three different types of gray cast iron (gray iron grade 250, high-carbon gray iron and titanium alloyed gray iron), used in brake disc rotors, was studied and compared with the results obtained with a compact graphite iron (CGI). The wear tests were carried out in a pin-on-disc wear-testing machine, the pin being manufactured from friction material usually used in light truck brake pads. The rotating discs (500 rpm) were subjected to cyclical pressures of 0.7, 2 and 4 MPa and forced cooled. The wear was measured by weighing discs and pads before and after the test. The operating temperatures and friction forces were also monitored during each test. The results showed that compact graphite iron reached higher maximum temperatures and friction forces as well as greater mass losses than the three gray irons at any pressure applied. However, when compact graphite iron was tested with lower applied pressures and same friction forces sustained by the gray iron rotors, CGI presented the same performance, as did the gray cast iron.

An approach to elucidate the different response of PVD coatings in different tribological tests

Abstract In this paper, the different performances of duplex (i.e. with a prior plasma nitriding treatment) and non-duplex PVD coatings in micro-abrasive wear tests and impact tests are discussed, taking into account some key properties, such as nanohardness ( H ), elastic modulus ( E ) and the H / E ratio. The nanohardness and elastic modulus of the coatings were determined by nanoindentation and were characterised by means of several analytical methods, such as glow discharge optical emission spectroscopy (GDOES), X-ray diffraction (XRD), surface profilometry, Knoop hardness measurements, scratch tests and scanning electron microscopy (SEM). Similar H / E ratios were found for all coatings under investigation. Duplex (Ti,Al)N coatings exhibited the best wear resistance in micro-abrasive wear tests. The results obtained in such tests suggested the occurrence of abrasive wear by plastic deformation, with the hardest coatings displaying the lowest wear rates. The highest wear rates were recorded for duplex and non-duplex Cr–N coatings. Conversely, a duplex Cr–N coating exhibited the best performance in impact tests using a tungsten carbide ball. The duplex Cr–N coating displayed the lowest elastic modulus among all coatings tested, which can be attributed to the presence of a small amount of α-Cr metallic phase. This coated system also showed the smallest difference between the substrate and coating elastic moduli, indicating that low elasticity mismatch between the coating and substrate is desirable for achieving good performance in impact tests. The differing behaviours exhibited by duplex (Ti,Al)N and Cr–N coatings in different tribological tests reveal the importance of selecting the best coating for a given tribological application.

The effect of testing temperature on corrosion-erosion resistance of martensitic stainless steels

Conventional AISI 420 and high-nitrogen martensitic stainless steels were tested under corrosion–erosion conditions in slurry composed by substitute ocean water and quartz particles. The tests were performed at 0, 25, and 70 ◦ C, with mean impact angles of 20 and 90 ◦ . Polarization tests in H2SO4 solution containing chloride ions were also carried out at the same temperatures. Both conventional and high-nitrogen specimens were tempered at 200 and 450 ◦ C before the tests. The high-nitrogen specimens were produced through gas nitriding of AISI 410S (13%Cr–0.03%C) and AISI 410 (13%Cr–0.15%C) stainless steels at 1100 ◦ C. These treatments allowed obtaining interstitial contents (nitrogen + carbon) at the surface of the specimens equivalent to the carbon content of conventional AISI 420 stainless steel. The best corrosion–erosion resistance was obtained in the nitrided AISI 410S samples tempered at 200 ◦ C and tested at 0 ◦ C under 20 ◦ -impact angle. Increasing testing temperature led to higher mass losses and wear rates due to the intensification of intergranular and pitting corrosion mechanisms, especially in the conventional AISI 420 stainless steels. In tests performed at 0 and 25 ◦ C, a reduction in the wear rate for longer testing times was observed, which was mainly associated to fragmentation and roughness changes of the abrasive particles. The mass losses under normal impact conditions were systematically higher than under oblique incidence, and some evidences of mass removal by brittle fracture were found after SEM examination of the worn surfaces.

Corrosion–erosion of nitrogen bearing martensitic stainless steels in seawater–quartz slurry

AISI 410S stainless steel was nitrided at 1473 K in N2 atmosphere, direct quenched and tempered at temperatures between 473 and 873 K. Martensitic cases with circa 0.52 wt.% N at the surface were obtained. Corrosion–erosion tests were carried out in slurries composed by quartz particles and tap or substitute ocean water. The concentration of solids, the impact angle and the pH of solution were fixed, while the temperature, surface changes and mass losses were monitored during the tests. Quenched and tempered AISI 410 and 420 stainless steels were used as comparison materials. The results showed that the erosion resistance and the corrosion–erosion resistance of the nitrided steel tempered at 473 K were higher than those of the AISI 410 and 420 steels tempered at the same temperature. This behavior was due to the higher hardness and better intergranular, pitting and generalized corrosion resistance of the nitrided alloy. The synergism between corrosion and wear was more important in the AISI 410 and 420 samples.

The particle size effect on abrasive wear of high-chromium white cast iron mill balls

Granite grinding tests, under dry and wet conditions, were performed to assess the influence of abrasive particle size to the wear behavior of martensitic high-chromium white cast iron mill balls. The tests were performed, at first, using raw granite particle sizes between 0.074 and 19.1 mm, and then with coarse and fine granite fractions obtained after screening the raw granite in a 3.36 mm sieve. It is demonstrated that the relative particle/ball size relationship is the determining parameter to ball wear. The highest ball wear rates were observed for fine granite grinding under dry (120 mg/cycle) and wet (129 mg/cycle) conditions. The lowest wear rate (ca. 50 mg/cycle) was observed for coarse granite grinding (dry and wet). These different results were attributed to the different size relationships between grinding body diameter and granite particles size. For wet-grinding of raw granite, the mineral components may influence significantly the wear behavior. Feldspar can act as a bonding agent, gluing fine quartz particles to the coarse granite and to the balls surface and turning the dependence of the relationship between the relative sizes of ball and granite particle less important to the wear process. This explains why wet-grinding of raw granite results in a ball wear two times greater (106 mg/cycle) than dry-grinding (51 mg/cycle).

Correlation between microstructure and cavitation–erosion resistance of high-chromium cast steel—preliminary results

Abstract Cavitation–erosion is a complex and highly localized phenomena involving mechanical, chemical and metallurgical parameters. The development of new materials depends on the understanding of the relationship between microstructure and cavitation–erosion. This paper investigates the role played by the microstructure on cavitation–erosion rates of 35Cr–25Ni–3Mo and 35Cr–8Ni–3Mo–2Nb, with and without tungsten addition in the as-cast condition. The difference in the microstructures was a consequence of distinct cooling rates due to the casting mold geometry. Metallographic techniques were used to reveal the microstructure. Cavitation tests were made by means of a vibratory apparatus. The performance of the alloys is compared with AISI 304 austenitic stainless steel. All alloys tested presented an improved performance when compared with the AISI 304. Alloys solidified with a high cooling rate presented best results and this behavior is attributed to the differences in the microstructure. For high-chromium cast steel, the increase of the austenite content decreases cavitation resistance. It was also observed that finer carbide particle morphology has a beneficial effect on the cavitation resistance of these materials.

Simulation of solidification paths in high chromium white cast irons for wear applications

Abstract Thermodynamic calculations of the solidification paths in the Fe-Si-Cr-C system using the CALPHAD approach have been used for the interpretation of the solidification microstructures of high chromium white cast irons containing high silicon contents. The results show a reasonable agreement between experiments and calculations for alloys up to 2 wt% Si. The results suggests that the stability of the cementite phase is underestimated in the thermodynamic database. The calculations predict a change in the topology of the phase diagram, with the cementite primary field disappearing in favour of a new ternary eutectic involving liquid, austenite, graphite and M 7 C 3 carbide, this is partially in agreement with the observed microstructures for the alloys containing 4 wt%Si. The calculations predict the existence of a complex invariant peritectic reaction involving liquid, graphite, austenite, cementite and M 7 C 3 carbide in the Fe-Si-Cr-C system.

The effect of load and relative humidity on friction coefficient between high density polyethylene on galvanized steel—preliminary results

This paper presents the influence of applied load and relative humidity (RH) in the friction coefficient of high-density polyethylene (HDPE) pin on hot dip galvanized steel disc. The experimental results showed that friction coefficient is proportional to the applied load. The measured friction coefficient was affected by environment RH depending on applied load. For low applied load, the friction coefficient varies following humidity alteration of testing environment, i.e., increase in humidity increases the friction coefficient, while for high applied load, there was observed no variation on friction coefficient. The wear rate of HDPE pin in 10 and 20 N applied load range suggests changes in the wear regime, from mild to severe.

Wear and Corrosion Evaluation of Electric Fuel Pumps with Ethanol/Gasoline Blends

The automotive electrical fuel pumps for gasoline and alcohol fueled vehicles engines are lubricated by the fuel itself. The new flexible fuel engine technology, specially in Brazil, the fuel pump is designed to be lubricated by gasohol (E22) or strait hydrated ethanol fuel but it is also exposed to the variable gasoline/alcohol blends in the flex-fuel engines. This paper presents the influence of different fuel blends, ethanol and gasohol, to the fuel pump wear and corrosion behaviors. The tested fuel pumps were designed for gasohol only engines. The fuel pumps were tested in a bench device, which simulates the vehicle fuel circuit, using gasohol (E22), hydrated ethanol (E100) or 60 % in volume ethanol-gasoline mixture (E60). The scanning electron microscopy examinations and roughness measurements were performed for tribological analysis of fuel pump gears. The observed wear and/or other deterioration mechanisms were mainly due to the abrasion and corrosion. The tests showed that abrasion mechanisms were more pronounced in the E22 fuel and the corrosion mechanisms were more damaging in the E60 and E100 fuels. The fuel pumps gears lubrication regime was calculated and the tested fuels lubricities were also measured.

Hot rolling mill roll microstructure interpretation: A computational thermodynamics study

The microstructure of the interface of a high chromium cast iron/ductile cast iron composite hot rolling mill roll has been interpreted with the help of Fe-Cr-Si-C laboratory alloys and thermodynamic calculations of their solidification paths. It has been shown that the mill roll presents two limiting microstructures: the ductile cast iron core and the white cast iron shell. While the core is heavily contaminated with chromium, originating from the partial dissolution of the shell during core pouring, the shell shows a typical high chromium white cast iron micro-structure, since it remains solid during processing. The high chromium contents in the core originate a typical “mottled” cast iron microstructure, combining nodular graphite and ledeburite. The region between the two limiting microstructures is called interface. As the distance from the core toward the shell increases in the interface, the content of chromium increases but that of silicon decreases. The resulting microstructural gradient shows ledeburitic M3C, hexagonal-section M3C, duplex M3C/M7C3 carbides, and M7C3 carbide, which could be well correlated with the calculated solidification paths of the laboratory samples.