Fretting fatigue properties of plasma nitrided AISI 316 L stainless steel: Experiments and finite element analysis

This study investigates the effects of thickness, hardness and composition of modified layer on the plain and fretting fatigue properties of the nitrided 316 L steel plasma nitrided under various processing conditions. Fretting fatigue behaviour of untreated and nitrided material is also analysed with the finite element method. Experimental and theoretical fatigue life results are compared. The result indicates that the nitriding process improved the fretting fatigue properties of 316 L stainless steel. The experimental test results are close to theoretical fretting fatigue life results, thus it yields that the established model in the numerical analysis is consistent in this regard.     

Fretting fatigue properties of plasma nitrided AISI 316 L stainless steel: Experiments and finite element analysis

This study investigates the effects of thickness, hardness and composition of modified layer on the plain and fretting fatigue properties of the nitrided 316 L steel plasma nitrided under various processing conditions. Fretting fatigue behaviour of untreated and nitrided material is also analysed with the finite element method. Experimental and theoretical fatigue life results are compared. The result indicates that the nitriding process improved the fretting fatigue properties of 316 L stainless steel. The experimental test results are close to theoretical fretting fatigue life results, thus it yields that the established model in the numerical analysis is consistent in this regard.     

Effect of Plasma Nitriding Environment and Time on Plain Fatigue and Fretting Fatigue Behavior of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V fatigue test samples at 520°C in two environments (nitrogen and nitrogen–hydrogen mixture in a ratio of 3:1) for two time periods (4 and 18 h). Plain fatigue and fretting fatigue tests were conducted on unnitrided and plasma nitrided samples. Plasma nitriding degraded lives under both plain fatigue and fretting fatigue loadings. The samples nitrided in nitrogen exhibited superior lives compared with the samples nitrided in the nitrogen–hydrogen mixture, possibly due to the relatively higher hardness (and presumably lower toughness) of the nitrided layer of the samples nitrided in the nitrogen–hydrogen mixture environment. For those samples nitrided in the nitrogen–hydrogen mixture, those nitrided for 18 h exhibited superior lives compared with those nitrided for 4 h. This trend was observed for samples nitrided in nitrogen gas at lower stress levels only; the converse was true at higher stress levels of 550 MPa and 700 MPa under plain fatigue loading. However, under fretting fatigue loading, the plasma nitriding time did not influence the lives significantly.     

A study on fretting fatigue characteristics of Inconel 690 at high temperature

Inconel 690 alloy is used in nuclear power plant steam generator tubes. Fretting fatigue experiments were performed on Inconel 690 specimens at room temperature and at the nuclear power plant operating temperature of 320 °C. By comparing the fretting fatigue test data at room temperature and 320 °C, this study analyzed the change in characteristics related to the fatigue limit at 10⁷ cycles. In addition, this study attempted to measure changes in the friction force for repetitive cycles in fretting fatigue tests, and analyzed the mechanism of fretting fatigue by observing the fracture surfaces and performing spectrum analysis.     

Fretting fatigue behavior of Al7075-T6 at sub-zero temperature

In some fretting fatigue applications, such as aero industry, the temperature may drop well below −50 °C Fretting fatigue behavior of aluminum alloy Al7075-T6 is investigated at temperatures of 24, 0, −25 and −50 °C in this work. The results show that (i) normal fatigue life increases considerably at sub-zero temperatures up to around 85% for low working stresses and reduces to about 40% for higher working stresses; (ii) fretting fatigue life at sub-zero temperatures rises significantly up to around 220% for low working stresses and reduces to about 50% for higher working stresses; (iii) ultimate strength of material changes from −15% to 15% under the fretting fatigue test conditions; and finally (iv) some parameters such as mechanical properties and fatigue behavior of material at low temperatures, contact load relaxation, crack closure, oxidation and some unknown sources can be thought to be responsible for fretting fatigue behavior of Al7075-T6 at sub-zero temperatures.     

Erosion–corrosion and corrosion properties of DLC coated low temperature gas-nitrided austenitic stainless steel

Low temperature nitriding of stainless steel leads to the formation of a surface zone of so-called expanded austenite, i.e. by dissolution of large amounts of nitrogen in solid solution. In the present work the possibility of using nitrogen expanded austenite “layers” obtained by gaseous nitriding of AISI 316 as substrate for DLC coatings are investigated. Corrosion and erosion–corrosion measurements were carried out on low temperature nitrided stainless steel AISI 316 and on low temperature nitrided stainless steel AISI 316 with a top layer of DLC. The combination of DLC and low temperature nitriding dramatically reduces the amount of erosion–corrosion of stainless steel under impingement of particles in a corrosive medium.     

Influence of temperature on the fretting response between AISI 301 stainless steel and AISI 52100 steel

Fretting of AISI 301 stainless steel sheet in contact with AISI 52100 steel from 20 °C to 550 °C in air and argon has been studied. Transitions in the mechanical properties of 301SS and oxidative behavior of this pair have been identified as a function of temperature. Strength and ductility of 301SS is reduced from 20 °C to 250 °C, increasing susceptibility to fretting damage. Steady state friction decreases as temperature increases, reducing cyclic stresses. Wear resistance increases in this temperature range, increasing fatigue damage due to the increase in fatigue life associated with increased wear. This study aims to identify the causes of the transitions in behavior and determine the net outcome of the competing effects with regard to fatigue damage.     

Fretting damage in thin sheets: Analysis of an experimental configuration

A method for evaluating fretting damage in thin sheets was developed for AISI 301 stainless steel in full hard condition in contact with AISI 52100 steel and cast ANSI A356 aluminum. Samples were subjected to fretting and then were subsequently fatigue tested to determine the impact of the fretting damage on fatigue life. A finite element model of the experimental configuration was used to determine the response for the experimental conditions imposed. The values of Fatemi-Socie critical-plane fatigue damage parameter are shown to correspond to the trends in the observed residual fatigue life for contact with AISI 52100 steel.     

The effect of hydrogen gas environment on fretting fatigue strength of materials used for hydrogen utilization machines

The objective of this study is the characterization of the fretting fatigue strength in a hydrogen gas environment. The test materials were a low alloy steel SCM435H, super alloy A286 and two kinds of austenitic stainless steels, SUS304 and SUS316L. The test was performed in hydrogen gas at 0.12 MPa absolute pressure. The purity of the hydrogen gas was 99.9999%. The fretting fatigue limit was defined by the fretting fatigue strength at 30 million cycles. For all materials, the fretting fatigue strength in the hydrogen gas environment increased in the short-life region. However, the fretting fatigue strength in the hydrogen gas environment decreased in the long-life region when exceeding 10 million cycles except for SCM435H, while there was no reduction in the fretting fatigue strength in air between 10 and 30 million cycles. The reduction rate was 18% for A286, 24% for SUS304 and 7% for SUS316L. The tangential force coefficient in the hydrogen gas environment increased when compared to that in air. It can be estimated that this increase is one of the causes of the reduced fretting fatigue strength found in a hydrogen gas environment. In order to discuss the extension of the fretting fatigue life in hydrogen gas observed at the stress level above the fretting fatigue limit in air, continuous measurement of the fretting fatigue crack propagation was performed in a hydrogen gas environment using the direct current potential drop method. As a result, it was found that the extension of the fretting fatigue life was caused by the delay in the start of the stable crack propagation.     

Relations between oxidative wear and Cr content of steels

Dry sliding wear tests at 25-400 °C were performed for 45, 4Cr5MoSiV1 and 3Cr13 steels; the relations between oxidative wear and Cr content of steels were explored. The low and medium-Cr steels had a substantially lower wear rate and increasing tendency than the high-Cr steel at 25-200 °C, but the contrary case occurred at 400 °C. With an increase of ambient temperature, the wear rate of the low and medium-Cr steels first decreased, then increased and reached the lowest value at 200 °C, while the wear rate of the high-Cr steel decreased monotonously with the lowest value at 400 °C. At 25 °C, trace tribo-oxides reduced wear to some extent in adhesive-dominated wear for the low and medium-Cr steels. At 200 °C, a small amount of tribo-oxides formed and reached a thickness of 10 μm on contacting asperities in the low and medium-Cr steels, thus oxidative mild wear prevailed. At 400 °C, a great amount of tribo-oxides appeared in the low and medium-Cr steels; unexpectedly, the high-Cr steel had more tribo-oxides than the low or medium-Cr steels in some cases. Its high wear resistance may be attributed to Cr-strengthened adhesion power of tribo-oxides and matrix.     

Elevated temperature fretting fatigue of Ti-17 with surface treatments

Fretting fatigue of Ti-17/Ti-8-1-1 contacts at 316 °C is examined experimentally. Different surface treatments are analyzed, including coatings, lubrication, and levels of shot peening. The evolution of friction is examined for a range of surface treatment. Fretting fatigue life for baseline specimens are obtained for a range of load parameters to determine loads that yield fretting fatigue lives of approximately 100,000 cycles. This applied load level was maintained constant for the different combinations of surface treatments to investigate the influence of surface treatment on fretting fatigue life. The Cu-Ni-In and Al-Br coatings and MoS₂ and Everlube lubricants are removed early in the fretting fatigue experiment; hence these surface treatments had little effect on fretting fatigue life. Shot peening increases fretting fatigue lives by about 60%. Block loading experiments show that minor cycles reduce fretting fatigue life.     

An experimental study on bending fretting fatigue characteristics of 316L austenitic stainless steel

Bending fretting fatigue tests of 316L austenitic stainless steel plates against 52100 steel cylinders have been carried out under same normal load and varied bending loads. Tests of plain bending fatigue were carried out as a control group. The S-N curves of the bending fatigue were made. The results indicated that there was an obvious drop of life under the condition of bending fretting fatigue due to higher local contact stress. A dislocation model of micro-crack nucleation mechanism, as a manner of zig-zag mode, was created to explain the nucleation of fretting fatigue cracks.     

The effect of rubber contact on the fretting fatigue strength of railway wheel tire

The cause of the ICE train derailment, which occurred in 1998 at Eschede, was fatigue failure originating on the inside of the wheel tire. Rubber-sprung resilient wheels were used for the trailer cars. The wheel tire is mounted on the wheel disc. Thirty-four rubber pads were arranged between the wheel disc and the wheel tire. It was postulated that fretting fatigue between the rubber block and the inner side of the tire might have an influence on the initiation of the incipient crack. In order to clarify the influence of the rubber contact on the fatigue strength of the tire, fretting fatigue experiments under rubber contact conditions were performed. During the fundamental fretting fatigue test using bridge pads and small size carbon steel specimens, no typical fretting damage such as fretting wear and minute cracks were observed due to contact of the rubber. Stress conditions of the rubber-sprung wheel under vertical and lateral wheel loads were evaluated by a three-dimensional elastic stress analysis. Since the rubber is a super-elastic material, the Mooney-Rivlin model was used in the FEM calculation. It was found that the wheel tire is subjected to a cyclic stress during one revolution of the wheel and the maximum stress occurred at the center of the inner surface of the tire where the fatigue crack initiated. Fatigue strength of the wheel tire was determined by the rotating bending fatigue testing of specimens taken from the tire. It was found that the tire with an 862 mm diameter at a wheel load of 80 kN had a safety factor more than 3.5 from a fatigue limit diagram with a failure probability of 0.01. To confirm the fretting damage under the rubber contact and the result of the fatigue strength evaluation, fatigue tests of a full size wheel were made. After 20 million cycles at the wheel load of 280 kN, which was just below the endurance limit estimated by the endurance limit diagram, no fretting damage and no fatigue cracks were observed. The wheel was, however, fractured at 1.56 million cycles under the maximum load of 308 kN, which was just above the endurance limit. The estimation of the safety factor of 3.5 estimated from the endurance diagram was confirmed by the full size fatigue testing. It was concluded that there was no effect of fretting due to the rubber contact on the fatigue strength of the rubber-sprung single-ring railway wheel.     

Fretting fatigue strength of SCM435H steel and SUH660 heat‐resistant steel in hydrogen gas environment

Utilisation of hydrogen is expected to be one of the solutions against the problems of exhaustion of fossil fuels and reduction of carbon dioxide emissions. Evaluation of the materials for hydrogen utilisation machines is required. The objectives of this study are the characterisation of fretting fatigue strength of low‐alloy steel SCM435H and heat‐resistant steel SUH660, and the validation of effectiveness of nitriding in hydrogen gas environment. Fretting fatigue tests were conducted up to 3 × 10⁷ cycles. The decrease of fretting fatigue strength in hydrogen gas environment was found at the long‐life region exceeding 10⁷ cycles. The amount of the decrease of the fretting fatigue limit at 3 × 10⁷ cycles was 11% for SCM435H and 15% for SUH660. However, at the stress level above the fretting fatigue limit in air, the finite life in hydrogen gas increased more than that in air. The cause of extension of fatigue life was the delay of start of stable crack propagation. Fretting fatigue crack, which was smaller than 200 µm in length, consumed approximately 60% of the fatigue life in hydrogen gas environment. Fretting fatigue crack was steadily propagated after the test was started in air. Observations of the fretted surface showed that the fretting wear process in hydrogen gas environment was dominated by adhesion. Tangential force coefficient was higher in hydrogen gas environment than that in air. It is considered that the adhesion has a close relation to crack initiation in hydrogen gas environment, and as a result, the failure of specimen occurred at a lower stress level comparing the fretting fatigue limit in air. Copyright © 2008 John Wiley & Sons, Ltd.     

The corrosion wear behaviour of selected stainless steels in potash brine

Tests were conducted at 25 and 85 °C to evaluate the corrosion wear resistance of selected stainless steels in potash brine using a reciprocating motion wear apparatus. Four materials were tested: Ferralium 255 (UNS S32550), AL6XN (UNS N08367), 254SMO (UNS S31254) and AISI 1018 (UNS G10180) for comparative purposes. The evaluation methods employed included weight loss analysis, optical microscopy and scanning electron microscopy (SEM). The results show that Ferralium 255 has superior corrosion wear resistance in potash brine environment compared to AISI 1018 plain-carbon steel and the other stainless steels tested. Wear surface analysis using SEM shows evidence of brittle fracture damage, which is attributed to the presence of Cl⁻.     

High temperature fretting wear behavior of WC-25Co coatings prepared by D-gun spraying on Ti-Al-Zr titanium alloy

Detonation gun (D-gun) spraying is one of the most promising spraying techniques for producing wear-resistance coatings. A thick layer (about 0.3 mm thickness) of WC-25Co with high hardness was covered on Ti-Al-Zr titanium alloy by D-gun spraying and the fretting wear behavior of WC-25Co coatings was studied experimentally on a high precision hydraulic fretting wear test rig. An experimental layout was designed to perform fretting wear tests at elevated temperatures from room temperature (25 °C) to 400 °C in ambient air. In the tests, a sphere (Si₃N₄ ceramic ball) was designed to rub against a plane (Ti-Al-Zr titanium alloy with or without WC-25Co coatings). It was found that the fretting running regimes of WC-25Co coatings were obviously different from those of Ti-Al-Zr titanium alloy. The mixed fretting regime disappeared in WC-25Co coatings, and the boundaries in the running condition fretting map (RCFM) showed hardly any change as temperature increased. The worn scars were examined using a laser confocal scanning microscope (LCSM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that the coefficients of friction (COF) of WC-25Co coatings at elevated temperatures were nearly constant in the partial slip regime and very low in the steady state. The fretting damage of the coatings was very slight. In the slip regime, the WC-25Co coatings exhibited a good wear resistance, and the wear volume of the coatings obviously decreased with increasing tested temperature. The fretting wear mechanisms of WC-25Co coatings were delamination, abrasive wear and oxidation wear at elevated temperature. The oxide debris layer formed at higher temperature was denser and thicker on top of WC-25Co coatings, thus providing more surface protection against fretting wear, which played an important role in the low fretting wear of the coatings.     

Fabrication and characterization of ZnO thin film for hydrogen gas sensing prepared by RF-magnetron sputtering

A ZnO thin film-based gas sensor was fabricated using a SiO₂/Si substrate with an integrated platinum comb-like electrode and heating element. The structural characteristics, morphology, and surface roughness of the as-grown ZnO nanostructure were investigated. The optical properties were examined by UV–vis spectrophotometry. The film revealed the presence of a c-axis oriented (0 0 2) phase of 20.8 nm grain size. The sensor response was tested for hydrogen concentrations of 50, 70, 100, 200, 400, and 500 ppm at operating temperatures ranging from 250 °C to 400 °C. The sensitivity toward 50 and 200 ppm of hydrogen at the optimum operating temperature of 350 °C were about 78% and 98%, respectively. The response was linear within the range of 50–200 ppm of hydrogen concentration. Our results demonstrated the potential application of ZnO nanostructure for fabricating cost-effective and high-performance gas sensors.     

Effect of nitrogen on the corrosion-erosion synergism in an austenitic stainless steel

High temperature gas nitrided AISI 304L austenitic stainless steel containing 0.55 wt% N in solid solution, was corrosion, erosion and corrosion-erosion tested in a jet-like device, using slurry composed of 3.5% NaCl and quartz particles. Scanning electron microscopy analysis of the damaged surfaces, mass loss measurements and electrochemical test results were used to understand the effect of nitrogen on the degradation mechanisms. Increasing the nitrogen content improved the corrosion, erosion and corrosion-erosion resistance of the AISI 304L austenitic stainless steel. Smoother wear mark contours observed on the nitrided surfaces indicate a positive effect of nitrogen on the reduction of the corrosion-erosion synergism.     

Wear behaviour of hardfaced Fe-Cr-C alloy and austenitic steel under 2-body and 3-body conditions at elevated temperature

Fe-based hardfacing alloys are widely used to protect machinery equipment exposed to different loading situations where abrasives play a dominant role in restricting lifetime of tools. Wear at elevated temperatures is superposed by the effect of oxidation of the wearing surface. In view of the above, two hardfacing alloys based on Fe-Cr-C incorporating Nb, Mo and B to ensure improved performances at elevated temperature were deposited onto mild steel under optimised gas metal arc welding (GMAW) condition. 2-body erosive wear behaviour was evaluated from room temperature up to 650 °C under 30° and 90° impact angle. For 3-body impact/abrasion conditions tests were done with a specially designed cyclic impact abrasion tester (CIAT) at room temperature and 600 °C. The wear behaviour of the hardfacings was compared with austenitic stainless steel. Results indicate that 2-body erosive wear rate of the hardfacing increases with test temperature and with increase in impact angle, whereas wear behaviour of the austenitic stainless steel is non-sensitive to the testing temperature at normal impact. In 3-body impact abrasion testing similar behaviour can be seen; cyclic tests in CIAT at enhanced temperatures result in breaking of coarse carbides, whereas wear mechanisms of the austenitic steel result in massive abrasion and formation of a mechanically mixed layer (MML).     

Influence of flow conditions on the corrosion of AISI 304L stainless steel

Hydrodynamic and electrochemical noise measurements (ENMs), of AISI 304L stainless steel, were made in a pipe test section of 28 mm inside diameter for a range of flow regimes from laminar to turbulent. Mean flow velocities through the test section were controlled at 0.04, 0.07, 0.11, 0.36, 1.8 and 2.7 m s⁻¹, equivalent to Reynolds numbers of 1000, 2000, 3000, 10 000, 50 000 and 75 000, respectively. Standard hydrodynamic parameters were employed to characterise and evaluate the complex interrelationship between the mass transfer rate of oxygen and momentum transfer through turbulence to the metal/solution interface. For AISI 304L stainless steel, pitting typically occurs in the form of metastable pits which either repassivated before achieving stability or grow to become stable pits. Metastable pitting was evident under all flow regimes. The fluid flow, whether laminar or turbulent, had little overall effect on the nucleation rates of metastable pitting events. Conversely, stable pit growth was most evident during laminar flow immediately before the transition to turbulent flow and close to the critical velocity (∼1.5 m s⁻¹).