Friction and wear of Si3N4 ceramic/stainless steel sliding contacts in dry and lubricated conditions

Austenitic stainless steel AISI 321 is one of the most difficult-to-cut materials. In order to investigate the wear behavior of Si₃N₄ ceramic when cutting the stainless steel, wear tests are carried out on a pin-ondisk tribometer, which could simulate a realistic cutting process. Test results show that the wear of Si₃N₄ ceramic is mainly caused by adhesion between the rubbing surfaces and that the wear increases with load and speed. When oil is used for lubrication, the friction coefficient of the sliding pairs and the wear rate of the ceramic are reduced. A scanning electron microscope (SEM), an electron probe microanalyzer (EPMA), and an energy dispersive x-ray analyzer (EDXA) are used to examine the worn surfaces. The wear mechanisms of Si₃N₄ ceramic sliding against the stainless steel are discussed in detail.     

Adhesion phenomena in the secondary shear zone in turning of austenitic stainless steel and carbon steel

This paper aims to increase the understanding of the adhesion between chip and tool rake face by studying the initial material transfer to the tool during orthogonal machining at 150 m/min. Two types of work material were tested, an austenitic stainless steel, 316L, and a carbon steel, UHB 11. The tools used were cemented carbide inserts coated with hard ceramic coatings. Two different CVD coatings, TiN and Al₂O₃, produced with two different surface roughnesses, polished and rough, were tested. The influences of both tool surface topography and chemistry on the adhesion phenomena in the secondary shear zone were thus evaluated. Extensive surface analyses of the inserts after cutting were made using techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM). As expected, cutting in the stainless steel resulted in a higher amount of adhered material, compared to cutting in the carbon steel. Remnants of built-up layers were found on the surfaces of the 316L chips but not on the UHB 11 chips. Moreover, it was shown that for both materials the tool roughness had a profound effect, with the rougher surfaces comprising much higher amounts of adhered material than the polished ones. Non-metallic inclusions from both types of workpiece steels accumulate in the high temperature area on the inserts. The general tendency was that higher amounts of transferred material were found on the TiN coating than on the Al₂O₃ coating after cutting.     

Wear behavior of Al2O3/Ti(C,N)/SiC new ceramic tool material when machining tool steel and cast iron

Design, fabrication and application of ceramic cutting tools are one of the important research topics in the field of metal cutting and advanced ceramic materials. In the present study, wear resistance of an advanced Al₂O₃/Ti(C,N)/SiC multiphase composite ceramic tool material have been studied when dry machining hardened tool steel and cast iron under different cutting conditions. Microstructures of the worn materials were observed with scanning electronic microscope to help analyze wear mechanisms. It is shown that when machining hardened tool steel at low speed wear mode of the kind of ceramic tool material is mainly flank wear with slight crater wear. The adhesion between tool and work piece is relatively weak. With the increase of cutting speed, cutting temperature increases consequently. As a result, the adhesion is intensified both in the crater area and flank face. The ceramic tool material has good wear resistance when machining grey cast iron with uniform flank wear. Wear mechanism is mainly abrasive wear at low cutting speed, while adhesion is intensified in the wear area at high cutting speed. Wear modes are dominantly rake face wear and flank wear in this case.     

Friction and Wear Behavior of Plasma-Sprayed Al2O3-13 wt.%TiO2 Coatings Under the Lubrication of Liquid Paraffin

Two types of ceramic composite coatings (denoted as N-AT13 coating and M-AT13 coating) were fabricated on 1Cr18Ni9Ti stainless steel substrate from ultra-fine and coarse Al₂O₃-13%TiO₂ feedstocks by air plasma spraying. The friction and wear behavior of as-prepared coatings sliding against Al₂O₃ and stainless steel balls under the lubrication of liquid paraffin was evaluated with an SRV friction and wear tester (Optimol, Germany). The fractured and worn surfaces of the coatings were observed using a scanning electron microscope and a field-emission scanning electron microscope; and the wear mechanisms of the coatings were discussed based on scanning electron microscopic analysis and energy dispersive spectrometric analysis. Results show that N-AT13 coating possesses a unique microstructure and strong inter-splat bonding, thereby showing increased microhardness and bonding strength as well as much better friction-reduction and wear resistance than M-AT13 coating. Moreover, there exist differences in the wear mechanisms of N-AT13 and M-AT13 coatings which slide against ceramic and stainless steel balls under the lubrication of liquid paraffin. Namely, with the increase of normal load, the burnishing of N-AT13 coating coupled with Al₂O₃ ball is gradually transformed to grain-abrasion and deformation, while M-AT13 coating is dominated by grain-pullout and brittle fracture in the whole range of tested normal load.     

The influence of Al2O3 reinforcement on the properties of stainless steel cold spray coatings

The effect of Al₂O₃ additions to type 316 austenitic stainless steel cold spray coatings was studied. Adding Al₂O₃ to the feedstock powder increased the overall deposition efficiency, though the Al₂O₃ itself deposited less efficiently than the stainless steel. Shear testing of the coatings using a shear lug test revealed a change in fracture from cohesive to adhesive with increasing alumina addition. The corrosion behaviour, assessed using anodic polarisation tests of the coatings, showed a shift towards the polarisation behaviour of bulk stainless steel with Al₂O₃ additions. All of these changes in coating behaviour with Al₂O₃ additions suggest an improved degree of metallurgical bonding, likely due to increased plasticity in the stainless steel particles.     

TEM analysis and wear resistance of the ceramic coatings on Q235 steel prepared by hybrid method of hot-dipping aluminum and plasma electrolytic oxidation

The hybrid method of PEO and hot-dipping aluminum (HDA) was employed to deposit composite ceramic coatings on the surface of Q235 steel. The composition of the composite coatings was investigated with X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The cross-section microstructure and micro-hardness of the treated specimens were investigated and analyzed with scanning electron microscopy (SEM) and microscopic hardness meter (MHM), respectively. The wear resistance of the ceramic coatings was investigated by a self-made rubbing wear testing machine. The results indicate that metallurgical bonding can be observed between the ceramic coatings and the steel substrate. There are many micro-pores and micro-cracks, which act as the discharge channels and result of quick and non-uniform cooling of melted sections in the plasma electrolytic oxidation ceramic coatings. The phase composition of the ceramic coatings is mainly composed of amorphous phase and crystal Al₂O₃ oxides. The crystal Al₂O₃ phase includes κ-Al₂O₃, θ-Al₂O₃ and β-Al₂O₃. The grain size of the κ-Al₂O₃ crystal is quite non-uniform. The hardness of the ceramic coatings is about HV1300 and 10 times higher than that of the Q235 substrate, which was favorable to the better wear resistance of the ceramic coatings.     

Self-lubrication of sintered ceramic tools with CaF2 additions in dry cutting

An Al₂O₃/TiC ceramic cutting tool with the additions of CaF₂ solid lubricant was produced by hot pressing. The fundamental properties of this ceramic cutting tool were examined. Dry machining tests were carried out on hardened steel and cast iron. The tool wear, the cutting forces, and the friction coefficient between the tool–chip interface were measured. It was shown that the friction coefficient at the tool–chip interface in dry cutting of hardened steel and cast iron with Al₂O₃/TiC/CaF₂ ceramic tool was reduced compared with that of Al₂O₃/TiC tool without CaF₂ solid lubricant. The mechanisms responsible were determined to be the formation of a self-lubricating film on the tool–chip interface, and the composition of this self-lubricating film was found to be mainly CaF₂ solid lubricant, which was released and smeared on the wear track of the tool rake face, and acted as lubricating additive between the tool–chip sliding couple during machining processes. The appearance of this self-lubricating film contributed to the decrease of the friction coefficient. Cutting speed was found to have a profound effect on this self-lubricating behavior.     

Mechanical property and cutting performance of yttrium-reinforced Al2O3/Ti(C,N) composite ceramic tool material

Effects of yttrium on the mechanical property and the cutting performance of Al₂O₃/Ti(C,N) composite ceramic tool material have been studied in detail. Results show that the addition of yttrium of a certain amount can noticeably improve the mechanical property of Al₂O₃/Ti(C,N) ceramic material. As a result, the flexural strength and the fracture toughness amount to 1010 MPa and 6.1 MPam^1/2, respectively. Cutting experiments indicate that the developed ceramic tool material not only has better wear resistance but also has higher fracture resistance when machining hardened #45 steel. The fracture resistance of the yttrium-reinforced Al₂O₃/Ti(C,N) ceramic tool material is about 20% higher than that of the corresponding ceramic tool material without any yttrium additives.     

Surface pretreatment of austenitic stainless steel and copper by chemical, plasma electrolytic or CO2 cryoblasting techniques for sol-gel coating

The surface pretreatments of the austenitic stainless steel and copper surfaces for the sol-gel coating were carried out by chemical, plasma electrolytic or CO₂ cryoblasting techniques. With the austenitic stainless steel the smoothest surfaces were obtained with plasma electrolytic cleaning, after which the measured contact angles of water were clearly decreased revealing improved hydrophilicity. As well with the copper samples the smooth surface and improved hydrophilicity was obtained with the plasma electrolytic cleaning, but oxide layer formed to the copper surface immediately after the treatment. CO₂ cryoblasting provided rough surface with wetting properties close to the original surface both for austenitic stainless steel and copper surfaces. CO₂ cryoblasting provided best appearance for the copper surface because no oxidation happened with that treatment. XPS and SIMS studies showed that with the plasma electrolytic treatment the surface layer of the austenitic stainless steel enriched of chromium and the oxide layer formed on the surface was less than 10 nm thick. With the chemical cleaning and CO₂ cryoblasting, the chromium enrichment to the stainless steel surface was less. However XPS and SIMS studies showed that chemical treatment provided thinner oxide layer to copper surface than plasma electrolytic treatment.     

Friction behaviour of heat isolating coatings in machining: mechanical, thermal and energy-based considerations

This paper deals with possible modifications of the frictional behaviour exhibited during the cutting process resulting from the influence of the most-commonly used heat isolating coatings deposited on a WC-Co carbide substrate. For this study, three- and four-layered coatings with intermediate Al₂O₃ ceramic layer and a monolayer TiAlN coating, which offer superior thermal protection of the carbide substrate, were examined. Orthogonal cutting tests were carried out by end-turning medium carbon steel and austenitic stainless steel workpieces. The experimental study was aimed at determining the fundamental frictional characteristics: dimensions of the tool-chip contact area, the friction force, the mean friction coefficient, the specific frictional energy and the corresponding thermal effects: the contact temperature and the frictional heat flux. Subsequently, results obtained for the mechanical, energy-based and thermal approaches to the frictional behaviour occurring in the carbide/ceramic coating-steel tribo-pairs were verified experimentally and the results obtained are discussed in detail.     

Experimental investigation of the cutting temperature when turning with coated indexable inserts

This paper deals with an experimental investigation into the different factors which influence the temperature which occur at the coating/substrate–chip interface when machining a medium carbon steel and an austenitic stainless steel. Both flat-faced and grooved inserts coated with TiC, TiC/TiN and TiC/Al₂O₃/TiN were used. A standard K-type thermocouple embedded in the workpiece was used to convert measured efms to the interfacial temperature. Some optimal coating structures for high speed machining of these steels corresponding to the minimum interface temperature were selected. In particular, it was observed that by the proper selection of the thermal properties of the coating and the workpiece materials, which result in a substantial increase in the interface temperature, the effect of a thermal barrier in the top layer of the coating can occur.     

Hemocompatibility evaluation of plasma-nitrided austenitic stainless steels at low temperature

In this study, plasma-nitrided austenitic stainless steel was prepared using a microwave system as a function of the nitriding duration. The nitride layers were characterized via scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy, atomic force microscopy and a Vickers micro-hardness tester. The effects of plasma nitriding on the compatibility of blood with the austenitic stainless steel were also investigated. Based on the XRD and TEM observations, it was inferred that only a single γ_N phase was detected in the whole process of experiments. The γ_N layer, which was formed on austenitic stainless steel, exhibited lower platelet adhesion and activation than the untreated specimens. The clotting time of the PN specimens was prolonged and increased with the treatment time. This work suggested that the blood-compatible manner of plasma nitriding by controlling surface characteristic on austenitic stainless steel improved the anticoagulant properties, and made austenitic stainless steel suitable candidates in the field of surgical and medical instruments.     

Micro-EDM process investigation and comparison performance of Al3O2 and ZrO2 based ceramic composites

This paper investigates the micro-EDM behaviour of an Al₃O₂ and ZrO₂ based electrically conductive ceramic composites. The influence of the generator parameters on material removal rate, relative tool wear, surface quality and material removal mechanism is investigated towards the definition of suitable micro-EDM technologies. The study is based on a design of experiments, supported by a fundamental investigation of the generator parameters. Similar variations trends to the machining of steel are observed within the investigated process window, for exception of the tool wear performance. The developed EDM technologies are finally validated through the fabrication of industrial demonstrators.     

Self-lubricating mechanisms via the in situ formed tribo-film of sintered ceramics with hBN addition in a high humidity environment

Sliding wear tests against monolithic Si₃N₄ and austenitic stainless steel, respectively, were performed on Si₃N₄ ceramic with the addition of hBN solid lubricants. The friction coefficients and wear rates were measured. The wear surface features were examined by scanning electron microscopy (SEM) and laser scanning microscopy (LSM), and the chemical characterization of worn surface was made by Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Results showed that the friction coefficient and the wear rate decreased with the increase of hBN up to 20 vol% at high relative humidity (RH95%). When Si₃N₄-hBN ceramic composites sliding against stainless steel, with further increases in hBN content, the wear rate increased rapidly. The mechanism responsible were determined to be an in-situ formed tribo-chemical film composed of B-O and Si-O compounds between the pin-disc sliding couple. SEM observations showed that a black surface film is formed on the wear surface depending on the hBN content. The surface film associated with small friction coefficient of 0.03 and low wear rate with the magnitude of 10^− 6 mm³/Nm was formed by the releasing and smearing of the tribo-chemical reaction products of hBN and moisture on the wear surface when with 20 vol%hBN content. This tribo-chemical film acted as solid lubricant film between the sliding couple, and thus the couple entered to a state of boundary lubrication. Hence, the friction coefficient and the wear rate were significantly reduced. For Si₃N₄-hBN/stainless steel sliding pair, even at high relative humidity, no tribo-chemical film was observed on samples with 30 vol%hBN content, just because of a large degradation of mechanical properties of the composite with higher hBN content. At low relative humidity (RH25%), the wear mechanism for Si₃N₄-hBN sliding couple was mainly dominated by mechanical wear (abrasive or adhesive wear) due to the absence of tribo-chemical film on the wear surfaces, and higher friction coefficient and wear rate were obtained.     

Examination of wire electrical discharge machining of Al2O3p/6061Al composites

Alumina particle reinforced 6061 aluminum matrix composites (Al₂O₃p/6061Al) have excellent physical and chemical properties than those of a traditional metal; however, their poor machinability lead to worse surface quality and serious cutting tool wear. In this study, wire electrical discharge machining (WEDM) is adopted in machining Al₂O₃p/6061Al composite. In the experiments, machining parameters of pulse-on time were changed to explore their effects on machining performance, including the cutting speed, the width of slit and surface roughness. Moreover, the wire electrode is easily broken during the machining Al₂O₃p/6061Al composite, so this work comprehensively investigates into the locations of the broken wire and the reason of wire breaking.The experimental results indicate that the cutting speed (material removal rate), the surface roughness and the width of the slit of cutting test material significantly depend on volume fraction of reinforcement (Al₂O₃ particles). Furthermore, bands on the machined surface for cutting 20 vol.% Al₂O₃p/6061Al composite are easily formed, basically due to some embedded reinforcing Al₂O₃ particles on the surface of 6061 aluminum matrix, interrupt the machining process. Test results reveal that in machining Al₂O₃p/6061Al composites a very low wire tension, a high flushing rate and a high wire speed are required to prevent wire breakage; an appropriate servo voltage, a short pulse-on time, and a short pulse-off time, which are normally associated with a high cutting speed, have little effect on the surface roughness.     

Mechanical and tribological properties of nanocomposite TiSiN coatings

TiSiN coatings with a thickness of 2.5 μm were deposited using a Large Area Filtered Arc Deposition (LAFAD) technique with TiSi targets having different Si content. The influence of the Si content in the coatings on the mechanical properties and tribological behaviors of the TiSiN coatings were systematically studied using nanoindentation and a pin-on-disk tribometer. Nanoindentation results show that the hardness and Young's modulus of the TiSiN coatings increase with increasing Si content in the coatings. Wear test results indicate that the wear rate and friction coefficient of the 440a stainless steel coupons were significantly reduced by deposition of the TiSiN coatings, and the tribological behaviors of the TiSiN coatings are strongly dependent on the Si content in the coatings and the testing ball material. TiSiN coatings exhibit similar friction coefficient when tested against Al₂O₃ and 302 stainless steel balls, but increasing Si content in the coatings causes an increase in the friction coefficient of the TiSiN coatings. With the increase in the Si content in the coatings, the wear rate of the TiSiN coatings decreases when tested against Al₂O₃ balls, but increases significantly when tested against 302 stainless steel balls. The capability of forming a transfer layer on the ball surface contributes to the change in the friction coefficient and wear rate with Si content in the coating and ball materials.     

Effect of Surface Roughness and Structure Features on Tribological Properties of Electrodeposited Nanocrystalline Ni and Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Coatings

Metal matrix composite coatings obtained by electrodeposition are one of the ways of improving the surfaces of materials to enhance their durability and properties required in different applications. This paper presents an analysis of the surface topography, microstructure and properties (residual stresses, microhardness, wear resistance) of Ni/Al₂O₃ nanocomposite coatings electrodeposited on steel substrates from modified Watt’s-type baths containing various concentrations of Al₂O₃ nanoparticles and a saccharin additive. The residual stresses measured in the Ni/Al₂O₃ coatings decreased with an increasing amount of the co-deposited ceramics. It was established that the addition of Al₂O₃ powder significantly improved the coatings’ microhardness. The wear mechanism changed from adhesive-abrasive to abrasive with a rising amount of Al₂O₃ particles and coating microhardness. Nanocomposite coatings also exhibited a lower coefficient of friction than that of a pure Ni-electrodeposited coating. The friction was found to depend on the surface roughness, and the smoother surfaces gave lower friction coefficients.     

Enhancement of Corrosion Resistance of Type 304 Stainless Steel Through a Novel Thermo-mechanical Surface Treatment

The paper describes a novel thermo-mechanical surface treatment approach, involving conventional shot blasting followed by laser surface heating, to engineer microstructural modification in type 304 austenitic stainless steel for enhancing its corrosion resistance. Thermo-mechanical surface treatment resulted in the formation of fine recrystallized grains with some strain-induced martensite on the modified surface. Surface treatment of type 304 stainless steel brought about significant improvement in its resistance against uniform as well as pitting corrosion. Electrochemical impedance spectroscopic studies showed improved polarization resistance (R _p) value for thermo-mechanically treated surface indicating formation of a more protective passive film than that formed on the untreated surface. In contrast to untreated type 304 stainless steel specimens where pits preferentially initiated at the site of Al₂O₃ inclusions, thermo-mechanically treated specimen exhibited only general dissolution with a few repassivated and shallow pits. Grain refinement and dispersion of alumina inclusions on the modified surface are considered to be the key factors responsible for improvement in uniform and pitting corrosion resistance of type 304SS.     

Erosive abrasive wear behaviour of stainless steel surface produced by plasma transferred arc hardfacing

Abstract

Erosive abrasive wear is caused by high speed impact of particles entrained in a fluid system on the surfaces of components such as boilers and furnaces. Erosive abrasive wear in boilers results from the impact of hard particles such as ash or clinker entrained in flue gases and can lead to serious damage. The life of boiler and furnace components encountering erosive abrasive wear in service, which are most commonly fabricated from carbon steels, can be improved by hardfacing with a wear resistant material. The effects of wear parameters such as particle size, flux and velocity on the erosive abrasive wear behaviour of a stainless steel surface produced by the plasma transferred arc hardfacing have been investigated using an experimental design approach. The wear resistance of the stainless steel surface was found to be twice that of the carbon steel substrate.     

Influence of aluminum phosphate on the tribocorrosion performance of chemically bonded phosphate ceramic coatings

In this study, chemically bonded phosphate ceramic coatings (CBPCCs) with different contents of aluminum phosphate (AP) are prepared on stainless steel (AISI 304L). Differential scanning calorimetry, X-ray diffraction, contact angle test, and a tribocorrosion experiment are carried out to clarify the role of AP in the tribocorrosion performance of CBPCCs. The results show that, with the increase in the AP content, the enthalpy of curing increases because of the greater formation of the bonding phase AlPO₄. Both in static corrosion and in tribocorrosion, the corrosion current density of CBPCCs achieves the lowest value when the weight ratio of AP to polytetrafluoroethylene is about 0.78. Additionally, the influence mechanism of AP on tribocorrosion is clarified. AlPO₄ from the reaction between AP and Al₂O₃ has excellent mechanical properties and can enhance the wear resistance of CBPCCs by reducing the mechanical wear and the increased wear due to corrosion. The alumina particles wrapped by AlPO₄ can form a dense and smooth surface and change the direction of electrolyte propagation, which leads to the increase in the tribocorrosion resistance of CBPCCs.