Austenitic Stainless Steel Substrate Research Articles

Microstructure and dry-sliding wear properties of TiC-reinforced composite coating prepared by plasma-transferred arc weld-surfacing process

A wear resistant TiC titanium carbide-reinforced composite coating was fabricated on 1Cr18Ni9Ti austenitic stainless steel substrate by plasma-transferred arc (PTA) weld-surfacing process using Fe–Ti–C powder blends. The microstructure, microhardness and dry-sliding wear behavior of the composite coating were investigated using optical microscopy (OM), X-ray diffraction (XRD), scanning electron micrograph (SEM), energy-dispersive X-ray analysis (EDS), microhardness tester and ring-on-ring wear tester. The formation mechanism of the composite coating has been discussed. Results show that the composite coating consists of primary TiC carbide as the reinforcing phase and TiC/γ-Fe eutectics as the matrix. The composite coating is metallurgically bonded to the 1Cr18Ni9Ti austenitic stainless steel substrate. The TiC/γ-Fe composite coating has high hardness and excellent wear resistance under dry-sliding wear test condition.

Microstructure and wear characteristics of nickel based hardfacing alloys deposited by plasma transferred arc welding

In the present investigation, a nickel based hardfacing alloy (AWS NiCr–B) was deposited on an austenitic stainless steel substrate 316LN using the plasma transferred arc welding process. The deposit was characterised by hardness measurements, microstructural examination and sliding wear assessment. Identification of precipitates was carried out using X-ray diffraction and SEM/EDAX. These studies revealed the presence of chromium rich carbides and borides in a γ-Ni matrix. Down to a distance of 1 mm from the interface, the hardness of the deposit was found to be 52 HRC. The sliding wear behaviour of the hardfacing alloy was investigated in air in the room temperature to 550°C range, with a pin on disk configuration using a cylindrical pin with tip radius of 3 mm under loads of 30, 40 and 50 N. Wear experiments were conducted up to a sliding distance of 180 m at a sliding speed of 0·1 m s−1. The elastic modulus and Poisson's ratio of the hardfaced deposits were evaluated by the ultrasonic method and these values were used for calculating initial Hertzian contact stress. The study showed that, while significant wear loss occurred at room temperature, there was practically no measurable weight loss at temperatures of 300 and 550°C. This could be attributed to the formation of an oxide layer at the surface during wear testing.

Effects of TiO 2 on the mechanical properties of the Al 2O 3–TiO 2 plasma sprayed coating

Plasma sprayed ceramic coatings are successfully used in many industrial applications, where high wear and corrosion resistance with thermal insulation are required. In this study, various types of Al 2O 3–TiO 2 plasma sprayed coatings in different compositions (Al 2O 3–13 wt.% TiO 2, Al 2O 3–40 wt.% TiO 2 and Al 2O 3–50 wt.% TiO 2) were prepared on an AISI 304L austenitic stainless steel substrate. The effects of TiO 2 addition on the properties of the coating were investigated in terms of microhardness and fracture toughness values. The results obtained from experimental work were evaluated with standard characterisation techniques. The results indicated that an increase in TiO 2 amount improves fracture toughness and lowers the microhardness values of the coatings.

Effect of surface preparation on the evolution of the passive films formed on AISI 304L

AbstractIn this work, an insight into the effect of surface roughness in the composition and evolution of the oxide film electrogenerated on an austenitic stainless steel substrate is presented. The obtained results point out the importance of Ni on the oxide layers formed in alkaline media, which can condition their resistance to chloride attack. Polished samples show better corrosion performance than abraded ones owing to Ni enrichment at the metal‐oxide interface. Copyright © 2006 John Wiley & Sons, Ltd.

A study of the solid–liquid interface in cobalt base alloy (Stellite) coatings deposited by fusion welding (TIG)

Microstructural features present at the interface between a weld deposited Stellite 6 hard facing and an austenitic stainless steel substrate are described. Elemental X-ray maps indicate that diffusion of carbon from the liquid Stellite to the austenitic stainless steel takes place along grain boundaries resulting in the formation of chromium carbide “arms” that penetrate along the austenite grain boundaries in the interfacial region.

Characterisation of nickel based hardfacing deposits on austenitic stainless steel

Nickel based hardfacing alloys Colmonoy-5 and Colmonoy-6 deposited on type 316L austenitic stainless steel substrate using the gas tungsten arc welding process, were characterised for their microstructure and hardness variations across the deposit/substrate interface, and for identification of the principal precipitates present in these hardface deposits. Hardness measurements and electron probe microanalysis (EPMA) across the interface revealed the presence of a dilution zone 2·5 mm wide in the Colmonoy-6 deposit and 1·5 mm wide in the Colmonoy-5 deposit. EPMA and X-ray diffraction studies of the precipitates showed that he blocky type precipitates were chromium borides and the needle-like precipitates were chromium carbides. Also, stress relief heat treatment at 1123 K for 4 h was found to have no significant effect on the hardness of these hard face deposits.

Residual stress and cracking in expanded austenite layers

The residual stress state and mechanical properties of an expandedaustenite layer produced by plasma immersion ion implantation(PI3) on type 316 austenitic stainless steel substrates at different temperatureswere investigated. Residual stress data were obtained using the substratecurvature technique for six different treatment temperatures in the range360–520 °C. Lattice expansion, nitrogen concentration with depth and mechanical properties of thelayer were investigated using x-ray diffraction (XRD), glow discharge optical emissionspectroscopy (GDOES) and nano-indentation, respectively. Layer strength and fracturetoughness behaviour were investigated using tensile testing with optical microscopy tostudy the cracking evolution in situ. The results showed that for the treatments at360–420 °C lattice expansions greater than 8% were achieved with nitrogen concentrationsnear 40 at.%. Two distinct stress–temperature regions were identified fromthe curvature measurements: (i) for treatment temperatures less than450 °C, high compressive residual stresses in the range 2–3 GPa werefound and the fracture resistances of these layers were less than7 MPa m1/2, and (ii) for treatment temperatures above450 °C, the residual stresswas significantly lower (≈0.7 GPa) but remained constant and the fracture toughness of the layer was improved by afactor of two.

Analysis on Residual Stress in Electron Beam-Physical Vapor Deposited Thermal Barrier Coating using Hard Synchrotron X-Rays

The distribution of the residual stress in the thermal barrier coating, which was made by an electron beam-physical vapor deposition (EB-PVD) method, was determined using X-ray stress measurements. As the bond coating, NiCoCrAlY was low-pressure plasma sprayed on the substrate of austenitic stainless steel. The 8 mass% Y2O3-ZrO2 was coated on the bond coating using the EB-PVD method as the top coating. The top coating had the preferred orientation with the <111> axis direction perpendicular to the coating plane. The distribution of the in-plane residual stress in the top coating was measured using laboratory X-rays. The value of the in plane stresses was deter-mined by the sin2 φ method after the separation of the 133 and 331 diffractions. The distribution of the out-of-plane strain in the top coating was measured using the strain scanning method with hard synchrotron X-rays. The out-of-plane strain was obtained from the 333 diffraction which had strong intensity due to the preferred orientation. The measured value of the in-plane stress in the top coating was a large compression, and steeply decreased near the interface between the top and the bond coating. The distribution of the out-of-plane stress showed a compression, and its magnitude was smaller than that of the in-plane stress.

X-ray elastic constants of chromium nitride films deposited by arc-ion plating

Thin films have been successfully utilized to improve the property of mechanical components. However, it is generally known that mechanical properties, such as elastic constants and tensile strength of thin films, are different from those of bulk material, and they are not known in the present state. In many times, x-ray stress measurement revealed a very high compressive residual stress state in the film when bulk elastic constants were used in the stress calculation. The purpose of this research is to investigate the elastic constants of chromium nitride (CrN) films. The film was deposited on austenitic stainless steel (JIS: SUS304) substrates by the arc-ion-plating (AIP) method under the following conditions: the pressure of nitrogen atmosphere was maintained at 2.63 Pa, the substrate temperature of about 573 K, the arc discharge current of 100 A, the bias voltage between −300 and −100 V, and the substrate rotating rate at 3 rpm. The lattice strain of CrN films was measured by x-ray method at various loading stages and the x-ray elastic constants of CrN films were evaluated.

The adhesion of hot-filament CVD diamond films on AISI type 316 austenitic stainless steel

Steel ball indentation and scratch adhesion testing of hot filament chemical vapour deposited diamond films onto AISI type 316 austenitic stainless steel substrates using two different interlayer systems, namely chromium nitride and borided steel, have been investigated. In order to compare the adhesion of these films with that of a well-known and strongly adherent system, detailed adhesion tests were performed on diamond films grown on molybdenum substrates as well. Scanning electron microscopy analysis of various indented regions on the diamond-coated steel and molybdenum samples in combination with the measurement of the acoustic emission signals during loading, indicate that the adhesion of the coatings on the stainless steel substrates with the CrN interlayer is comparable and only slightly less than that of the strongly adhering diamond films on the molybdenum samples. The critical load value derived from the acoustic emission signals at which partial delamination of the diamond films is first observed, is significantly lower for the diamond-coated steel with the boride interlayer than that obtained with the CrN interlayer for the present deposition conditions used. The steel ball indentation tests also show that the hardness and thickness of the interlayer have a strong effect on the penetration depths of the indents. Scratch tests performed on the diamond coated stainless steel specimens with the boride interlayer show no significant coating failure for loads up to 80 N.

High-temperature wear resistance of a laser clad TiC reinforced FeAl in situ composite coating

A rapidly solidified TiC reinforced FeAl in situ composite coating was fabricated on an austenitic stainless steel substrate by laser cladding using Fe–Al–Ti–C elemental powder blends. Because of the in situ incorporation of TiC and the mixed metallic-covalent atomic bonds of the FeAl matrix, the coating has good high-temperature wear resistance under sliding wear test conditions.

Laser Cladding of Austenitic Stainless Steel with Hardfacing Alloy Nickel Base

A nickel base alloy Colmonoy 6 was chosen as a candidate material for hard facing many components in the prototype fast breeder reactor. This alloy offers outstanding wear resistance and high hardness at elevated temperatures. Previous research using the gas tungsten arc welding process revealed that the hardness of the deposit is influenced by the dilution from the base metal up to a deposit thickness as high as 2.5 mm. The present study aims to control the level of dilution in the hard face deposits by carrying out deposition using a low heat input laser cladding process. The samples were characterised by macroscopic and metallographic examination, and microhardness measurements, SEM - EDAX and XRD analysis were used to determine their properties. The study demonstrated that by controlling laser cladding parameters, thin deposits with a low level of dilution can be laid on austenitic stainless steel substrate. Cracking of the deposit was minimised by controlling the heating and cooling rates.

Corrosion resistance of austenitic stainless steel separator for molten carbonate fuel cell

STS310S and SC-STS310S (simultaneously co-deposited chromium and aluminum onto 310S austenitic stainless steel substrate by pack-cementation process) were used as separator materials on the cathode side of a molten carbonate fuel cell. With the STS310S, corrosion proceeded via three steps; a formation step of unstable corrosion product, a protection step against corrosion until breakaway, and an advance step of corrosion after breakaway. The final corrosion product was LiFeO2 and the loss of mass was 6.5 mg/cm2 after a corrosion test of 480 hr at 650°C. The SC-STS310S showed more effective corrosion resistance, however, than did common STS310S. There was especially no corrosion loss on the SC-STS310S after the 480 hr corrosion test. It is anticipated that it will be very useful as an alternative separator on the cathode side off the MCFC in the future.

Hydrogen permeation resistance of plasma-sprayed Al 2O 3 and Al 2O 3–13wt.% TiO 2 ceramic coatings on austenitic stainless steel

Al 2O 3 and Al 2O 3–13wt.% TiO 2 ceramic coatings were prepared on 21Cr–6Ni–9Mn austenitic stainless steel substrates by plasma spraying. The phase contents and microstructures of the plasma-sprayed coatings were investigated by means of X-ray diffraction (XRD), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). Also, the hydrogen permeation resistance was measured by thermal hydrogen charging. The results showed that plasma-sprayed Al 2O 3 and Al 2O 3–13wt.% TiO 2 ceramic coatings can improve the hydrogen permeation resistance of 21Cr–6Ni–9Mn austenitic stainless steel effectively, and the hydrogen resistance efficiency of Al 2O 3 coating was higher than that of Al 2O 3–13wt.% TiO 2 coating. Al 2O 3 coating displayed a denser structure than Al 2O 3–13wt.% TiO 2 coating. The phase contents analysis revealed that the presence of the Ni(Cr, Fe, Ti) 2O 4 phase in the Al 2O 3–13wt.% TiO 2 coating in addition to γ-Al 2O 3 and α-Al 2O 3. It was found that the bonding between the plasma-sprayed ceramic coatings and austenitic stainless steel substrates was mechanical rather than metallurgical.

Effect of applied pulse voltage on nitrogen plasma immersion ion implantation of AISI 316 austenitic stainless steel

Plasma immersion ion implantation (PIII) of nitrogen was performed for 4 h on AISI 316 austenitic stainless steel substrates at a temperature of 400 °C. The substrate bias was varied between −1 and −20 kV with different duty cycles so as to keep the substrate temperature fixed. The implanted ions were evident to the depths of a few microns, which is much greater than their implantation depths, resulting in an enhancement of surface microhardness. A load dependent surface microhardness is observed which is nearly independent of the applied bias. Glancing angle X-ray diffraction patterns indicate the formation of expanded austenite at all biases. X-ray photoelectron spectroscopy indicates the formation of CrN in the first 175 Å of the surface for high bias. The results indicate that if implantation accompanies diffusion, then PIII at low bias is suitable enough for nitrogen incorporation in materials. Lower voltages also mean greater conformity between the ion sheath and the sample surface, and hence better treatment uniformity.

Evaluation of Corrosion Resistance of Coated and Uncoated Stainless-Steel Separators at Cathode Side for Molten Carbonate Fuel Cell

In order to evaluate the corrosion resistance of a cathode-side separator for a molten carbonate fuel cell (MCFC), SUS316 and SACC-SUS316 (chromium and aluminum were simultaneously deposited by diffusion into SUS316 austenitic stainless steel substrate using the pack-cementation process) were used as the separator materials. In the case of SUS316, corrosion proceeded via three steps: the formation of a corrosion product until the corrosion product becomes stable; the protection against corrosion until breakaway occurs; and the advancement of corrosion after breakaway. Since SUS316 showed a high corrosion rate in the cathode environment, it would be impossible to use it as a separator without suitable surface modification because of the occurrence of severe stability problems of the cell during long-term operation. In contrast, SACC-SUS316 showed higher corrosion resistance than the present separator material, SUS316. No corrosion was observed on SACC-SUS316 after 480 h at 923 K. Therefore, this material is thought to be very useful as an alternative separator at the cathode side for MCFC in the future.

The Effect of Post-Treatment of a High-Velocity Oxy-Fuel Ni-Cr-Mo-Si-B Coating Part 2: Erosion-Corrosion Behavior

In this paper, a study of the erosion-corrosion characteristics of a Ni-Cr-Mo-Si-B coating applied by the high-velocity oxy-fuel (HVOF) process on to an austenitic stainless steel (UNS S31603) substrate are reported. The coatings were studied in the as-sprayed condition, after vacuum sealing with polymer impregnation and after vacuum furnace fusion. The erosion-corrosion characteristics were assessed in an impinging liquid jet of 3.5% NaCl solution at 18 °C at a velocity of 17 m/s at normal incidence in two conditions: (1) free from added solids and (2) containing 800 ppm silica sand. The methodology employed electrochemical control and monitoring to facilitate the identification of the separate and interrelated erosion and corrosion contributions to the erosion-corrosion process. The rates of erosion-corrosion damage were drastically accelerated in the presence of the suspended solids. The application of cathodic protection significantly reduced the deterioration process. The study showed the effect of sealing with polymer impregnation did not significantly alter the erosion-corrosion behavior of the sprayed coating. However, there was a significant improvement in erosion-corrosion durability afforded by the postfusion process. The mechanisms by which the improved performance of vacuum-fused coatings is achieved are discussed.

F-0229 固体粒子衝突によるCr-Ni系被膜の摩耗特性(S35-4 薄膜の開発・評価)(S35 トライボロジーと機械要素の新たな展開)

For the evaluation of tribological properties of thin hard coatings, several experimental techniques are normally used, such as scratch testing and testing against abrasive, erosive, and sliding wear, and fretting. We have proposed slurry jet, a new type of solid particle impact test, in order to quickly and sensitively evaluate wear properties of thin coatings. In this paper, slurry jet 1 μm alumina particles were impacted at high velocity perpendicular to thin Cr-Ni-N coatings deposited on an austenitic stainless steel (SUS304) substrate material. For the same kind of coatings, the coating with nitrided substrate exhibited the higher wear resistance compared with untreated substrate. When the Ni concentration increases, the hardness becomes small and the wear rate increases. The Cr-Ni-N coatings with the larger hardness proved to have the higher wear resistance.

溶融炭酸塩燃料電池環境における陰極側ステンレス鋼セパレータ板の腐食挙動

In order to evaluate the corrosion resistance of a cathode-side separator for a molten carbonate fuel cell (MCFC), SUS316 and SACC-SUS316, in which chromium and aluminum were simultaneously deposited by diffusion into a SUS316 austenitic stainless-steel substrate by a pack-cementation process, were used as separator materials. In the case of SUS316, corrosion proceeds via three steps: formation of a corrosion product until the corrosion product becomes stable, protection against corrosion until breakaway occurs and the advance of corrosion after breakaway. Because SUS316 exhibited a rapid corrosion rate in the cathode environment, it would be impossible to use this separator without suitable surface modification due to the occurrence of a severe problem involving the stability of the cell during long-time operation. In contrast, SACC-SUS316 was demonstrated to exhibit more effective corrosion resistance than the present separator, SUS316. In particular, there was no corrosion behavior exhibited by SACC-SUS316 after 480 h at 923 K. Moreover, it is considered that this will be very useful as an alternative separator at the cathode side in MCFCs in the future.

Surface modification produced by a nitrogen operated plasma focus device: the role of the ion beam in the heating of a substrate

The role of the nitrogen ion beam generated with a small energy plasma focus (PF) device in the thermal processing of an austenitic stainless steel substrate is discussed. A numerical solution of the heat equation which takes into account the temperature variations of the thermal coefficients of the material is presented. By using several characteristics of the beam determined in previous works, it is found that the energy content of the beam is not enough to promote a strong heating of the outer layers of the substrate, which is required to explain the introduction of foreign particles to depths well beyond the ion range in the material, and also the martensitic transformation of steel up to a depth of ≈0.6 μm found in this work. The surface treatment is thus attributed to a plasma bubble generated by the disruption of the plasma column, and some evidence of its presence is obtained by employing a Faraday cup (FC). When the numerical model is used with an input energy density corresponding to the experimental value, and with a delivery time equal to the temporal width of the bubble, the evolution of the temperature profiles along the substrate depth shows a melting front reaching the proper depth to explain the penetration of Ti and N atoms found in a previous work, and the martensitic transformation depth presented in this work.