Austenitic Stainless Steel Coatings Research Articles

Microstructure and wear characteristics of austenitic stainless steel coatings fabricated through various directed energy deposition

Austenitic stainless steels are widely used in automotive and marine environments because of their high toughness, corrosion resistance, and wear resistance. The present comparative study focuses on the microstructure and wear resistance of double-layer austenitic stainless-steel coatings prepared on a ductile iron substrate using circular spot high-speed laser-directed energy deposition (DED) and broad-beam laser-DED. The results indicate that while the deposition process does not alter the physical phase of coating, it does influence the preferred orientation of surface grains. Both coatings exhibit characteristics of hypoeutectic alloys, where the harder eutectic structure serves as a skeleton to resist external pressure. The high-speed laser-DED coating demonstrates higher hardness and wears resistance due to its denser eutectic structure. In addition, its finer microstructure produces smaller wear debris, contributing to the formation of a denser oxide film, thereby enhancing wear resistance.

Fracture strain improving via structural austenitic stainless steel-coated 22MnB5 plates

A total of 316 austenitic stainless steel (ASS) coatings were deposited on 22MnB5 press-hardening steel plates by varying the substrate bias voltages using a magnetron sputtering technique and quenched in a flat mold with cooling water. The substrate bias current and ion-bombardment energy densities increased up to 0.5 mA/mm2 and 50 J/mm2 at a high voltage of −100 V, and, therefore, the variations in the coatings’ morphologies were owing to the increases in the ion bombardment. The porous bulk pattern appeared in the quenched ASS coating at −100 V, clearly different from the porous columnar structure of the others at −50 and −75 V. The γ-Fe and α-Fe phases were observed from the diffraction peaks, presented the ASS coating and 22MnB5 substrate, respectively. There was no intermetallic compound (IMC) peak detected. In addition, the diffusion layer of the quenched ASS-coated plate was observed, in which its morphology was different from the quenched martensite (M) plate, and proved to be the α-Fe microstructure by the very low α-Fe peak at the standard (110) position. The bright image of TEM and the select area electron diffraction pattern indicated the nanostructure of the quenched ASS coating. The nanohardness of the ASS coating, diffusion layer, and M plate (7.36, 3.60, and 6.25 GPa, respectively) was detected, indirectly proving an α-Fe structure of the diffusion layer. The fracture angles of the 316-coated plates significantly improved from 51.82° at −50 V, 53.77° at −75 V to 57.38° at −100 V, as the ASS structure changed to be porous bulk pattern. The clearance of IMC, coating’s porous bulk pattern, and the low hardness α-Fe diffusion layer benefited for the fracture strain by lengthening the pathway of the crack’s development and blocking the further crack’s propagation, respectively.

Comparative analysis of microstructure and corrosion resistance in laser-clad austenitic and martensitic stainless-steel coatings

Post-casting austenite often possesses better corrosion resistance than martensite. In order to compare the difference of corrosion resistance between austenitic stainless steel coating (ASSC) and martensitic stainless steel coating (MSSC) in the powder metallurgical state, two stainless steel Fe-based alloy coatings of the same process parameter were prepared on the surface of 40Cr steel by using laser cladding technology. Through SEM, EBSD, XRD and electrochemical tests, the microstructure, phase and cross-section metallurgical bonding condition of the coating were studied, and the difference in corrosion resistance between the two was comprehensively analyzed. The results showed that the main phase structure of ASSC was the FCC phase, and the main phase structure of MSSC was the BCC phase. The average self-corrosion current (9.92 × 10−8 A/cm2) and average self-corrosion rate (1.04 × 10−3 g/m2·h) of MSSC were 4.77 % and 5.62 % of ASSC, respectively. In addition, the polarization resistance, impedance value, and passivation film density of MSSC are higher than ASSC, MSSC has less damage from corrosion. The combination of factors, such as fabric refinement and passivation film density, makes the corrosion resistance of MSSC better than ASSC.

Effect of chromic acid anodization on the corrosion resistance of laser cladding austenitic stainless steel coatings based on orthogonal tests

In this paper, Ni transition layer and Fe-based alloy coatings were prepared on HT250 by laser cladding technology, and the corrosion resistance of the coatings was further enhanced by the chromic acid anodization (CAA) surface treatment process. The effects of time (t), current intensity (I), and temperature (T) on the microstructure and corrosion resistance of the coating after CAA were explored based on the three-factor and three-level orthogonal test method. The results show that after CAA, the intergranular morphology of the coating is corroded, the intragranular organization is exposed and protrudes, and the micro-morphology shows a multi-layer "skeleton" overlapping structure. The main phases were transformed from γ-Fe (FCC) to CrNi (FCC) and FeNi (BCC). The corrosion residue of the original coating is a lamellar metal-carbide weave, whereas the CAA coating is fibrous. The order of influence of CAA process parameters on corrosion depth and maximum impedance value is I >t >T. I on the degree of densification of the passivated film is 1.03 and 1.81 times higher than T and t, respectively. The best corrosion resistance of the sample was obtained at t = 30 min, I = 0.1 A, and T = 40 ℃, and its corrosion rate (2.83 × 10−3 g/m2·h) was 29.88 % lower than the original coating (4.03 × 10–3 g/m2·h).

Effect of different overlap cladding transition layer – Austenitic stainless steel coating and defect degree on corrosion resistance

The effects of overlap rate and defects on the corrosion resistance of laser fusion clad austenitic stainless steel coatings were studied. In this paper, the Ni transition layer and Fe-based coating were sequentially prepared on grey cast iron, and the corrosion morphology and corrosion mechanism of the coating were comprehensively analyzed through physical phase, microstructure and electrochemical tests. The coating phase was mainly γ-Fe, which formed strong selective orientation and texture strength at the (100) crystal plane; overlap ratio and defects affected the recrystallization changes, and the stresses near the defects were high. Increased overlap rate (Fe-based alloy 50 % → 66.7 %) could result in microstructure refinement, reduced corrosion rate v (A8 6.22×10−4 g/m2·h→A9 3.12×10−5 g/m2·h), and improved corrosion resistance. Corrosion cracking extended the crack and embrittled the alloy at the tips of the cracks, so that its (|Z|max 0.67 ∼ 1.31×104 Ω cm2) influence on the corrosion resistance was much higher than that of the pore (|Z|max 5.85 ∼ 10.2×104 Ω cm2). The best corrosion resistance of the process was achieved with an overlap ratio of 66.7 % for both the Ni transition layer and the Fe-based coating.

Effect of NiAl Bond Layer on the Wear Resistance of an Austenitic Stainless Steel Coating Obtained by Arc Spray Process

<div>The present investigation has been conducted to study the tribological and adhesion properties of X10CrNi18-8 austenitic stainless steel (ASTM 301) coatings deposited on aluminum alloys such as AU4G by using the arc-spraying process. These coatings were made with and without a bond-coat layer, which is constituted by NiAl. The structure of the phases that are present in coatings was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The measurements of microhardness and tribological behavior at different loads were also performed on the surface of the coatings. Adherence test was also carried out using four-point bending tests. The SEM showed that the dense microstructures of coatings have a homogeneous lamellar morphology with the presence of porosities and unmelted particles. The main phase of coating corresponds to a solid solution as a face-centered cubic (fcc). The microhardness of coatings is nearly four times that of the two substrates of aluminum alloys. The four-point bending test results showed that the NiAl bond layer increases the critical interfacial fracture energy <i>G</i> <sub>IC</sub>, the force to share the multilayer is more important.</div>

Effect of Various Heat Treatments on the Microstructure of 316L Austenitic Stainless Steel Coatings Obtained by Cold Spray.

Industries developing cold spray aim at dense and resistant coatings for component repair. However, as-sprayed 316L coatings display non-equilibrium microstructure and brittle fracture behavior. Improving their mechanical properties requires controlling their microstructure; post-spraying heat treatment is a promising approach. The recovery and recrystallization of coatings were little studied, and heat treatments reported in literature mostly used holding for long time in furnaces, not adapted to on-site repairs. This study aimed at gaining insights into recovery and recrystallization mechanisms of 316L coatings, for a broader range of heat treatment kinetics. A study of powders and as-sprayed coatings was conducted to characterize the initial state. In situ XRD measurements provided input for heat treatment definition. Microscopy, room temperature XRD and hardness measurements allowed to better understand the microstructural evolutions and to select treatments leading to original microstructures. In this work, a variety of microstructures were produced by adapting heat treatment conditions for a given set of spraying parameters. The recrystallization path of the heterogeneous skin-core microstructure of deposited particles, as well as the interaction between grain growth and precipitation was revealed. A novel, optimized fast heat treatment led to a fully recrystallized, fine-grained coating and significantly reduced hardness.

Friction surfacing of AISI 904L super austenitic stainless steel coatings: Microstructure and properties

Microstructure, texture, pitting corrosion resistance and hardness of surfaces and cross-sections of the friction-surfaced (FSed) super austenitic stainless steel 904L coatings fabricated at various spindle speeds were investigated. The microstructure of the coatings was governed by both dynamic recovery (DRV) and continuous dynamic recrystallization (cDRX) owing to the high stacking fault energy (SFE) of 904L. The grain orientations in DRV were in A 2 ⁎ shear texture component, while the rotated cube textures were related to the cDRXed grains. Immersion tests of the FSed coatings in 3.07 mol/L Cl − solution showed that the corrosion pits were slightly preferred to generate at the {111} DRVed grains on the coating surfaces, since these grains were likely to have a higher elastic strain during FS. Compared with AISI 304, the pitting potential of the FSed coatings in 3.5 wt% NaCl solution was significantly shifted to nobler direction and also insensitive to spindle speed owing to the high SFE of 904L. However, the passive films of the FSed coatings were thinner and more difficult to reform, as evidenced by slightly larger average pit diameters and lower protection potentials owing to the high residual stress caused by FS. • Microstructures of FSed 904L coatings were governed by DRV in A 2 ⁎ shear component and cDRX in rotated cube textures. • Increment of spindle speed tended to enhance cDRX but suppress DRV at the same time. • The FSed coatings could maintain excellent pitting corrosion resistance of as-received 904L. • Due to high SFE of 904L, elastic strain in {111} grains was reduced. • Crystallographic effect on pitting cororsion resistance of the coatings was weakened. • Increase in misorientation density induced by cDRX led to hardness improvement and ductility reduction for the coatings

Predominant Solidification Modes of 316 Austenitic Stainless Steel Coatings Deposited by Laser Cladding on 304 Stainless Steel Substrates

AISI 304 austenitic steel is one of the stainless steels most widely used as a substrate for coating using a laser as a heat source (laser cladding). The AISI 316 steel contains similar quantities of alloying elements as 304 steel, with the addition of 2 pct molybdenum, which provides greater corrosion resistance compared to 304 steel. Due to its better mechanical and corrosion resistance, AISI 316 steel was used here as a coating to improve the properties of a 304 substrate. The depositions were evaluated considering their geometric and microstructural characteristics, which were correlated with variations of the deposition parameters. The power, speed, and amount of coating metal added were altered, while the other parameters were kept constant. Increases of power and speed resulted in an increase of the diluted region, whereas increase of the amount of coating material led to decreased dilution. Two main types of solidification were observed in the same depositions: one with austenite (γ) as the primary phase, and the other with ferrite (δ) as the primary phase. Different substructures were apparent in the same type of solidification.

Investigation of Austenitic Stainless Steel Coatings on Mild Steel Produced by Friction Surfacing Using a Conventional CNC Machining Center

The friction surfacing process allows deposition of similar and dissimilar coatings in the solid state, avoiding some of the problems associated with conventional coating methods in which fusion is involved. In the present work, a viability assessment of producing AISI 304 austenitic stainless steel coatings on AISI 1020 low-carbon steel substrates using a machining center with Computerized Numerical Control (CNC) instead of dedicated friction surfacing equipment was pursued. The influence of consumable rod rotation and translation speed, as well as substrate surface roughness on the geometry and adhesion of the coatings was evaluated. The microstructure of the stainless steel coatings was investigated by optical and scanning electron microscopy, while microhardness analysis was performed in order to evaluate properties near the coating-substrate interface. Finally, the electrochemical corrosion behavior of the coatings and the as-received AISI 304 steel consumables in 0.5M H2SO4 solution containing naturally dissolved O2 was compared. The results revealed that the friction surfacing process can be applied in non-specialized machinery, since the manufactured coatings exhibited good adhesion and corrosion resistance. The formation of hard bands in the coatings was identified near the interface region and the adhesion of the coatings was found to be influenced by initial substrate roughness.

Effects of Carbon and Boron on Structure and Properties of Austenitic Stainless Steel Coatings Fabricated by Laser Remanufacturing

The coatings are fabricated using austenitic stainless steel powder with various contents of carbon and boron via laser remanufacturing technique. A new synchronous lateral powder feeding device is adopted to avoid surface oxidation of molten pool. The authors find that the strength can be increased but plasticity is decreased of with the rise of boron content due to the formation of lamellar borides phase structures, which are very brittle and have high hardness. In addition, the authors also find that the tensile strength and hardness are enhanced by increasing the content of carbon, while the plasticity is deteriorated due to the formed carbide in the grain of the austenitic stainless steel coating.

Hardening of HVOF-Sprayed Austenitic Stainless-Steel Coatings by Gas Nitriding

Austenitic stainless steel exhibits an excellent corrosion behavior. The relatively poor wear resistance can be improved by surface hardening, whereby thermochemical processes offer an economic option. The successful diffusion enrichment of bulk material requires a decomposition of the passive layer. A gas nitriding of high velocity oxygen fuel spraying (HVOF)-sprayed AISI 316L coatings without an additional activation step was studied with a variation of the process temperature depending on the heat-treatment state of the coating. A successful nitrogen enrichment was found in as-sprayed condition, whereas passivation prevents diffusion after solution heat treatment. The phase composition and microstructure formation were examined. The crystal structure and lattice parameters were determined using X-ray diffraction analysis. The identified phases were assigned to the different microstructural elements using the color etchant Beraha II. In as-sprayed condition, the phase formation in the coating is related to the process temperature. The formation of the S-phase with interstitial solvation of nitrogen is achieved by a process temperature of 420 °C. Precipitation occurs during the heat treatment at 520 °C. In both cases, a significant increase in wear resistance was found. The correlation of the thermochemical process parameters and the microstructural properties contributes to a better understanding of the requirements for the process combination of thermal spraying and diffusion.

Effect of Cold-Spray Conditions Using a Nitrogen Propellant Gas on AISI 316L Stainless Steel-Coating Microstructures

Cold-spray techniques have been a significant development for depositing metal coatings in recent years. In cold-spray processes, inexpensive nitrogen gas is widely used as the propellant gas in many industries. However, it is difficult to produce austenitic stainless steel coatings with dense microstructures with cold-spray techniques when using nitrogen propellant gas because of work hardening. In this study, the effects of cold-spray conditions using a nitrogen propellant gas on AISI 316L stainless steel coatings were examined. It was found that a higher nitrogen propellant gas temperature and pressure produce coatings with dense microstructures. The measured AISI 316L coating hardness values suggest that AISI 316L particles sprayed at temperatures of 700 and 800 °C soften due to the heat, allowing uniform deformation on the substrate and consequently forming dense coating microstructures. In addition, AISI 316L powder with particle diameters of 5–20 µm resulted in a denser coating microstructure than powder with particle diameters of 10–45 and 20–53 µm. Finally, the standoff distance between the nozzle and the substrate also affected the AISI 316L coating microstructures; a standoff distance of 40 mm produced the densest microstructure.

Termal Püskürtme Yöntemi ile Üretilmiş AISI 316L Paslanmaz Çelik Kaplamaların Karşılaştırmalı İncelenmesi

In this study, austenitic stainless steel (316L) coatings were formed using both Wire Flame Spray Forming (WSF) and High Velocity Oxy Fuel (HVOF) deposition processes after a NiCr bond layer was deposited on low carbon steel substrate. The coatings were characterized by light optical microscope (LOM) and microhardness measurements. Corrosion resistance of 316L austenitic stainless steel coatings applied onto low carbon steel via WSF and HVOF spray processes was analyzed by using the potentiodynamic polarization scanning (PDS) technique. The wear behaviour of the coatings against Al 2 O 3 ball was investigated with a reciprocating tester under dry friction conditions. It was found that the HVOF sprayed coating showed higher hardness and better wear resistance than the WSF coating. However, the overall corrosion resistance of the HVOF deposited coating was inferior to that of the WSF coating.

Carbon Doped Austenitic Stainless Steel Coatings Obtained by Reactive Magnetron Sputtering

Carbon Doped Austenitic Stainless Steel Coatings Obtained by Reactive Magnetron Sputtering

Effect of Process Parameters on Friction Surfaced Coating Dimensions

Friction surfacing is a novel technology to build corrosion and wear resistant coatings and build functionally graded metallic layers. In this work, the coating dimensions as affected by process parameters and high temperature strength of consumable rods have been compared. Friction stir welding equipment, RM-1 model procured from MTI was used. Carbon steel, austenitic stainless steel and Ni-based alloy coatings were deposited. Following process parameter ranges were used: rotational speed: 1000-2000 RPM, feed rate: 50-150 mm/min and axial load: 3-12 kN. Results showed that the coating width and thickness decreased with a) increased magnitude of the process parameters used and b) increased high temperature strength of the consumable rod.

Surface hardness improvement of plasma-sprayed AISI 316L stainless steel coating by low-temperature plasma carburizing

Low-temperature carburizing below 773K of austenite stainless steel can produce expanded austenite, known as S-phase, where surface hardness is improved while corrosion resistance is retained. Plasma-sprayed austenitic AISI 316L stainless steel coatings were carburized at low temperatures to enhance wear resistance. Because the sprayed AISI 316L coatings include oxide layers synthesized in the air during the plasma spraying process, the oxide layers may restrict carbon diffusion. We found that the carbon content of the sprayed AISI 316L coatings by low-temperature carburizing was less than that of the AISI 316L steel plates; however, there was little difference in the thickness of the carburized layers. The Vickers hardness of the carburized AISI 316L spray coating was above 1000HV and the amount of specific wear by dry sliding wear was improved by two orders of magnitude. We conclude that low-temperature plasma carburizing enabling the sprayed coatings to enhance the wear resistance to the level of carburized AISI 316L stainless steel plates. As for corrosion resistance in a 3.5 mass% NaCl solution, the carburized AISI 316L spray coating was slightly inferior to the as-sprayed AISI 316L coating.

Dynamic recrystallization in friction surfaced austenitic stainless steel coatings

Friction surfacing involves complex thermo-mechanical phenomena. In this study, the nature of dynamic recrystallization in friction surfaced austenitic stainless steel AISI 316L coatings was investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the alloy 316L undergoes discontinuous dynamic recrystallization under conditions of moderate Zener–Hollomon parameter during friction surfacing.

Synthesis and Characterization of (C, N)-Alloyed Stainless Steel Coatings by High Energy Ion Assisted Magnetron Sputtering Deposition

In this article, (C, N) alloyed austenitic stainless steel coatings (SSC) (or hybrid S-phase with both carbon and nitrogen) were produced by a magnetron sputtering deposition process combined with ion implantation (CMSII). This technique involves a periodical high energy ion bombardment of the coating during its growth, which has a beneficial effect on the structure and properties of the deposited coating. The influence of the nitrogen and carbon addition to the deposition atmosphere on the structure, chemical composition, and coating morphology was investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and glow discharge optical spectrometry (GDOS) techniques. Wear tests were carried out and the results were compared with low temperature plasma nitrided austenitic stainless steel. Corrosion behavior in Ringer's solution was also evaluated.

Microstructure and Properties of Friction Surfaced Stainless Steel and Tool Steel Coatings

Friction surfacing is a novel solid state surface coating process with several advantages over conventional fusion welding based surfacing processes. In this work, austenitic stainless steel (AISI 310) and tool steel (H13) coatings were friction deposited on mild steel substrates for corrosion and wear protection, respectively. Microstructural studies were carried out by using optical and scanning electron microscopy. Shear tests and bend tests (ASTM A264) were conducted to assess the integrity of the coatings. This study brings out the microstructural features across the coating/substrate interface and its mechanical properties, showing good metallurgical bonding between stainless steel and tool steel coating over mild steel.