Surface Alloying Process Research Articles

Experimental and Machine Learning Study on Friction Stir Surface Alloying in Al1050-Cu Alloy

This study employs friction stir processing to create a surface alloy using Al1050 aluminum as the base material, with Cu powder applied to enhance surface properties. Various parameters, including tool rotation speed, feed rate, and the number of passes, are investigated for their effects on the microstructure and mechanical properties of the resulting surface alloy. The evaluation methods include tensile testing, microhardness measurements, and metallographic examinations. The initial friction stir alloying pass produced a non-uniform stir zone, which was subsequently homogenized with additional passes. Through the plasticization of Al1050, initial agglomerates of copper particles were compacted into larger ones and saturated with aluminum. The alloyed samples exhibited up to an 80% increase in the strength of the base metal. This significant enhancement is attributed to the Cu content and grain size refinement post-alloying. Additionally, machine learning techniques, specifically Genetic Programming, were used to model the relationship between processing parameters and the mechanical properties of the alloy, providing predictive insights for optimizing the surface alloying process.

Substrate dilution and interface structures of tungsten coating deposited by double-glow plasma surface alloying on stainless steel substrate

W-coating layers with varying thicknesses up to 10 μm were deposited by double-glow plasma surface alloying (DGPSA) on finely polished stainless steel (SS304L) substrates to investigate the influence of the substrate on both the W-coating and interface structures. The examination revealed substrate dilution and the presence of oxide crystallites, predominantly FeWO4 and WO2, at the interface between W and SS304L. These observations correlated with the occurrence of cracking and peeling-off of the W-coating. Both Cr and Ni showed decreased distribution in the interface layer compared to their distribution in the W-coating and SS304L substrate. In comparison, Fe demonstrated a more noticeable compositional gradient, decreasing monotonically from SS304L across the interface to the W-coating. The depth distribution of O indicated that its inclusions were influenced not only by DGPSA deposition but also by post-deposition ion-beam milling. Additionally, the presence of spherical particles directly on the substrate's surface provided evidence for surface alloying reactions, while the columnar grains within the interface oxide layer were associated with the texture features of the W-coating, as confirmed by X-ray diffraction and pole-figure measurements. These findings offer valuable insights into the surface alloying process facilitated by DGPSA and its potential for developing W-coatings tailored for plasma-facing applications.

Study of Wear of an Alloyed Layer with Chromium Carbide Particles after Plasma Melting

Depending on operating conditions, metals and alloys are exposed to various factors: wear, friction, corrosion, and others. Plasma surface alloying of machine and tool parts is now an effective surface treatment process of commercial and strategic importance. The plasma surface alloying process involves adding the required elements (carbon, chromium, titanium, silicon, nickel, etc.) to the surface layer of the metal during the melting process. A thin layer of the compound is pre-applied to the substrate, then melted and intensively mixed under the influence of a plasma arc, and during the solidification process, a new surface layer with optimal mechanical properties is formed. Copper-based alloys—Cu-X, where X is Fe, Cr, V, Nb, Mo, Ta, and W—belong to an immiscible binary system with high mechanical strength, electrical conductivity, and magnetism (for Fe-Cu) and also high thermal characteristics. At the same time, copper-based alloys have low hardness. In this article, wear tests were carried out on coatings obtained by plasma alloying of CuSn10 and CrxCy under various friction conditions. The following were chosen as a modifying element: chromium carbide to increase hardness and iron to increase surface tension. It is noted that an increase in the chromium carbide content to 20% leads to the formation of a martensitic structure. As a result, the microhardness of the layer increased to 700 HV. The addition of CuSn10 + 20% CrxCy and an additional 5% iron to the composition of the coating improves the formation of the surface layer. Friction tests on fixed abrasive particles were carried out at various loads of 5, 10, and 50 N. According to the test results, the alloy layer of the Fe-Cr-C-Cu-Sn system has the greatest wear resistance under abrasive conditions and dry sliding friction conditions.

Dissolution-induced oxide synthesis using SiO2 microparticles for oxide dispersion strengthening of Fe-based alloys

This study reports on a single-track laser surface alloying process that utilizes SiO2 powder to disperse both SiO2 particles and oxide inclusions in 316L stainless steel for oxide dispersion strengthening (ODS) purposes. In this process, the SiO2 powders partially dissolve in the melt pool, and the released silicon and oxygen atoms nucleate to form oxide inclusions in-situ within the metal matrix. This dissolution-induced oxide synthesis route demonstrated a high potential for ODS, achieving a high particle number density (6.6 × 104 mm−2) and area fraction (3.3%) comparable to that of bulk 316L samples produced via directed energy deposition. The hardness of the SiO2/316L composites reached a maximum of 232.4 HV compared to that of the 316L substrate (average 170.8 HV). The improvement in hardness was theoretically explained and quantified, significantly originating from the enhanced dislocation density strengthening mechanism resulting from the large difference in the coefficient of thermal expansion between SiO2 and 316L.

In-Situ Production of Metal Matrix Composites Layers by TIG Surface Alloying to Improve Wear Resistance of Ductile Cast Iron Using a Buffer-Layer and Post Weld Heat Treatment

A TIG surface alloying process was applied to modify the surface of ductile cast iron samples. Using this process, in-situ metal matrix composite (MMC) layers were produced on samples to improve their wear resistance. These layers were made by melting substrate surface and powders as additional material into this melt pool. The efficiency of preheating of the samples to prevent cold cracks during solidification was verified. Moreover, a buffer layer produced in situ to decrease the mismatches between the chemical and physical properties of the materials was also tested. Post-weld heat treatment (PWHT) was used to increase the tribological characteristics of the layers and eliminate adverse effects of the heat-affected zone (HAZ) created by the fusion of the substrate surface. The results showed that, in the samples without preheating, the formation of cold cracks occurred. Additionally, layers produced without a buffer layer showed defects, such as shrinkage and porosity. However, using both preheating and a buffer layer prevented cold cracks, discontinuities, shrinkage, and porosity defects in the layers. Furthermore, PWHT allowed for the transformation of brittle martensite into tempered martensite at the HAZ. MMC layers presented high hardness of up to 1230 HV and wear resistance up to 5.8 times greater compared to the substrate samples without layers.

Investigation of the Implementation of Laser Surface Alloying of Cu with Cr-WC.

This paper presents research on the microstructure and mechanical properties of an alloyed composite copper (Cu) surface layer, reinforced with a mixture of chromium–tungsten carbide (Cr–WC) powders. Copper alloying was performed using a high-power diode laser (HPDL). In the tests, three mixtures of powders with different percentage contents (75%Cr 25%WC, 50%Cr 50%WC, 25%Cr 75%WC) were injected into the melting pool during the laser surface alloying process. Microstructural evolution and the properties of the surface layer of copper after laser alloying were investigated. Structural investigations were performed using light microscopy, scanning and transmission electron microscopy (SEM, TEM) and X-ray diffraction (XRD). Microhardness and wear resistance of the modified surface layer were examined as well. After laser treatment the applied powders appear as uniformly distributed particles in the alloyed zone as well as nanoscale precipitates in the Cu matrix. Several types of precipitate characteristics, in terms of morphology, structure and chemical composition, were observed. Laser alloying of the surface layer modified the microstructure, which resulted in an increase in the hardness of the surface layers compared to the base material.

Simultaneous Optimization of Laser Energy and Coating Thickness in Surface Alloying of Al with Fe

In the two-step deposition technique of the laser surface alloying process, the alloying elements are introduced onto the bulk material’s surface. In such process, two main parameters determine the alloying quality: the thickness of the coating and the laser energy supplied onto the specimen. In this work, the laser surface alloying of aluminium (Al) with iron (Fe) is carried out by optimizing both parameters. This is accomplished by assessing the improvement in the hardness after laser treatment. In general, the thicker coating desires higher laser energy to cause surface melting and sequentially diffusion of Fe into molten Al to occur. This is indicated by the linear relationship between the thicknesses for the peak hardness value with the laser energy whereby the optimum energy shifted to higher energy for a thicker coating. The increase in laser energy increases Fe particle’s chance to migrate via diffusion into the bulk Al substrate. However, at 140μm the optimized energy reaches a peak value at 455mJ which is the maximum energy to be supplied in this process before the coating is lost due to excessive ablation. For thicker coatings, the laser’s action does not penetrate enough onto the substrate to cause sufficient melting of the Al surface for alloy formation. The maximum hardness obtained was 40.8 HV at the optimum condition for 140μm thickness treated with 455 mJ. The formation of an alloyed compound is further confirmed by x-ray diffraction technique whereby compounds such as AlFe, Al13Fe4, and AlFe6Si are present in the treated specimens.

Characterisation and oxidation behaviour of plasma surface alloyed on γ-TiAl alloy

ABSTRACT The double glow plasma surface alloying process (DGP) is an emerging alternative technology for fabricating thermal barrier coating. In spite of its merits such as gradient metallurgical bond and thickness controllability, DGP method is less well known than electron beam-physical vapour deposition and plasma spraying technique for the bond coatings. This paper serves as a preliminary study into the use of this technology for preparation of gradient MCrAlY bond coating on titanium alloys, with a focus on the oxidation performance at 750, 850 and 950°C. In this study, a gradient MCrAlY bond coating was successfully synthesised on γ-TiAl alloy by DGP. The as-deposited coating was composed of γ′-Ni3Al, γ-TiAl, AlCr2 and σ-NiCoCr. The maximum load that the as-deposited coating could bear was 60 N. The MCrAlY coating exhibited much better oxidation resistance than the bare TiAl alloy due to the formation of multilayer oxide scales. The research opportunities for further optimisation of this type of MCrAlY coatings are also discussed.

Surface-Alloying during Pb Underpotential Deposition on Au

Surface-alloys can form spontaneously during the deposition of one metal onto another, especially in systems with a large lattice mismatch that do not have bulk counterparts (so-called immiscible systems). The spontaneous surface alloying has been widely studied in Ultra High Vacuum (UHV) [1], but these materials have not been exploited much in practical applications. Surface-alloying in an electrochemical environment is an ideal route to the design of new functional materials. Electrochemically controlled surface-alloying would allow room-temperature conditions and better scalability making it more viable and versatile for practical applications.The focus of our study was the surface-alloying during underpotential deposition (UPD) of Pb on Au(111) [2,3]. As shown in Fig 1.a, the cyclic voltammetry (CV) of Pb UPD on Au (111) has asymmetric anodic and cathodic peaks (labelled in the order of their associated appearance). The most positive anodic peak A2 is often associated with the dealloying of Pb incorporated in the Au surface. The electrochemical measurements and the in-situ Scanning Tunnelling Microscopy (STM) characterisation during Pb UPD on Au(111) have shown that the Pb ML stripping is followed by a significant Au surface roughening [2]. During Pb ML formation and dissolution, the top-surface Au atoms get displaced, creating highly mobile Au ad-islands and vacancy islands [2]. The in-situ surface stress measurements have shown a tensile stress relaxation caused by the alloying/dealloying of Pb-Au during Pb ML formation and dissolution [2,4-5].In this study, we used two different electrochemical protocols to examine the surface alloying process: 1) repeated potential cycling within the UPD range and 2) polarisation at a fixed potential in the UPD region. By following the changes in electrochemical behaviour, we established the range of potentials and conditions at which the surface-alloys form. In addition to that, we investigated the structural and compositional changes by surface sensitive techniques such as X-ray Photoelectron Spectroscopy (XPS), Ultraviolet Photoelectron Spectroscopy (UPS), Energy-Filtered Photoemission Electron Microscopy (EF-PEEM) and Work Function (WF) mapping.To study the 'dynamic' alloying, the potential was cycled repeatedly between 0.0 V and 0.5 V (vs Pb/Pb2+), as marked in Fig 1.a, over the potential range negative from the A2 anodic peak. The potential was cycled up to 400 times. After each 100th cycle, the potential was extended to the whole Pb UPD region to observe the changes in the cathodic and anodic peaks. For illustration, Fig 1.b and Fig 1.c show the changes of peaks A2 and A3 with the number of cycles. While both peaks show changes of the shape and total charge, we observe a significant shift of the peak A2 suggesting dramatic changes associated with the morphology of the surface and the amount of alloyed Pb in the top surface layer. The Pb-Au surface alloy composition, based on the charge under the A2 peak, increase from 17% up to 25% of Pb (after 400 cycles) as shown in Fig 1.d. Similar changes of the CV peaks have been observed after the polarisation at the fixed potential of 0.2 V (vs Pb/Pb2+) in the Pb UPD region for different times (15 min - 60 min).Furthermore, the Pb UPD on Au(111) has been studied in the presence of chloride. These results show gradual changes in positions and shapes of all characteristic peaks of the Pb UPD leading to complete disappearance of the A2 dealloying peak, which have not been reported before.

Fabrication of TiC-Reinforced Surface Layers on Ductile Cast Iron Substrate by Laser Surface Alloying

This chapter presents a novel method for analysis and optimization of the in-situ formation of TiC-reinforced composite surface layers (TRL) on a ductile cast iron substrate during the laser surface alloying process, combining the experimental approach with the computational thermodynamics. The microstructure of the TRLs has been assessed by light optical microscopy, scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction. The results of thermodynamic calculations with the Scheil-Gulliver model showed a good agreement with the experimental results, indicating that the actual solidification path for the analyzed Fe-C-Si-Ti alloy systems under the investigated range of laser processing conditions is close to the Scheil-Gulliver assumption.

Effect of Bio-Fluid on the Corrosion Properties of Tungsten Surface Alloyed Under Nitrogen on Austenitic Stainless Steel

Stainless steel is mostly used in applications where resistance to corrosion is of prime importance. The surface-treated stainless steels are widely used in many applications. AISI304 stainless steel has a low surface hardness and a relatively high wear rate. AISI304 stainless steel bar and Tungsten (W) were chosen as the substrate and the alloying material, respectively. The W powder was pasted over the surface of the AISI304 stainless steel using a PVA binder. The surface modification process was carried out using the heat generated by a Gas Tungsten Arc (GTA). The corrosion behavior of substrate and surface alloyed. AISI304 stainless steel was studied using the TAFEL polarization test. The corrosion was studied in Hanks balance salt solution. The study revealed that pitting corrosion occurs on the surface of the specimens, but Icorr value increased by an order of magnitude two. The increase in corrosion current is attributed to the formation of the oxides, and carbides formed in the surface of the modified layer. This implies that surface alloying with W enhances the corrosion resistance of the AISI304 stainless steel. The investigation concludes that the surface alloying process with W using GTA is effective for modifying the surface properties of AISI304 stainless steel.

Experimental and numerical study of laser surface alloying of Al<SUB align="right">xCu<SUB align="right">0.5FeNiTi high entropy alloy

High entropy alloy possesses superior properties such as high hardness, wear-resistance, thermally stable, high strength to weight ratio, etc. required in industries. The development of high entropy alloy is critical due to the high segregation possibilities of multi-component systems. Processing of high entropy alloy can be done using laser surface alloying. This work reports 3D simulation and, subsequently, an experimental comparison of laser surface alloying process. Such a comparison is crucial to understand the influence of process parameters on bead geometry formation for better process optimisation. This work deals with the processing of AlxCu0.5FeNiTi high entropy alloy over aluminium alloy (AA1050) substrate. The quality parameters (dilution percent, aspect ratio, and bead angle) obtained from experimental and numerical studies are compared. The calculated melt pool depth and width are in a good agreement with the experimental results. An error of 1.72%, 13.95%, and 6.09% in dilution percent, aspect ratio, and bead angle is reported.

A study on in-situ synthesis of TiCN metal matrix composite coating on Ti–6Al–4V by laser surface alloying process

Laser surface alloying of Ti6Al4V substrate with in-situ synthesized TiCN was carried out by melting preplaced titanium and graphite powders in 3:1 ratio (wt%) in nitrogen atmosphere at different scan speeds in 400–1400 mm/min range, maintaining the laser power and the beam diameter constant at 1200 W and 3 mm respectively. Molten pool thermal history during the alloying process was recorded using an IR pyrometer. With the decrease in scan speed, the cooling rate was found to decrease, while the molten pool lifetime increased which caused densification of TiCN dendritic structure. Though it enhanced the hardness, coatings were found to fail exhibiting brittle fracture during the scratch test, while coatings processed at higher scan speeds (800 mm/min −1400 mm/min) were found to be intact. Further, coatings processed at higher scan speeds also exhibited better wear resistance. Linear polarization electro-chemical corrosion test was performed on the coatings and it was observed that even corrosion properties were better in case of coatings processed at higher scan speeds.

Impact of Surface Alloying of Nickel on Microstructure, Hardness and Wear on Aluminium–12%Silicon Alloy

An investigation was carried out to determine the effect of nickel on the microstructure, hardness and wear behaviour of surface alloying on aluminium–12%silicon alloy. The heat source utilized for modifying the surface was gas tungsten arc. Two hundred-micrometre-thick Ni–P coating was pre-deposited using electroless process on the aluminium–12%silicon alloy substrate. The surface alloying process was performed on the coated surface. By using microhardness tester and pin-on-disc wear testing machine, the hardness and wear rate of the modified layer were calculated, respectively. A refined grain structure was observed with the fusion of Ni in the alloyed layer. That was attributed to the rate of cooling in the modified layer. As a result of nickel addition, the hardness was improved and wear rate was found to decrease.

Improving anti-oxidation performance of 430 SS by fabricating co-contained spinel coating as solid oxide fuel cells interconnect

PurposeThe purpose of this study is to improve the performance of AISI 430 stainless steel (430 SS) in increasing its oxidation resistance, suppressing coating spalling and cracking, sustaining appropriate conductivity and blocking Cr evaporation as an interconnect material for intermediate temperature solid oxide fuel cells; a protective co-contained coating is formed onto stainless steel via the surface alloying process and followed by thermal oxidation.Design/methodology/approachIn this work, oxidation behavior of coated specimen is studied during isothermal and cyclic oxidation measurements. Moreover, the conductivity is also investigated by area specific resistance (ASR) measurement.FindingsCo-contained spinel layer shows an outstanding performance in preventing oxidation and improving conductivity compared with uncoated specimens. The protective spinel coating also reduces the ASR for coated specimen (0.0576O cm2) as compared to the uncoated specimen (1.87296O cm2) after isothermal oxidation.Originality/valueThe probable mechanism of co-contained alloy converting into spinel and the spinel transfer electron is presented.

Hard-yet-tough high-vanadium hierarchical composite coating: Microstructure and mechanical properties

In this work, we report a high-vanadium hierarchical coating prepared on the surface of nodular cast iron substrate by a low-cost plasma transferred arc (PTA) surface alloying process. The coating consists of a graded layer with an alloyed zone (AZ) rich in submicron sized granular (V-Ti-Nb-Cr-Mo) composite carbides on top of intermediate melted zone characterized by refined ledeburite and martensite. The dense spherical particles in the AZ are FCC structured MC-type (M = V, Ti and Nb) carbides which tend to aggregate while M7C3 and M2C carbides nucleate on MC. The super-lattice V8C7 maintains its cube-on-cube orientation relationship with TiC. The hardness of the AZ is 9.6 ± 1.0 GPa, ~ 4 times that of the substrate. Nano- and micro-indentations point at a superior strength-toughness in the AZ, where cracks are deflected and bridged by the spherical MC carbides in a compressive residue stress state. The fracture mode appears to be rather ductile in the AZ whereas brittle failure appears in both the melted zone and substrate. TEM and EDS results confirm that such a microarchitecture design, assisted by the rapid solidification rate of the PTA process, concurrently activates various strengthening micromechanisms including the precipitation hardening and grain refinement.

Sliding wear behaviour of Ni-Cr alloying on Ti6Al4V based on double-glow plasma surface metallurgy technology

To improve the wear resistance of Ti6Al4V alloy, Ni-Cr alloy coatings with 40 at.%Ni were prepared on Ti6Al4V alloy surface by double-glow plasma surface metallurgy technique. The friction and wear behaviour of the coatings sliding against Si3N4 at room temperature and 500 °C were comparatively studied. The results show that the alloy coatings comprise a deposited layer, a diffusion-modified layer and a heat-affected zone. The deformed deposition layer plays an anti-friction effect as a soft film. The tribological behaviour of diffusion layer is abrasive wear. Ni-Cr surface alloying process significantly reduces the friction coefficient of Ti6Al4V alloy and improves the wear resistance properties of Ti6Al4V alloy.

Microstructure, hardness and wear rate of heat treated Titanium surface alloyed AISI 304 stainless steel

AISI 304 stainless steel bar and commercially pure titanium were chosen as the substrate and the alloying material, respectively. The surface alloying process was done using heat generated by the gas tungsten arc source. The surface alloying AISI 304 stainless steel specimens were heat treated in the furnace for 6 h. The intermetallic compound precipitates were observed in the surface alloyed layer. The elemental analysis were observed using the EDS analysis. There was an increase in hardness and decrease in the wear rate on the surface alloyed layer after the heat treatment process.

Production of Castings with Differentiated Surface Properties

Problems. Surface layers get the most intensive external influences during the operation of molded parts of machines and mechanisms, therefore their structure and properties determine the operability of products as a whole. To achieve high surface strength and durability of parts, various technological processes are used in the industry, but most of them do not make it possible to obtain a surface layer with the desired properties of the required thickness. In this case, more promising can be the technological process of surface alloying (the manufacture of products with differentiated surface properties). Objective. The aim of the paper is to develop a technological process for the production of castings with specified surface properties. Methods. Each core was coated with an alloying coating, coated cores were dried in the air during the day, the mold and cores were heated and collected just before pouring them with metal. Results. It is necessary to use ferromanganese, ferrotitanium and ferrochrome for the manufacture of wear-resistant parts, which allow obtaining on the casting surface an alloyed layer with a thickness up to12 mm and hardness up to 68 NRA. Such process parameters fully meet the operational requirements for products that operate under abrasive or water abrasion wear. Conclusions. To increase the hardness of the working surfaces, certain chemical elements, ferroalloys and chemical compounds such as carbides, borides and nitrides can be used as fillers of alloying coatings.

Microstructural Evolution During Laser Surface Alloying of Ductile Cast Iron with Titanium

AbstractDiode laser surface alloying process was used to the in-situ synthesis of TiC-reinforced composite surface layers on the ductile cast iron substrate. The obtained composite surface layers were investigated using optical and scanning electron microscopy, and XRD diffraction.It was found that the morphology and fraction of TiC phase is directly dependent upon both the concentration of titanium in the molten pool and also the solidification rate. With increasing titanium content, the fraction of TiC increases, whereas the fraction of cementite decreases. The TiC phase promotes a heterogeneous nucleation of primary austenite grains, what reduces a tendency of cracking in the alloyed layers.