Multilayer Alloy Research Articles

Electron beam wire cladding of nickel alloys and stainless steel on a reactor pressure vessel steel

Claddings made of nickel-base alloys or stainless steel are frequently used in the oil, chemical, and power generation industries to protect low-alloy steels from corrosion. Arc weld overlays, which are commonly deposited, often exhibit microstructures near the fusion line that are susceptible to cracking. Due to its very localized and controlled heat input, electron beam welding has the potential to produce claddings with a more resistant microstructure. In this study, multi-layer nickel-base alloy and stainless steel claddings were fabricated by wire-feed electron beam additive manufacturing. Dilution was high because of the specific wire melting technique. It was found that the degree of dilution had a considerable influence on the precipitation of secondary phases, which, however, did not impair the integrity of the claddings. The influence of dilution on the formation of precipitates could be rationalized with thermodynamic calculations. In the nickel-base alloy claddings, the fusion line was sharp without any interfacial martensite. Only a few potentially detrimental type-II grain boundaries were found. Instead, epitaxial solidification was prevalent. This was attributed to metastable melting that was caused by high heating rates. Thus, electron beam-based manufacturing could produce claddings that are more resistant to disbonding than standard arc weld overlays.

Microstructure and Wear Resistance of Multi-Layer Ni-Based Alloy Cladding Coating on 316L SS under Different Laser Power.

We prepared three kinds of Ni based alloy cladding coatings on 316L stainless steel at different power levels. The microstructure of the cladding layer was observed and analyzed by XRD, metallographic microscope, and SEM. The hardness of the cladding layer was measured, and the wear resistance of it was tested by a friction instrument. The results show that the effect of laser cladding is good, and it has good metallurgical bonding with the substrate. Different microstructures such as dendritic and equiaxed grains can be observed in the cladding layer. With the increase in laser power, more equiaxed and columnar dendrites can be observed. The phase composition of the cladding layer is mainly composed of γ–Ni solid solution and some intermetallic compounds such as Ni3B, Cr5B3, and Ni17Si3. The results of EDS show that there are some differences in the distribution of C and Si between dendrites. The hardness of the cladding layer is about 600 HV0.2, which is about three times of the substrate (~200 HV0.2). Through the analysis of the wear morphology, the substrate wear is serious, there are serious shedding, mainly adhesive wear, and abrasive wear. However, the wear of the cladding layer is slight, which is abrasive wear, and there are some grooves on the surface.

Multilayer and high-entropy alloy-based protective coatings for solving the issue of critical raw materials in the aerospace industry

Aerospace is an actively developing industry that continuously requires the implementation of modern technologies. The rapid growth in new vehicle production demands much support. Hence, the problem of resources with complicated supply and distribution is always of current interest. These critical raw materials (CRMs) are involved in almost all areas of aerospace manufacturing and service. An efficient and profitable solution to the problem of critical materials can be found in protective coatings, especially in such advanced concepts as multilayer and high-entropy alloy (HEA)-based coatings. In this paper, we study both ways of manufacturing effective coatings. We have shown that multilayer CrN/MoN coatings with exceptional toughness and hardness could find promising applications in the aerospace industry. The developed strategy for the novel materials screening based on the prediction of their properties has been demonstrated on the example of the refractory HEA-based coatings. A brief state of the art of the EU critical raw materials and their place in the aerospace/defence industry has been given.

Formation of CuCrCoFeNiO high entropy alloy thin films by rapid thermal processing of Cu/CrNiO/FeCo multilayers

This study presents the synthesis of High Entropy Alloy (HEA) films starting from elemental Cu and binary alloy CoFe and CrNiO multilayers, followed by rapid thermal processing (RTP). By that, the HEA films (HEAFs) were formed by phase formation via short-range and fast diffusion processes. Multilayers with a total thickness of 760 nm consisting of 16 repetitions of a Cu (11 nm)/CrNiO (16.5 nm)/CoFe (20 nm) sequence were annealed at temperatures from 600 °C to 1000 °C for 5 min. The reaction products were then analyzed by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM) combined with electron energy loss spectroscopy (EELS), in order to identify the phase transformations and elemental distributions. A duplex FCC structure containing CrCoFeNiO HEA and pure Cu phase was successfully synthesized at 600 °C and 800 °C by the solid-state reaction. CuCrCoFeNiO HEA formed within in a Cu nanocrystalline matrix. As the annealing temperature increased, the oxygen content in the films decreased, Both HEA and Cu possess significant 〈111〉 preferred orientation. The HEA phase demonstrated a typical microstructure of alloys with intensive nano-twins. Moreover, the grain growth kinetics of the HEA phase was evaluated, and the activation energy was found to be 185(10) kJ/mol. This is comparable to that of conventional stainless steel (~150 kJ/mol) and less than half of the value for CrCoFeNi bulk (434 kJ/mol). A surface energy-driven grain growth mechanism of the HEAFs via multilayer alloy formation is proposed in this study. The mechanical properties, hardness and Young's modulus, were measured via nanoindentation, and the strengthening mechanism was proposed and compared with current literature.

Process-structure relationship in the directed energy deposition of cobalt-chromium alloy (Stellite 21) coatings

In this work, we accomplished the crack-free directed energy deposition (DED) of a multi-layer Cobalt-Chromium alloy coating (Stellite 21) on Inconel 718 substrate. Stellite alloys are used as coating materials given their resistance to wear, corrosion, and high temperature. The main challenge in DED of Stellite coatings is the proclivity for crack formation during printing. The objective of this work is to characterize the effect of the input energy density and localized laser-based preheating on the characteristics of the deposited coating, namely, crack formation, microstructural evolution, dilution of the coating composition due to diffusion of iron and nickel from the substrate, and microhardness. It is observed that cracking is alleviated on preheating the substrate and depositing the coating at a moderate energy density (~200 J·mm−3). The main finding is that cracking of DED-processed Stellite 21 coating at higher levels of energy density is linked to the elemental segregation of chromium and molybdenum, which form hard and brittle phases in the inter-dendritic regions. Cracking in the inter-dendritic regions is caused by residual stresses resulting from the steep thermal gradients at higher input energy. Localized laser-based preheating and moderate energy density mitigate steep temperature gradients and thereby avoid thermally induced cracking of the Stellite coating along the inter-dendritic regions.

Compositionally Modulated Multilayered Zn-Co Deposits for Better Corrosion Resistance

Zn-Co compositionally modulated multilayer alloy (CMMA) deposits have been developed onto mild steel using single bath technique. Multilayer alloy coatings have been galvanostatically produced using square current pulses. The switched cathode current density and number of layers have been designed for improved corrosion resistance. Experimental data revealed that multilayer coating with 120 layers at 10/30 mA/cm2 demonstrated ~ 125 times higher resistance to corrosion than monolayer alloy coating of the same thickness. The improved corrosion resistance of multilayer coatings is due to small changes in the wt.% cobalt, leading to change in the phase structure of deposit in alternate layers. The defects and failures occurring in a single layer in the deposition process are covered by the alternatively deposited coating layers. Therefore, the direction of the corrosive agent is extended or blocked. Further, the better corrosion resistances afforded by Zn-Co CMMA coatings were explained through changes in electronic properties at the interface, supported by Mott-Schottky’s plot. However, the decrease of corrosion resistance at a high degree of layering is attributed to the less relaxation time for redistribution of solutes in the diffusion layer, during plating. Potentiodynamic polarization and electrochemical impedance data showed its good protection ability. The enhanced corrosion resistance of multilayered deposits is due to small change in cobalt content, leading to alter the phase structure of the alternate-layers of the deposits. The structural morphology and the topographical structure of the coating were analyzed by scanning electron microscopy and atomic force microscopy. Evaluation of the chemical composition of the alloy coatings was carried out by x-ray photoelectron spectroscopy.

Fractography, Fracture Toughness and Structural Turbulence Under Low-Temperature Shock Loading of a Nonequilibrium Titanium Alloy Ti–6Al–4V

The titanium alloy Ti–6Al–4V with strongly nonequilibrium α- and β-phases has been studied for the first time. For this, it was subjected to cross-helical rolling (CHR) at T = 1000°C (above the polymorphic transformation temperature), and then quenched in water in order to partially preserve vanadium in the α-phase, and aluminum in the β-phase. Under active uniaxial tension, the non-equilibrium VT6 alloy was deformed in the absence of strain hardening at room temperature. Alloys treated with CHR below the polymorphic transformation temperature showed traditional parabolic hardening. The non-equilibrium of the VT6 alloy caused a strong increase in its impact toughness at low temperatures down to T = –70°C. The fatigue life of a nonequilibrium alloy has doubled. If the initial alloy has ductile-brittle fracture at low negative temperatures, then the nonequilibrium alloy deforms viscously with all signs of structural turbulence. Structural turbulence in a nonequilibrium alloy manifests itself in the temperature range from 20 to –70°C, during deformation of 3D-printed samples, under conditions of shock separation of diffusion-sintered multilayer VT6 alloy packets.

Zn–Ni compositionally modulated multilayered alloy coatings for improved corrosion resistance

ABSTRACT Zinc–Nickel monolayer (single layer) and compositionally modulated multilayer alloy coatings were developed on to mild steel from acidic sulphate bath; and their corrosion performance were studied using potentiodynamic polarization and electrochemical impedance spectroscopy methods. The coating layers were formed galvanostatically by single bath technique, using square current pulses and triangular current pulses. For the best efficiency of the deposits against corrosion, the switched cathode current density and the number of layers were optimized. Under optimized conditions, Zn–Ni multilayer alloy coatings were produced at the current density 3.0/5.0 A dm−2 having 300 layers were ∼65 (square) and ∼48 (triangular) times more corrosion resistant respectively than the single layer alloy coating of the same thickness. Scanning electron microscopy has been employed to investigate, the formation of multilayer alloy coatings as well as the morphology of the surface before and after corrosion studies.

Fabrication of preferentially oriented Al4043 alloy and its wear anisotropy

The multilayered Al4043 alloy was successfully fabricated in a preferred orientation using Cold Metal Transfer (CMT) based Additive Manufacturing (AM). The Electron Backscattered Diffraction (EBSD) analysis over the fabricated component probed that the CMT torch angle played a huge role in achieving preferred orientation and texture. Sample built with torch angle of 10° exhibited predominantly 〈111〉 texture and sample built with 15° torch angle showed 〈101〉 textured grains. Microstructural analysis revealed that the fabricated component was configured with columnar dendrites and little equiaxed grains. The XRD pattern revealed that Mg2Si and Al9Si multiphase precipitates were discretely present in remnant α-Al matrix. The fabricated components were subjected to wear analysis in two different sliding directions namely parallel and perpendicular to the direction of columnar dendrite growth. Topographical maps and worn morphology quantified that irrespective of the texture, the sliding direction of the intender showed a greater impact on wear resistance. In both the textured components intender sliding perpendicular to the columnar dendrite growth direction was characterized with superior wear resistance than parallel direction.

Microstructural Changes with Annealing of a Nanostructured Al Alloy Severely Plastic Deformed by Four-Layer Stack Accumulative Roll-Bonding Process.

Microstructural changes with annealing of a nanostructured complex aluminum alloy fabricated by 3 cycles of four-layer stack ARB process using different Al alloys were investigated in detail. The four-layer stack ARB process using AA1050, AA5052 and AA6061 alloy sheets was performed up to 3 cycles without a lubricant at room temperature. The sample fabricated by the ARB is a multi-layer aluminum alloy sheet in which the AA1050, AA5052 and AA6061 aluminum alloys are alternately stacked to each other. The layer thickness of each alloy became thinner and elongated to the rolling direction with the number of ARB cycles. The grain size decreased with increasing of the number of ARB cycles, and became about 160 nm in thickness after 3 cycles. The complex Al alloy still showed ultrafine grained microstructure to annealing temperature of 300 °C, but it had a heterogeneous structure containing both the ultrafine grains and the coarse grains due to an occurrence of discontinuous recrystallization after 350 °C.

Development of nanocrystalline multilayer Ni–Fe alloy coatings: characterization and its corrosion behaviour at elevated temperature

The present work deals with the galvanostatic fabrication of Ni–Fe nanostructured composition-modulated multilayer alloy (CMMA) coatings on steel panel from the newly optimized acid-sulphate bath solution. The recurring cathode current density combination (RCCC) and the number of layers have been optimized for enhanced performance of the coatings against corrosion. Corrosion behaviour of the nanostructured multilayered coatings was evaluated by Tafel extrapolation and electrochemical impedance spectroscopy (EIS) methods in 3.5% NaCl solution. Under optimal conditions, the CMMA coatings developed were more corrosion-resistant than the monolithic alloy coatings obtained from the same bath. Least corrosion rate (CR) was witnessed at 300 layers, above which saturation of corrosion resistance at a high temperature was found, which is attributed to a shorter relaxation time for redistribution of metal ions during multilayer deposition. Hardness and roughness of the coatings were evaluated using Vickers hardness test and atomic force microscope, respectively. Phase structure of the coatings was discussed using X-ray diffraction technique. The cross-sectional view of the coatings was characterized by scanning electron microscope. CR analysis and the surface morphology of the optimized coatings exposed to high temperature revealed the better performance of CMMA coatings at the elevated temperatures compared to the monolithic coatings.

Effect of welding sequence on stress and deformation field of Invar alloy multi-layer and multi-pass welding: A simulation study

The welding sequence has an important influence on the formation of stress and deformation in multi-layer and multi-pass welding (MLMPW). In this paper, a 3D finite element model of Invar alloy welding that can calculate the welding stress and deformation has been established using MSC. Marc. The simulation results show that there is high residual tensile stress in the welding zone. For six-layer twelve-pass welding, the welding sequence has little effect on maximum stress value. Meantime, welding deformation is mainly distributed far from the weld metal area and is mainly affected by welding sequence under similar other welding conditions. It is found that the deformation angle of welding sequence D is the smallest, with a value of [Formula: see text].

Surface Modification and Wear Resistance of Electroless Ni-P Based Duplex Alloy Coating

Ni-P-W multi-layered alloy coating was electrolessly deposited on 10 x 15 x 1.5 mm mild steel capons. The coated samples were heat treated between 200 – 800 °C and the resultant effect of the annealing on the small scale structure and mechanical properties of coating was studied by using X-ray diffraction, Scanning electron microscopy, nano-indenter, pin-on disc wear tester and interferometry Spectroscopy. The result shows that the as-deposited amorphous duplex coatings crystallise in steps as the annealing temperature increases and this gives raise to new phase formation in the mechanical properties of the coating. The study reveals the impact of high temperature annealing on the microstructure, morphology and microhardness of this duplex coating within certain temperature range; which was attributed to the formation of new Ni3P and Ni-W phases, its grain refinement and consequently, better linear microhardness and wear resistance relationship within given temperatures.

Corrosive wear of multi-layer Fe-based coatings laser cladded from amorphous powders

Since amorphous alloys exhibit good wear and corrosion resistance, they are supposed to be applied as a candidate implant material. In this work, using laser cladding, Multi-layer Fe-based alloy coatings were fabricated from amorphous powders on 316L stainless steel (SS) substrate. When the number of cladding layers increases, the microstructure of the coating was mainly composed of γ-Fe firstly, then evolved to γ-Fe and α-Fe solid solutions, and then to a composite of amorphous and crystalline phases. The surface hardness of the coating was also enhanced consequently to over 1200 HV. During reciprocate sliding against an Alumina ball in a simulated body fluid (Ringer's solution), the volume loss and the coefficient of friction (COF) of the coatings generally decreased firstly and then increased with the number of cladding layers. During sliding at open circuit, the drop in open circuit potential (OCP) of all the Fe-based coatings, except for the 1-layer one, was not as significant as that of the 316 SS substrate. Moreover, when applying a cathodic potential during sliding, no obvious protective effect was obtained for the coatings, which indicates that the multi-layer Fe-based coatings possess a good corrosion-induced wear resistance in comparison to 316L SS. Because of the formation of an electric double layer, the fixed potential of 100 mVSCE or −600 mVSCE was beneficial to reduce the COF, especially for 316L SS. The tribocorrosion at OCP showed that the 2-layer coating possessed the best corrosive wear resistance, and its COF and volume loss were about 3 and 5.6 times lower than those of the substrate. The material loss in Ringer's solution at OCP is mainly controlled by the mechanical wear for the coatings and the synergism between corrosion and wear for the substrate. Furthermore, this work provides a way to optimize the tribology system by adjusting the number of cladding layers to reduce COF and wear in a simulated body fluid.

Microstructure and performance of brazed diamonds with Ni–Cr+multilayer graphene composite alloy

The aim of this paper is to provide a way of reducing unfavorable thermal damage of diamonds in the current brazing practice. To realize such objective, a new kind of composite alloy, with a relatively uniform distribution of multilayer graphene on Ni–Cr brazing filler alloy particles’ surface, was proposed to braze diamonds. Morphology of brazed samples was observed and interfacial microstructure characterization of them was analyzed. The thermal residual stress of brazed diamonds was measured by Raman spectroscopy. The mechanical performance of brazed diamonds was measured. Microstructure of alloy and brazed diamonds after etching was analyzed. The results show that the morphology of brazed diamond samples with No.1 composite alloy containing 1 wt % multilayer graphene was better. The thermal residual stress of brazed diamonds with No.1 composite alloy was decreased by 6.6%, meanwhile, the static pressure strength and toughness against impact were increased by 9% and 7.9%, respectively, in comparison with those of brazed diamonds with Ni–Cr brazing filler alloy. Cr and Ni elements were adsorbed by multilayer graphene and led to the formation of C-containing phases. The multilayer graphene layer was located between the chrome carbide layer and Ni–Cr alloy. Therefore, the unfavorable thermal damage to diamond grits was reduced by multilayer graphene.

Small-angle scattering tomography of precipitation-hardened multilayer Al/Al-Zn/Al model alloys

Tomographic images constructed from small-angle X-ray scattering (SAXS) intensities utilizing microbeams have been examined for a model multilayered aluminum alloy sample heat-treated to form spatially modulated composition and microstructures. Spatial distributions of composition and precipitation microstructure have been examined by one-dimensional scanning SAXS measurements and two-dimensional tomographic images of attenuation parameters and integrated intensity of SAXS intensity. Reconstructed images using the integrated intensity reflected the distribution of precipitates in terms of their volume fraction over the sample inside the sample, and agreed with more detailed analysis made in the one-dimensional case.

Effect of a high magnetic field on hard magnetic multilayered Fe-Pt alloys

Abstract Fe-50 vol%Pt multilayers that were prepared by accumulative roll-bonding were annealed in vacuum for 2 h at various temperatures between 723 K and 823 K. Some samples were annealed without any high magnetic field (HMF). Others were subjected HMF up to 31.2 T, applied in either in-plane or out-of-plane directions. The annealing partially transformed the original multilayered structure into a polycrystalline hard-magnetic FePt magnetic phase with ordered L10 structure. Textured FePt/Fe nanocomposite foils were formed under HMF. Magnetic anisotropic behavior was observed in the annealed FePt/Fe composite because of the textured nanostructure. HMF annealing decreased grain size and increased the (0 0 1) texture along the HMF direction. In the sample annealed with out-of-plane HMF, both coercivity and maximum energy product were enhanced because of higher (0 0 1) out-of-plane texture and finer nanoscaled grain sizes compared to other samples. An in-plane HMF appeared to strongly inhibit phase transformation. This inhibition likely resulted from a change in Gibbs free energy and the diffusion inhibition caused by HMF.

Zn–Fe multilayered alloy coatings produced by electrodeposition

Zn–Fe multilayered alloy coatings were deposited on mild steel substrates using the dual bath electrodeposition technique. The produced coatings consisted of alternate Zn–1 wt% Fe and Zn–10 wt% Fe alloy sub-layers. Their periodicity length (total thickness of two adjacent alternate sub-layers) ranged between 2 and 8 μm. The surface and the cross-sectional morphology of those coatings were studied with the aid of a metallurgical microscope and a scanning electron microscope. The crystal structure of the electrodeposited multilayered coatings was investigated using an X-ray diffractometer. The Zn–1 wt% Fe and Zn–10 wt% Fe alloy sub-layers consisted of two phases: the η-phase (Zn–Fe solid solution) and the δ1-phase (intermetallic FeZn7). A microhardness tester equipped with a Vickers intender was used to examine the microhardness of the produced coatings. It was found that the microhardness increased with the decrease of periodicity length, following a modified Hall–Petch relationship.

Interface bonding properties of multi-layered metal composites using material composition method

Abstract In order to explore the interfacial bonding properties of multi-layered metal composites in depth, using ZChSnSb8-4 alloy as research object, instead of atomic substitution modeling, taking into consideration of the content ratios of Cu6Sn5, SnSb and Sn in the alloy, crystal structure modeling using material composition method was built with molecular dynamics simulation software of Materials Studio, the bonding properties of the interface between steel body and Babbitt alloy with or without Sn layer were simulated and analyzed respectively. The interfacial bonding energy of steel and Babbitt alloy with or without Sn layer was calculated under the same conditions. At the same time, the bonding energy between the adjacent alloy interfaces of the structure with or without Sn layer was calculated and analyzed, the formula for calculating the interface bonding energy of multi-layered alloy materials is put forward, and the basis for judging the dangerous interface is given. The simulation results show that the minimum interfacial bonding energy of the three-layer material is 39.92% higher than that of the two-layer material. Therefore, the three-layer structure bushing has better bonding performance and is less likely to be destroyed in engineering practice. Meanwhile, it is demonstrated that when the temperature is 543.15K, the interfacial bonding energy of the bushing is the maximum, and the interfacial bonding performance is the optimal.

Effects of tool path in remanufacturing cylindrical components by laser metal deposition

Laser metal deposition as an additive manufacturing process has been widely utilized for component repair. In this study, in order to investigate the influence of tool path on characteristics of coatings for cylindrical part repair, multi-layer cobalt-based alloy was coated on cylindrical tool steel substrates using the blown powder laser metal deposition process following the helix (H), circle-line-circle (CLC), and line-arc-line (LAL) routes. A series of analysis was performed on the coatings including shape’s profile, powder-catch efficiency, microstructure, EDS, XRD, and Vickers hardness. The result shows coatings fabricated using the H and CLC routes have consistent thickness while more material was deposited near the middle for the LAL route. Powder-catch efficiency for the CLC and LAL paths was up to 28% while it was only 14% for the H route. The microstructure near the coating’s starting point was columnar dendrites growing parallel to the heat flux direction. Cooling speed reduced after several layers’ coating and equiaxed-like morphology appeared. Much gas porosity was discovered near the interface for LAL-coated samples. EDS and XRD analysis show Fe was diffused into the coatings. Microhardness measurement reveals that the hardness of LAL fabricated samples was slightly higher than the hardness of H and CLC samples. The result shows that the CLC path is more suitable for repairing/coating cylindrical components due to a relatively consistent shape, a high powder-catch efficiency, and defect-free deposits.