Intermetallic Phases Research Articles

Role of ilmenite particles on high temperature wear behavior and coefficient of friction of LM30 aluminium alloy composites

In this study, experimental approach involves material preparation via stir casting, extensive testing, and characterization. Optical microscopy, Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) analysis reveal the uniform distribution of ilmenite particles within the alloy matrix and the formation of intermetallic phases. The thermal characteristics analysis demonstrates reduced 29 % coefficient of thermal expansion (CTE) in the composites, in the case of 15 wt% fine ilmenite particles reinforced composite. Hardness tests improvements in hardness, with the 15 wt% (32–50 μm) ilmenite Aluminium Metal Matrix Composite (AMC) exhibiting a 69% increase over the base alloy. Wear testing at various temperatures and loads showed the superior wear resistance of the composites compared to the base alloy, with the C3-15 composite outperforming cast iron typically used in brake drums. The wear rate of LM30 and LM30 + 15 wt% ilmenite (32–50 μm) (C3-15) sample is 38.8671 x 10−4 mm3/m and 10.50768 x 10−4 mm3/m at 200 °C and 68.67 N applied load, respectively. The coefficient of friction analysis further supports the enhanced performance of the composites. The coefficient of friction (COF) of LM30 + 15 wt% ilmenite (32–50 μm) (C3-15) is 0.29898, 0.47645 at 9.81 N and 68.67 N load, respectively measured at a temperature of 200 °C. Examining worn surfaces and debris provides insights into the wear mechanisms, including adhesion and abrasive wear. Overall, this research suggests the potential suitability of ilmenite-reinforced LM30 alloys as alternatives to traditional brake drum materials, offering improved thermal stability and wear resistance.

Optimization and analysis of sustainable magnesium-based alloy (Mg-Zn-Ca-Y) for biomedical applications

Due to strength and biodegradability, magnesium (Mg) and its alloys are potential biodegradable implant materials. However, pure Mg corrodes more rapidly in the physiological environment, causing rapid deterioration before bone repair. The discrepancy between bone healing and Mg implant deterioration encourages the development of new Mg alloys with other acceptable alloying elements to achieve the desired high corrosion resistance and mechanical properties. In this work, different concentrations of yttrium (Y), that is, Mg-4zn-0.2ca-xY, (x= 3,6,9,12% wt), are added to Mg-based alloys. The microstructure, mechanical characteristics, corrosion behavior, and biocompatibility of the alloys were carefully investigated. When Y concentrations are high, Mg alloys with Y change significantly. High Y concentrations in Mg alloys containing yttrium (Y) suppress intermetallic phases along grain boundaries and form chemically stable Y oxide layers on the surfaces, changing their microstructures and improving their corrosion resistance. Cytotoxicity analysis showed that human osteoblast cells were not significantly affected by the Y-containing Mg alloys. The benefits of using Y as an alloying element to simultaneously adjust Mg alloys with higher strength and slower deterioration are presented.

Ni active sites isolated by antimony toward enhanced propyne semi‐hydrogenation

AbstractRegulating Ni active sites toward the formation of target product is of great importance for designing high‐performance cost‐effective catalysts for catalytic semi‐hydrogenations but remains challenging. Herein, we report the fabrication of NiSb intermetallic catalyst via structural transformation from a layered double hydroxides precursor for boosting propyne semi‐hydrogenation. Systematic characterizations, including x‐ray diffraction, atomic‐resolution electron microscopy, and x‐ray absorption spectroscopy, provide evidence for the formation of P63/mmc NiSb intermetallic phase in the synthesized NiSb catalyst. The host Ni active sites are demonstrated to be isolated by the high‐electronegativity p‐block guest Sb sites, which deliver remarkably high selectivity to target propene, that is, up to propene selectivity of 96% at nearly full propyne conversion. Temperature‐programmed surface reaction and temperature‐programmed desorption measurements combined with theoretical calculations unravel that the excellent selectivity originates from kinetically more favorable desorption of propene than its hydrogenation to propane on the regulated Ni active sites.

Aqueous Synthesis of Plasmonic Gold-Tin Alloy Nanoparticles.

This protocol describes the synthesis of Au nanoparticle seeds and the subsequent formation of Au-Sn bimetallic nanoparticles. These nanoparticles have potential applications in catalysis, optoelectronics, imaging, and drug delivery. Previously, methods for producing alloy nanoparticles have been time-consuming, require complex reaction conditions, and can have inconsistent results. The outlined protocol first describes the synthesis of approximately 13 nm Au nanoparticle seeds using the Turkevich method. The protocol next describes the reduction of Sn and its incorporation into the Au seeds to generate Au-Sn alloy nanoparticles. The optical and structural characterization of these nanoparticles is described. Optically, prominent localized surface plasmon resonances (LSPRs) are apparent using UV-visible spectroscopy. Structurally, powder X-ray diffraction (XRD) reflects all particles to be less than 20 nm and shows patterns for Au, Sn, and multiple Au-Sn intermetallic phases. Spherical morphology and size distribution are obtained from transmission electron microscopy (TEM) imaging. TEM reveals that after Sn incorporation, the nanoparticles grow to approximately 15 nm in diameter.

Изучение влияния содержания гафния и эрбия на формирование микроструктуры при литье алюминиевого сплава 1590 в медный кокиль

Introduction. High-magnesium aluminum alloys are widely used in the automotive, building and aerospace industries due to its low specific gravity and high strength. The characteristics of such alloys can be improved by small additions of scandium and zirconium. However, scandium is very expensive, so in new generation alloys its amount is tended to be reduced. In the recently developed 1590 aluminum alloy, this was achieved by addition of erbium and hafnium. The objective of the paper is to study the effect of erbium and hafnium concentrations on the modification of the cast structure in 1590 aluminum alloy at high solidification rates. Research Methods. The paper investigates the microstructure, chemical composition and size of intermetallic compounds in specimens from ten alloy 1590 modifications with different hafnium and erbium contents cast into a copper chill mold with a solidification rate of 10 °C/sec. The grain structure was studied using an optical microscope. The chemical composition and size of the intermetallic phases were studied using a Tescan Vega 3 scanning electron microscope. Results and discussion. It is established that as the amount of hafnium and erbium increases, the cast structure is modified. In general, grain refinement with the addition of hafnium and erbium can be explained by a higher degree of supercooling between the solid and liquid phases. At a hafnium content of 0.16 %, the dendritic structure begins to transform into an equiaxed grain structure. This transformation can be explained by the appearance of primary intermetallic compounds of the Al3Sc type in the liquid phase. Such intermetallic compounds are identified at a concentration of erbium and hafnium equal to 0.16 %. Moreover, in all alloys eutectic intermetallic compounds are identified that contained manganese and iron and had no effect on the cast structure. Comparison with previously obtained results on the grain size of specimens cast into a steel mold shows that with higher solidification rate, the structure modification in 1590 alloy is getting less efficient. This is explained by an increase in the concentration of transition elements in the solid solution, primarily scandium, necessary for the formation of primary intermetallic particles.

Microstructure-properties relation of hydrostatically extruded absorbable zinc alloys: Effect of Mg and Cu addition on corrosion properties and biocompatibility

Pure Zn is well-known for its appropriate corrosion rate, making it suitable for use as future absorbable implants. Yet, it suffers from insufficient strength, thus, both plastic deformation and alloying are required. Hydrostatic extrusion has proven to be an efficient technique, providing high mechanical properties for zinc alloys. However, its effect on degradation rate and biocompatibility of Zn alloys remains unknown. Thus, within the present study, an attempt to evaluate those properties has been made on hydrostatically extruded pure Zn, Zn–Mg and Zn–Mg–Cu alloys. The materials were characterized by advanced microscopy techniques and uniaxial tensile tests. Corrosion properties were assessed based on electrochemical and static immersion tests. Finally, the cytotoxic effect of zinc extracts on endothelial cells were examined by standard MTT assays combined with confocal imaging.The results showed that hydrostatic extrusion results in significant refinement of α-Zn grains and the intermetallic phase Mg2Zn11 for the investigated alloys. The alloys exhibited ultimate tensile strength exceeding 300 MPa and elongation higher than 20%. Corrosion tests demonstrated that all the materials showed a similar level of degradation rate. Moreover, the uniform distribution of the intermetallic phase contributed to homogeneous corrosion of Zn alloys. Biological studies indicated that the least cytotoxic response in endothelial cells was obtained for the Zn–Mg alloy. Such an effect was caused by the limited amount of released Zn ions in the favor of Mg ions.The refinement of α-Zn grains and intermetallic phases caused by hydrostatic extrusion were key factors determining the performance of Zn-based materials.

The Beneficial Effect of Iron in Aluminum-Cerium-Based Cast Alloys

Iron (Fe) has been considered a major impurity since it is detrimental to the mechanical properties of many cast aluminum alloys due to the formation of Fe-containing brittle intermetallic phases. Fe is found naturally as an impurity in bauxite ore, resulting in Fe contamination of aluminum alloys with increasing contamination from current recycling practices. The Al–Ce–Fe system was investigated using CALPHAD (CALculation of PHAse Diagrams) modeling and experimental casting techniques. It was found that additions of Fe to the Al–Ce system are beneficial to the strength (slightly) and ductility (significantly) of the ternary alloys, which is attributed to the formation of fine metastable Al8CeFe2 phase with aggregate morphology and equilibrium Al10CeFe2 phase, suppressing coarse proeutectic Al11Ce3 phase in near-eutectic Al–Ce alloys. Heat treatment study showed that the metastable Al8CeFe2 phase transforms to predicted equilibrium Al10CeFe2 phase at 500 °C, with essentially no intermetallic or grain coarsening; thus, the alloy displayed excellent property retention. The Al–Ce–Fe alloy system offers opportunities for sustainable, recyclable alloy development using low-cost Fe and low-cost cerium (a byproduct of rare-earth extraction).

Effect of welding parameters on weld surface roughness, hardness, and microstructure in laser-welded 340BH-steel and pure vanadium

This study delves into the influence of laser welding parameters on the microstructural evolution, surface roughness, and hardness of dissimilar lap joints formed by welding 340BH steel (upper) to cold-rolled pure vanadium (bottom) in an attempt to successfully develop metal membranes by adopting a novel technological route. Specifically, we examined power levels of 0.3 kW and 0.4 kW combined with varying welding speeds (40 mm/s, 50 mm/s, and 60 mm/s). The results indicate that defect-free joints were achievable at the higher welding speed of 60 mm/s. This conclusion is supported by the observed surface roughness profile. Elemental interdiffusion and temperature play pivotal roles in the formation of these dissimilar joints. These factors determine the dimensions of the heat-affected zone (HAZ) and the fusion zone (FZ) under all welding conditions. Notably, the high cooling rates during laser welding hindered the formation of intermetallic phases both in the FZ and at the interface between the metals. Microstructural examination of the HAZ/FZ on the Fe side showed a coarser microstructure when using a power of 0.4 kW, in contrast to the lath martensite observed at 0.3 kW. These observations align with the cooling curve derived from finite element analysis (FEA). FEA was also used to estimate temperature profiles throughout the welded area, and the results were consistent with experimental data. Further microstructural analysis using electron backscattered diffraction (EBSD) revealed a significant phenomenon: the formation of recrystallized grains of vanadium in the HAZ near the FZ on the vanadium side. Microhardness tests, conducted to gauge joint quality, displayed varying hardness levels across the base metal (BM), HAZ, and FZ interfaces. At a power of 0.3 kW, the HAZ displayed greater hardness than the FZ and BM due to the formation of lath martensite. Conversely, at a power setting of 0.4 kW, a reduction in hardness was observed within the HAZ, attributable to coarser ferrite formation.

Ultrathin Template Approach to Synthesize High‐Entropy Intermetallic Nanoparticles for Hydrogen Evolution Reaction

Intermetallic nanoparticles (i‐NPs) have received considerable attention as high‐performance catalysts for diverse catalytic applications. However, high‐entropy i‐NPs have been rarely reported due to particle growth and phase separation in the multicomponent alloy. In this study, for the first time, an integrated approach of template and structure transformation is introduced to synthesize a series of sub ≈ 5 nm multicomponent i‐NPs with varying compositions. Firstly, ultrathin PtCu nanosheets (NSs) are directly converted into bimetallic PtCu i‐NPs. Furthermore, these PtCu NSs are also used as templates for epitaxial growth of the other metals, followed by annealing to obtain high‐loading, novel compositions and uniform i‐NPs with ternary, quaternary, and quinary compositions, including high‐entropy i‐NPs. Interestingly, L10 intermetallic phases are obtained when Fe is introduced. As a proof‐of‐concept application, these high‐entropy i‐NPs showed superior catalytic performance for the hydrogen evolution reaction , which can be attributed to the negatively shifted d‐band center of Pt, thereby resulting in reduced H* adsorption energy at Pt sites as supported by density functional theory calculations. Overall, this research presents a promising method for the development of i‐NPs with various compositions.

Deformation mechanisms and their role in the lack of ductility in the refractory-based high entropy alloy AlMo0.5NbTa0.5TiZr

The deformation mechanisms in the refractory high entropy alloy AlMo0.5NbTa0.5TiZr have been investigated, with their potential impact on ductility. Specifically, the modes of plasticity active in the B2 matrix and in an alloyed version of the phase Al4Zr5 found at grain and subgrain boundaries were explored by use of nano-indentation. For the B2 phase, a combination of weak-beam dark-field and superlattice imaging revealed dissociation of 〈111〉 superdislocations into two superpartial dislocations, bounding an anti-phase boundary (APB), following the reaction: a〈111〉= a/2〈111〉+APB+a/2〈111〉. The dislocations in the B2 phase exhibited long, relatively straight screw segments and short edge segments, such that the mobility of the edge dislocations appears to be higher than that of the screw segments. Evidence of a B2 to bcc slip transmission process has been observed through use of stereo-pair imaging and anaglyph construction. This process involves the transmission of slip from the B2 matrix, followed by the decorrelated motion of the two a/2〈111〉 dislocations in the bcc precipitate, demonstrated by the increased separation of the dislocations within the bcc phase. Regarding the deformation of the Al4Zr5 intermetallic phase, it was found that indentation of this phase resulted in no evidence of dislocation generation and motion, and cracking at the edges of the given indent. It has been concluded that the lack of plasticity of this phase is the cause of the room temperature brittle nature of this alloy.

Correlation between d Electrons and the Sweet Spot for the Hydrogen Evolution Reaction: Is Platinum Always the Best Electrocatalyst?

Herein, two Laves intermetallic series, ZrCo1.75M0.25 and NbCo1.75M0.25 (M = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt), were synthesized, and their hydrogen evolution reaction (HER) activities were examined to reveal the influence of d electrons to the corresponding HER activities. Owing to the different electronegativity between Zr and Nb (χZr = 1.33; χNb = 1.60), Co and/or M elements receive more electrons in ZrCo1.75M0.25 than that of the Nb one. This leads to the overall weak H adsorption energy (ΔGHad) of ZrCo1.75M0.25 series compared to that of NbCo1.75M0.25 and rationalizes well the superior HER activity of the Rh member compared to that of the Pt one in the ZrCo1.75M0.25 series. Under industrial conditions (333 K, 6.0 M KOH), ZrCo1.75Rh0.25 only requires an overpotential of 110 mV to reach the current density of 500 mA/cm2 and can be operated at high current density over 400 h. This work demonstrates that with a proper combination between elements in intermetallic phases, one can manipulate d electrons of the active metal to be closer to the sweet spot (ΔGHad = 0). The Pt member may no longer exhibit the best HER activity in series, and all elements exhibit the potential to outperform the Pt member in the HER with careful control of the d electron population.

Fast epitaxial brazing of DD6 single crystal superalloy using novel NiCoCrAlNbTi high entropy filler alloy

In recent years, Ni-based single crystal superalloys are widely applied in the fabrication of blades and vanes in aero-engine industry due to the excellent high temperature properties. In this study, a novel high entropy filler without Si and B was proposed. The melting point of the newly developed Ni-Co-Cr-Al-Nb-Ti filler was 1155ºC and fast epitaxial brazing DD6 single crystal superalloy was realized under the brazing condition of 1200ºC for 30 min. Furthermore, the influence of aging heat treatment on the interface microstructure and joint strength was investigated. The as-brazed joint interface mainly consisted of γ, γ’, γ’’-(Ni,Co,Cr)3Nb and NiAl phase. After aging treatment, element distribution became more uniform and the size of intermetallic phase was refined. The γ+γ’ phase in brazing seam exhibits same [001] orientation with DD6 substrate. The orientation relationship between γ and γ’’ was also analyzed. The joint tensile strength tested at 980ºC was 559 MPa.

Effect of indium and yttrium on the corrosion behavior of AZ63 magnesium alloy

Indium (In) and yttrium (Y) can activate and alleviate the corrosion of magnesium alloy, respectively. The effects of 1 wt% In and 1 wt% Y on the microstructure and electrochemical behaviors of Mg-6 wt%Al-3 wt%Zn (AZ63) magnesium alloy are investigated via materials characterizations associated with electrochemical techniques. The results showed that co-alloying of In and Y would increase the number of intermetallic phases in AZ63 by generating discrete Al2Y phase and continuous Mg17Al12 phase. During the process of corrosion, the corrosion of Mg-6 wt%Al-3 wt%Zn-1 wt%In-1 wt%Y(AZ63InY) initiates from the intermetallic phases and propagates locally. The corrosion products are apt to adhere on the corroded surface, underneath which a severe corrosion takes place due to the enhanced dissolution-reprecipitation effect of In on activating Mg.

Dissimilar friction stir welding and post-weld heat treatment of Ti-6Al-4V and AA7075 producing joints of unprecedented strength

Dissimilar welding of Ti and Al alloys is challenging due to the potential formation of brittle intermetallics, which can compromise weld strength. Friction stir welding (FSW) is an advanced joining method with the potential to drastically reduce or prevent the formation of intermetallic phases because melting is avoided. However, in previous studies, dissimilar joints of Ti-6Al-4V and EN AW-7075 with satisfactory strength could not be achieved. Thus, we investigated friction stir welding of these two materials in a butt configuration, and analyzed the effects of post-weld heat treatments on the mechanical properties. Tensile strengths of 441 MPa in the as-welded condition and 505 MPa after heat treatment were achieved, significantly surpassing strength values reported in earlier studies. Microscopic investigations showed no evidence of formation of brittle intermetallic phases, and ductile fracture was observed. Our results show that FSW is a very promising candidate for future aerospace applications requiring dissimilar joining of Ti and Al alloys.

Influence of Ni and PWHT on microstructure evolution and mechanical properties of GTA-welded duplex stainless steel and super duplex stainless steel joints: A comparative investigation

In the present investigation, a new endeavor has been made to analyze the impact of the secondary process (post-weld heat treatment (PWHT)) as well as Ni addition on the microstructure and mechanical characteristics of welds. Welds between similar joining materials from duplex stainless steels (DSS), as well as super DSS (SDSS), were made by the gas tungsten arc welding (GTAW) process. For DSS, after PWHT with the addition of Ni element, the amount of austenite rises and becomes more uniformly distributed with curved boundaries, while for SDSS, the microstructure mainly consists of intergranular and Widmanstätten austenite. According to the comparison of phase percentages obtained based on both ASTM E1245 and ASTM E562, a good balance between ferrite and austenite phases of joint materials was achieved. X-ray diffraction analyses on both joints revealed that phases are mainly ferrite and austenite with different lattice parameters without evidence of unwanted intermetallic phases. The addition of Ni increases the hardness values of DSS weld metal compared to the base metal due to an increased amount of Widmanstätten austenite and ferrite in the microstructure. The lowest ductility was obtained for the SDSS weld sample with the addition of Ni and PWHT because of the existence of secondary austenite in the weld metal and the Widmanstätten morphology of the austenite. The effect of PWHT on the development of microstructure and mechanical behaviors was more than the effect of nickel powder on weld samples.

Laser metal deposition of titanium on stainless steel with high powder flowrate for high interfacial strength

Direct joining of titanium and stainless steel 316 L with a strong interface is very challenging due to the formation of the brittle intermetallic compounds FeTi and Fe2Ti in the intermixing zones and to the high residual stress induced by the mismatch of the thermal expansion coefficients. In this bimetallic directed energy deposition study, firstly, deposition of Ti on stainless steel was carried out using conventional process parameter regime to understand the interfacial cracking susceptibility and then a novel high powder flowrate approach is proposed for controlling the dilution and constraining the intermetallic phases forming at the interface. The influence of high temperature substrate preheating (520 °C) on the cracking susceptibility and interface strength was also investigated. The deposited Ti samples and their interfaces with the 316 L substrate were characterized with optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy to investigate the geometry, microstructures and chemical compositions in relation to the cracks. The high powder flowrate deposition of Ti on stainless steel 316 L results in an extremely thin dilution region (~ 10 μm melt pool depth in the substrate) restricting the formation of the intermetallic phases and cracks. The ultimate shear strength of the interfaces of the crack free sample was measured from cuboid deposits and the highest measured strength is 381 ± 24 MPa, exceeding the weaker base material pure Ti. The high interfacial strength for high powder flowrate deposition is due to the substantial attenuation and shadowing of the laser beam by the in-flight powder stream as demonstrated by the high-speed imaging resulting in an extremely small dilution region.

Effect of Ti content on achieving development of mechanical properties and wear resistance of CoCrFeNiMoTix high entropy alloy

To achieve the synergy among density, strength, ductility, wear performance and thermal stability, a series of newly developed CoCrFeNiMoTix (x = 2 and 16.666 at. %) high entropy alloys (HEAs) via multiple phases nano crystalline structure were successfully fabricated using mechanical alloying (MA) following by spark plasma sintering (SPS). The results demonstrated that the SPSed Ti2-HEA and Ti16.6-HEA have a multiple phases structure consisting of FCC structure (Ni-type as a major phase), two types of BCC structure (Mo-type and Ti-type), topologically close packed (TCP) phases (laves, sigma (σ) and R phases) and geometrically close packed (GCP) phase (L12 precipitates). The micro hardness, strength and specific strength were increased from 711 HV, 1770 MPa and 197 MPa.Cm3/g for the Ti2-HEA to 817 HV, 1830 MPa and 236 MPa.Cm3/g for the Ti16.6-HEA, respectively, which were affected by more percentages of precipitates, intermetallic and BCC phases. Besides, fracture strain, coefficient friction, wear rate and the surface roughness were decreased from 16%, 0.19, 4.9*10−4 mm3 N−1 m−1 and 54.2 for the Ti2-HEA to 14.5%, 0.17, 2.7*10−4 mm3 N−1 m−1 and 31.6 for the Ti16.6-HEA. The ultimate shear strength (USS) values at 300 °C, 400 °C, 500 °C and 600 °C were increased from 960 MPa, 820 MP, 646 MPa and 24 MPa for the Ti2-HEA to 1180 MPa, 1010 MP, 802 MPa and 94 MPa for the Ti16.6-HEA, respectively. The Ti16.6-HEA illustrated higher thermal stability at all temperatures, where the USS slightly was decreased from 300 °C to 500 °C with a sudden drop at 600 °C.

Gold Coated Silver Bonding Wire and Its Consistent Reliability Performances

Thermal aging of gold coated silver bonded ball with aluminium bond pads exhibited a stable interface without Kirkendall voids until 4000h at 200°C for an un-molded device tested under vacuum. Ball and stitch pull remains in strength and remained constant until 4000 hours of aging. The growth of aluminides at the bond interface is about 4.5µm for 4000 hours of aging. The electrical resistance of the bonded ball remains the same until 4000 hours at 175°C for an epoxy molded device, molded with 5 to 7 pH green epoxy molding compound containing low chlorine and sulfur. Interestingly, the bonded ball interface of epoxy molded device has sustained 480h on biased Highly Accelerated Stress Test (bHAST) at +20V bias, 130°C, 85%RH. The bonded ball interface is stable until 1000 hours on unbiased HAST (uHAST) at 130°C, 85% RH as well. Cross-sectional ovservations of the bonded balls revealed the presence of intermetallic phases at the bond interface. However, formation of Kirkendall voids or crack propagatioon due to galvanic corrosions are absent.

A simulation of Al-Si coating growth under various hot stamping austenitization parameters: An artificial neural network model

22MnB5 hot stamping steels are pre-coated with an Al-Si layer to prevent oxidation and decarburization during the austenitization process, which includes heating and soaking within a furnace. Above ∼577 °C, the Al-Si coating transforms into Fe-Al and Fe-Al-Si intermetallic phases because of diffusion and solidification. In the present work, a deep neural network (DNN) model was developed to predict coating intermetallic growth under various heating rates and soaking conditions. The DNN model was trained using experimental data (energy dispersive x-ray spectroscopy chemical scans) collected from our coating growth characterization work. The heating rate (r), heating time (th), soaking time (ts), and the distance of each measured point away from the coating surface (d) are defined as input parameters, and the outputs are the weight percentage of Al, Fe, and Si. The model successfully predicted the chemical composition of the training dataset, which consisted of a single-stage heating process, followed by a soaking stage at a constant temperature. To validate the model, complex two-stage heating tests were conducted, and the intermetallic coating growth was quantified. The DNN model successfully predicted the two-stage heating test coating profiles, despite a minimal error that was due to the variation in as-received coating thickness. The DNN model predicts the overall experimental trends that show the heating rate has little effect on the transformed intermetallic species, but it affects the transformation rate of the intermetallic phases. Moreover, the higher heating rate test (after 750℃) resulted in the formation of the island shaped τ1 and/or τ2 phase, while the heating rate before 750℃ does not affect the morphology of the τ1 and/or τ2 phase.

Chromium diffusion coatings for improving the oxidation behavior of refractory metals at intermediate temperatures

Due to their very high melting points and high mechanical strength at elevated temperatures, refractory metals are promising structural materials for high temperature applications. However, their application is strongly restricted by their insufficient oxidation resistance. In this fundamental study, four different refractory metals (Mo, Nb, Ta, and W) were chromized by pack cementation to investigate the influence of chromium diffusion coatings on their oxidation resistance at intermediate temperatures. Thermodynamic calculations were used to find the most suitable conditions for the pack cementations. The formation of a homogeneous single-phase bcc Cr layer with a thickness below 10 μm on the sample surface was observed on all four refractory metals. In the case of Nb and Ta, intermetallic Cr2X-Laves phases (X = Nb, Ta) formed underneath the bcc Cr layer while an interdiffusion zone formed on Mo. The concentration profiles of the deposited Cr layers were used to determine the diffusion coefficients graphically via Boltzmann-Matano analysis. The Cr-coated samples were analyzed via thermogravimetric analysis at 700 °C and 900 °C for up to 100 h in dry synthetic air. Optical and electron microscopy, EPMA, EBSD and XRD were used to investigate the chromium diffusion layers and the oxide scales.