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In this study, a TiNbCrTa refractory complex concentrated alloy (RCCA) was prepared using vacuum arc remelting. The microstructural evolution and mechanical properties of both as-cast and heat-treated RCCA samples were analyzed. Heat treatment (HT) was performed at 800–1200 °C for 1 h in a vacuum-sealed environment. These samples exhibited a formation of Cr2Nb and Cr2Ti Laves phases. A variation in elemental distribution was observed, with interdendritic (ID) regions showing higher fractions of Ti and Cr, while the dendritic regions had a greater concentration of Ta and Nb. Micro-segregation at the IDs was confirmed through energy dispersive x-ray spectroscopy mapping, which inferred the formation of Cr- and Ti-rich phases during HT at 800–1200 °C. High-temperature HT at 1200 °C for 1 h led to the evolution of the hcp omega phase. Prolonged HT at 1200 °C for 96 h resulted in the evolution of a Cr-rich Laves phase (Cr2Ta), which was homogeneously distributed within the microstructure, indicating an unstable microstructure. Furthermore, despite prolonged HT, a variation in the elemental distribution persisted due to the presence of dendritic and ID regions. Electron backscattered diffraction analysis revealed the presence of bcc and hcp phases in the dendritic and ID regions, respectively, of the as-cast and HTed samples. The as-cast samples demonstrated a high compressive strength of approximately 2 GPa. Micro-hardness values increased with the HT temperature up to 1000 °C. Further increases under HT conditions did not significantly reduce the microhardness value, whereas prolonged HT at 1200 °C led to an increase in the microhardness value. Overall, the newly developed TiNbCrTa RCCA exhibited high-strength behavior even after the phase transformation. [ABSTRACT FROM AUTHOR]

Conventional molecular dynamics (MD) simulations struggle when simulating particles with steeply varying interaction potentials due to the need to use a very short time step. Here, we demonstrate that an event-driven Monte Carlo (EDMC) approach was first introduced by Peters and de With [Phys. Rev. E 85, 026703 (2012)] and represents an excellent substitute for MD in the canonical ensemble. In addition to correctly reproducing the static thermodynamic properties of the system, the EDMC method closely mimics the dynamics of systems of particles interacting via the steeply repulsive Weeks–Chandler–Andersen (WCA) potential. In comparison to time-driven MD simulations, EDMC runs faster by over an order of magnitude at sufficiently low temperatures. Moreover, the lack of a finite time step in EDMC circumvents the need to trade accuracy against the simulation speed associated with the choice of time step in MD. We showcase the usefulness of this model to explore the phase behavior of the WCA model at extremely low temperatures and to demonstrate that spontaneous nucleation and growth of the Laves phases are possible at temperatures significantly lower than previously reported. [ABSTRACT FROM AUTHOR]

The article presents the study of the magnetocaloric effect (MCE) for the rhombohedral Laves phase of Pr 2 Rh 3 Ge, which shows a magnetic order below T C = 8.5 K. We have established that the compound exhibits a continuous second-order type of transition which was demonstrated and confirmed by several different techniques, mainly by analyzing universal curves of normalized entropy change as a function of scaled temperature. The observed MCE, in our opinion, is a consequence of an indirect exchange coupling between the magnetic sublattices of the rare earth ions, which, however, does not exclude the potential contribution of sublattice-containing transition metals. In this paper, the procedure to evaluate the MCE from magnetization and specific heat data is described. As a result, important parameters such as the isothermal magnetic entropy change (Δ S M), adiabatic temperature change (Δ T a d ), relative cooling power (RCP), and the temperature averaged entropy change (TEC) were determined. The highest values of − Δ S M , Δ T a d , and RCP for a field change (Δ μ 0 H) of 5 T at T C are 5.96 J/kg K, 3.87 K, and 72.62 J/kg, respectively. These results obtained for Pr 2 Rh 3 Ge seem to be, however, low compared to the values obtained for the rhombohedral Laves phases, belonging to the group of ternary germanides RE 2 Rh 3 Ge containing heavy rare earth metals (RE = Gd, Tb, Ho, and Er). Nevertheless, we believe that the results presented in this work extend and complement the current knowledge on the magnetocaloric properties of this family of materials. [ABSTRACT FROM AUTHOR]

AbstractA laser cladding technique was employed to produce a Fe50-XMn30Co10Cr10NbX (X = 2.5, 5, 7.5, 10at%) high entropy alloy coating. This study delved into the influence of Nb concentration on the coating’s phase constitution, microstructural features, hardness, and wear resistance. The high entropy alloy coating exhibited a multifaceted structural composition, encompassing FCC (Face-Centered Cubic), HCP (Hexagonal Close-Packed), and BCC (Body-Centered Cubic) structures, along with the presence of Laves phase. Notably, the incorporation of Nb led to an augmentation in the Laves phase and modifications within the microstructure. The hardness of the cladding layer is higher than that of the substrate. With the increase of Nb content, the hardness of the cladding layer increases first and then decreases; the average hardness of the Fe42.5Mn30Co10Cr10Nb7.5 cladding layer is the highest, the maximum hardness is 429.8Hv, and the average hardness is 382.3Hv. The friction coefficient and weight loss of the cladding layer decreases first and then increases with the increase of Nb content. The friction coefficient and weight loss of the Fe42.5Mn30Co10Cr10Nb7.5 cladding layer are the smallest, which are 0.0132 g and 0.5974, showing the best wear resistance. The wear types of high entropy alloy cladding layer are both adhesive wear and abrasive wear. The addition of Nb into high entropy alloy will form the Laves phase, which can improve the mechanical properties of high entropy alloy. [ABSTRACT FROM AUTHOR]

Emergent phases often appear when the electronic kinetic energy is comparable to the Coulomb interactions. One approach to seek material systems as hosts of such emergent phases is to realize localization of electronic wavefunctions due to the geometric frustration inherent in the crystal structure, resulting in flat electronic bands. Recently, such efforts have found a wide range of exotic phases in the two-dimensional kagome lattice, including magnetic order, time-reversal symmetry breaking charge order, nematicity, and superconductivity. However, the interlayer coupling of the kagome layers disrupts the destructive interference needed to completely quench the kinetic energy. Here we demonstrate that an interwoven kagome network—a pyrochlore lattice—can host a three dimensional (3D) localization of electron wavefunctions. Meanwhile, the nonsymmorphic symmetry of the pyrochlore lattice guarantees all band crossings at the Brillouin zone X point to be 3D gapless Dirac points, which was predicted theoretically but never yet observed experimentally. Through a combination of angle-resolved photoemission spectroscopy, fundamental lattice model and density functional theory calculations, we investigate the novel electronic structure of a Laves phase superconductor with a pyrochlore sublattice, CeRu2. We observe evidence of flat bands originating from the Ce 4f orbitals as well as flat bands from the 3D destructive interference of the Ru 4d orbitals. We further observe the nonsymmorphic symmetry-protected 3D gapless Dirac cone at the X point. Our work establishes the pyrochlore structure as a promising lattice platform to realize and tune novel emergent phases intertwining topology and many-body interactions. [ABSTRACT FROM AUTHOR]

In practical applications, intermetallic compounds like Laves phase and metal carbides adversely affect the performance of nickel‐based superalloys. Using a high‐temperature confocal laser scanning microscope, the solidification process of as‐cast GH3625 alloy containing Mg at different cooling rates (−20, −35, and −50 °C min−1) is studied. Fitting curves of the volume fraction of the solid phase with solidification temperature before and after Mg treatment are obtained. Trends of solid phase transformation rates with solidification temperature are determined. Differential scanning calorimetry is employed to analyze and statistically evaluate the melting temperature range and enthalpy of each phase during the melting process. Experimental results demonstrate that Mg treatment significantly accelerates the alloy solidification at the cooling rates of −20 and −35 °C min−1, while reducing the area of residual liquid phase at the same solidification temperature, disrupting the Laves/NbC eutectic relationship, and regularizing NbC morphology, transitioning its distribution from aggregation to dispersion. After Mg treatment, the precipitation of the Laves phase is significantly reduced. As a result, the influence mechanism of Mg treatment on the phase transformation and microstructure of GH3625 is clarified based on homogeneous nucleation theory. [ABSTRACT FROM AUTHOR]

In this study, we conducted two heat treatment processes, namely double aging (DA) and solid solution followed by double aging (SA), on the Inconel 718 alloy fabricated by selective laser melting (SLM). The aim was to investigate the microstructure evolution and mechanical properties of Inconel 718 under different heat treatment conditions. To achieve this, we employed advanced techniques such as Scanning Electron Microscope (SEM), electron backscattered diffraction (EBSD), energy dispersive spectroscopy (EDS), x-ray diffraction (XRD), Tofwerk time-of-flight secondary ion mass spectrometer (TOF-SIMS), and transmission electron microscopy (TEM). Our experimental findings reveal the presence of cellular high-density dislocation substructures in the as-received (AR) specimens, with a significant accumulation of Laves phase precipitates at grain boundaries and subgrain boundaries. After the DA treatment, the cellular substructure persists, with higher concentrations of γ" and γ' strengthened phases compared to AR specimen. Conversely, the SA specimen undergoes almost complete recrystallization, resulting in the dissolution of brittle Laves phases and a substantial increase in the content of strengthening phase γ" and γ'. As a consequence of the precipitation of the γ" and γ' strengthened phase and the modification of the microstructure, the material exhibits enhanced strength and hardness, albeit at the expense of reduced plasticity. The investigation of the relationship between heat treatment processes and precipitation behavior indicates that the SA heat treatment yields favorable mechanical properties that strike a balance between strength and plasticity. [ABSTRACT FROM AUTHOR]

FeCrAl alloy is considered a promising material for light water reactor fuel cladding due to its excellent elevated temperature oxidation resistance and radiation performance. The effects of 0.21 wt% Nb or 0.23 wt% La additions on the microstructure, second phase, yield strength and toughness of FeCrAl alloy are studied. The morphology and number fraction of inclusions in FeCrAl alloys are analyzed. The addition of 0.21 wt% Nb in FeCrAl alloy promotes the precipitation of nanoscale (Fe,Cr)2(Nb,Ti) Laves phase and refining grain size. The addition of La‐modified Al2O3 and MgO·Al2O3 inclusions to La2O3 and LaS, and La2O3 is favorable to promote the heterogeneous nucleation of α‐Fe. The fracture mode of the FeCrAl alloy with 0.21 wt% Nb or 0.23 wt% La transitions from dimple fracture and quasi‐cleavage fracture to dimple fracture, in comparison with Nb‐free or La‐free FeCrAl alloy. Nb and La additions improve the yield strength and toughness of FeCrAl alloy. The addition of Nb exhibits a more pronounced strengthening effect on FeCrAl alloy compared with the addition of La. [ABSTRACT FROM AUTHOR]

This work deals with the effects of two individual isothermal aging experiments (450 °C/5000 h and 700 °C/2500 h) and the subsequent room-temperature electrolytic hydrogen charging of TP316H stainless steel on its Charpy V-notch (CVN) impact toughness and fracture behavior at room temperature. Microstructural analyses revealed that aging at 700 °C resulted in the abundant precipitation of intermediary phases, namely, the Cr23C6-based carbide phase and Fe2Mo-based Laves phase, whereas aging at 450 °C resulted in much less pronounced precipitation of mostly intergranular Cr23C6-based carbides. The matrix phase of 700 °C-aged material was completely formed of austenitic solid solution with a face-centered cubic (FCC) crystal structure, whereas an additional formation of ferritic phase with a base-centered cubic (BCC) structure was detected in 450 °C-aged material. The performed microstructure observations correlated well with the obtained values of CVN impact toughness, i.e., a sharp drop in the impact toughness was observed in the material aged at 700 °C, whereas negligible property changes were observed in the material aged at 450 °C. The initial, solution-annealed (precipitation-free) TP316H material exhibited a notable hydrogen toughening effect after hydrogen charging, which has been attributed to the hydrogen-enhanced twinning-induced plasticity (TWIP) deformation mechanism of the austenitic solid solution. In contrast, both aging expositions resulted in significantly lowered hydrogen embrittlement resistance, which was likely caused by hydrogen trapping effects at the precipitate/matrix interfaces in thermally aged materials, leading to a reduced TWIP effect in the austenitic phase. [ABSTRACT FROM AUTHOR]

The solid solution design strategy bolsters the comprehensive mechanical properties of high/medium entropy alloys (H/MEAs), yet its utilisation within hexagonal close-packed (HCP) H/MEAs remains notably limited. Here, exploring the impact of reduced Cr content (x = 0.3, 0.1, and 0) from the HfZrTiCr0.5 prototype alloy, our study successfully obtained a novel HCP single phase MEA and investigated the relationship between microstructure and mechanical properties. Decreasing Cr content led to the diminishing presence of the Laves phase, culminating in a single HCP phase solid solution at x = 0.1. The Laves phase, arising from negative enthalpy between Cr and other elements and lower atomic radius of Cr, acted as crack initiation sites, resulting in brittle fracture (x = 0.5) alloy and limited plasticity strain of 3.5% (x = 0.3). Conversely, the HfZrTiCr0.1 alloy exhibited impressive combined yield strength (1360 MPa) and plasticity strain (14.5%), attributed to prominent solid solution strengthening and enhanced dislocation movement within the solid solution structure. These findings offer insights into manipulating Cr content to form HCP solid solution structures, potentially broadening solid solution alloy design strategies for superior mechanical properties in HCP H/MEAs. [ABSTRACT FROM AUTHOR]

Precipitation behavior and mechanical properties of a silicon (Si) micro-alloying Ni-based alloy, considered as important structural materials in turbine, were investigated during exposure at 700 °C for up to 5000 h. Results reveal that the primary precipitates of solution-annealed Si micro-alloying alloys are MC carbide and Laves phase, but only MC carbide appears in alloy without Si addition. MC carbide decreases and Laves phase increases with increasing Si content. During thermal exposure at 700 °C, γ′′, δ, M6C and M23C6 precipitate and the major precipitate changes from γ′′ to δ and then to M6C with increasing Si content. Moreover, Si suppresses the formation of film-like M23C6 carbide at grain boundary. Compared with solution-annealed alloys, the yield strength increases drastically after exposure at 700 °C. Moreover, with increasing Si content, the tensile properties almost keep at the same level when Si content is less than 1.0 wt.%. This indicates that γ′′, δ and M6C all have excellent strengthening effect in the present alloy. However, adding 1.5 wt.% Si significantly deteriorates the performance due to M6C coarsening and the formation of the cluster of blocky Laves phase. The strengthening effect of M6C has significant size effect. Consequently, it can be concluded that adding Si can efficiently improve castability and enhance steam oxidation resistance, and meanwhile keep excellent mechanical properties by controlling Si content. [ABSTRACT FROM AUTHOR]

Nickel-based superalloy Inconel 718 was prepared by selective laser melting and carbon element invasion was unexpectedly generated. In this work, the microstructural evolution, phase transformation and mechanical properties variations in the As-built state and after four conventional heat treatments (SHT + Age, SHT, Age, SR), as well as the effect of carbon intrusion, were studied. The results showed that the brittle phase Laves increased due to poor printing, and all the Laves phases were reduced and eliminated after heat treatment. The Laves phases generated the δ phase in the near areas and the γ ′ / γ ″ phase in the relatively distant areas due to diffusion effect. However, the NbC phase could not be eliminated after heat treatment and remains at the grain boundaries. Age heat treatment produces a special Laves phases, ductile network Laves phase. The intrusion of carbon element was observed by XRD and EDS. The diffused C element captures the Nb element, robbing the element of the main strengthening phase γ ″ and causing the reduction of ultimate tensile strength, yield strength and microhardness of SHT (538 Mpa, 307 Mpa, 286 HV), SR (739 Mpa, 454 Mpa, 241 HV) and SHT + Age (1051 Mpa, 903 Mpa, 485 HV) under high-temperature treatment than As-built (786 Mpa, 510 Mpa, 322 HV). Under lower temperatures on Age (1097 Mpa, 863 Mpa, 479 HV), the effect of carbon intrusion is not obvious. However, the solid solution strengthening and interstitial strengthening of carbon element greatly increase the ductility of SHT (8.54%) and SR (12.12%). [ABSTRACT FROM AUTHOR]

In this paper, compositions within the TiZrAlCrMn, TiZrAlCrFe, and TiZrAlMnFe alloy systems that form the C14 Laves phase are investigated. The design, synthesis, structural, and hydrogen storage characterizations for an equiatomic and a non‐equiatomic composition for each alloy system are presented. Additionally, the further development of a thermodynamic method for the calculation of pressure‐composition‐isotherms (PCIs) is presented of C14 Laves phase alloys that absorb hydrogen by solid solution. Overall, the results shown in this paper indicate that Al‐containing multicomponent alloys can present promising hydrogen storage performance under high pressures. Nonetheless, high concentrations of aluminum in highly concentrated (equiatomic) alloys can have a negative impact on the hydrogenation properties. The Ti0.29Zr0.05Al0.05Cr0.26Mn0.35 composition showed promising hydrogenation/dehydrogenation properties. The gravimetric capacity of this alloy is ≈1.76 wt.% H2 and the PCIs measured indicate that this material has potential for high‐pressure hydrogen storage and compression applications. The use of the presented thermodynamic model for the design of multicomponent alloys is suggested. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of Ti content on the microstructure, mechanical and damping properties of FeCoNi-based multi-principal element alloys. A series of as-cast (FeCoNi)100-xTix medium-entropy alloys with different Ti contents were prepared using electric arc melting. The results show that the composition of (FeCoNi)100-xTix medium-entropy alloy appears sequentially with increase in Ti contents as a single-phase FCC solid solution phase (γ), L12-(Ni, Co)3Ti precipitated phase (γ'), HCP-structured Widmanstätten laths structure and HCP-Fe2Ti-Laves phase. The strength of these alloys decreases after an initial rise due to an increase in the volume fraction of precipitated phases, the Widmanstätten laths structure and the Laves phases, while the ductility generally decreases. Among all samples, the (FeCoNi)95Ti5 alloy has balanced strength and ductility (tensile strength: ~ 840 MPa, elongation: ~ 25%) as well as good damping properties (Q−1: ~ 0.04). This work provides rich data for the study of the formation of multiple phases and their mechanisms of action. [ABSTRACT FROM AUTHOR]

The corrosion behavior of unaged and thermally aged Ni–25Cr–10Fe–3Si–xMo (x = 0, 3 wt%) alloys was studied beneath KCl–ZnCl2 deposits at 650°C. The results indicated that the addition of Mo promoted the formation of a continuous Si‐rich protective layer and improved the corrosion performance of the unaged Ni–25Cr–10Fe–3Si–xMo alloys. The precipitates formed after long‐term aging greatly affect the corrosion resistance of the thermally aged alloys. The M23C6 along the grain boundaries is beneficial to improve corrosion resistance, however, the dispersed Laves phase and Sigma deteriorate corrosion resistance. [ABSTRACT FROM AUTHOR]

The fusion zone microstructures in K-TIG-welded and post-weld solution heat-treated new superalloy VDM Alloy 780 were examined. In addition, the kinetics of the base metal grain growth during solution heat treatments were analyzed. (S)TEM analyses show that major interdendritic microconstituents formed in the fusion zone due to elemental microsegregation are MC carbides and coarse irregularly shaped Laves phase. Additionally, minor secondary interdendritic phases are found to include γ′, γ″, and tiny plate-like Laves particles. To prevent any potential deterioration of mechanical properties caused by the irregular Laves phase, post-weld solution heat treatments (PWSHTs) at 954 °C to 1060 °C/1 hours were performed to remove the Laves phase. PWSHT at 954 °C only partially eliminates the Laves particles while forming an abundance of interdendritic δ/η phase. Laves phase is dissolved entirely without forming δ/η platelets after PWSHT at 1060 °C. It is proven that Laves eutectics in VDM Alloy 780's fusion zone can be eliminated through PWSHT without significantly coarsening the base metal's grain size in comparison to Alloy 718 as a result of substantial grain growth inhibition likely caused by solute segregation at grain boundaries. [ABSTRACT FROM AUTHOR]

Laves phase-reinforced high-entropy alloys (HEAs) have drawn widespread interest due to their excellent mechanical performance at room/elevated temperatures. In this work, we prepare a few (AlCoCrFeNi)100-xTax (x = 0, 2, 4 and 6) HEAs and assess the effect of Ta on their microstructure and mechanical properties. With increasing Ta addition, their microstructures of the HEAs evolve from a fully body-centered cubic (BCC) microstructure to a hypoeutectic microstructure (primary BCC + eutectic phase). The volume fraction of the Laves phase increases with increasing Ta addition. The strengthening mechanisms of these HEAs are precipitation strengthening and solid solution strengthening. According to an assessment of the contributions of the two strengthening mechanisms, precipitation strengthening dominates the total strength. Moreover, Ta addition cannot transform the fracture mechanisms of these HEAs, which all exhibit brittle fracture. [ABSTRACT FROM AUTHOR]

The microstructure and impact toughness evolution of G115 steel after long-term (ranging from 500 h to 10,000 h) aging at 700 °C were investigated in this study. The results showed that the microstructure of the G115 steel evolved from a finer-grained matrix with minor precipitates to a coarse-grained matrix with more precipitate with aging time, presenting a decrease in the local deformation degree in the matrix. The impact toughness of the steel decreased with aging time, presenting the largest decline at the initial aging times. The decrease in impact toughness was attributed to the coarsening of precipitates (M23C6 and Laves phase) in the steel matrix. The stable impact toughness during the whole aging process (from 500 h to 10,000 h) should be related to the comprehensive effects, including the precipitation of the Laves phase, the increase in high-angle grain boundaries, and the softening of the metal matrix. [ABSTRACT FROM AUTHOR]

In this work, wire arc additive manufactured (WAAM-ed) Inconel 617- and 625-wmo grade alloys are characterized in detail for the type and distribution of precipitates in as-built and heat-treated conditions. The analyses are carried out near (~1 mm) and away (~10 mm) from the substrate along the build direction to investigate the effect of the substrate on the nature of precipitate formation. For each analysis location, morphological and chemical information of at least 400 precipitate features was identified and classified using stoichiometric analysis of SEM-EDS data combined with feature analytics. Carbides and carbonitrides are present in both Inconel 600 series alloys but Laves phase precipitates are identified only in the case of Inconel 625 wmo alloy. It is observed that the nature of precipitates size distribution is not altered significantly when compared between the two analysed locations for a particular grade. Furthermore, Laves phase precipitates closer to the substrate (1 mm) are richer in iron because of the effect of mild steel substrate on precipitation characteristics in Inconel 625 alloy. Our novel characterization approach will pave the way for comparing the microstructures of additively manufactured samples printed using different process parameters and variations. [ABSTRACT FROM AUTHOR]

CoCrCuFeMnNix (x = 0 mol, 0.5 mol, 1.0 mol, 1.5 mol, and 2.0 mol, named Ni0, Ni0.5, Ni1.0, Ni1.5, and Ni2.0, respectively) high-entropy alloys (HEAs) were prepared using vacuum hot pressing sintering. The atmospheric oxidation behavior of the alloys was studied using a constant-temperature oxidation discontinuous weighing method. The kinetic curve of the alloys after oxidation at 800°C for 50 h follows a parabolic law. A high Ni content corresponds to a small oxidation weight gain of the alloy. After 50 h of oxidation, the oxidation weight gain and oxidation rate constant Kp value of Ni2.0 alloy are the smallest at 3.03 mg/cm2 and 6.59 × 10−12 g2 cm−4 s−1, respectively. The outer oxide layer of the alloys is composed of loose and porous Mn-containing oxides (Mn4O3 or Mn3O2), and the dense layer is composed of continuous and dense Cr2O3. The increase in Ni content promotes the formation of NiCr2O4 oxides with a spinel structure, inhibits the formation of porous MnO, improves the thermal stability of FCC phase, and weakens the volatilization of Cr2O3, thereby improving the oxidation resistance of HEAs. The oxidation mechanism of the alloys is mainly selective oxidation, which involves the outward diffusion of metal cations and the inward permeation of oxygen ions. [ABSTRACT FROM AUTHOR]

The microstructure and eutectic precipitates in a novel 15Cr–30Ni–2Ti–3Cu valve alloy produced by electroslag remelting, and the evolution of eutectic precipitates and dissolution kinetics of Laves phase during homogenization were studied. The microhardness of the valve alloy reaches a value of 247.8 HV after the homogenization at 1273 K (1000 °C)/6 hours + 1413 K (1140 °C)/5.5 hours, and the hardness uniformity reaches a maximum after the homogenization at 1223 K (950 °C)/6 hours + 1413 K (1140 °C)/5.5 hours. The secondary dendrite arm spacing in the as-cast ingot is 48.75 μm, and the area fractions of Fe2Ti Laves phase, (Ti,Nb)C, Sigma phase and γ′-Ni3(Ti,Al) phase are 2.83, 0.92, 0.09 and 0.01 pct, respectively. The Laves phase dissolved obviously even at the lowest homogenization temperature 1223 K (950 °C). The eutectic (Ti,Nb)C phase begins to dissolve at 1223 K (950 °C), and the dissolution degree is much lower than that of Laves phase. The homogenization degree of alloying elements after single-stage homogenization is much lower than that of dual-stage homogenization. The dissolution kinetics of Laves phase established based on the Johnson-Mehl-Avrami-Kolmogorov model shows that the activation energy of Laves phase in alloy is 275.8 kJ/mol. The reverse diffusion of Mo from Laves phase into matrix is the determining step of Fe2Ti Laves phase dissolution. [ABSTRACT FROM AUTHOR]

This study investigated the temperature dependence of IN718 corrosion behavior in 3.5 wt. % NaCl solution, comparing conventionally rolled (Roll) and SLM-manufactured (SLM) samples. While both exhibited degradation with increasing temperature, the Roll sample presented a significantly higher susceptibility to corrosion by increasing the temperature from 25 to 70 °C. Rapid corrosion current density (icorr) of the Roll sample, which increased from 0.25 to 1.3 μA cm2, suggested the preferential γ-matrix dissolution and microgalvanic attack triggered by Laves phases and carbides acting as preferential dissolution sites. Conversely, the SLM sample showcased less segregation and fewer carbide phases due to its high cooling rate, resulting in a milder icorr rise (0.45–0.6 μA cm2). The findings hold promise for a more comprehensive understanding of IN718 performance and can guide the selection of optimal fabrication methods for components exposed to corrosive and high-temperature environments. [ABSTRACT FROM AUTHOR]

The effects of heat treatment temperature on the microstructure and mechanical properties of Cu0.3Cr2Fe2Ni3Mn2Nbx high-entropy alloys (HEAs) were studied. Results indicate that in the as-cast state, an Nb0 alloy is composed of a single FCC phase, and a Laves phase gradually forms as Nb content increases. After heat treatment at 800 °C, BCC solid solution phases rich in Cr, Fe, and Mn form in all alloys. The BCC phases in the Nb0.2 and Nb0.4 alloys decompose after heat treatment at 900 and 1000 °C, respectively, and the microhardness of the as-cast Cu0.3Cr2Fe2Ni3Mn2Nbx HEAs increases from 127 to 203 HV with increasing Nb content. After heat treatment, the microhardness of the alloys considerably improves, and the Nb0.4 alloy has the highest microhardness after heat treatment at 800 °C (approximately 346 HV). After heat treatment at 900 and 1000 °C, the microhardness of the three alloys decreases. The yield strength of the as-cast Cu0.3Cr2Fe2Ni3Mn2Nbx HEAs increases with Nb content and shows a trend of first increasing and then decreasing with increasing heat treatment temperature. The strengthening mechanism of the heat-treated alloys is mainly attributed to the second-phase strengthening of the Laves phase and the solid solution strengthening of the BCC phase. [ABSTRACT FROM AUTHOR]

Incorporating strengthening phase with a higher thermal stability than traditional L12-ordered Ni3Al phase offers a promising avenue for developing the next-generation Ni-based superalloys. In this study, a powder metallurgy superalloy featuring addition of high-melting-point δ-Nb3Al was fabricated to investigate the high-temperature oxidation behavior at 900 °C. Heterogeneous and accelerated oxidation resulting from the various phase transition products in the alloy were observed. Notably, the preferential oxidation of δ-Nb3Al to Nb2O5 causes obvious surface bulges and cracks. The matrix and Laves phase form oxide layers containing a discontinuous Al2O3. The oxidation mechanism was elucidated through the formation oxidation diagrams based on Gibbs formation energy and total valence of Al2O3. The low Al content in matrix and the high Nb content in Laves phase were identified to cause the discontinuity of surface Al2O3 layer. Additionally, Nb could impede oxygen diffusion within Al2O3 by reducing oxygen vacancy concentration. The findings will provide optimization guidance for the composition design and oxidation protection of novel δ-Nb3Al-strengthened Ni-based superalloys. [ABSTRACT FROM AUTHOR]

The precipitate dissolution and grain growth during the solution treatment of a newly developed Ce‐containing 15Cr–22Ni–1Nb steel are investigated. The dissolution of eutectic NbC is the result of the elements diffusion along the concentration gradients, and honeycomb (Fe,Cr,Ni,Si)2(Nb,Mo) Laves phase transforms into a more stable Mo2C‐type M2C carbide. As the cerium content is increased from 0 to 0.0630 mass%, the area fraction of eutectic precipitates in forged and solution‐treated 15Cr–22Ni steel is decreased first and then increased. For the steel with 0.0055 mass% cerium content, the substantial reduction in the area fraction of precipitates during hot forging and solution treatment is ascribed to the severe abnormal grain growth. In the case of 15Cr–22Ni steel with 0.0019 and 0.0630 mass% cerium content, the average size of austenite grains after solution treatment is reduced, the multipeak development of grain size distribution is restrained, the range of grain size distribution is narrowed, and the variation coefficient of grain growth, the critical size of abnormally grown grain, and the proportion of abnormally grown grain are all decreased. The variation coefficient of grain growth and the critical size of abnormally grown grain in the steel are increased as the solution time is extended, whereas the proportion of abnormally grown grain presents a general trend of reduction. The established mathematical model of grain growth in the paper can be well applied to predict and control the average size of austenite grains in 15Cr–22Ni steel after solution treatment. [ABSTRACT FROM AUTHOR]

In this work, 52Ti–12V–36Cr + 4 wt% Zr alloy was synthesized at laboratory and large scales for comparative analysis of the hydrogen storage performance. A 5 g and 2 kg BCC solid solution alloy is synthesized by arc melting and induction melting, respectively. Crystal structure investigation revealed that both samples crystallized into a primary BCC phase and a secondary laves phase with no significant difference in the overall XRD pattern. First hydrogenation studies showed the maximum hydrogen storage capacity of arc melted alloy (AM) and induction melted alloys (IM) alloy are 3.5 wt% and 2.9 wt%, respectively, at room temperature under a hydrogen pressure of 20 bar. No visible incubation period was observed in AM alloy, whereas IM alloy showed an incubation period of 32 min with slower kinetics. The appearance of the incubation period and sluggish kinetics can be due to the formation of a passive layer during induction melting that changes the hydrogen sorption properties. The microstructural analysis confirmed the carbon contamination from the induction melting crucible and formation of the TiC phase in the matrix, which was absent in the AM alloy, significantly affecting hydrogen storage capacity. The enthalpy and entropy of 2 kg alloy are −65.84 kJ/mol and 188.92 J/mol-K. [Display omitted] • 52Ti–12V–36Cr + 4 wt% Zr synthesized successfully on a large scale. • Comparison of samples from laboratory-scale arc melting and large-scale induction melting. • Hydrogen storage capacity for the arc melted sample is 3.5 wt%, and the induction melted sample is 2.9 wt%. • Microstructure shows the formation of the Ti–C phase in the induction melted sample. [ABSTRACT FROM AUTHOR]

The cubic C15 CaAl2 Laves phase is an important brittle intermetallic precipitate in ternary Mg–Al–Ca structural alloys. Although knowledge of the mechanical properties of the co-existing phases is essential for the design of improved alloys, the fracture toughness of the C15 CaAl2 intermetallic has not yet been studied experimentally due to limitations posed by macroscale testing of defect-free specimens. Here, miniaturised testing techniques like micropillar splitting and microcantilever bending methods are used to experimentally determine the fracture toughness of the CaAl2 Laves phase. It is found that the toughness value of ~ 1 MPa·√m obtained from pillar splitting with a sharp cube corner geometry is largely insensitive to sample heat treatment, the ion beam used during fabrication, micropillar diameter, and surface orientation. From correlative nanoindentation and electron channelling contrast imaging supported by electron backscatter diffraction, fracture is observed to take place mostly on {011} planes. Atomistic fracture simulations on a model C15 NbCr2 Laves phase showed that the preference of {011} cleavage planes over the more energetically favourable {111} planes is due to lattice trapping and kinetics controlling fracture planes in complex crystal structures, which may provide insights into the experimental results for CaAl2. Using rectangular microcantilever bending tests where the notch plane was misoriented to the closest possible {112} cleavage plane by ~ 8° and the closest {001}, {011}, and {111} planes by > 20°, a toughness of ~ 2 MPa·√m was determined along with the electron microscopy observation of significant deviations of the crack path, demonstrating that preferential crystallographic cleavage planes determine the toughness in this material. Further investigation using pentagonal microcantilevers with precise alignment of the notch with the cleavage planes revealed similar fracture toughness values for different low-index planes. The results presented here are the first detailed experimental study of fracture toughness of the C15 CaAl2 Laves phase and can be understood in terms of crack plane and crack front-dependent fracture toughness. [ABSTRACT FROM AUTHOR]

Theoretical studies on the total energy, and hydrogen absorption thermodynamics on Zr(Cr 0.5 Ni 0.5) 2 intermetallic compound were performed using absorption models on the most stable sites. In the first stage, Density Functional calculations provide the absorption energies corresponding to hydrogen in different environments. From there, 28 hydrogen absorption locations were found and the corresponding absorption energies were specifically determined. Then, with this information, a theoretical approximation based on the concept of local absorption isotherm and Fermi-Dirac statistics was applied to study the thermodynamics of the system. In this case, and due to the absence of lateral interactions, exact expressions of the thermodynamic functions can be derived. The process was monitored by following the surface coverage as a function of the chemical potential (absorption isotherm), the energy and configurational entropy of the adsorbed phase and the differential heat of absorption. Interesting behaviours were observed and discussed in terms of the absorption microscopic properties (energy distribution of the absorption sites). [Display omitted] • Computed DFT absorption sites energies are used to model absorption isotherms. • A statistical model is based on the integral absorption equation formalism. • The main thermodynamic absorption functions are derived in an exact and closed form. • Absorption isotherms, energy and entropy are discussed using binding energies. • Microscopic properties can be obtained from macroscopic experimental measurements. [ABSTRACT FROM AUTHOR]

The as‐cast microstructure, microsegregation of alloying elements, and microstructure evolution during homogenization of the newly designed 15Cr–30Ni–Fe heat‐resistant alloy are studied. Ti, Nb, Si, and Mo segregate at the interdendritic region. The brittle eutectic Laves phase contains Fe, Ti, Ni, Nb, Si, and Mo, which is identified as the Fe2Ti Laves phase. The activation energy for the Fe2Ti Laves phase dissolution is close to the activation energy for Ti diffusion in the γ matrix based on the Johnson–Mehl–Avrami–Kolmogorov analysis. The back‐diffusion of Ti to the γ matrix is the limiting step for the dissolution of Fe2Ti Laves phase. The kinetic equation of homogenization considering lattice parameters and pre‐exponential factor correction is established. After the double‐stage homogenization at 980 °C/10 h + 1140 °C/4 h, the volume fraction of the Laves phase decreases from 5.11% to 0.26%, and the large eutectic Laves phase is completely dissolved. The reduction in the standard deviation of microhardness at different soaking times effectively reflects the gradual decrease in the degree of microsegregation of alloying elements. The average grain size of the alloy after homogenization is 410 ± 63.1 μm, which is beneficial to control the further refinement of grain during the subsequent hot working. [ABSTRACT FROM AUTHOR]

Laser polishing (LP) provides a fast and efficient way of remelting part surfaces manufactured by additive manufacturing to alter both their geometric as well as physical properties. Depending on the laser parameters, remelted surfaces with different properties are achieved, with a majority exhibiting lower surface roughness compared to the original surface. In this study, a high-power continuous fiber laser is used to polish Inconel 718 (IN718) surfaces produced by depositing a single layer of clads on a steel substrate by the powder-blown directed energy deposition (DED) process. Polishing was performed under different sets of parameters, namely, laser power, beam diameter, feed rate or feed, hatch spacing, and the number of polishing passes. Their effects on the surface roughness profiles and the microstructural properties of the sample cross section were analyzed after one and two polishing passes. Optical microscopic images of the sample's cross sections show the presence of supersaturated γ γ' + γ" phase particles, precipitates, Laves phases, and δ phase needles. The combined effect of high-temperature gradients and lower solidification rates in certain regions within the cross section results in undercooled regions and pseudo-heat treatment of unmelted regions close to the undercooled regions. These results are corroborated by indenting the various regions of the IN718 sample cross section with a pyramidal diamond indenter in the form of a grid, resulting in different micro-hardness values due to different densities of precipitate and phase transformed particles. [ABSTRACT FROM AUTHOR]

We here use density functional theory and the creation-relaxation algorithm to investigate the appearance of polymorphism in α-Fe, driven by irradiation-induced microstructural changes. Local constriction leads to magnetic instability and provides excess energy required for structural phase transformation. Under extreme conditions, α-Fe undergoes local transformations into icosahedral C15 Laves phase with highly close-packed stacking and internal short-range ferromagnetic ordering, antiparallel to the bulk magnetisation. Analysing local magnetic moments and atomic volumes, in conjunction with the magneto-volume relations of different Fe structures, suggests two other alternatives for local phase transformation under irradiation conditions: the double-layer antiferromagnetic γ-Fe and non-magnetic ϵ-Fe. This work predicts the formation of icosahedral C15 Laves phase structure with short-range ferromagnetic order in irradiated α-Fe using dynamic first-principles calculations. This finding suggests potential detection through advanced magnetic-based transmission electron microscopy techniques, with implications for understanding radiation damage in structural materials. [ABSTRACT FROM AUTHOR]

This study reports on the as-cast microstructures of AlCrFeMnV, AlCrFeTiV, and AlCrMnTiV equimolar multi-principal element alloys. Thermodynamic modeling predicts that these alloys solidify as BCC solid solutions, with additional phases forming at lower temperatures. We present the measured densities, the elastic modulus values measured by nanoindentation, and the Vickers microhardness of the alloys. These properties are correlated to the underlying microstructures, as measured by x-ray diffraction, scanning electron microscopy, and atom-probe tomography. The densities of the alloys range from 5.53 to 6.42 × 10 3 kg m − 3 . The elastic modulus of AlCrFeMnV, AlCrFeTiV, and AlCrMnTiV are 211, 194, and 175 GPa, respectively, and their Vickers microhardness values are 3.9, 6.1, and 5.7 GPa, respectively. After arc-melting, AlCrFeMnV and AlCrFeTiV are BCC solid solutions while AlCrMnTiV has two phases: a BCC phase and a minor hexagonal C14 Laves phase that is enriched in V and Cr. [ABSTRACT FROM AUTHOR]

In recent years, high-entropy alloys (HEAs), as a novel class of hydrogen storage materials, have been deemed highly promising due to their extensive compositional tunability and the unique high entropy effects. This study aims to enhance the comprehensive hydrogen storage performance of the TiVNbCr-based HEA by introducing Ni. The effects of Ni addition on the microstructural evolution of the alloy and its impact on activation properties, hydrogen absorption and desorption kinetics, thermodynamics, and cycling performance under the complex physicochemical environment of multiple principal elements was systematically investigated. The findings indicate that Ni addition shortens the activation incubation period of the alloy but more Ni reduces the intrinsic hydrogen absorption kinetics. In the Ti 25 V 30 Nb 10 Cr 33 Ni 2 alloy, a high reversible hydrogen storage capacity of up to 2.2 wt% at room temperature was achieved, surpassing most of the currently reported body-centered cubic (BCC)-structured high-entropy hydrogen storage alloys. Furthermore, the influence of Ni on the alloy's hydrogen desorption kinetics and cycling hydrogenation performance was studied. Results from 110 cycles of testing reveal that the introduction of Ni-induced Laves phases can act to relax stress, thereby reducing strain accumulation during the hydrogen absorption and desorption cycling process. This could provide guidance for the design of high-entropy hydrogen storage alloys with extended cycling lifetimes. • Minor Ni in TiVNbCr alloy boosts reversible H storage to ∼2.21 wt% at 303 K. • More Ni cuts alloy's activation time but lowers H absorption kinetics. • Using precipitates to relax stress suggested for long-life H storage alloy design. [ABSTRACT FROM AUTHOR]

Utilizing a preliminary interatomic potential, this work represents an initial exploration into the thermomechanical behavior of NbCr solid solutions. Specifically, it examines the effect of different amounts of Cr solute, for which information in the literature is limited. The employed interatomic potential was developed according to the embedded atom model (EAM), and was trained on data derived from density functional theory calculations. While the potential demonstrated reasonable accuracy and predictive power when tested, various results highlight deficiencies and encourage further development and training. Mechanical strength, heat capacities, thermal expansion coefficients, and thermal conductivities were found to decrease with Cr content. Elastic coefficients, too, were observed to be strongly dependent on Cr composition. The Pugh embrittlement criterion was not satisfied for any of the compositions and temperatures explored. Gibbs free energy calculations performed on C14, C15, and C36 NbCr 2 allotropes predicted the C36 structure to be the most thermodynamically favorable across all investigated temperatures and it was found that C36 becomes increasingly more stable relative to the other two phases with increased pressure. The inability of this work to accurately capture the stability of the different Laves phases is most likely due to the shortcomings in the developed potential. [ABSTRACT FROM AUTHOR]

Ultrasonic frequency pulse assisted TIG welding (UFP-TIG) experiments were conducted to join Inconel 690 alloy (IN690) by adding Inconel 718 alloy (IN718) as the filler. The effect of the filler on the microstructure, mechanical properties, and ductility dip cracking (DDC) susceptibility of IN690 joints were investigated. The results show that a variety of precipitates, including MC-type carbide and Laves phases, are formed in the weld zone (WZ), which are uniformly dispersed in the interdendritic region and grain boundaries (GBs). The increase in the thickness of the IN718 filler facilitates the precipitation and growth of Laves phases and MC carbides. However, the formation of Laves phases in the WZ exhibits a lower bonding force with the matrix and deteriorates the tensile strength of IN690 joints. Due to the moderate content of Laves phases in the WZ, the IN690 joint with 1.0 mm filler reaches the maximum tensile strength (627 MPa), which is about 96.5% of that of the base metal (BM). The joint with 1.0 mm filler also achieves the highest elongation (35.4%). In addition, the strain-to-fracture tests indicate that the total length of cracks in the joint with the IN718 filler decreases by 66.49% under a 3.8% strain. As a result, the addition of the IN718 filler significantly improves the mechanical properties and DDC resistance of IN690 joints. [ABSTRACT FROM AUTHOR]

The low hardness and poor wear resistance of laser-cladding 316L stainless steel impose significant constraints on its practical applications. In this study, a strategy for strengthening laser-cladding 316L stainless steel with WMoTaNb refractory high-entropy alloy as a reinforcement material is proposed. The results confirm that the coating primarily comprises a body-centered cubic (BCC) Fe-based solid solution, a network-distributed hexagonal Fe2X (X = W, Mo, Ta, and Nb) Laves phase, and a diffusely distributed face-centered cubic (FCC) (Ta, Nb)C phase. The Fe-based solid solution distributes along columnar and fine dendrites, while the Laves phase and (Ta, Nb)C phase are in the inter-dendrites. The presence of a significant number of network Laves phases exhibiting high strength and hardness is the primary factor contributing to the enhancement of coating microhardness. The hardness of the composite coating is increased by nearly twice compared to that of the 316L coating, resulting in an improved wear resistance. The present work can shed light on designing and fabricating 316L stainless steel coating with enhanced hardness and wear resistance. [ABSTRACT FROM AUTHOR]

The material design concept of high-entropy alloy (HEA) is proposed for Tribaloy alloys. In this research, three HEAs are created by mixing Co-based T-800 and Ni-based T-700 Tribaloy alloys in different ratios and fabricated via spark plasma sintering (SPS) process. The phase transformation behavior of the mixed powders of T-800 and T-700 is investigated with differential scanning calorimetry (DSC) analysis. The microstructures of the SPS specimens and solidified DSC samples of the created HEAs are studied using SEM and XRD, showing that they consist of fcc Co, Mo, and Ni solid solution with minor hcp Co solid solution, various Laves phase, mainly Co3Mo2Si, CoMoSi, Ni3Mo2Si, Mo2Si, and CrSi2, and complex intermetallic compounds. The hardness and dry-sliding wear resistance of the created SPS HEAs are evaluated and compared with the initial alloys (T-800 and T-700). It is shown that the hardness and wear resistance of T-800 are much higher than that of T-700, which is attributed to the excellent properties of element Co; the created HEAs exhibit better hardness and wear performance than T-700 but worse than T-800. The HEA having an equal mixture ratio of T-800 and T-700, with the largest configurational entropy of 1.58R, performs the best in wear resistance among the HEAs. [ABSTRACT FROM AUTHOR]

This study investigates the potential of nanostructuring the equiatomic high entropy alloy TiVZrNbHf by high-pressure torsion to improve its already promising hydrogen absorption properties. The detailed microstructural analysis of the material after processing demonstrates that a homogenous single-phase nanocrystalline structure can be obtained despite shear band development. Due to the metastable character of many high entropy alloys, this analysis was complemented by investigating the thermal stability of the alloy under both vacuum and hydrogen pressure. For the latter, the material was characterized via in situ X-ray diffraction during hydrogen charging at 500 °C, giving a detailed insight into the phase evolution during initial absorption and subsequent cycling. These experiments evidenced the inherent metastability of TiVZrNbHf, which resulted in its decomposition into a bcc, hcp, and C14 Laves phase under both vacuum and hydrogen atmospheres. Despite decomposition, the material retained its nanocrystalline structure under hydrogen pressure, presumably due to hydride formation, while significant grain growth occurred under vacuum. These findings deepen the understanding of the deformation and hydrogen charging behavior of this promising high entropy alloy, suggesting an approach for engineering such alloys for enhanced stability and performance, particularly in solid-state hydrogen storage applications. [ABSTRACT FROM AUTHOR]

The Cr–Ti system was investigated by several experimental methods and first-principles calculations. The thermodynamic activity of the body-centered cubic solid solution was measured by Knudsen effusion mass spectrometry. The stability of all three polymorphic structures of the Laves phase (C14, C15, and C36) was determined by differential thermal analysis, and the equilibrium tie-lines with the solid solution were obtained by combining results from diffusion couples and equilibrated alloys. The enthalpy of formation of the Laves phases with the corresponding end-members were calculated using density functional theory and the obtained values were integrated in the models. The experimental and computed data available in the literature was reviewed and the binary system was assessed by the Calphad method. The present evaluation results in an improved thermodynamic description, which can describe the experimentally observed activity in a large temperature range. The temperatures of the invariant reactions between the C15 and the C36 phase with the Cr-rich and the Ti-rich bcc solid solution were significantly modified. The difference of the temperature of transformation between the C15 and the C36 polytypes on both sides of the Laves phase is much smaller than reported previously. [ABSTRACT FROM AUTHOR]

• Mg-rich nm-scale precipitates exist in the C36 and the C14 laves phases. • The electrochemical activity (C15>C36>α-SS>C14) accounts in the passive state. • Interconnected C14 laves phases increases the corrosion current density. • Small and dispersed C15 laves phases decrease the corrosion current density. • Interconnected C36 laves phases cause minimal corrosion current densities. The electrochemical corrosion mechanisms of Mg alloys were extensively studied in previous investigations of different chemical compositions, modified surface states and various electrolyte conditions. However, recent research focused on the active state of Mg dissolution, leading to unresolved effects of secondary phases adjacent to a stable α-solid solution passive layer. The present study investigates the fundamental electrochemical corrosion mechanisms of three different Laves phases with varying phase morphologies and phase fractions in the passive state of Mg-Al-Ca alloys. The microstructure was characterized by (transmission-) electron microscopy and synchrotron-based transmission X-ray microscopy. The electrochemical corrosion resistance was determined with a standard three-electrode setup and advanced in-situ flow cell measurements. A new electrochemical activity sequence (C15>C36>α-Mg>C14) was obtained, as a result of a stable passive layer formation on the α-solid solution. Furthermore, nm-scale Mg-rich precipitates were identified within the Laves phases, which tend to inhibit the corrosion kinetics. [Display omitted] [ABSTRACT FROM AUTHOR]

CoCrFeNiZr0.3 is a two-phase coexisting (Laves + FCC) high-entropy alloy with high strength, excellent corrosion resistance, and thermal stability. However, the inhomogeneous distribution of the eutectic structure among the dendrites has a detrimental effect on the coordinated deformation of the material. The current study shows that the grain size, weave structure, and second phase distribution of high-entropy alloys can be significantly changed by thermal deformation, which affects the mechanical and physical properties, as well as the chemical stability of the alloys. In this study, the thermal deformation behavior of CoCrFeNiZr0.3 biphasic hypoeutectic high-entropy alloy was investigated using a Gleeble-3500 thermal simulation tester under the conditions of deformation temperature of 950–1100 °C and deformation rate of 0.001–1 s−1. The results show that CoCrFeNiZr0.3 high-entropy alloy has higher deformation activation energy, which means its deformation resistance is larger. In addition, the microstructure with finer grain size and uniform distribution of Laves phase can be obtained by EBSD analysis after compression at 1000 °C and 0.01 s−1. [ABSTRACT FROM AUTHOR]

An alloy based on the Laves phase, which hydrogenated at room temperature, and magnesium powder were used to create the composite material. Using the method of hydrogen dispersion, the alloy was crushed into a powder with a size of 30 μm. Composite materials were obtained by mixing magnesium with a size of 100 μm and the resulting powders from the alloy for 8 h, followed by pressing. This made it possible to obtain a new type of materials for hydrogen batteries, since they cannot be produced by the traditional casting method, because they do not have mutual solubility. [ABSTRACT FROM AUTHOR]

In recent years, multicomponent alloy systems such as high entropy alloys (HEA) have been synthesized by the conventional alloying strategy where all the elements are mixed in equiatomic or near-equiatomic proportions and processed mostly by mechanical alloying, vacuum arc melting or vacuum induction melting and selective laser melting. In this article, we have explored the possibility of sequential alloying strategy where a binary equiatomic mixture is chosen to start the alloy preparation which is followed by mixing of other elements sequentially in subsequent steps maintaining the equiatomic proportions throughout the process using mechanical alloying and vacuum arc melting. Equiatomic CoCrFeMnNiTi alloy has been synthesized in this study using initial equiatomic Fe and Cr and subsequent addition of Co, Ni, Mn and Ti by mechanical alloying as well as vacuum arc melting. During sequential alloying by mechanical alloying, there is the formation of initially FeCr body-centered cubic (BCC) phase, and by subsequent addition of other elements, the phases evolved were FeCrCo-BCC, FeCrCoNi-face-centered cubic (FCC), FeCrCoNiMn-BCC + FCC and FeCrCoNiMnTi-BCC + FCC. Due to vacuum arc melting, there is a marginal change in the evolved phase when sequential alloying was conducted by the addition of Mn (FeCrCoNiMn) and additional NiTi-rich phase for FeCrCoNiMnTi. Sequential alloying has been proven to be a superior technique for the development of multicomponent alloys as the formation of Laves and R phase may be avoided as was observed in equiatomic multicomponent alloy with similar composition (FeCrMnTi and CoCrFeMn) developed by melting and casting. [ABSTRACT FROM AUTHOR]

This work aims to study the influence of heat treatment on the microstructure of laser metal deposited multi-layered Inconel 718 alloy. As-deposited samples were subjected to standard heat treatment, and the resulting microstructure and mechanical properties are studied. When observed under optical microscope and scanning electron microscope, the microstructure revealed microstructural homogenisation. In this case, the grain morphology shows that Nb-rich Laves phase in as-deposited sample is converted to small irregular granules in post heat treatment. The main finding of this study is that after heat treatment, the continuous bands of Nb-rich Laves phase are dissolved into small patches, as observed in elemental mapping through Energy Dispersive Spectroscopy. Also, Nb and Ti are distributed uniformly in the microstructure forming γ´ (Ni3Ti) and γ´´ (Ni3Nb) strengthening precipitates in Ni matrix. The precipitates developed has resulting in 50–60% higher hardness (419 HV) in the heat-treated sample compared to as-deposited sample. [ABSTRACT FROM AUTHOR]

Tribaloy™ T800, a Co-based alloy, exhibits remarkable tribological properties by virtue of its high-volume fraction of intermetallic Laves phase making it an attractive hard-facing material. Hard-facing by laser deposition results in dilution from the substrate, and thereby, the properties of the clad are altered. This paper reports the influence of processing parameters on the dilution, microstructure, and wear behaviour of Tribaloy™ T800 on AISI 316 stainless steel. A systematic set of 20 clads was deposited by varying laser power and cladding speed, keeping powder flow and spot diameter constant. While dilution decreased at lower laser powers (800 and 1000 W) with increasing cladding speed (5–20 mm s−1), at higher laser powers (1200 and 1400 W), the opposite trend was observed. The Fe intermixing from the substrate along with the cooling rate governs the volume fraction and size of the Laves phases which controls the properties of T800 clads. The clad with the least geometric dilution (5.7%) exhibits the lowest wear rate of 0.54 × 10−5 mm3 N−1 m−1, increasing to 2.88 × 10−5 mm3 N−1 m−1 as the dilution increased to 60%. [ABSTRACT FROM AUTHOR]

Due to the recurrent starting and stopping operations of automobiles during service, their engines' hot ends are continually subjected to high-temperature cyclic oxidation. Therefore, it is crucial to develop ferritic stainless steels with better high-temperature oxidation resistance. This study focuses on improving the high-temperature cyclic oxidation performance of 18Cr-Mo (444-type) ferritic stainless steel by alloying with high-melting-point metal W and the rare earth element Ce. For this purpose, a high-temperature cyclic oxidation experiment was designed to simulate the actual service environment and investigate the high-temperature cyclic oxidation behavior and microstructure evolution of 444-type ferritic stainless steel alloyed with W and Ce. The oxide structure and composition formed during this process were analyzed and characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS) and electron probe X-ray micro-analyzer (EPMA), in order to reveal the mechanism of action of W and Ce in the cyclic oxidation process. The results show that 18Cr-Mo ferritic stainless steel alloyed with W and Ce exhibits an excellent resistance to high-temperature cyclic oxidation. The element W can promote the precipitation of the Laves phase between the matrix and the oxide film, and the small-sized Laves phase can inhibit the interfacial diffusion of oxidation reaction elements and prevent the inward growth of the oxide film. The element Ce can refine oxide particles and reduce the thickness of the oxide film. CeO2 particles within the oxide film can serve as nucleation sites for the formation of oxide particles from reactive elements, and they also contribute to pinning the oxide film, thereby enhancing its adhesion. [ABSTRACT FROM AUTHOR]

Microstructure and mechanical properties of P92 steel after 70,000 h service at about 601 °C were investigated, and the normalizing and tempering state P92 steel sample was produced for comparative research. Microstructure changes and carbide precipitation were observed by OM, SEM and TEM + EDS. Tensile properties and impact toughness changes were tested, and the influence of microstructure on the mechanical properties was analyzed. The results showed that microstructure changes were martensite recovery, dislocation density decline and Laves phase precipitation and coarsening during long-term service. Creep damage formed in the service P92 pipe was not very homogeneous along the thickness direction. The creep cavities distributed in the central area of the pipe were more and larger than those in other areas. After 70,000 h service at 601 °C, tensile strength and yield strength at room temperature decreased slightly, but the yield strength at high temperature decreased sharply. The impact toughness was reduced to approximately the min. value of the standard requirement. The re-heat treatment (normalizing + tempering) can recover the hardness, room temperature tensile properties and impact toughness, but cannot completely recover the high temperature tensile properties. [ABSTRACT FROM AUTHOR]

The wrought nickel–chromium–cobalt Nimonic 90 alloy is widely used in turbine blades, piston rings and forged tools due to their high stress-rupture strength and creep resistance up to 920∘C. The application components showed unavoidable wear behaviors at high loads due to the reduced resistance of the components. Hence, in order to increase the wear resistance of this alloy, Inconel 625 and Nimonic 90 particle depositions have been carried out on Nimonic 90 substrate through the laser-cladding techniques to study the microstructure, mechanical and tribological behaviors of alloys. The phases, microstructure and microhardness of the claddings were investigated by X-ray diffractometry (XRD), Transmission electron microscopy (TEM), Scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS) and hardness test, respectively. Results showed that the mean thickness of the interfacial layer of Inconel 625 and Nimonic 90 was 18.51 ± 4 μ m and 90.68 ± 7 μ m, respectively. The microstructure of the cladding surfaces resulted in dendritic and interdendritic structures. An overall analysis found that the gamma-Ni and hard laves phases were presented in Inconel 625 and Nimonic 90 clad surfaces, respectively. Nimonic 90 clad surface had a high hardness and wear resistance compared with Inconel 625 clad surface and substrate due to the present hard laves phase. Besides, the roughness of the Nimonic 90 clad surface was lower compared with the Inconel 625 clad surface and substrate. [ABSTRACT FROM AUTHOR]