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In this work, we apply a multi-scale model combining finite-element method (FEM) and phase-field model (PFM) to simulate the evolution of solidification microstructures at different locations within a molten pool of an additively manufactured IN718 alloy. Specifically, the FEM is used to calculate the shape of molten pool and the relative thermal gradient G at the macroscale. Then, the calculated thermal information is input into PFM for microstructure simulation. Finally, the morphology of solidification structures and formation of Laves phase at different sites are studied and compared. We found that the solidification site with a large angle between the temperature gradient and the preferred crystalline orientation could build up a high niobium (Nb) concentration in the liquid during solidification but has less possibility of forming continuous long chain morphology of Laves phase particles. This finding provides an understanding of the microstructure evolution inside the molten pool of IN718 alloy during solidification. Further, the finding indicates that the site with a large misorientation angle will have a good hot cracking resistance after solidification.

The 50% laser additive manufactured (50%LAMed) tensile samples of Inconel 718 superalloy, i.e., the laser-deposited zone and the substrate zone, occupied 50% volume fraction respectively along the tensile direction, have been fabricated by using laser additive manufacturing (LAM) technology. The inter-dendritic Laves phases were reserved because solution heat treatment could not be used in case of the deteriorating mechanical properties of a forging substrate. Meanwhile, most of the γ″ phases were precipitated in the inter-dendritic area, leading to local stress concentration around the Laves phases in the process of a tensile test. With tensile stress increasing, the degree of deformation and fracture of the Laves phases was closely related to the morphologies of themselves. For the long striped Laves phases, in order to deform with the austenite matrix, they slipped and broke up into small parts. For most of the granular Laves phases, they did not break up and held original morphologies in the process of the tensile test. The broken Laves phases were separated from the γ matrix, and micropores formed at the surface between them. The fracture mechanism was the microvoid coalescence ductile fracture, and the Laves phases were the main nucleuses for the formation of micropores. This study indicates that the mechanical properties of 50%LAMed Inconel 718 can be improved by controlling the morphologies of the Laves phases.

In order to improve the hydrogen storage properties of Laves phase AB2-type alloys, a series of Ti1−xZrxMn1.0Cr0.85Fe0.1 (x = 0.1–0.5) alloys were prepared by arc melting. The effects of Zr content on microstructure and hydrogen storage properties was investigated in detail. Crystal structure characterizations confirmed that all the alloys exhibit a single-phase C14 Laves structure, and the lattice parameters increase with increasing Zr content. The hydrogen storage measurements of the alloys indicate that with increasing Zr content, the hydrogen storage capacity initially increases and then decreases. The hydrogen absorption and desorption measurements of the alloys were performed by a Sieverts-type apparatus. Pressure–composition–temperature (P-C-T) tests at various temperatures showed that all the alloys display sloped plateaus. Increasing Zr content results in a gradual decrease in hydrogen absorption and desorption plateau pressures. Moreover, these alloys exhibit varying degrees of hysteresis, which also becomes more pronounced with a rise in Zr content. In summary, the Ti0.7Zr0.3Mn1.0Cr0.85Fe0.1 alloy demonstrates the best comprehensive hydrogen storage capacity. Further investigation on the cyclic performance of the Ti0.7Zr0.3Mn1.0Cr0.85Fe0.1 alloy was conducted. It was found that the alloy particles undergo significant pulverization after hydrogenation cycles, but the alloy maintained good phase structure stability and hydrogen storage performance.

To investigate the comprehensive effects of the Al and Zr element contents on the microstructure evolution of the AlNbTiVZr series light-weight refractory high entropy alloys (HEAs), five samples were studied. Samples with different compositions were designated Al1.5NbTiVZr, Al1.5NbTiVZr0.5, AlNbTiVZr, AlNbTiVZr0.5, and Al0.5NbTiVZr0.5. The results demonstrated that the actual density of the studied HEA samples ranged from 5.291 to 5.826 g·cm−3. The microstructure of these HEAs contains a solid solution phase with a BCC structure and a Laves phase. The Laves phase was further identified as the ZrAlV intermetallic compound by TEM observations. The microstructure of the AlNbTiVZr series HEAs was affected by both the Al and Zr element contents, whereas the Zr element showed a more dominant effect due to Zr atoms occupying the core position of the ZrAlV Laves phase (C14 structure). Therefore, the as-cast Al0.5NbTiVZr0.5 sample exhibits the best room temperature compression property with a compression strength (σp) of 1783 MPa and an engineering strain of 28.8% due to having the lowest ZrAlV intermetallic compound area fraction (0.7%), as characterized by the EBSD technique.

Microstructure and properties of laser deep penetration welded Inconel 625 nickel-based alloys and SUS304 stainless steel were investigated. Weld microstructures, room temperature tensile properties and stress rupture properties, impact toughness, and hardness of dissimilar welded joints were evaluated. The experimental results showed that the microstructure of fusion zone near the fusion line in the SUS304 side was mainly cellular, whereas that near the fusion line in the Inconel 625 was predominantly columnar dendrites. Laves phases were precipitated at the grain boundary of cellular and in the interdendritic regions of fusion zone in the different form. The white transition layer was generated, and the signification change of concentrations was occurred at the fusion boundary between weld metal and SUS304. The microstructure at the fusion boundary between weld metal and Inconel 625 was characterized by dendritic boundary melting and thickening and accompanied with a lot of Laves phases precipitated in the interdendritic regions. The tensile strength tests indicated that the dissimilar butt joints ruptured in the fusion zone. The toughness of dissimilar weld metal was declined sharply compared to the two base metals. Fractographic analysis revealed that segregation of Nb and Mo in the interdendritic regions deteriorated the tensile strength and toughness of laser dissimilar weld metal. The corrosion resistance of weld metal was higher than that of SUS304 as a considerable amount of Mo elements in the weld metal inhibiting the generation and development of pitting corrosion.

Laves phase binary intermetallics AB2 (A = Ti, Zr; B = Cr, Mn, and Fe) are investigated through hybrid density functional theory (HF-DFT). The calculated structural properties are found consistent with experiments. Cohesive energy (Ecoh), formation enthalpy (ΔH), and elastic properties demonstrated that these compounds are stable in C15 Laves phase. The electronic band profiles and electrical resistivity (ρ) confirmed the metallic nature of these intermetallics and showed that ZrMn2 is a good conductor among the series. The ground state optimized energies (Eo) and magnetic susceptibility (χ) by post-DFT treatment revealed that TiFe2, ZrMn2 and ZrFe2 are ferromagnetic (FM), ZrCr2 is antiferromagnetic (AFM), whereas TiCr2 and TiMn2 are paramagnetic (PM). The elastic parameters show that all these intermetallics are ductile, incompressible, and elastically anisotropic.

In this study, Inconel 718 (IN718) superalloys were fabricated by laser additive manufacturing (LAM) under different laser power. The microstructure and precipitation phase of IN718 superalloys were examined by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectrometer (EDS) methods. The results show that the micropores of the specimens decrease with the increasing laser power. Meanwhile, the morphology of Nb-rich Laves phase changed from skeleton-like to island-like, and the sizes reduced from 10 to below 2 μm. When the laser power of 1200 W is applied, the dense microstructure and the uniformly distributed Laves phase with smallest volume and quantity are observed. The dry sliding test is performed to record the coefficient of friction (CoF) and wear loss of IN718 superalloys, and then the wear surface is detected by a laser scanning confocal microscope (LSCM) and a SEM. The results indicate that the laser power played a crucial role in wear performance of the specimens. At an optimal laser power of 1200 W, a relatively stable friction state and the lowest wear rate of 1.355 × 10 −3  mm 3  N −1  m −1 are obtained during the wear process. Less debris and slighter plastic deformation are detected and the wear mechanism is abrasive wear and adhesive wear.

The influence of austenitizing temperature on the microstructure and mechanical properties of an Fe-Cr-Ni-Mo-Ti maraging stainless steel was investigated. The grain size, Laves phase, and retained austenite in steels given different solution treatments were observed using optical microscopy, scanning electron microscopy, and x-ray diffraction. Relationships with mechanical properties were measured by tensile testing. The grain growth rate was relatively slow at temperatures of 800-1000 °C then rapidly increased at higher temperatures. Low-temperature austenitization augmented the retention of austenite, the fraction of which decreased with an increase in austenitizing temperature. The Laves phases, which precipitated in austenite during austenitization at 800-900 °C, were preserved after quenching. The solution treatment had a significant effect on the final tensile properties of the steel after aging, due to the presence of retained austenite and Laves phase reducing its strength.

The creep deformation and rupture behavior of P92 steel weld joint fabricated by narrow-gap TIG (NG-TIG) welding process have been investigated at 923 K over a stress range of 80-140 MPa. The prior-austenite grain size, M 23 C 6 precipitate size and hardness have been found to vary significantly in the weld joint. The reduction in hardness from weld metal to base metal with a trough at the outer edge of heat-affected zone (HAZ) has been observed. Coarsening of M 23 C 6 precipitate, recovery of martensite lath dislocation structure and formation of subgrain structure led to lower hardness in the intercritical HAZ. The creep rupture life of NG-TIG weld joint was lower than the base metal, the difference in creep rupture life between base metal and weld joint has been increased significantly with decrease in applied stress. The fracture location in the joint changed from base metal at high-stress regime to the fine grain (FG) HAZ (Type IV cracking) under lower stress level. Fracture in the FGHAZ evidenced the significant reduction in ductility, localized deformation and extensive localized cavitation. Extensive Laves phase formation with significant loss of solution strengthening contribution from tungsten and coarsening of M 23 C 6 precipitate with prolonged creep exposure led to reduction in hardness and more extensive cavitation in the FGHAZ resulting in premature Type IV failure of the weld joint. Weld strength reduction factor about 0.59 has been evaluated for 10 5  h at 923 K.

High-performance Ferritic (HiperFer) steels are a novel class of heat-resistant, fully ferritic, Laves phase precipitation hardened materials. In comparison to conventional creep strength-enhanced 9–12 wt.% Cr ferritic–martensitic steels, HiperFer features increased mechanical strength, based on a thermodynamically stable distribution of small (Fe,Cr,Si)2(Nb,W) Laves phase precipitates, and—owing to its increased chromium content of 17 wt.%—improved resistance to steam oxidation, resulting in superior temperature capability up to 650 °C. Previous publications focused on alloying, thermomechanical processing, and basic mechanical property evaluation. The current paper concentrates on the effect of heat treatment on microstructural features, especially Laves phase population, and the resulting creep performance. At 650 °C and a creep stress of 100 MPa, an increase in rupture time of about 100% was achieved in comparison to the solely thermomechanically processed state.