Metals and Materials International最新文献

This study examines the impact of short aging treatment on FeMnAlC low-density steel. The intragranular κ carbides exhibit an increase in size and undergo a morphological transformation from nanosphere to lamellar as the short aging temperature rises from 500 ℃ to 900 ℃. The volume fraction peaks at 600 ℃, and at 700 ℃, intergranular κ carbides, accompanied by α-phase precipitation, infiltrate the austenite matrix. Upon surpassing the κ carbide dissolution threshold, further increases in aging temperature result in its dissolution into the matrix. The Rockwell hardness attains a maximum of 38.5 HRC at 700 ℃. The low-temperature impact toughness decreases initially from 31 J at 500 ℃ to below 5 J, then rises to 17.5 J at 900 ℃. This increase is attributed to the presence of excessive intergranular κ carbides, which induce brittle fracture.

The effects of the baking temperature and time on the mechanical properties of Al-Mg-Si alloys laser-arc hybrid welds were investigated. Increasing the baking temperature promoted the precipitation of the nano-sized βʹ, efficiently enhancing the weld seam. Owing to this, the microhardness of the weld seam increased to 96.0 ± 2.4 HV with the high-temperature baking process (220 ℃-0.5 h), leading to a 13% increase in tensile strength. Consequently, the joint coefficient of Al-Mg-Si alloy laser-arc hybrid welded joints reached 0.7, meeting the requirements for automotive industrialization.

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During power generation, the turbine inlet temperature of an industrial gas turbine is increasing continuously. As a high inlet temperature results in changes to microstructure of superalloys along with mechanical degradation, a highly reliable thermal barrier coating is typically developed by doping an additional element on barrier coating. To investigate the effect of such doping on barrier coating and interdiffusion behavior, Al-, Ti-, and Ta-doped NiCoCrAlY bond coat – IN 792 superalloy diffusion couples were fabricated and assessed in an isothermal oxidation test performed at 1000 °C. The results showed that the addition of Al content in the NiCoCrAlY bond coat did not suppress the change in the microstructure of the IN792. The addition of Ti in the bond coat retarded the diffusion of Ti in IN 792 superalloy, while the formation of the γʹ depletion layer of IN 792 superalloy was suppressed; however, the γ phase under the interface was instead depleted, and topologically close packed phase (TCP) phase was formed. Meanwhile, the addition of Ta in the bond coat forms (Ta, Ti)C at the interface. The carbides partially suppress the Ti diffusion of the IN792 superalloys, thus causing a reduction in the γʹ depletion layer. The experimental results indicate that the main factor for microstructure change is the Ti diffusion of IN 792 superalloys. The addition of Ta in the NiCoCrAlY bond coat is expected to improve the lifetime of the turbine blade by suppressing the change in the microstructure of the IN 792 superalloy without the formation of TCP phase.

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In this study, radial pore continuous gradient porous bone scaffolds were designed and optimized based on the Gyroid single-cell structure to meet the demand for high-performance bone implants in bone tissue engineering. Ti–6Al–4V alloy scaffolds with varying single-cell sizes and porosities were fabricated using laser powder bed fusion (PBF-LB) technology for comparative analysis. The findings revealed that the radial pore continuous gradient porous structure exhibited superior mechanical properties and permeability, coupled with a large specific surface area and a helical trajectory for fluid permeation. These features significantly enhanced cell attachment and promoted bone regeneration. The mechanical properties of the scaffolds were further refined, and their toughness was improved through heat treatment of the Ti–6Al–4V alloy. Among the tested designs, the G3-60 scaffold demonstrated the most balanced performance, achieving an elastic modulus of 8.23 GPa, a yield strength of 300.09 MPa, a maximum specific surface area of 3559.362 mm², and a permeability of 2.984 × 10⁻³m² at a flow velocity of 0.1 mm/s. This scaffold not only provides exceptional mechanical load-bearing capacity and permeability but also offers a substantial surface area to support osteoblast attachment and proliferation. These results provide critical theoretical insights and technical guidance for the future design and clinical application of advanced bone implants.

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In this paper, in order to investigate the effect of stress-induced martensitic transformation (SIMT) on the deformation behavior and microstructure evolution of metastable β titanium alloy, the β solution treated Ti-10 V-2Fe-3Al (Ti-1023) alloy was compressed at room temperature and its deformation behavior was analyzed. Optical microscopy (OM) and electron backscatter diffraction (EBSD) were used to study the microstructure evolution of alloys at different strain. The results show that the various deformation mechanisms have been presented in the stress-strain curve and strain hardening rate curve of the Ti-1023 alloy different during the compression deformation, respectively, and the SIMT gradually activated (ε < 5%). There are significant changes in the content and morphology of α″-martensite due to the SIMT and deformation induced martensitic twinning (DIMT) gradually activated with the strain increasing, which the α″-martensite segmented continuously into smaller grain sizes (~ 6 μm) leading to grain refinement strengthening effect. Simultaneously, there is specific orientation relationships (SORs) between β-matrix and α″-variants with < 100 > _β // <100 > _α″, < 110 > _β // <010 > _α″, and < 110 > _β // <001 > _α″. Moreover, the average values of kernel average misorientation (KAM) and geometrically necessary dislocations (GNDs) significantly increased, indicating that the SIMT and DIMT activated continuously with a high volume fraction of α″-martensite would lead to higher dislocation density.

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In this study, five near fully dense (relative densities > 99.75%) Invar 36 samples were fabricated by laser powder bed fusion (LPBF) technology under the constant laser energy density (E_v) of 78.1 J/mm³. The effects of laser power and scanning speed on the thermal expansion behavior of these samples were investigated. The results indicate that under the same E_v, the average coefficient of thermal expansion (CTE) of fabricated sample at 150 W and 600 mm/s is only 0.14 × 10^–6/°C (− 60 ~ 25 °C), 0.37 × 10^–6/°C (25 ~ 100 °C), and 1.58 × 10^–6/°C (25 ~ 200 °C). Its significantly lower CTE values attributes to larger residual stress, which can enhance the spontaneous volume magnetostriction of invar 36 alloy. The lager residual stress is induced by the competitive growth of grains at the overlap of molten pools and inadequate remelting of shallower molten pools. This study provides profound insights into the understanding of the thermal expansion behavior of invar 36 alloys, laying the foundation for the fabrication of high-performance invar 36 alloy components in the future.

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Different Ce contents added to 254SMO super austenitic stainless steel (254SMO-Ce_x) are prepared by vacuum arc melting method, and the solidification structure evolution at a cooling rate of 100 °C min⁻¹ is observed by high-temperature confocal scanning laser microscopy (HT-CSLM). The results show that the dendritic solidification structure of 254SMO-Ce_x is significantly refined and the initial solidification temperature decreases with the increase of Ce contents. The addition of Ce element significantly increases the number of austenite nucleation and changes the types of inclusions in the 254SMO. The inclusions in 254SMO are mainly Al₂O₃ and Ca–Mg–Al–O spherical oxides, and the inclusions in 254SMO-Ce_x are Ce₂O₃, and the number and size of inclusions increase with the increase of Ce contents. In addition, Ce element changes the morphology and precipitation mechanism of sigma (σ) and ferrite (δ) phases. Both δ and σ phases precipitated in 254SMO-Ce_x are formed by a divorced eutectic reaction in the later stage of solidification, and are mainly distributed in the interdendritic position and grain boundary of the crystal, respectively.

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