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TiC/Inconel 718 functionally gradient materials are prepared by direct energy deposition technology. The effect of TiC content on microstructure and mechanical properties of TiC/Inconel 718 functionally gradient materials is studied. With the increase of TiC content, the microhardness and carbide grain of the specimen are improved, and the density is reduced. The grain of the specimen changes from columnar dendrites to equiaxed crystal, and the equiaxed crystal size is decreased with the increase of TiC content. However, when TiC content is above 10 wt%, the number and size of the Laves phase, coarse TiC primary, and TiC secondary dendrite are increased which causes the generation of cracks. When the TiC content is above 5 wt%, the size of carbide and the number of cracked UMT increase and the impact toughness decreases. Therefore, the optimal maximum TiC content of TiC/Inconel 718 functionally gradient materials is 5 wt% when the laser power is 2200 W. [ABSTRACT FROM AUTHOR]

FeCrAl alloy is one of potential candidates for accident‐tolerant‐fuel (ATF)‐cladding materials due to its excellent oxidation and corrosion resistance at accident temperature, combining good mechanical properties at service temperature. Alloying strategy is an important way for improving comprehensive properties of FeCrAl alloy through the precipitation of fine Laves phase. Zr alloying can stabilize the Laves phase due to its lower diffusion coefficient and solubility in body‐centered‐cubic ferrite matrix. Herein, it is found that Zr addition changes the dynamic precipitation features of Laves phase in FeCrAl alloy during high‐temperature deformation, from only one type of Fe2M (M = Nb, Mo, Ta) Laves phase to Fe2Zr combining Fe2M‐type Laves phase. The Fe2Zr‐type Laves phase precipitates dynamically first, and the interface precipitates between which with ferrite matrix creates more nucleation sites for subsequent precipitation of Fe2M Laves phase. The results can be possibly applied for alloy design and microstructure tailoring in series of FeCrAl alloys used for ATF cladding in the near future. [ABSTRACT FROM AUTHOR]

TiC/Inconel 718 alloys with different TiC contents are prepared by direct energy deposition technology. The influence of laser power on the microstructure evolution and mechanical properties of the specimens is investigated. According to the microstructure evolution and mechanical properties, it can be observed that the different TiC contents of specimens have the appropriate laser power. The excessive laser power could lead to the generation and coarsening of the Laves phase, and the increasing of dendrite spacing, which causes the formation of cracks. The appropriate laser powers are respectively 1800 and 2000 W when the TiC contents are 5 and 10 wt%. When the TiC content is 15 wt% and laser power is 2000 W, the good metallurgical bond and refined microstructure of the specimens without penetrating cracks are obtained. The penetrating cracks of the specimens have form when TiC content is 20 wt%, which indicates that the TiC maximum content of TiC/Inconel 718 composites should be less than 20 wt% when the laser power does not exceed 2000 W. With the increasing of laser power, the difference of theoretical density between actual density is reduced and the average hardness is not changed. [ABSTRACT FROM AUTHOR]

Multiscale structures, renowned for their remarkable properties, have garnered significant attention due to advancements in design methodologies and manufacturing technologies. In this study, a novel multiscale concurrent topology optimization (MCTO) method is proposed to address the issues associated with the dis-connectivity phenomenon between microstructures and the large number of design variables. To reduce the design variables significantly, the ordered material field series expansion (MFSE) method is adopted to describe the distribution of multiple microstructures. To ensure the continuous transition of different microstructures, a correlation-driven connection (CDC) method is proposed. In this method, adjacent regions between different microstructures arranged in order are combined to form a connected material field, the microstructural connectivity is then driven by the correlation function. Hence, the proposed framework incorporates the feature of the macroscopic interpolation scheme and the spatial correlation defined in the MFSE method to effectively ensure multiple microstructural connectivity without additional optimization constraints. Moreover, the number of design variables is reduced by an order of magnitude, complemented by several accelerated strategies, showcasing improved optimization efficiency. Several benchmark 2D/3D MCTO examples including complex design domains are presented featuring multiple connectable microstructures to demonstrate the effectiveness and efficiency of the proposed method. Compared with other connectivity frameworks and two-stage multiscale topology optimization, the proposed method shows a noteworthy performance enhancement. [ABSTRACT FROM AUTHOR]

To apply the dental Co-Cr-Mo-W alloy restorations fabricated by selective laser melting to clinical use cases, it is necessary to perform a subsequent heat treatment (HT) after SLM processing. However, investigations regarding the effects of HT temperatures on microstructures and mechanical properties inherent in SLM-manufactured Co-Cr-Mo-W alloys are still insufficient. In this article, the microstructure variation during HT at different temperatures and its effect on mechanical properties were systematically investigated and discussed. The Co-Cr-Mo-W dental alloys fabricated by SLM were heat treated at 750 °C, 850 °C, 950 °C, 1050 °C, and 1150 °C for 1 hour and subsequently air cooled. Then, the microstructures were characterized and the mechanical properties evaluated. The results showed that, during HT, Co3(Mo, W)2Si intermetallic compounds with hcp crystal structures precipitated in specimen matrixes and at grain boundaries. With heat treatment temperatures increasing from 750 °C to 950 °C, the number of precipitates gradually increased, and the volume gradually grew. When the temperature increased to ≥ 1050 °C, the number of intermetallic compounds decreased. On the other hand, with increasing HT temperatures, the content of ε-Co phases increased initially but then dropped, reaching a maximum of 97.5 pct at 950 °C and a minimum of 4.4 pct at 1150 °C. Furthermore, there is a coherent relationship between hcp phases (ε-Co) and fcc phases (γ-Co), and the two lattice cells allow the relative orientation of {0001}ε//{111}γ, 〈11-20〉ε //〈110〉γ. Mechanical test results showed that, with increasing HT temperatures, the 0.2 pct yield strength (0.2 pctYS) and ultimate tensile strength (UTS) increased initially and then dropped, reaching a maximum value at 850 °C. Conversely, the ductility decreased initially and then rose, reaching a minimum at 850 °C and 950 °C. The mechanical properties depended primarily on the change of volume fractions of the ε-Co in mixture as well as the size, morphology, and distribution of precipitates. Additionally, specimens heat-treated at 1050 °C for 1 hour were superior to as-SLM (AS) specimens in both strength and ductility. [ABSTRACT FROM AUTHOR]

Two kinds of experimental ferritic/martensitic steels (HT-9) with different Si contents were designed for the fourth-generation advanced nuclear reactor cladding material. The effects of Si content and tempering temperature on microstructural evolution and mechanical properties of these HT-9 steel were studied. The microstructure of experimental steels after quenching and tempering were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM); the mechanical properties were investigated by means of tensile test, Charpy impact test, and hardness test. The microscopic mechanism of how the microstructural evolution influences mechanical properties was also discussed. Both XRD and TEM results showed that no residual austenite was detected after heat treatment. The results of mechanical tests showed that the yield strength, tensile strength, and plasticity of the experimental steels with 0.42% (% in mass) Si are higher than that with 0.19% Si, whereas hardness and toughness did not change much; when tempered at 760 °C, the strength and hardness of the experimental steels decreased slightly compared with those tempered at 710 °C, whereas plasticity and toughness increased. Further analysis showed that after quenching at 1050 °C for 1 h and tempering at 760 °C for 1.5 h, the comprehensive mechanical properties of the 0.42% Si experimental steel are the best compared with other experimental steels. [ABSTRACT FROM AUTHOR]

Surface mechanical attrition treatment (SMAT) was performed on a reduced ferritic/martensitic (RAFM) steel to form a nanostructured (NS) layer on the surface of the sample. Both electron backscatter diffraction (EBSD) and TEM were used to investigate the microstructure evolution during SMAT. The experimental results showed that there were three different zones after SMAT: (i) The "ultrafine grain" (UFG) zone, observed at the top-most surface region, (ii) the "transition zone" in which the original grains were fragmented under the severe plastic deformation and (iii) the "deformed zone" in which the original grains were simply deformed. The average grain sizes increased rapidly with the increase of depth, while the Vickers hardness decreased with the increase of depth, and this phenomenon could be explained in terms of boundary strengthening and dislocation strengthening. The number fractions of medium-angle grain boundaries (MAGBs) and medium-high-angle grain boundaries (MHAGBs) in UFG zones were larger than those in the transition zone and the deformed zone. However, the number fraction of the low-angle grain boundaries (LAGBs) was extremely small in all the zones after SMAT, especially in the transition zone. [ABSTRACT FROM AUTHOR]

The microstructure evolution on the rolling surface of GCr15 steel subjected to rolling-sliding and pure rolling contact loading was systematically investigated. Experimental results showed that the pearlite structure of the surface layer in the rolling-sliding sample transformed into nanocrystalline α-Fe–C alloy in which cementite underwent severe decomposition while the pearlite lamellae appeared unperturbed in the pure rolling sample. A white etching layer (WEL) was also detected in the surface of the rolling-sliding sample. The WEL formation was found to be due to cyclic shear plastic deformation instead of frictional heating. A surface layer of Fe 3 O 4 was detected in the pure rolling samples. Microhardness depth profiles of the rolling-sliding and pure rolling samples also showed different trends. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the effect of arc spraying power on the microstructure and mechanical properties of Zn–Al coatings deposited on carbon fiber reinforced epoxy composites (CFRE composites). The bond strength between the Zn–Al coatings and the substrates was tested on a RGD-5 tensile testing machine. The microstructures and phase composition of the as-sprayed coatings were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results showed that both the melting extent of Zn–Al particles and the bond strength of the coatings were evidently improved by increasing the spraying power. Moreover, the content of crystalline Zn–Al coatings was slightly changed. Observation of fracture surfaces showed that the Zn–Al coatings could bond well with the carbon fiber bundles using 40kW spraying power. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, PbSn coatings were deposited on carbon fiber reinforced epoxy composites (CFRE composites) by means of plasma spraying with four groups of processing parameters (g1, g2, g3 and g4). The microstructure and phase composition of the as-sprayed coatings were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The bonding strength of the coatings to the substrates was detected on a RGD-5 tensile testing machine. It was indicated that high melting extent of the coating, strong bonding between the coatings and the substrate, as well as low porosity could be achieved with the g3 parameters. However, the phase composition and the content of crystalline phases of PbSn coatings varied slightly with different processing parameters. [ABSTRACT FROM AUTHOR]

The Fe-16Cr-2.5Mo damping alloy was microalloyed with different amount of Zr element ranging from 0% to 0.5%. In this study, the effects of the different amount of Zr on the microstructure, mechanical properties and damping property of Fe-16Cr-2.5Mo alloys were investigated. The results suggested that the mean grain sizes of the Fe-16Cr-2.5Mo alloys with 0%, 0.1%, 0.3% and 0.5% Zr addition were 440 μm, 285 μm, 155 μm and 98 μm, respectively. The grain refinement strengthening was caused by Zener pinning and it leaded to improving the strength and elongation of the alloys. In addition, the Fe-16Cr-2.5Mo alloy with 0.1% Zr amount exhibited an impact toughness of 296J, which was much higher than those (<12J) of the alloys with more Zr element or without. On the other hand, Zr (Fe, Cr) 2 or Zr carbide precipitations (>0.5 μm) formed in the alloys notablely, based on the results of TEM and EDX. The large precipitations were apt to establish the cleavage initiation sites, thus damaging the impact toughness of the alloy. The maximum internal friction (Q −1 ) of the alloys fluctuated within 0.016–0.014 with the increase of Zr content at a low strain amplitude (9 × 10 −6 ∼3 × 10 −4 ). However, their damping properties are still marvelous. [ABSTRACT FROM AUTHOR]

Cementite dissolution behavior of pearlitic steels subjected to rolling-sliding contact deformation is comprehensively investigated by combining experimental characterization and phase-field modeling. An elasto-plastic phase-field model, incorporating the elastic strain-induced free energy contribution from first-principles calculations and the plastic counterpart from a rolling-sliding contact finite element model assisted with a plastic strain accumulation model, is originally proposed to simulate the real-time evolution of cementite volume fraction, cementite morphology and carbon distribution for different rolling cycles and contact depths. Upon experimental validations, the proposed model predicts more accurate and realistic results than Sauvage’s model. A three-stage behavior of cementite dissolution is also revealed, which well explains an experimentally observed significant cementite dissolution gradient along the depth direction. Besides, the effect of ferrite/cementite interface thickness and the initial lamellae thickness of cementite on cementite dissolution kinetics is studied. The proposed phase-field model can not only help understand the mechanism of cementite dissolution, but also give new sights into quantitative predictions of the mechanical properties and even the rolling contact fatigue life of pearlitic rail steels in service. [ABSTRACT FROM AUTHOR]

Alumina (Al 2 O 3 ) ceramics were metallized by magnetron sputtering Ti/Mo bilayer films on the surface with a subsequent high temperature sintering and were brazed to Kovar alloy (Fe-Ni-Co) using Ag-Cu eutectic alloy. The Ti/Mo metallization film and the brazing seam microstructures were investigated and the correlation between the Al 2 O 3 /Kovar joining strength and the microstructures of the brazing seam was discussed. The results show that the joining strength is related to the thickness of the Ti/Mo adhension layer which depends on the holding time during brazing. The mutual diffusion of the elements at the interface firstly increases the thickness of the adhension layer as the holding time increases and the Mo film acts as a barrier layer to block the diffusion of Ti atoms into the seam. The optimal brazing joining strength of 72.6±5.0 MPa could be achieved at a brazing temperature of 810 °C for 14 min However, if the holding time is further prolonged, Mo atoms will diffuse into the (Ni, Cu) solid solution, resulting in the diffusion of Ti atoms and the adhension layer becoming indistinguishable. Therefore, the intermetallic Ni 3 Ti forms in the seam and the titanium oxide changes from TiO to Ti 2 O 3 or Ti 3 O 5 , which leads to the joint strength decreasing. [ABSTRACT FROM AUTHOR]

Abstract: The triangle-shape carbon fiber reinforced plastics and the round-shape carbon fiber reinforced plastics were manufactured and the effects of carbon fiber shapes on the flexural properties were investigated. The microstructures and the cross-section areas of the round-shape carbon fiber and the triangle-shape carbon fiber were discussed. As a result, it was found that the triangle-shape carbon fiber reinforced plastics showed higher flexural strength and flexural modulus than round-shape carbon fiber reinforced plastics, and the tensile strength and tensile modulus did not reduced, which was attributed to that the triangle-shape carbon fiber reinforced plastics had larger interfacial contact area than round-shape ones, and the wider interfacial contact area between reinforcement and matrix that could effectively transfer the applied load. The flexural properties of fiber reinforced plastics were improved due to the stronger interfacial binding force. [Copyright &y& Elsevier]

• The dense CrAlN and CrAlSiN coatings with Cr interlayer were deposited on the Zircaloy samples by multi-arc ion plating. • The oxidation resistance of Zircaloy samples in high-temperature steam was effectively improved by surface coating. • The oxidation behaviors and mechanisms of two types of coatings in 1000 °C and 1200 °C steam were studied and discussed. • The distribution and diffusion behaviors of nitrogen bubbles in two types of coatings during oxidation were studied. • The added silicon in the CrAlSiN coating can improve the corrosion resistance but impact the structural integrity of coating. CrAlN and CrAlSiN coatings were deposited on Zircaloy samples by multi-arc ion plating (MAIP) and the microstructure, hardness, and oxidation resistance of the two types of coatings in high-temperature steams were investigated. The coatings can effectively protect the substrate from oxidation during exposure in 1000 °C steam for 2 h and can delay the oxidation of substrate for more than 15 min in 1200 °C steam. Mixed oxide layers formed and suppressed the elemental diffusion during oxidation. Nitrogen bubbles were found inside the mixed oxide. The CrAlSiN coatings showed better oxidation resistance but they cracked more easily. [ABSTRACT FROM AUTHOR]

• The corrosion behavior of SLM and Cast Co-Cr-Mo-W alloy was investigated by electrochemical techniques. • The lower content of precipitates generates a more homogenous structure and improve the corrosion resistance. • The large precipitates act as effective micro-cathode resulting in pitting corrosion and high corrosion rate. In this paper, we investigated the influence of microstructure on corrosion behavior of Selective laser melting (SLM) and Cast Co-Cr-Mo-W alloy by using electrochemical techniques. The passive property and non-corrodibility of SLM Co-Cr-Mo-W alloy were mainly ascribed to the microstructure (content and structure distribution of precipitates). The higher content of precipitates can cause severe microsegregation phenomenon and form an inhomogeneous structure, which is the main reason for the inferior corrosion resistance. In addition, the segregated large precipitates work as effective micro-cathode, resulting pitting corrosion and increased corrosion rate. [ABSTRACT FROM AUTHOR]