Metallurgical and Materials Transactions A最新文献

Upon solidification, graphitic cast irons undergo a volume change whose amplitude depends on two opposite terms, the contraction associated with austenite formation and the expansion due to graphite crystallization. During cooling after solidification, further precipitation of graphite occurs that continuously changes the physical properties of the material and possibly affects the eutectoid transformation that transforms the matrix from austenitic to ferritic or ferritic-pearlitic. This work intended to study the density of graphitic cast irons at high temperature, i.e., in the temperature range where the matrix is austenitic. High-temperature laboratory X-rays have been carried out on several alloys containing various carbon and silicon contents to characterize the austenite mean lattice parameter. By complementing these results with literature data, a statistical analysis was carried out that expresses the austenite mean lattice parameter as a function of temperature and composition, evidencing the high uncertainty related to the austenite carbon content. Finally, one of the investigated alloys was submitted to a simultaneous dilatometry and X-ray analysis in a synchrotron from room temperature to 1050 °C. The data are used to discuss the austenite lattice parameter prediction and the possibility of density prediction.

In the present study, the isobaric heat capacity of ultralight magnesium-lithium alloys with composition of 21, 25 and 30 at. pct Li were measured in the temperature range 185–775 K, most measurements were made for the first time. Measurements were performed by the method of differential scanning calorimetry using a DSC 404 F1 setup. The estimated uncertainty of the obtained results was 2–3 pct. The temperature dependences and the tables of recommended data on their basis were developed for scientific and practical application. For all studied Mg-Li alloys an abrupt change in the heat capacity was observed at the temperatures of about 220–260 K, which is apparently caused by the martensitic phase transformation. It was found that the specific molar heat capacity values of Mg-Li alloys containing 21–30 at. pct Li in the temperature interval of 250–685 K practically coincide with each other and can be estimated within the limits of DSC measurement uncertainties using the heat capacity temperature dependence of solid magnesium. It is possible to estimate the heat capacity of the studied alloys (with an accuracy not exceeding the measurement uncertainty) using the Neumann-Kopp rule, but in a much narrower temperature range of 250–456 K.

In this study, the effect of the Fe-rich intermetallic compound phases (IMC) on the solidification cracking susceptibility (Hot Tearing Susceptibility, HTS) of the Al–Mn–Cu alloy and the associated controlling factors were investigated. Using the Al–1.15Mn–1.0Cu–0.5Si–0.08Ti–0.016B–0.15Fe and Al–1.15Mn–1.0Cu–0.5Si–0.08Ti–0.016B–0.4Fe alloys, the HTS and mechanical properties in the partially solidified state were experimentally obtained. As a result, the HTS decreased with the increasing Fe contents. In addition, the tensile strength of the alloys in the partially solidified state (σ_max) increased with the increasing Fe contents. The fraction of solid cohesion considering the Fe-rich IMC phase (f_{sc IMC}) based on the Campbell’s model (f_{sc Campbell}) is proposed as the controlling factor of σ_max. The f_{sc Campbell}, which simulates the two-phases model of the α-Al and liquid phases, did not consistently demonstrate the dependence of σ_max on f_{sc Campbell} for the two alloys (σ_max = f(f_{sc Campbell})). However, when employing the f_{sc IMC}, which incorporates the Fe-rich IMC phase in a three-phases model, a consistent correlation is observed between f_{sc IMC} and σ_max for the two alloys (σ_max = f(f_{sc IMC})). Therefore, it is suggested that the controlling factor influencing the change in σ_max with the Fe content should be the f_{sc IMC}. Additionally, the bonding of primary α-Al phase together with Fe-rich IMC phase that is crystallized at the grain boundary will increase σ_max, contributing to the reduction of HTS.

Squeeze casting is an advanced manufacturing process for aluminum and magnesium alloys, which produces high integrity and heat-treatable cast components. The physics involved in squeeze casting is pressurized solidification and it is important to understand the fundamental knowledge of pressurized solidification and to develop numerical models both at macro- and micro-scales. This review presents the major challenge and novel research dedicated to macro- and micro-modeling on squeeze casting of aluminum and magnesium alloys, including metal displacement and free surface tracking, thermal–mechanical coupled simulation, casting–mold interfacial heat transfer model, shrinkage defect and macrosegregation prediction, pressurized solidification and microstructure modeling, through-process modeling, etc. Finally, the prospects of the macro- and micro-modeling on squeeze casting process are presented.

In this paper, the in situ TaC/Ni composites were prepared by reactive sintering method using Ta, Ni and graphite as raw materials, and their oxidation behavior at 873, 973 and 1073 K in air is investigated by static cyclic oxidation method. The results present that the oxidation behavior of composites conforms to the linear kinetic law. At 873 K, the oxidation of TaC and Ni–Ta matrix generate NiO, Ta₂O₅, TaO₂ and NiTa₂O₆. The oxide scale is consisted by double continuous layers, including the outer NiO and inner Ta₂O₅ layer, due to the diffusion of Ni ion through the oxide ion vacancies in Ta₂O₅. The Oxygen inward diffuse along the interface between TaC and Ni–Ta matrix, and then dissolves in TaC and replaces C sites to generate Ta oxides. At 973 K, more Ta oxides occupy the oxide scale, forming the alternative distribution of NiO and Ta oxides, resulted from the accelerated diffusion of Ta ions. At 1073 K, the oxide scale is mainly taken up by NiTa₂O₆ with slight NiO. The formation reaction of Ta₂O₅ and NiTa₂O₆ shows high Pilling Bedworth ratio near to 2, resulting in the expansion and compressive stress in oxide scale. The oxidation of composites is primarily controlled by the inward diffusion of Oxygen, leading the formation of non-protective oxide scale with pores and cracks on surface. One effective method to improve the oxidation resistance of TaC/Ni composites is to restrict the formation of Ta₂O₅ and NiTa₂O₆, to inhibit the appearance of cracks in oxide scale.

Surface properties of dental implant materials, whether they are physical, chemical, mechanical, or biological, influence the processes of osseointegration and the development of the biological seal at the implant-soft tissue interface. In turn, successful occurrence of these steps prevents peri-implant diseases. This goal can be achieved through the application of surface treatments of a bioactive nature leading to an effective implant-bone union. Our work focuses on a thorough characterization of bioactive surface properties obtained through alkaline treatment on two different surfaces used in the dental implant industry, namely, a surface blasted with calcium phosphate particles and a micro-arc anodized surface. The results show that the alkaline treatment modifies the surface properties of both blasted and anodized samples. Modification is related to the formation of a nanoporous amorphous sodium titanate hydrogel that exhibits high bioactivity in an SBF medium. To assess in vitro biocompatibility and bioactivity, a 48-hour cell culture assay was conducted using dental pulp mesenchymal stem cells. All samples demonstrated cell adhesion, growth, and intercellular communication, indicating that the surfaces are biocompatible and non-cytotoxic. However, samples subjected to alkaline treatment exhibited qualitatively superior bioactivity and in vitro behavior and among them, the blasted sample produced the surface with best performance.

Wide-gap brazing has been widely utilized as one of the go-to alternatives to welding in the repair of turbine components in the aerospace and power generation industries. In this study, differential scanning calorimetry, electron microscopy, and thermodynamic calculations were used to determine the influence of brazing time and temperature on the microstructural evolution for a layered wide-gap brazing process using a MAR-M247/BNi-9 system. Once liquefied, rapid braze infiltration into the MAR-M247 skeleton occurred via capillary action. During infiltration, partial and complete dissolution of the MAR-M247 skeleton occurred, which lead to diffusional solidification at 1068 (^circ )C. Upon further and complete infiltration, it was found that rapid densification was achieved prior to isothermal brazing temperatures. The post-braze microstructure contained (gamma )-Ni matrix grains, precipitated Cr, W, Mo-rich M(_{x})B(_{y}) borides, athermal solidification products along matrix grain boundaries and triple junctions, as well as internal porosity. It was found that brazing temperature dictated the athermal solidification products with binary eutectic (CrB + (gamma )-Ni) at 1150 (^circ )C and ternary eutectic (Cr + (gamma )-Ni + Ni(_{3})B) at 1180 (^circ )C and 1205 (^circ )C. These findings agreed with Scheil–Gulliver predictions. Brazing time influenced the compositional homogeneity of the braze liquid, altering solidification behavior. This resulted in higher and lower solidification ranges for shorter and longer brazing times, respectively. Further, it was found that liquid fraction within the brazement increased with both brazing temperature and time, suggesting a persistent liquid phase. This finding was accompanied by an increase in volume fraction of athermally solidified intermetallics, consistent with an increase in liquid phase with increased brazing time and temperature. Lastly, (gamma )-Ni grain growth occurred, although heterogeneity between the upper and lower regions of the brazement was observed. The upper region displayed larger grains on average when compared to the lower region. This was attributed to boride migration during liquid infiltration, which may have hindered grain growth via a grain boundary pinning mechanism.

The present study investigated a new configuration of friction stir welded joints from two aluminum alloys. Dissimilar welds AA6082/AA1350 were examined, whereas, for AA1350, two states were investigated—coarse-grained (CG) and ultrafine-grained (UFG). Changes in the mechanical and electrochemical properties regarding the microstructure evolution across the welds were discussed. The average grain size in the stir zone (SZ) for all materials equaled 4 to 5 µm with a fraction of high-angle grain boundaries of about 77 pct, indicating the occurrence of continuous dynamic recrystallization. Changes in the microhardness across the welds were connected with differences in grain size (AA1350) and dissolution of β″ precipitates in the SZ of AA6082. As a result, the tensile strength of the welds decreased compared to base materials AA6082 and AA1350 UFG; however, there was an increase when compared to the base material AA1350 CG. Electrochemical experiments revealed that pitting corrosion occurred for AA1350, while for AA6082, it was a combination of pitting and intergranular corrosion. The depth of corrosion attack was higher for AA1350, with a maximum value of ~ 70 µm for base materials, while in the SZ, a depth decreased to 50 µm. For the AA6082, the maximum depth was measured in the SZ and did not exceed 30 µm.

With the push towards sustainable alloy production, using recycled material in casting Al alloys has become essential. However, high recycle content (HRC) aluminum alloys typically have a high iron content, leading to the formation of Fe-bearing intermetallic particles (Fe-IMCs) that affect the mechanical performance and formability of the alloy. Historically, 2D microscopy-based characterization techniques have been used to assess the size and morphology of these Fe-IMCs. While widely used, these 2D techniques are often incapable of capturing the complex 3D interconnected morphologies of the Fe-IMCs. In this work, we present a methodology for the high-throughput compositional and 3D morphological characterization of Fe-IMCs in a primary (AA 5182) and a high recycle content (HRC alloy) in the as-cast and homogenized states, using a combination of 3D X-ray Computed Tomography (XCT) and energy-dispersive X-ray spectroscopy (EDS). To capture the differences in morphology of the Fe-IMCs in the commercial and HRC alloys, we introduce a new 3D morphological descriptor—the particle-to-convex hull volume ratio (p/h). Finally, the effect of homogenization on the Fe-IMCs morphology was tracked using p/h, and a comprehensive analysis of the Fe-IMCs’ compositional and morphological evolution was presented.

This study addresses challenges in elucidating the mechanism of phase transformations occurring in steel of near-peritectic composition. The importance of using and integrating, complementary experimental techniques is emphasized. While thermal analysis tools such as Differential Scanning Calorimetry (DSC) and Differential Thermal Analysis (DTA) are vital, they offer limited insight on events occurring during cooling. Employing standard thermal analysis (DSC) alongside high-temperature microscopy, incorporating simultaneous thermal analysis within a high-temperature microscope, and concentric solidification, two of steels of near-peritectic composition were investigated. Key findings include the correlation between heating rates and completion temperatures of phase transformation in the DSC heating experiments; absence of a peritectic transition inferred from DSC cooling curves supported by visual observation, and insights into restricted austenite phase nucleation attributed to diffusional constraint and limited nucleation sites. This investigation not only contributes to understanding phase transformation behaviour in peritectic steels, but more generally provides a framework for utilizing different techniques synergistically to address complexities in the interpretation of the mechanism of phase development.