Tuning effect of silicon substitution on magnetic and high frequency electromagnetic properties of R2Fe17 and their composites

In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R₂Fe₁₇ compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R₂Fe₁₇ compounds, making the R₂Fe_17–xSi_x-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (f_RL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ ?10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm_1.5Y_0.5Fe₁₅Si₂-paraffin composite (d = 1.0 mm) and the maximum RL of ?53.6 dB is achieved for Nd₂Fe₁₅Si₂-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites.     

Improving oxidation resistance of porous FeAl-based intermetallics with high boron/yttrium alloying

The coalloying with high contents of chromium (Cr), boron (B) and yttrium (Y) for porous B2-structured FeAl intermetallics fabricated through reactive synthesis was conducted. The oxidation behaviors of porous FeAl-based materials were investigated by evaluating the pore-structure evolution, oxidation kinetics and oxide-scale configuration. The results show that with the coalloying of high contents of Cr, B and Y, the oxidation mass gains of porous FeAl materials at 600?800 °C are significantly reduced. The combination of B enriched on the surface of oxide scales and Y located at the scale?metal interface promotes the formation of thin protective nodular α-Al₂O₃ oxide scales. It is indicated that introducing relatively high contents of reactive elements such as B and Y can benefit the selective growth of α-Al₂O₃ scales at relatively low temperatures without pre-treatment.     

Corrosion of structural constituents of 2017 aluminium alloy in acidic solutions containing inhibitors

The objective of this study is to establish the corrosion behaviour of the most important structural constituents of the aluminium alloy 2017 in orthophosphoric acid solutions containing heteropolyoxomolybdate, tungstate and vanadate. These are potential candidates for replacing toxic hexavalent chromium species in stripping solution for anodic coatings. The corrosion rate of the alloy is estimated with linear polarisation method. It decreases from 0.58 mA cm⁻² in uninhibited solution to 0.10 mA cm⁻² in a solution containing heteropolyoxomolybdate species. Microscopic studies reveal that heteropolyoxomolybdate species inhibit corrosion of the matrix and intermetallic Al₁₅(Fe,Mn)₃(Si,Cu)₂ but not Mg₂Si. Intermetallic Al₂Cu remains not corroded. Heteropolyoxotungstate species virtually do not inhibit the corrosion of the alloy. The solution containing vanadium species is not stable with time and the corrosion rate is not determined. Nevertheless, corrosion of the matrix is inhibited, but intermetallics Al₁₅(Fe,Mn)₃(Si,Cu)₂ together with Mg₂Si are dissolved. X-ray photoelectron spectroscopy is used for examination of a corrosion product precipitated on the surface.     

Influence of high pressure and manganese addition on Fe-rich phases and mechanical properties of hypereutectic Al−Si alloy with rheo-squeeze casting

The influence of high pressure and manganese addition on Fe-rich phases (FRPs) and mechanical properties of Al?14Si?2Fe alloy with rheo-squeeze casting (RSC) was investigated. The semi-solid alloy melt was treated by ultrasonic vibration (UV) firstly, and then formed by squeeze casting (SC). Results show that the FRPs in as-cast SC alloys are composed of coarse β-Al₅(Fe, Mn)Si, δ-Al₄(Fe, Mn)Si₂ and bone-shaped α-Al₁₅(Fe, Mn)₃Si₂ phases when the pressure is 0 MPa. With RSC process, the FRPs are first refined by UV, and then the solidification under pressure further causes the grains to become smaller. The peritectic transformation occurs during the formation of α phase. For the alloy with the same composition, the ultimate tensile strength (UTS) of RSC sample is higher than that of the SC sample. With the same forming process, the UTS of Al?14Si?2Fe?0.8Mn alloy is higher than that of Al?14Si?2Fe?0.4Mn alloy.     

Crystal Structure,Chemical Bonding and Magnetism Studies for Three Quinary Polar Intermetallic Compounds in the (Eu1?xCax)9In8(Ge1?ySny)8 (x = 0.66, y = 0.03) and the (Eu1?xCax)3In(Ge3?ySn1+y) (x = 0.66, 0.68; y = 0.13, 0.27) Phases

Three quinary polar intermetallic compounds in the (Eu_1−xCa_x)₉In₈(Ge_1−ySn_y)₈ (x = 0.66, y = 0.03) and the (Eu_1−xCa_x)₃In(Ge_3-ySn_1+y) (x = 0.66, 0.68; y = 0.13, 0.27) phases have been synthesized using the molten In-metal flux method, and the crystal structures are characterized by powder and single-crystal X-ray diffractions. Two orthorhombic structural types can be viewed as an assembly of polyanionic frameworks consisting of the In(Ge/Sn)₄ tetrahedral chains, the bridging Ge₂ dimers, either the annulene-like “12-membered rings” for the (Eu_1−xCa_x)₉In₈(Ge_1−ySn_y)₈ series or the cis-trans Ge/Sn-chains for the (Eu_1−xCa_x)₃In(Ge_3−ySn_1+y) series, and several Eu/Ca-mixed cations. The most noticeable difference between two structural types is the amount and the location of the Sn-substitution for Ge: only a partial substitution (11%) occurs at the In(Ge/Sn)₄ tetrahedron in the (Eu_1−xCa_x)₉In₈(Ge_1−ySn_y)₈ series, whereas both a complete and a partial substitution (up to 27%) are observed, respectively, at the cis-trans Ge/Sn-chain and at the In(Ge/Sn)₄ tetrahedron in the (Eu_1−xCa_x)₃In(Ge_3−ySn_1+y) series. A series of tight-binding linear muffin-tin orbital calculations is conducted to understand overall electronic structures and chemical bonding among components. Magnetic susceptibility measurement indicates a ferromagnetic ordering of Eu atoms below 5 K for Eu_1.02(1)Ca_1.98InGe_2.87(1)Sn_1.13.     

改善铝合金中富Fe相析出形态的技术进展

总结了改善铝合金中富Fe相析出形态的技术进展。指出通过添加稳定化元素、工艺控制等可以优化富Fe相的析出形态并使颗粒细化,促使其发挥颗粒增强的作用,有利于改善铝合金的性能。展望了高Fe含量铝合金材料的研究与开发前景,并提出该类材料将成为新的研究热点之一。     

Short fatigue cracks in intermetallic γ‐TiAl‐alloys

Fatigue crack growth at room temperature and its relation to the local microstructure is studied for four different γ‐TiAl‐alloys with microstructures ranging from coarse and fully lamellar to fine and partly lamellar. It is shown that the number of cycles to failure depends strongly on the efficiency of the first barrier to crack extension, as crack growth rates may increase rapidly once this barrier has been breached by a specific crack. The crack extension behaviour for two typical barriers (colony boundary and twin boundary) is studied using high‐resolution optical and scanning electron microscopy.     

TEM analysis of 2205 duplex stainless steel to determine orientation relationship between M23C6 carbide and austenite matrix at 950 °C

Microstructures of 2205 duplex stainless steel were examined using transmission electron microscopy. During isothermal heating at 950 °C, M₂₃C₆ carbide was formed on the austenite grain boundaries with two types of morphologies: “larva” and “triangle”. The orientation relationship between the M₂₃C₆ carbide and the austenite matrix is cubic-to-cubic. In addition, these two types of precipitates have a twin relationship with each other. Based on the STEM-EDS data, the silicon content of triangle M₂₃C₆ carbide is higher than that of the larva M₂₃C₆ carbide, revealing that the silicon content in the M₂₃C₆ carbide plays an important role in determining the orientation relationship between the M₂₃C₆ carbide and the austenite matrix.     

Structural and mechanical stability of the nano-crystalline Ni–Ti (50.9 at.% Ni) shape memory alloy during short-term heat treatments

In this study, the nano-crystalline Nitinol (50.9 at.% Ni) was prepared by 40% cold deformation. Subsequently it was subjected to 15-min-heat treatments at 300–550 °C. Changes of the structure and mechanical properties were studied by transmission electron microscopy, micro X-ray diffraction, differential scanning calorimetry, Vickers hardness measurements, tensile and bend-type fatigue testing. It was shown that the cold drawn material contains textured nano-crystalline B2 grains of 50 nm in thickness and a high concentration of lattice defects. Its tensile strength, hardness and fatigue life were 1521 MPa, 421 HV0.05 and 2435 bending cycles to fracture, respectively. After heat-treatment up to 450 °C/15 min the material underwent Ni₄Ti₃ precipitation and partial recovery processes. Heat-treatments at above 450 °C induced recrystallization, grain and precipitate growth. Hardness and fatigue lives showed maxima of 692 HV0.05 and 5883 cycles, respectively, after heat-treatments at 450 °C/15 min. In contrast, both tensile strength and B2 → B19′ transformation stress decreased with increasing heat-treatment temperature, but a decrease of the tensile strength after heat-treatments at 300–450 °C was slow (tensile strength after heat-treatment at 450 °C/15 min was 1486 MPa). The observed variations of mechanical characteristics were discussed in relation to structural changes observed.