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.     

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.     

固液反应球磨制备Cu-Sn金属间化合物

研究通过Cu球对液态金属Sn在不同温度及时间内球磨制备Cu-Sn金属间化合物的过程,采用X射线和扫描电镜及透射电镜等分析手段分析产物特征.结果表明,在球料比为10：1,转速为80r/min的条件下,用Cu球对液态Sn进行不同时间及温度的液态球磨后,得到了不同的金属间化合物.在400℃时金属间化合物为Cu6Sn5,500℃及600℃时产物为Cu3Sn.加铜粉可以加快反应速度.采用固液反应球磨技术在高温下可以形成粒度很小,甚至达到纳米级的金属间化合物粉末.与机械合金化相比,固液反应球磨技术生成金属间化合物的速度较快,且成分单一.     

Effect of Co addition on the martensitic transformation and magnetocaloric effect of Ni–Mn–Al ferromagnetic shape memory alloys

A series of Ni_50−xCo_xMn₃₂Al₁₈ (x = 3, 4, 5, 6, 7, and 8) alloys were prepared by the arc melting method. The martensitic transformation (MT) shifts to a lower temperature with increasing Co concentration and can be tuned to occur from a ferromagnetic austenite to a weak-magnetic martensite in the range of 6 ≤ x ≤ 8. The field-induced metamagnetic behavior was realized in Ni₄₂Co₈Mn₃₂Al₁₈ sample in which a large magnetic entropy change of 7.7 J/kg K and an effective refrigerant capacity value of 112 J/kg were obtained under the field of 60 kOe. The large magnetocaloric effect and adjustable MT temperature suggest that Ni–Co–Mn–Al alloys should have promising potential as magnetic refrigerants.     

Electronic structure and ferromagnetism of Fe11NiSi4, Fe11CoSi4, Fe11CrSi4 and Fe3Si from first principles

Based on the density functional theory (DFT), the plane-wave pseudopotential method was used to calculate structural stabilities, electronic structures, and ferromagnetism of Fe₃Si, Fe₁₁NiSi₄, Fe₁₁CoSi₄ and Fe₁₁CrSi₄ intermetallic compound. This study showed that the Fe₁₁NiSi₄ and Fe₁₁CrSi₄ phase are more stable than Fe₃Si phase, especially Fe₁₁NiSi₄, but decreased with Fe₁₁CoSi₄ phase. Calculating the density of states and the Mulliken electronic populations showed that Fe₁₁NiSi₄ had the highest structural stability because of its Fermi level, which was close to the bottom of the pseudo-gap. Fe₁₁NiSi₄ also had the largest Mulliken population, which increased the metallic bonding of the alloying system. The total magnetic moments of Fe₁₁NiSi₄, Fe₁₁CoSi₄ and Fe₁₁CrSi₄ were 20.04μ_B, 19.98μ_B, and 18.81μ_B, respectively. These magnetic moments mainly originated from the 3d spin polarization of Fe and those of additional atoms.     

AuCuI（A8AuA4Cu）化合物无序化路径跟踪的原子移动新机制

以由AAu8和ACu4干基因组成的AuCuI（AAu Cu8 A4）化合物的无序化实验路径为例,介绍了3个发现和1个方法。发现AuCuI（AAuCu8A4）化合物抗拒温度变化保持结构稳定性的能力归因于AAu8和ACu4基因的势阱深度远超过其振动能,这导致其无序化实验路径是亚平衡的;发现AuCuI（AAu Cu8 A4）适应温度变化改变结构的原子移动新机制是合金基因的＂共振激活-同步交换＂机制,这导致无序化是非均匀性和递次性的亚平衡转变;发现无序化过程中存在跳变有序度,导致存在跳变温度和升温速度增加跳变温度降低的＂逆反效应＂,即所谓的＂Retro效应＂。采用实验混合焓路径法,建立了一整套亚平衡全息网络路径图。     

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.     

Structural,electronic, elastic,mechanical and thermal behavior of RESn3(RE = Y,La and Ce) compounds: A first principles study

The structural, electronic, elastic, mechanical and thermal properties of the isostructural and isoelectronic nonmagnetic RESn₃ (RE = Y, La and Ce) compounds, which crystallize in AuCu₃-type structure, are studied using first principles density functional theory based on full potential linearized augmented plane wave (FP-LAPW) method. The calculations are carried out within PBE-GGA, WC-GGA and PBE-sol GGA for the exchange correlation potential. Our calculated ground state properties such as lattice constant (a₀), bulk modulus (B) and its pressure derivative (B′) are in good agreement with the experimental and other available theoretical results. We first time predict the elastic constants for these compounds using different approximations of GGA. All these RESn₃ compounds are found to be ductile in nature in accordance with Pugh's criteria. The computed electronic band structures and density of states show metallic character of these compounds. The elastic properties including Poisson's ratio (σ), Young's modulus (E), shear modulus (G_H) and anisotropy factor (A) are also determined using the Voigt–Reuss–Hill (VRH) averaging scheme. The average sound velocities (v_m), density (ρ) and Debye temperature (θ_D) of these RESn₃ compounds are also estimated from the elastic constants. We first time report the variation of elastic constants, elastic moduli, Cauchy's pressure, sound velocities and Debye temperatures of these compounds as a function of pressure.