时效处理对Mg-2.0Zn-0.5Zr-3.0Gd生物降解镁合金组织、力学性能及耐腐蚀性能的影响

通过金相显微分析(OM)、扫描电镜观察(SEM)、透射电镜观察(TEM)和拉伸性能测试研究不同时效时间对Mg-2.0Zn-0.5Zr-3.0Gd生物镁合金显微组织及力学性能的影响,通过质量损失和电化学方法研究合金在模拟体液(SBF)中的耐腐蚀性能。结果表明:时效时间为4~20 h时,合金中析出相的尺寸及数量随时效时间的延长而增加,析出相主要以纳米级棒状和颗粒状的(Mg,Zn)3Gd相形式存在,部分棒状析出相与α-Mg基体具有共格界面关系。合金的强度及伸长率随时效时间的延长先升高后降低。在120 h的浸泡实验中,合金的平均腐蚀速率、点蚀孔洞的数量及孔洞尺寸随时效时间的延长而逐渐增大,腐蚀速率随浸泡时间延长呈现出先减小、后增大、再缓慢减小以及最后趋于稳定的过程。     

热处理对GWZK94合金微观组织与力学性能的影响

为了改善铸态GWZK94合金微观组织的不均匀性，使用电阻加热炉在温度505-520 ℃范围内保温8-20 h进行热处理实验。本文采用光学显微镜（OM）,差示扫描量热仪（DSC），X射线衍射仪（XRD），扫描电子显微镜（SEM），能谱仪（EDS）,电子背散射衍射技术（EBSD），万能试验机和维氏硬度计进行微观组织演变及力学性能分析。铸态合金组织主要包括树枝状α-Mg基体，包含亚稳态层错（SFs）的片层结构，共晶相Mg24(Gd, Y, Zn)5，块状长周期有序堆垛结构(LPSO, Mg12(Gd, Y) Zn)和少量的富稀土相。在均匀化处理过程中，片层结构和共晶相Mg24(Gd, Y, Zn)5逐渐溶于基体中，同时块状LPSO相体积分数逐渐减小并伴随有片层状LPSO相像晶粒内部生长，颗粒状相在晶界附近析出。加热温度为520 ℃时出现复熔三角晶界，说明此时发生了合金的过烧现象。经过均匀化处理后，合金的极限抗拉强度（UTS）和合金屈服强度（TYS）表现出了与组织演变规律相同的变化趋势，同属得到了较为均匀的硬度分布情况。最佳的均匀化制度为515 ℃/16 h.     

Coherency strain induced hardening in bulk polycrystalline ceramics: A case study with MgO-based “ceramic alloys”

The role of coherency strain at the matrix/precipitate interface toward hardening of bulk polycrystalline “ceramic alloys” has been established here. Formation of “near ideal” bulk polycrystalline ceramic microstructure characterized by the presence of uniformly distributed coherent “ultra-fine” MgCr₂O₄ particles (size: ~25 nm) within matrix (MgO) grains was achieved via solid-state precipitation during aging treatment of bulk supersaturated MgO–Cr₂O₃ solid solutions (formed during pressureless sintering in air, followed by fast cooling). The as-aged MgO–MgCr₂O₄ “ceramic alloys” exhibited hardness increment by ~73% over that of phase pure bulk MgO upon aging for just 10 hours at 1000°C in air. Evidences toward the presence of significant coherency strains across the MgO/MgCr₂O₄ coherent interfaces were obtained with transmission electron microscopy. Analysis based on hardening mechanisms and comparisons with MgO–MgFe₂O₄ system, having lesser hardening due to lower misfit strain at MgO/MgFe₂O₄ coherent interfaces (despite greater content of second-phase particles), confirm the dominant role of coherency strains toward hardness enhancement in “ceramic alloys.”     

GSH-responsive polyglutamic acid nanocarriers for dual targeted cancer therapy

In order to reduce the toxic side effects of chemotherapeutic drugs and improve the targeting and efficiency of cancer treatment, the development of drug delivery system has received great attention. In this study, second generation polyglutamic acid dendrimers (G₂) are used as basic materials to produce porous nanoparticles through cross link by crosslinkers containing disulfide bonds. The crosslinked products (G₂)_n have negative electricity and abundant voids, which enable them to adsorb the electronegative anticancer drug DOX. At the same time, in order to transport DOX to the tumor site, we modified FA on DOX and encapsulated it in magnetic mesoporous silica (FA-DOX-MSNs). Therefore, the final nanoparticles (FA-DOX-MSNs/(G₂)_n) not only have dual targeting ability to transport DOX to the tumor site, but also have reductive responsiveness that can release drugs responsively in the tumor cells. In addition, it has good biocompatibility and endocytosis ability.     

Controlling Corrosion Resistance of a Biodegradable Mg–Y–Zn Alloy with LPSO Phases via Multi-pass ECAP Process

Mg-RE(rear earth) alloys with long period stacking(LPSO) structures have great potential in biomedical applications. The present work focused on the microstructure and corrosion behaviors of Mg 98.5 Y_1 Zn_(0.5) alloys with 18 R LPSO structure after equal channel angular pressing(ECAP). The results showed that the ECAP process changed the grain size and the distribution of LPSO particles thus controlled the total corrosion rates of Mg 98.5 Y_1 Zn_(0.5) alloys. During the ECAP process from 0 p to 12 p, the grain size reduced from 160–180 μm(as-cast) to 6–8 μm(12 p). The LPSO structures became kinked(4 p), then started to be broken into smaller pieces(8 p), and at last comminuted to fine particles and redistributed uniformly inside the matrix(12 p). The improvement in the corrosion resistance for ECAP samples was obtained from 0 p to 8 p, with the corrosion rate reduced from 3.24 mm/year(0 p) to 2.35 mm/year(8 p) in simulated body fluid, and the 12 p ECAP alloy exhibited the highest corrosion rate of 4.54 mm/year.     

抗氢合金J75中低∑CSL晶界的形成与演化

以铁镍基抗氢合金J75为研究对象,采用单步形变热处理和电子背散射衍射(EBSD)技术,研究了低∑CSL晶界的形成和演化过程。结果表明:采用5%预变形+1000℃退火的单步形变热处理方法,可将J75合金中低∑CSL晶界的比例提升至70%以上,形成具有∑3n取向关系的晶粒团簇;退火过程中,低∑CSL晶界比例的提升主要是由于∑3n界面比例的提升,其中∑3占绝大比例。发现一种∑3再生过程,其机制在于:由于∑3ic迁移能力强,在退火过程中与其他∑3相遇会形成∑9晶界,而∑9与∑3相遇,倾向于发生∑9+∑3→∑3,导致∑3的再生;不连续大角度随机晶界(R)与低∑CSL晶界相遇会形成R/∑晶界,当R/∑晶界为低∑CSL晶界时,则构成较多具有低∑CSL晶界的网络,打断了R晶界的连通性。     

Effects of heat treatment on microstructure and mechanical properties of Inconel 625 alloy fabricated by wire arc additive manufacturing process

The microstructure and mechanical properties of Inconel 625 alloy fabricated by wire arc additive manufacturing process were evaluated under as-prepared and heat-treated conditions. A dendritic Ni-based solid solution phase along with (Nb, Ti)C carbide, Laves, and δ-Ni₃Nb secondary phases were developed in the microstructure of the as-prepared alloy. Solution heat treatment led to the dissolution of Laves and Ni₃Nb phases. In addition, dendrites were replaced with large columnar grains. Aging heat treatment resulted in the formation of grain boundary M₂₃C₆ carbide and nanometric γ″ precipitates. Hardness, yield and tensile strengths, as well as elongation of the as-prepared part, were close to those of the cast alloy and its fracture occurred in a transgranular ductile mode. Solution heat treatment improved hardness and yield strength and declined the elongation, but it did not have a considerable impact on the tensile strength. Furthermore, aging heat treatment caused the tensile properties to deteriorate and changed the fracture to a mixture of transgranular ductile and intergranular brittle mode.     

Comparison of Cu–Al–Ni–Mn–Zr shape memory alloy prepared by selective laser melting and conventional powder metallurgy

This work aimed to investigate and critically analyze the differences in microstructural features and thermal stability of Cu−11.3Al−3.2Ni−3.0Mn−0.5Zr shape memory alloy processed by selective laser melting (SLM) and conventional powder metallurgy. PM specimens were produced by sintering 106−180 µm pre-alloyed powders under an argon atmosphere at 1060 °C without secondary operations. SLM specimens were consolidated through melting 32−106 µm pre-alloyed powders on a Cu−10Sn substrate. Mechanical properties were measured through Vickers hardness testing. Differential scanning calorimetry was conducted to assess the martensitic transformation temperatures. X-ray diffraction patterns were collected to identify the metallurgical phases. Optical and scanning electron microscopy was used to analyze the microstructural features. β′₁ martensite was found, irrespective of the processing route, although coarser martensitic variants were present in PM-specimens. In conventional powder metallurgy samples, intergranular eutectoid constituents and stabilized austenite also formed at room temperature. PM-specimens showed similar average hardness values to the SLM-specimens, albeit with high standard deviation linked to the porosity. The specimens processed by SLM showed reversible martensitic transformation (T₀=171 °C). PM-processed specimens did not show shape memory effects.     

Liquid−liquid structure transition in metallic melt and its impact on solidification: A review

Understanding the nature of liquid structures and properties has always been a hot field in condensed matter physics and metallic materials science. The liquid is not homogeneous and the local structures inside change discontinuously with temperature, pressure, etc. The liquid will experience liquid−liquid structure transition under a certain condition. Liquid−liquid structure transition widely exists in many metals and alloys and plays an important role in the final microstructure and the properties of the solid alloys. This work provides a comprehensive review on this unique structure transition in the metallic liquid together with the recent progress of its impact on the following microstructure and properties after solidification. These effects are discussed by integrating them into different experimental results and theoretical considerations. The application of liquid−liquid structure transition as a strategy to tailor the properties of metals and alloys is proven to be practical and efficient.     

Microstructure and mechanical properties of squeeze-cast Al−5.0Mg−3.0Zn−1.0Cu alloys in solution-treated and aged conditions

The microstructure and mechanical properties at different depths of squeeze-cast, solution-treated and aged Al−5.0Mg−3.0Zn−1.0Cu alloy were investigated. For squeeze-cast alloy, from casting surface to interior, the grain size of α(Al) matrix and width of T-Mg₃₂(AlZnCu)₄₉ phase increase significantly, while the volume fraction of T phase decreases. The related mechanical properties including ultimate tensile strength (UTS) and elongation decrease from 243.7 MPa and 2.3% to 217.9 MPa and 1.4%, respectively. After solution treatment at 470 °C for 36 h, T phase is dissolved into matrix, and the grain size increases so that the UTS and elongation from surface to interior are respectively reduced from 387.8 MPa and 18.6% to 348.9 MPa and 13.9%. After further peak-aging at 120 °C for 24 h, numerous G.P. II zone and η′ phase precipitate in matrix. Consequently, UTS values of the surface and interior increase to 449.5 and 421.4 MPa, while elongation values decrease to 12.5% and 8.1%, respectively.