Effect of Zn Addition on the Microstructure and Mechanical Properties of Cast Mg-10Gd-3.5Er-xZn-0.5Zr Alloys

In this work, the effects of Zn content (0-2 wt%) on microstructural evolution and mechanical properties of cast Mg-10Gd-3.5Er-0.5Zr alloys are studied. The results show that the as-cast Mg-10Gd-3.5Er-xZn-0.5Zr alloys are mainly composed of Mg matrix and secondary (Mg, Zn)₃(Gd, Er) phases distributed along grain boundaries. With the increase in Zn content, the volume fraction of secondary (Mg, Zn)₃(Gd, Er) phases increases and the grains get refined. In the process of solid solution treatment, Zn addition can lead to the formation of long-period stacking ordered (LPSO) structures and the volume fraction of LPSO structures increases with Zn content. In addition, the Zn addition can reduce the vacancy formation energy and accelerate the diffusion rate of RE elements in Mg matrix. Because of the comprehensive effect of secondary phases and the accelerated diffusion rate, the base alloy and 2Zn alloy have less grain growth after solid solution treatment than that of the 0.5Zn alloy and 1Zn alloy. The precipitation process is also accelerated by enhanced diffusion rate. At room temperature (RT), the strengthening effect of β^'+ β₁ precipitates is more effective than that of LPSO structures, so the peak-aged 0.5Zn alloy exhibits the most excellent mechanical performance at RT, with yield strength of 219 MPa, ultimate tensile strength 296 MPa and elongation of 6.4%. While LPSO structures have stronger strengthening effect at elevated temperature than that of β^'+ β₁ precipitates, so the 1Zn alloy and 2Zn alloy have more stable mechanical performance than that of the base alloy and 0.5Zn alloy with the increase in tensile temperature.     

Effect of ageing on the microstructure and mechanical behaviour of a directionally solidified Ni3Al-based alloy

The effect of ageing in the temperature range from 1023 to 1373 K on the micro-structure and mechanical behaviour of a directionally solidified (DS) Ni₃Al-based alloy modified with additions of chromium and iron was investigated. The microstructure of the as-grown alloy consisted of well-aligned and equally spaced lamellas composed of β(B2) intermetallic compound NiAl (Cr, Fe), some β′(L1₀) martensite and spherical -Cr precipitates. The matrix consisted of γ′(L1₂) intermetallic compound Ni₃Al (Cr, Fe), γ-phase (Ni-based solid solution) and lath-shaped -Cr precipitates. Ageing at 1123 and at 1173 K was found to be the most effective in transforming the unstable lamellae to γ′-phase and -Cr precipitates. The change of microstructural characteristics such as volume fraction of lamellae, size, morphology and distribution of γ′-phase, γ-phase and -Cr precipitates significantly influenced the room-temperature yield strength and elongation of DS alloy after ageing. The strain-hardening exponent varied with the ageing temperature between 0.30 and 0.46 and the quasi-steady work-hardening rate between 2710 and 5340 MPa. In the specimens with the lowest amount of disordered regions, the strain-hardening exponent was found to be 0.46 and the quasisteady work hardening rate was determined to be 3340 MPa.     

Microstructural evolution and mechanical performance of cast Mg-3Nd-0.2Zn-0.5Zr alloy with Y additions

This work investigated the effects of different Y additions (0, 1.5, 3.0 and 4.5 wt.%) on the microstructural evolution and mechanical performance of cast Mg-3Nd-0.2Zn-0.5Zr alloy. The results show that as the Y content increases, the key secondary phases in as-cast alloys change from the Mg₁₂Nd type to the Mg₂₄Y₅ type. Meanwhile, the number density of Zn-Zr particles in the grains of as-quenched alloys gradually decreases. HAADF-STEM observations of peak-aged samples reveal that element Y is greatly enriched in the globular β′ precipitates, leading to a significantly increased volume fraction and promoted precipitation kinetics of β′ precipitates, resulting in enhanced strength of the alloy. Tensile tests reveal that, with the addition of 4.5 wt.% Y, the yield strength of the base alloy is substantially increased by 88 and 61 MPa after being aged at 200 and 225 °C under peak-aged conditions, respectively.     

Morphology of M23C6 precipitation in L12-ordered Ni3(Al, Cr)

A transmission electron microscope investigation has been performed on the morphology of M₂₃C₆ precipitation in L1₂-ordered Ni₃(Al, Cr) containing 0.1–0.5 mol% of carbon. By aging at temperatures around 1073 K after solution annealing at 1423 K, fine octahedral-shaped precipitates of M₂₃C₆ bounded by {111} facets appear first on the dislocations and then in the matrix. The shapes of the precipitates are not always equilateral but tetragonal or elongated octahedral ones appear during aging. Planar growth faults were observed in some of the octahedral precipitates. After prolonged aging or by aging at higher temperatures, these shapes of precipitates become unstable. The M₂₃C₆ precipitates then adopt a rod-like morphology elongated parallel to the 100 directions and characterized by steps bounded by {111} facets.     

3D Fe-Rich Phases Evolution and Its Effects on the Fracture Behavior of Al-7.0Si-1.2Fe Alloys by Mn Neutralization

The evolution of the 3D Fe-rich phases of Al-7.0Si-1.2Fe alloys with different Mn contents was visualized and characterized using synchrotron X-ray computed tomography, and the effect of Fe-rich phases with typical morphologies on the fracture behavior during tensile testing was analyzed. The results showed that the Fe-rich phase changed from platelet-like β-Al₅FeSi into α-Al₁₅(FeMn)₃Si₂ with various morphologies after the addition of Mn. The Mn addition not only significantly reduced the volume fraction, equivalent diameter and interconnectivity of the Fe-rich phase but also greatly increased the sphericity, surface thickness, and distribution of the mean curvature and surface thickness. Furthermore, the equivalent diameter of α-Al₁₅(FeMn)₃Si₂ had an inverse exponential function relationship with its sphericity. The 3D morphology of α-Al₁₅(FeMn)₃Si₂ can be summarized as massive and regular polyhedrons, hollow and regular polyhedrons, and multibranched polyhedrons. The fraction of the different 3D morphologies in each alloy is related to the Mn content, where excess Mn increased the number and volume fraction of the large Fe-rich particles with a low sphericity. The ductility of each alloy was significantly improved by the addition of Mn but gradually decreased when the Mn/Fe ratio exceeded 1.2. The increase in large α-Al₁₅(MnFe)₃Si₂ with a low sphericity was the main reason for the decreased ductility of alloys with a high Mn content.     

Eutectoid transformations accompanied by ordering

Eutectoid transformations accompanied by ordering, unlike ordinary ones, proceed through non-pearlitic modes of transformations. Eutectoid invariants are classified into two categories in binary systems. The eutectoid invariant of A3()→D0₁₉(₂) + L1₀(γ) in the Ti-Al binary system belongs to the first category, in which one product phase has an ordered structure of a parent phase. Its transformation product exhibits a γ/₂ lamellar structure consisting of nearly perfectly aligned alternate lamellae of γ and ₂, which is formed by precipitation of γ plates in either or ₂ matrix with the Blackburn orientation relationship. The eutectoid invariant of A1(γ)→D0₂₂(γ″) + L1₂(γ′) in the Ni₃V-Ni₃Al pseudo-binary system is an example of the second category, in which both product phases have different ordered structures of a parent phase. The transformation of a 75Ni-18V-7Al alloy results in a ‘checkerboard’ pattern consisting of a periodic array of columns of γ′ and two γ″ orientation variants, which are formed by phase separation simultaneous with ordering.     

Effect of Aging on the Microstructure and Mechanical Properties of 1460 Alloy

Effects of the aging temperature on the hardening response,the tensile properties and the precipitate microstructure evolution of 1460 alloy were studied in this work.It was found that Al3(Sc,Zr) and d0(Al3Li) phases were precipitated from the matrix at the very early aging stage,while the precipitation of T1(Al2Cu Li) and h0(Al2Cu) was much slower than that of the d0 phase.When aging at higher temperature(160 and 190 °C),the d0,T1 and h0 phases tended to form simultaneously and grow up very quickly.Conversely,the d0 and h00(Al2Cu) phases were precipitated separately and more dispersive at lower aging temperature(130 °C).Taken together,the alloy aged at 160 °C exhibited improved mechanical properties owing to the uniform dispersion of the fine T1 precipitates.     

β1受体反义基因治疗对肾性高血压大鼠心脏的保护作用

目的: 探讨阳离子脂质体混合物介导的β₁受体反义基因对肾性高血压大鼠血压和心脏的影响及机制。方法: 将24只雄性SD大鼠随机分成4组(n=6):两肾一夹模型组(2K1C组),两肾一夹模型+反义核苷酸组(尾静脉β₁-AS-ODN 0.5 mg·kg^-1,反义组),两肾一央模型+反向核苷酸组(尾静脉β₁-IN-ODN 0.5 mg·kg^-1,反 向组),假手术组。常规方法测定尾动脉收缩压、左室血流动力学指标及左心室重量指数(LVMI),以光镜观察心肌组织变化,免疫组织化学方法检测心肌Bcl-2、 Bax的表达。结果: 单剂反义寡核苷酸治疗可持续降压27 d,血压最低可降至120 mmHg左右;并可明显改善左室收缩、舒张功能;反义组的左室重量指数也显著低于2K1C组(P<0.01);心肌细胞病理变化也较2K1C 组改善;2K1C组心肌Bcl-2/Bax比值明显低于假手术组,而反义组与2K1C组相比,Bcl-2/Bax比值明显升高 (P<0.05)。结论: 以β受体为靶基因的反义基因单剂治疗在有效而持久的控制肾性高血压的同时,可显著逆转左室肥厚,改善左室功能,其机制可能与升高Bcl-2/Bax比值、抑制心肌细胞凋亡相关。说明β受体反义基因治疗对肾性高血压大鼠具有心脏保护作用。     

Effect of Magnesium on Microstructure Refinements and Properties Enhancements in High-Strength CuNiSi Alloys

Microalloying is an effective method to improve the comprehensive properties of copper alloys.The effects of magnesium on the microstructure,mechanical properties and anti-stress relaxation properties of CuNiSi alloys have been investigated.Results demonstrated that magnesium plays significant roles in refining the dendritic microstructure of the as-cast ingot,accelerating the precipitation decomposition,improving the mechanical properties and increasing the anti-stress relaxation properties.The incremental strength increase is due to the Orowan strengthening from the nanoscale Ni_2 Si and Ni_3 Al precipitates.As compared with the Cu-6.0 Ni-1.0 Si-0.5 Al(wt%) alloy,the ultimate tensile strength of the designed Cu-6.0 Ni-1.0 Si-0.5 Al-0.15 Mg(wt%) alloy increases from 983.9 to 1095.7 MPa,and the electrical conductivity decreases from 27.1 to 26.6% IACS,respectively.The stress relaxation rates of the designed Cu-6.0 Ni-1.0 Si-0.5 Al-0.15 Mg alloy are 4.05%at 25℃,6.62% at 100℃and 9.74% at 200℃after having been loaded for 100 h,respectively.Magnesium significantly promotes nucleation during precipitation and maintains small precipitate size.     

κ-阿片受体与β1-肾上腺素受体交互作用抑制异丙肾上腺素诱导的心肌肥大

目的: 观察选择性 kappa 阿片受体(kappa opi-oid receptor,κ-OR)与 β 肾上腺素受体(β adrenergicreceptor, β-AR)在心肌细胞肥大方面的交互作用。方法: 以 体 外 培 养 的 乳 鼠 心 肌 细 胞 为 模 型, 10 μmol°L^-1 的异丙肾上腺素(β肾上腺素受体激动剂,β-AR)诱导心肌肥大, 观察 1μmol°L^-1的 U50,488H(κ-OR激动剂,U50)对其作用。进一步探索在100 nmol°L^-1ICI118, 551(β₂ -AR 阻断剂)存在情况下,κ-OR的激活对心肌肥大的作用。用 Lowry's 法测心肌细胞的蛋白质含量;用消化分离法,并利用计算机图象分析系统测心肌 细胞的体积;用[³H]leucine 掺入法测定心肌细胞蛋白的合成。结果: 异丙肾上腺素使心肌细胞总蛋白含量、体积、蛋白合成明显增加;1 μmol°L^-1 的 U50, 488H 使 ISO 诱导的心肌细胞总蛋白含量、体积、蛋白合成减少, 这种作用可被选择性 κ-OR阻断剂-nor-BNI(norbinaltorphimine)抑制。在 ICI118, 551 存在的情况下, U50 也能起到减弱 ISO 诱导心肌细胞肥大的作用。结论: U50,488H 通过激活 κ-OR 与β₁ -AR 交互作用抑制 ISO 所诱导的心肌细胞肥大。     

Two-phase intermetallic alloy Ni3(Al, Si):microstructure and mechanical properties

Yield stress in compression (0.2% flow stress) from ambient temperature up to 800 °C has been studied on Ni₃(Al, Si) alloy with the atomic composition Ni₇₈Al₁₁Si₁₁. When annealed at 1000 °C, the alloy has a pure L1₂ (γ′) ordered structure. After subsequent annealing at 750 °C, the disordered solid solution of Al and Si in Ni (face centred cubic, γ) precipitates in fine coherent particles. Calorimetry helps to describe the various phase transformations necessary to obtain the last microstucture. Solute addition of Si, which replaces Al atoms, increases the 0.2% flow stress of Ni₃Al in the fully γ′ microstructure. The γ precipitation shifts the peak stress towards higher temperatures and stresses.     

Effect of ageing treatment on microstructures,mechanical properties and corrosion behavior of Mg-Zn-RE-Zr alloy micro-alloyed with Ca and Sr

Effects of ageing treatment on the microstructures, mechanical properties and corrosion behavior of the Mg-4.2Zn-1.7RE-0.8Zr-xCa-ySr [x=0, 0.2 (wt.%), y=0, 0.1, 0.2, 0.4 (wt.%)] alloys were investigated. Results showed that Ca or/and Sr additions promoted the precipitation hardening behavior of Mg-4.2Zn-1.7RE-0.8Zr alloy and shortened the time to reaching peak hardness from 13 h to 12 h. The maximum hardness of 77.1±0.6 HV for the peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy was obtained. The microstructures of peak-aged alloys mainly consist of α-Mg phase, Mg₅₁Zn₂₀ phase and ternary T-phase. The Zn-Zr phase is formed within the α-Mg matrix, and the Mg₂Ca phase is formed near T-phase due to the enrichment of Ca in front of the solid-liquid interface. Furthermore, fine short rod-shaped β′₁ phase is precipitated within the α-Mg matrix in the peak-aged condition. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy exhibits optimal mechanical properties with an ultimate tensile strength of 208 MPa, yield strength of 150 MPa and elongation of 3.5%, which is mainly attributed to precipitation strengthening. In addition, corrosion properties of experimental alloys in the 3.5wt.% NaCl solution were studied by the electrochemical tests, weight loss, hydrogen evolution measurement and corrosion morphology observation. The results suggest that peak-aged alloys show reduced corrosion rates compared with the as-cast alloys, and minor additions of Ca and/or Sr improve the corrosion resistance of the Mg-4.2Zn-1.7RE-0.8Zr alloy. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy possesses the best corrosion resistance, which is mainly due to the continuous and compact barrier wall constructed by the homogeneous and continuous second phases.

     

A comparative study of precipitation behavior of Heusler phase (Ni2TiAl) from B2-TiNi in Ni–Ti–Al and Ni–Ti–Al–X (X=Hf, Pd, Pt, Zr) alloys

In support of the design of high strength TiNi-based shape-memory alloys, the precipitation of L2₁–Ni₂TiAl phase from a supersaturated B2–TiNi matrix at 600 and 800 °C is studied using transmission and analytical electron microscopy (TEM/AEM), and 3D atom-probe microscopy (3DAP) in Ni–Ti–Al and Ni–Ti–Al–X (X=Hf, Pd, Pt, Zr) alloys. A B2/L2₁ fully coherent two-phase microstructure is confirmed to be analogous to the classical γ/γ′ system in terms of precipitate shape, spatial distribution and a minimum distance of separation between L2₁ precipitates as dictated by the interplay between strain and interfacial energies. The effects are also confirmed to disappear with loss of coherency. These results lend further support, at least qualitatively, to the theoretical predictions of microstructural dynamics of coherent aggregates. Selected cohesive properties of stable and virtual B2 compounds are calculated by an ab initio method, showing good agreement with measured site occupancy and lattice parameters. A simple analysis of the L2₁ precipitate size evolution suggests that in the case of alloys with Al, Zr or Hf substitution for Ti, the precipitates follow coarsening kinetics at 600 °C and growth kinetics at 800 °C, while for alloys with Pd or Pt substitution for Ni, precipitates follow one kinetic behavior at both temperatures. The temperature-dependent partitioning behaviors of Hf, Pd, Pt and Zr are established by quantitative microanalysis using AEM and nanoscale analysis using 3DAP. Both Hf and Zr prefer to partition to the B2 phase at 800 °C while they exhibit reverse behavior at 600°C. Pt also partitions to B2 at 800 °C, while Pd partitions to the L2₁ phase at both 600 and 800 °C. To describe the composition dependence of the lattice parameter of multicomponent B2 and L2₁ phases, the atomic volumes of Al, Hf, Ni, Ti and Zr in B2 and L2₁ phases are determined, providing a model for the control of interphase misfit in alloy design.     

稀土元素Er对Ti-6Al-4V-0.5Si合金组织与性能的影响

利用粉末冶金工艺制备了Ti-6Al-4V-0.5Si-xEr(wt%)合金,随后采用OM、XRD、TEM和拉伸试验机等分析手段研究了Er元素含量对固溶时效态(950 ℃×30 min(WQ)+480 ℃×4 h(AQ))试验合金显微组织和性能的影响。结果表明:试验合金经固溶时效处理后均为等轴和片状的双态组织。烧结过程中产生的Er₂O₃氧化物颗粒可以作为形核中心促进α相和β相的析出,起到细化晶粒的作用。随着Er元素含量的增加,晶粒尺寸由10~20 μm细化至5~10 μm。当Er元素含量为1.2%时,试验合金的抗拉强度达到峰值,为930.5 MPa,此时伸长率为9.24%,比未添加Er元素时Ti-6Al-4V-0.5Si合金分别提高了22.3%和10.0%。试验合金的拉伸断口形貌显示有韧窝出现,仅有少量的解理台阶,韧窝的存在可以分散材料断裂时产生的应力,使材料断裂前承受更大的变形。     

Influence of deformation on precipitation process in Mg–15 wt.%Gd alloy

Mg–Gd is a promising light hardenable alloy with a high creep resistance at elevated temperatures. The supersaturated solid solution of Gd in Mg decomposes in a sequence of the following phases: β″ (D0₁₉) → β′ (c-base centered orthorhombic-c-bco) → β (fcc) stable. Formation of the metastable β′ phase causes a strong hardening. Dislocations facilitate nucleation of precipitates. Dislocation density is, therefore, an important parameter which influences the precipitation process. This effect was examined in the present work by comparison the decomposition sequences in Mg–15 wt.%Gd alloy cold rolled to various thickness reductions. It was found that precipitation of the β′ phase starts at lower temperatures in the cold rolled specimens.     

罗红霉素对哮喘大鼠气道重塑中成肌纤维细胞、TGF-β1和 IFN-γ的影响

目的: 探讨成肌纤维细胞(myofibroblast,MF) 、转化生长因子β₁ (transforming growth factor-beta 1, TGF-β₁ ) 和 IFN-γ在哮喘气道重塑中的作用,并观察罗红霉素对哮喘气道重塑的影响。方法: SD大鼠 30 只, 随机分为哮喘组、生理盐水对照组、罗红霉素治疗组, 每组 10 只。利用卵白蛋白(ovalbumin,OVA)/Al(OH)₃ 致敏与 OVA 雾化吸入激发建立大鼠哮喘模型。免疫组化测定支气管上皮下成肌纤维细胞的 α-平滑肌肌动蛋白(α-smoothmuscle actin, α-SMA) 表达含量, 并使用图像分析技术进行积分吸光度(integral optical density, IOD) 定量分析测定 。ELISA 法测定支气管肺泡灌洗液(bronchoalveolar lavage fluid, BALF) 中 TGF-β₁ 和IFN-γ的浓度。结果: 定量分析测定的 IOD 值显示哮喘组支气管上皮下成肌纤维细胞 α-SMA 表达含量较生理盐水对照组增加(P<0.01) , 罗红霉素治疗组表达含量较哮喘组减少(P<0.05) 。ELISA 法测定哮喘组 BALF 中 TGF-β₁ 浓度较对照组升高(P<0.01) , 治疗组较哮喘组浓度降低(P<0.01) , 但仍高于对照组(P<0.05) 。哮喘组BALF 中 IFN-γ浓度较对照组降低(P<0.01) , 治疗组较哮喘组浓度高(P<0.01) , 但仍低于对照组(P<0.05) 。结论: 成肌纤维细胞在气道重塑中起重要作用。罗红霉素可能通过减少 TGF-β₁ ,增加 IFN-γ的产生, 从而抑制成肌纤维细胞增殖和表达, 起到抗哮喘气道重塑作用 。     

黄芪注射液对腹膜透析相关腹膜间皮细胞TGF-β1分泌与表达的影响

目的: 探讨黄芪对腹膜透析相关性腹膜纤维化的作用。方法: 人腹膜间皮细胞(HPMC) 做体外培养,第三代细胞用于实验。分5 组观察, 对照组为RPMI1640;PDS (peritoneal dialysis solution, 腹膜透析液) 组为加入PDS; 黄芪1、2、3 组为加入含黄芪注射液的PDS,黄芪终浓度分别为10、20、40 mg·ml^-1 。分别在24 h 采用ELISA 法检测细胞上清液中转移生长因子-β₁ (TGF-β₁) 的含量, 采用逆转录多聚酶链式反应(RT-PCR) 检测TGF-β₁ mRNA 表达。结果: 腹膜间皮细胞在PDS 干预下分泌TGF-β₁明显增加(P <0.05) 。腹膜间皮细胞经含不同浓度黄芪注射液的PDS 干预后, TGF-β₁分泌与PDS 组比较有显著下降(P <0.05) 。不同浓度黄芪注射液组之间比较无显著差异(P >0.05) 。腹膜间皮细胞在PDS 干预下TGF-β₁ mRNA 表达明显升高, 比对照组上升62.43%, 腹膜间皮细胞经含不同浓度黄芪注射液的PDS 干预后, TGF-β₁ mRNA 表达显著低于PDS 组(P <0.01) 。结论: 商业性腹膜透析液可促进腹膜间皮细胞分泌和表达TGF-β₁, 黄芪可以部分抵消这一作用所致的腹膜透析相关性腹膜纤维化。     

BXSB 狼疮小鼠肾组织TGF-β1异常表达及甲泼尼龙干预作用

目的: 研究转化生长因子-β₁ (TGF-β₁) 在BXSB小鼠狼疮肾炎(LN) 中的作用及甲泼尼龙(MPS) 是否可通过影响TGF-β₁ 表达而改善LN 。方法: 用逆转录-聚合酶链反应技术(RT-PCR) 和免疫组织化学方法检测BXSB 狼疮小鼠及BALB /c 小鼠肾组织TGF-β1 mRNA 及蛋白的表达情况, 并用甲泼尼龙对BXSB小鼠进行体内干预, 观察甲泼尼龙对BXSB 小鼠肾脏TGF-β₁ 表达的影响及各组小鼠24 h 尿蛋白量的变化。结果: RT-PCR 检测到BXSB 小鼠肾组织TGF-β₁mRNA 表达明显高于BALB /c 小鼠(P <0.01); 其中, BXSB 小鼠治疗组肾组织TGF-β₁mRNA 表达量显著低于对照组(P <0.01) 。BXSB 小鼠治疗组24 h尿蛋白量明显低于对照组(P <0.01) 。免疫组织化学检测示TGF-β₁ 表达于BXSB 小鼠肾小球系膜细胞、肾小管上皮细胞、血管内皮细胞、肾间质及肾小球浸润的炎症细胞胞质内, 其中BXSB 小鼠治疗组较对照组表达明显减弱, 而BALB /c 小鼠仅在少数肾小管上皮细胞有微弱表达, 且图像半定量分析显示各组有显著性差异(P <0.01) 。结论: TGF-β₁ 可能参与LN 发病;甲泼尼龙可能通过抑制肾组织TGF-β₁ 的表达来改善LN。     

Quantitative Electron Tomography for Accurate Measurement of Precipitates Microstructure Parameters in Al–Cu–Li Alloys

Mechanical theories show that properties of alloys are strongly dependent on the morphological parameters oftheir strengthening precipitates.However,accurate measurement of precipitates microstructure parameters is still a challenging task.In this article,we develop a quantitative electron tomography method by combining computer vision technology to accurately characterize the three-dimensional microstructure parameters,such as volume fractions,sizes and distributions,of the T₁ and δ’...     

Influence of High-Pressure Nitrogenation on the Structural,Magnetic and Magnetocaloric Properties of La0.5Pr0.5Fe11.4Si1.6

Nitrogenation of La_0.5Pr_0.5Fe_11.4Si_1.6 with a particle size of 100-150 μm was performed in a high-purity N₂ atmosphere of 40 MPa. La_0.5Pr_0.5Fe_11.4Si_1.6N_0.3 nitrogenated at 480 °C exhibits an increase in the Curie temperature T _C from 187 to 195 K. Moreover, for a field change from 0 to 1.5 T, the maximum hysteresis loss at T _C is remarkably reduced from 53 to 3 J kg^-1 and a large magnetic-entropy change ΔS _m of over 10 J kg^-1 K^-1 is maintained. For a La_0.5Pr_0.5Fe_11.4Si_1.6N_1.2 sample, nitrogenated at 550 °C, the XRD pattern clearly exhibits two 1:13 phases and, accordingly, the thermal magnetic curves exhibit two transitions, at 210 and at 295 K. The two transitions lead, for a field change of 5 T, to a ΔS _m larger than 2 J kg^-1 K^-1 over a large temperature range from 200 to 310 K with a maximum value of 5.3 J kg^-1 K^-1 at 225 K. Upon further increase in the nitrogenation temperature to 650 °C, the amount of the nitrogen-poor phase strongly decreases and a large amount of α-Fe precipitates, resulting in a large reduction in the MCE.