Densification Behavior and Wear Response of Spark Plasma Sintered Iron‐Based Bulk Amorphous Alloys

In the present study, spark plasma sintering (SPS) process is used to sinter Fe‐based bulk amorphous alloys from starting amorphous powder. The sintering was performed in supercooled liquid region (at 630 °C with uniaxial pressure of 70 MPa) where plastic flow of the amorphous powder results in better densification without crystallization. To study the crystallization behavior and its influence on mechanical behavior, the sintered discs were de‐vitrified by annealing at 700 and 800 °C. Detailed characterization of phase development, microhardness at different loads, and wear behavior of the as‐sintered and annealed alloys is presented.     

大块非晶合金在过冷液相区微塑性成形的研究进展

综述了大块非晶合金在过冷液相区微塑性成形的工艺、成形性能评价及有限元技术应用方面的研究进展.指出应用大块非晶合金在过冷液相区粘性流变特性的微塑性成形技术及分析和优化成形工艺的有限元技术发展迅速.展望了过冷液相区微塑性成形技术的进一步研究对大块非晶合金在MEMS典型精细零件加工方面应用的巨大推动作用.     

Investigation of Micro Formability of Bulk Amorphous Alloy in the Supercooled Liquid State Based on Fluid Flow and Finite Element Analysis

Research results on the viscous flow deformation behavior of bulk amorphous alloy in different systems are reviewed. The material exhibits an ideal Newtonian fluid at a high temperature. Analytical solution of lamellar fluid flow behavior is used to discuss the viscous flow behavior of the bulk amorphous alloy in the supercooled liquid state. A material model, which describes such deformation behavior of Mg60Cu30Y10 amorphous alloy,is introduced into the finite element method of microforming process. Surface feature size was investigated and found not sensitive to the micro formability. Bulk amorphous alloy may possibly be applied to microelectro-mechanical-systems (MEMS) fabrication.     

ZT3非晶合金在过冷液相区的塑性变形研究

目的 研究不同的应变速率和变形温度对Zr30.2Ti32.9Cu9Ni5.3Be22.6非晶合金(亦称ZT3)在过冷液相区塑性变形行为的影响。方法 首先,用真空非自耗电弧炉熔炼合金锭并吸铸成直径为8 mm、长度为60~80 mm的非晶合金圆棒;然后,通过等温晶化试验确定ZT3非晶合金在过冷液相区中对应不同温度时发生晶化转变所需的最短时间,并用热模拟试验机进行压缩变形的试验研究;最后,用X射线衍射仪测试ZT3非晶合金在过冷液相区塑性变形后的组织特性。结果 ZT3非晶合金在过冷液相区内的塑形变形行为与应变速率和变形温度有密切的关联性。不同的应变速率与变形温度都会对其塑性变形产生影响,但变形温度的影响比恒定应变速率更大。对ZT3非晶合金变形后的结构分析发现,应变速率对非晶态结构的影响大于温度。结论 ZT3非晶合金的等温晶化转变孕育时间最短为17 min,在小于17 min的时间内完成塑性变形即可抑制晶化转变的发生。当恒定应变速率为2×10^?3 s^?1时,将变形温度控制在355~375 ℃范围内有利于ZT3非晶合金在过冷液相区进行热压塑性成形。     

Li2O对SPS烧结AlN陶瓷致密化、显微结构和导热性的影响

研究了低温烧结助剂Li2O对SPS烧结AlN陶瓷烧结致密化过程、烧结体显微结构和导热性的影响.研究表明:在SPS烧结过程中,烧结助剂Li2O和Sm2O3(或Y2O3)的加入使AlN试样开始收缩并进入烧结初期阶段的温度从1550℃左右下降到1200℃以下;同时Li2O使AlN试样的烧结温度显著降低,完全致密化温度降低到1650℃左右.烧结体的显微结构表明:Li2O的加入有助于形成润湿性良好的液相,促进AlN陶瓷的液相烧结;但不利于快速烧结坯体中气体的扩散与逸出,使试样的致密度受到影响.同时,Li2O影响AlN晶粒的发育,使液相润湿性提高,晶界相均匀分布,增加了晶粒界面上的声子散射,对AlN材料的热导率产生不利影响.同时,添加1.0wt%Li2O和1.5wt%Sm2O3的AlN试样的热导率低于仅添加1.5wt%Sm2O3的试样.     

预退火温度对Cu基块状非晶玻璃转变及晶化的影响

采用差示扫描量热（Dsc）分析方法测定了Cu50Zr42Al8块状非晶合金在不同温度（350～450℃）预退火4h后的玻璃转变温度Tg、起始晶化温度Tx、晶化峰值温度Tp和玻璃转变过程中的比热容变化。结果表明：预退火处理试样的玻璃转变温度Tg、玻璃转变比热变化ΔCp，g随退火温度的升高呈现逐渐增加的趋势，而其起始晶化温度Tx和晶化峰值温度Tp随退火温度的变化不明显。并利用结构弛豫理论分析了预退火温度对玻璃转变和晶化的     

预退火温度对Cu基块状非晶玻璃转变及晶化的影响

采用差示扫描量热(DSC)分析方法测定了Cu50Zr42Al8块状非晶合金在不同温度(350～450 ℃)预退火4 h后的玻璃转变温度Tg、起始晶化温度Tx、晶化峰值温度Tp和玻璃转变过程中的比热容变化.结果表明:预退火处理试样的玻璃转变温度Tg、玻璃转变比热变化△Cp,g随退火温度的升高呈现逐渐增加的趋势,而其起始晶化温度Tx和晶化峰值温度Tp随退火温度的变化不明显.并利用结构弛豫理论分析了预退火温度对玻璃转变和晶化的影响.     

Temperature Stability and Flux Losses Over Time in Sintered Nd–Fe–B Permanent Magnets

Demagnetization occurring with time in a constant temperature is often assumed to be negligible, provided that the operating point of the magnet is above the knee of the $Bhbox{–}H$ curve. However, because it is important to ensure that no permanent flux losses occur in permanent magnets during their use in industrial applications, there is a clear need to quantify these time-dependent losses. We measured losses over time for four commercial sintered Nd–Fe–B magnet grades at five different temperatures (23$,^{circ}$ C–150$,^{circ}$ C). We tested samples with three different permeance coefficient (Pc) values for each material. The time-dependent losses measured fitted the logarithmic law of magnetic viscosity well. We demonstrated that the total flux loss in a lifetime of 30 years can be estimated according to the temperature, coercivity of the material, and the permeance coefficient of the magnet. With proper selection of the magnet material, in accordance with the designed Pc of the application, the total flux loss in 30 years can be minimized almost to zero even at 150$,^{circ}$ C.      

Zr基大块非晶合金在过冷液相区的尺寸效应研究

为了研究Zr55Cu30Al10Ni5大块非晶合金在过冷液相区的尺寸效应,进行了温度为421,431,441,451℃,应变速率为0.01,0.005,0.002,0.001s-1,尺寸为3,2,1,0.6mm下共计64组的压缩试验。根据得到的力和位移曲线求出真实应力应变曲线,分析曲线得到稳态流动应力、应力过冲峰值、应...     

Multiphysics Simulation and Experimental Investigation of the Densification of Metals by Spark Plasma Sintering

Multivariant experimental investigations and multiphysics microstructural modeling of the spark plasma sintering process of metallic powders have been performed up to a relative density of approximately 80%. In comparison, the effect of sintering temperature, pressure, and particle size on the interparticle contact area growth and axial shrinkage of cylindrical specimens of copper and nickel particles is measured in laboratory scaled tests. Herein, for the first time all relevant for sintering phenomena are considered simultaneously: the fully coupled thermo-electro-mechanical modeling of the spark plasma sintering processes, additionally taking into account for lattice, grain boundary, surface diffusion, electromigration, and thermomigration, has been carried out. The computational analysis of various physical phenomena allows to identify dominant and insignificant mechanisms. The two-level numerical simulation includes the modeling of the sintering setup at the macroscopic level and the neck formation process in particle chain systems at the microscopic level. The results of the numerical simulations show a very good agreement with the experimental data. Therefore, the impact of electrical and mechanical loads as well as of particle size on microscopic distribution of temperature, inelastic strain, and on densification has been studied by the finite element simulations.     

具有宽过冷液相区的Fe63Co7NbxZr10-xB20非晶态合金的热稳定性和磁性研究

利用单辊急冷法制备出厚约35μm宽5mm的 Fe63Co7NbxZr10-xB20条带,并研究了合金的热稳定性、非晶结构和磁性能.结果表明,含4at%Nb的Fe63Co7Nb4Zr6B20合金过冷液相区Δ Tx最宽,达到79K.合金系的饱和比磁化强度σs随着Nb含量的增加而线性减小.合金系经973K退火900s,由于α\|Fe等相的析出,使得合金的σs和Hc均迅速升高.