多场耦合烧结Fe-2Cu-2Ni-1Mo-0.8C合金的摩擦磨损性能

采用电场、磁场、应力场和温度场多场耦合成形与烧结一体化技术制备高致密Fe-2Cu-2Ni-1Mo-0.8C合金,利用光学显微镜和扫描电镜对该合金的显微组织以及磨损表面进行观察和分析,重点研究耦合外加脉冲磁场对合金耐磨性能的影响。结果表明,在电场、应力场和温度场三场耦合放电等离子烧结技术的基础上进一步耦合适合的脉冲磁场,可明显改善烧结合金微观组织和合金元素分布的均匀性,不仅提高合金的耐磨性,同时还可显著提高合金的耐磨性能均匀性。在峰值电流、基值电流、频率、占空比分别为2700A、360A、50Hz和50%的脉冲电流以及烧结压力为30MPa的条件下烧结铁基合金粉末3min,耦合外加脉冲磁场强度为2.36×106A/m时,烧结材料的耐磨性能最佳,合金的磨损机制主要为粘着磨损。     

电流辅助烧结过程的多物理场耦合体系模拟

通过建立热-力-电-扩散强耦合结合相场模型的控制方程,对碳化硅材料的电流辅助烧结致密化机理进行了模拟研究,其中考虑了以下三个方面的影响:电流密度对烧结激活能的影响通过扩散系数引入耦合方程,在模拟中实现了活化作用实时影响扩散行为;碳化硅材料电导率与温度变化的关系;通过碳化硅烧结宏观有限元计算给出微结构演化的电流与温度边界条件。在该耦合理论体系下,对不同温升率的微结构演化全过程进行了模拟,计算所得的致密化曲线均与实验结果相符。模拟结果表明,在电流辅助烧结中,活化作用可极大促进致密化过程;提高温升率使得扩散驱动力增大,进而提高致密化速率。     

双层气雾化喷嘴结构突出高度的数值分析

采用计算流体软件Fluent,通过对双层气雾化喷嘴气流场、颗粒粒径以及温度场的数值模拟,分析导液管突出高度对气流场、颗粒粒径以及温度场的影响。结果表明,导液管突出高度为6mm时气流场结构最优,雾化所得粒径最小。总结气雾化过程中液滴在特殊气流场中破碎的主要过程,为双层气雾化喷嘴结构设计及机理研究提供一定的借鉴意义。     

钼合金顶头制备技术研究进展

钼合金顶头是生产不锈钢等高合金含量无缝钢管的关键工具之一。从钼合金顶头的化学成分、掺杂工艺、粉体粒度和烧结工艺等方面入手,研究影响顶头力学性能和使用寿命的主要因素。分析了不同合金元素及添加方式对合金强韧化机理的影响,讨论了粉体掺杂工艺、粉体粒度分布及控制对于后续制备过程中获得致密、均一组织的影响,对比了传统烧结工艺、活化烧结技术和新型烧结技术的优缺点,并为今后烧结成形工艺的研究提供了一些新思路。     

注射成形和模压成形Cu-10Ni合金的烧结行为

分别采用模压成形和注射成形技术制备Cu-10Ni合金,研究该合金不同成形方式下的烧结行为.结果表明:合金的致密化过程和力学性能均受烧结温度的显著影响,烧结过程均包括合金化、均匀化和致密化3个阶段.模压成形坯在1000℃、注射成形坯在1050℃烧结后,致密化程度均较高、显微组织较好、力学性能较佳.其中,注射成形制备的Cu-Ni合金表现出致密化过程较长、滞后于模压成形合金的烧结行为,完成烧结所需的温度较高.     

铜粉激光烧结致密化过程数值模拟

通过建立金属粉末直接激光烧结过程的微观模型,对铜粉激光烧结行为进行数值模拟和实验研究,探索激光烧结致密化特征及烧结工艺、材料物性等对烧结过程和质量的影响.结果表明:激光烧结过程主要经历2个阶段:第一阶段表现为孔隙在金属熔体中的消除(约10-4s),实现快速致密化;第2阶段为熔膜的铺展或收缩引起形貌变化,但熔体中仍残留微孔,致密度基本不变.熔体表面张力、粘性、润湿性和熔膜厚度等因素对致密化进程有不同程度的影响.     

纳米氧化铝弥散强化铜的放电等离子体烧结动力学及机制

利用经典热压模型,系统研究纳米氧化铝颗粒弥散强化铜的放电等离子烧结(SPS)致密化过程与机理。结果表明,放电等离子烧结初期,氧化铝弥散强化铜的致密化过程由晶界滑移和晶界扩散共同控制。随保温时间延长,烧结机制转变为由晶界滑移所主导。烧结后期致密化主要以塑性变形的方式进行。纳米氧化铝颗粒抑制了铜的烧结致密化,导致材料的密度降低。抑制机理为氧化铝颗粒阻碍晶界和位错运动,导致晶界滑移和塑性变形的激活能提高,从而增大致密化抗力。在外力和纳米氧化铝颗粒的共同作用下,塑性变形的主要形式为孪生。     

金属粉末微波烧结机理研究进展

从微波场对金属粉末的电磁作用及微波场中金属粉末的烧结行为等角度, 综述了国内外金属粉末微波烧结机理的研究进展。在电磁作用方面, 总结了热效应与非热效应对于烧结过程的影响, 热效应对烧结的影响主要包括微波加热电磁功率的损耗和电磁聚焦现象, 非热效应对烧结的影响主要是放电效应和磁力效应。归纳了烧结颈长大过程中的物质迁移方式及烧结颈生长机理, 材料种类和工艺参数对物质迁移方式产生影响, 烧结颈的生长过程同温度场及电磁场密切相关。本文在综述了现有研究进展的基础上, 分析了目前研究的不足与欠缺, 展望了金属粉末微波烧结机理未来的研究方向。     

WC-6Co-1.5Al合金高能球磨-电场活化烧结工艺的研究

采用高能球磨-电场活化烧结工艺制备了WC-6Co-1.5Al超细晶硬质合金块体,并对球磨粉末特性,以及合金的微观组织进行了分析测试。研究结果表明,WC-6Co-1.5Al复合粉末的球磨过程是一个晶粒逐渐细化、晶格畸变逐渐增加、粉末体系能量逐渐增大的过程;利用电场活化烧结技术能在电流为1 560 A,压力为30 MPa,烧结时间为6 min的情况下获得较为致密的硬质合金块体;合金中WC晶粒分布均匀,且没有出现异常长大现象。     

热等静压对铸件致密化及组织演变机理的影响研究

研究了铸件制品的热等静压致密化机理,分析了铸件制品热等静压的致密化模型,综合应用合金的蠕变理论和粉末冶金的烧结理论,利用现有的物理和数学模型对铸件在热等静压过程中的内部孔洞类缺陷闭合过程机理进行了阐述。确认了热等静压过程中起主要致密化作用的孔洞形变机制,为选择制定合适的热等静压工艺参数提供了理论参考。     

Powder metallurgical production of 316L stainless steel/niobium composites for Proton Exchange membrane electrolysis cells

In this study, a composite made of a porous stainless steel (SS) 316L substrate coated with Nb was investigated as a novel porous transport layer (PTL) for proton exchange membrane electrolysis cells (PEMECs). The fabrication of such SS316L/Nb composites using scalable and automatable powder metallurgical techniques as tape casting, screen-printing and field assisted sintering technology/spark plasma sintering (FAST/SPS) was described. Sintering behaviour and the interdiffusion at the SS316L/Nb interface were investigated. Powder metallurgical techniques such as screen-printing are the preferred method to achieve a porous Nb coating, while FAST/SPS is the preferred method for a better control of the SS316L/Nb interface by lowered interdiffusion. First electrochemical performance tests with SS316L/Nb composites demonstrate they have potential to replace the state-of-the-art titanium-based PTLs. The use of SS316L is expected to decrease manufacturing costs of PTLs, while the addition of niobium layer, due to its excellent corrosion resistance in acid environment, aims to improve PEMECs lifetime and performance.     

Mechanical properties of fine grained hardmetals produced by pressureless and pressure assisted sintering technologies

Pressureless sintering and the two pressure assisted sintering technologies – sintering + hot isostatic pressing (sinter-HIP) and field assisted sintering technology (FAST) were used to produce a fine grained WC-6 Co hardmetal.

In order to compare the mechanical properties of the hardmetals, which result from different sintering technologies, the material strength was determined. In the present study the uniaxial three point bending test and the biaxial ball on three balls test were used as strength measuring methods. The results were described by the Weibull distribution function.

Additionally, the paper will analytically compare the two tests by describing the relation of the strength of the samples to their effective volumes. Based on this procedure components having arbitrary shapes and volumes can be designed.     

电场活化烧结制备Cu-10Cr-0.5Al_2O_3复合材料

对Cu-10Cr-0.5Al2O3(质量分数,%)混合粉末及球磨复合粉末,采用电场活化烧结技术制备高强高导电铜基块体材料,并研究脉冲峰值电流和通电烧结时间对烧结材料组织和性能的影响。结果表明,随着脉冲峰值电流增大,烧结材料的相对密度和导电率均提高,相对密度最高可达99%,硬度和抗弯强度则先上升后下降。当脉冲电流峰值为2.94 kA时,烧结材料具有较好的综合性能,相对密度、硬度、抗弯强度和电导率分别为97.5%、285HV、911MPa和50IACS%;随着通电烧结时间延长,烧结材料的密度、硬度、抗弯强度和导电率均逐渐上升,但烧结时间过长会引起硬度轻微下降;对Cu-10Cr-0.5Al2O3混合粉末进行球磨虽导致烧结材料的电导率下降,但可显著提高材料的硬度和抗弯强度。     

U-FAST在先进材料研发中的应用

本文介绍了升级版的电场辅助烧结技术U-FAST(SPS)技术,该技术采用了现代电源技术,具有更快的加热速度,可以广泛的应用于先进材料的研发。如应用在烧结碳化物(WC-Co)、热电材料(PbTe)、Zr-Cu-Al-Nb(块状金属玻璃)、复合材料、透明陶瓷材料、生物材料、金刚石增加复合材料(EDC)等,并介绍了应用U-FAST工艺生产的特点。在较低温度和较短时间下开始烧结过程且不会产生任何不利的晶粒生长,使U-FAST技术成为生产纳米晶和亚微米材料的理想工艺,将电场辅助烧烧结技术提升到新高度。     

金属粉末激光烧结过程中搭接率敏感性分析

依据金属粉末直接激光烧结(DMLS)的实际烧结过程,以304不锈钢粉作为烧结材料,利用Ansys有限元软件,对其烧结成形温度场进行了数值模拟。首先对多道烧结过程中温度场的变化规律进行了分析,进而分析不同搭接率对温度场的影响,得出搭接率对烧结效果的敏感性。结果表明:搭接率过低会导致相邻烧结道之间存在未烧结粉末区域;搭接率过高又会造成温度过量集中,热量积累严重。针对所研究的304不锈钢粉,搭接率在26%~33%之间时,烧结效果较好。     

低温共烧陶瓷专用烧结炉温度场的数学模型

文章利用传热学的知识结合低温共烧陶瓷（LTCC）专用烧结炉炉内辐射与强制对流综合传热的特点，建立了烧结炉温度场的数学模型，从而为烧结炉温度场的全局数值模拟奠定基础。     

Sintering of nano- and ultradispersed mechanically activated W-Ni-Fe powders and the manufacture of ultrahigh-strength heavy tungsten alloys

The structure and mechanical properties of nano- and ultradispersed mechanically activated heavy W-Ni-Fe and W-Ni-Fe-Co tungsten alloys (VNZh and VNZhK alloys, respectively) are studied. Mechanically activated nano- and ultradispersed charge powders are sintered by free sintering (thermally activated) and spark plasma sintering. The dependence of the density of the alloys made of the mechanically activated powders on the sintering temperature is found to have a nonmonotonic character with a maximum corresponding to the optimum sintering temperature. It is shown that an increase in the mechanical activation time and the acceleration of the milling bodies during mechanical activation lead to a decrease in the alloy particle size and the formation of nonequilibrium solid solutions and are accompanied by a decrease in the optimum sintering temperature of heavy tungsten alloys. Ultrahigh-strength tungsten alloys the mechanical properties of which are substantially higher than those of standard coarse-grained analogs are fabricated due to the optimization of the conditions of ball milling and high-rate spark plasma sintering of W-Ni-Fe powders.     

Effects of heating rate on densification and grain growth during field-assisted sintering of α-Al2O3 and MoSi2 powders

Two types of powders, electrically conductive MoSi₂ and insulating α-Al₂O₃, were sintered by a field-assisted sintering technique (FAST) using heating rates from 50 °C to 700 °C/min. The Al₂O₃ powders were sintered to 99 pct density at 1100 °C for 2 minutes under 45 Mpa pressure. For Al₂O₃, no exaggerated grain growth was observed and the final grain size inversely scaled with the heating rate. Such a grain growth behavior fits the literature models based on multiple transport mechanisms for constant-heating-rate sintering. The density reached by MoSi₂ under similar sintering conditions was 91 pct. The grain size was independent of the heating-rate value. Specific electrical field and pressure effects are shown to contribute to enhanced densification and minimal coarsening in each material.