316L不锈钢粉末注射成形件的烧结致密化行为

为了控制粉末注射成形零件的最终尺寸精度和力学性能,对316L不锈钢粉末注射成形件的烧结致密化行为进行了试验研究,分析了烧结温度和升温速率对试件致密化行为以及烧结件力学性能的影响.试验结果表明,致密化过程始于1080℃左右,主要在1200～1300℃的升温过程中快速进行,致密化速率随着升温速率的升高而升高.烧结件的抗拉强度、抗弯强度以及延伸率,不但取决于致密化程度,而且与微观结构有关.分析表明,将基于扩散控制和强度控制的烧结理论结合,可以有效地解释316L不锈钢粉末的致密化行为,需在现有的烧结模型中考虑强度影响因素,才能更真实地模拟烧结过程.     

升温速率对氧化铝粉末烧结行为的影响

采用不同的升温速率,在膨胀计中对脱脂后的氧化铝粉末射成形坯件进行一系列的烧结试验.结果表明,烧结致密化过程主要发生在升温阶段,快速升温有利于致密化的进行和抑止晶粒长大,但由于烧结时间较短和烧结炉最高温度的限制,产品的最终致密化程度不高.在低温时快速升温,高温时缓慢加热,可以获得较好的致密化效果和微观结构.试验和分析结果将为建立非等温烧结模型和烧结工艺参数的优化方法提供依据.     

Effect of heating mode and temperature on sintering of YAG dispersed 434L ferritic stainless steel

This study examines the effect of heating mode, sintering temperature, and varying yttria alumina garnet (YAG) addition (5 and 10 wt%) on the densification and properties of ferritic (434L) stainless steel. The straight 434L stainless steel and 434L–YAG composites were sintered in a conventional and a 2.45 GHz microwave furnace. The composites were sintered to solid-state as well as supersolidus sintering temperature at 1200 and 1400 °C, respectively. Both 434L and 434L–YAG compacts coupled with microwaves and underwent rapid heating (∼45 °C/min). This resulted in about 85% reduction in the processing time. For all compositions microwave sintering results in greater densification. As compared to conventional sintering, microwave sintered compacts exhibit a more refined microstructure, thereby, resulting in higher bulk hardness. The mechanical properties and sliding wear resistance of 434L stainless steel is shown to be sensitive both to the sintering condition as well as YAG addition and has been correlated to the effect of heating mode on the pore morphology.     

Effect of Hot Isostatic Pressing Loading Route on Microstructure and Mechanical Properties of Powder Metallurgy Ti_2AlNb Alloys

In this work, hot isostatic pressing(HIPing) technique was used to densify the Ti_2AlNb pre-alloyed powder.The influence of HIPing loading route parameters(temperature and rates of heating and pressurizing)on microstructure and properties of PM Ti_2AlNb alloys was studied. The results showed that HIPing loading route parameters affected the densification process and mechanical properties(especially high temperature rupture lifetime) of PM Ti_2AlNb alloys in the present work. A finite element method(FEM) model for predicting the final densification was developed and was used to optimize the HIPing procedure.     

Three dimensional simulation of microstructure evolution for ceramic tool materials

The observation and scientific quantitative characterization of three dimensional microstructure evolution during sintering process of ceramic tool materials is important to investigate the influence of nano-particles on mechanical properties. The relationship between microstructure and mechanical properties of ceramic tool materials can be established to direct the development of nano-composite ceramic tool materials by the research of the grain growth, grain boundary migration, distribution of nano-particles and microstructure densification at the different sintering temperature and pressure. In this paper, a 3D Monte Carlo model of three-phase nano-composite ceramic tool material is built and applied to simulate the microstructure evolution during sintering process. In this model, the grain boundary energy of each phase and interfacial energy between two phases are taken into consideration as the driving forces for grain growth. The sintering temperature and pressure are successfully coupled into the Monte Carlo simulation model. The microstructure evolution of defect free three-phase nano-composite ceramic tool materials is successfully simulated at different sintering temperature and pressure. The simulation results show that the higher the sintering temperature is, the faster the grain growth. However, the sintering pressure has little effect on the grain growth.     

TiB2/FeMo陶瓷的显微结构与力学性能

以Fe-Mo为助烧剂，通过热压制备了TiB2陶瓷．研究了烧结温度、烧结时间对材料显微结构和力学性能的影响，分析了烧结致密化过程．实验结果表明，随着热压烧结温度升高，材料抗弯强度、洛氏硬度出现峰值，热压烧结时间延长，抗弯强度有所下降．液相烧结的重排阶段致密化速率最快．     

An investigation on microwave sintering of Fe, Fe–Cu and Fe–Cu–C alloys

The powder characteristics of metallic powders play a key role during sintering. Densification and mechanical properties were also influenced by it. The current study examines the effect of heating mode on densification, microstructure, phase compositions and properties of Fe, Fe–2Cu and Fe–2Cu–0·8C systems. The compacts were heated in 2·45 GHz microwave sintering furnaces under forming gas (95%N₂–5%H₂) at 1120 °C for 60 min. Results of densification, mechanical properties and microstructural development of the microwave-sintered samples were reported and critically analysed in terms of various powder processing steps.     

The affect of densification and dehydroxylation on the mechanical properties of stoichiometric hydroxyapatite bioceramics

This paper reports the effects of processing densification on the mechanical properties of hydroxyapatite bioceramics. Densification of synthetic hydroxyapatite is conducted in the range 1000-1300 °C. X-ray diffraction and SEM microscopy are used to check the microstructure transformations. Vickers hardness, toughness and Young's modulus are analyzed versus the density and grain size. The sintering temperature and the particle size influence strongly the densification and the resulting mechanical properties. In addition, the critical sintering temperature appears around 1200 °C and the declined strength at the temperature up to 1200 °C is found sensitive to the dehydroxylation process of hydroxyapatite.     

复合掺杂8YSZ陶瓷性能的研究

以3Y-TZP/Bi_2O_3为复合添加剂制备8YSZ陶瓷材料,研究了复合掺杂对材料致密化、相组成、显微结构、力学性能及电学性能的影响.结果表明,3Y-TZP/Bi_2O_3复合添加剂的引入有利于材料的致密化,样品的烧结机理由固相烧结转变为液相烧结.引入3Y-TZP/Bi_2O_3后样品中出现了单斜相,且单斜相含量随四方相含量的增加而增加.材料的致密化使其具有良好的力学性能,同时对其电学性能也有一定的影响.     

粉末冶金多孔高氮奥氏体不锈钢的制备及性能

采用粉末冶金方法制备了多孔高氮奥氏体不锈钢并研究其力学性能和耐腐蚀性能。结果表明,高温气固渗氮能促进双相不锈钢向奥氏体不锈钢的转变,在其显微组织中出现了细条状和颗粒状CrN相析出物。随着造孔剂含量的提高孔隙率随之提高,而力学性能和耐腐蚀性能降低。与普通的多孔不锈钢相比,这种多孔高氮奥氏体不锈钢的力学性能更加优越,源于N的固溶强化和CrN等析出物的强化机制。随着孔隙率的提高多孔高氮奥氏体不锈钢的腐蚀倾向和腐蚀速率逐渐增大,造孔剂含量(质量分数)为10%的试样具有最佳的耐腐蚀性能。提高烧结温度有利于烧结块体的致密化,使腐蚀速率明显下降。     

Densification and crystallization in crystallizable low temperature co-fired ceramics

This article reports the impact of one critical process parameter, the heating rate during sintering from 530 to 850 °C, on the densification of a crystallized low temperature co-fired ceramics (LTCC). At a low heating rate the densification of LTCC is impeded by the competing crystallization processes, resulting in less shrinkage, lower density and consequently lower dielectric constant. Microstructural evidence is provided to analyze the multiple crystalline phases formed during sintering process. It is concluded that an optimized sintering profile should have a heating rate that allows full densification prior to onset of crystallization, follow by a full crystallization to limit the amount of residual glass for enhanced dielectric properties.     

元素粉末法制备TiAl金属间化合物的研究进展

元素粉末冶金因具有成本低、制备的合金组织均匀细小等优点而受到广泛关注。简要介绍了元素粉末法制备TiAl合金的研究进展,主要从反应机理、致密化行为和力学性能等方面进行综述。研究表明,Ti与Al元素的反应由扩散控制,借助TiAl3和TiAl2等中间相最终得到Ti3Al和TiAl相共存的反应产物。在高Nb–TiAl合金的Ti–Al–Nb三元系中,Nb元素主要通过形成中间产物——Nb–Al化合物最终均匀分布在基体相中。从原料和工艺两个角度总结了元素粉末法制备TiAl合金过程中影响致密化的因素,介绍了提高元素粉末法制备TiAl合金的热加工和力学性能的方法,总结了近年来元素粉末法制备TiAl合金的力学性能研究成果。目前来看,元素粉末法制备的TiAl合金力学性能已达到变形合金的水平。     

Microstructural evolution during the supersolidus liquid phase sintering of nickel-based prealloyed powder mixtures

A novel concept for full-density sintering is described. Two prealloyed powders with slight compositional differences are tailored to separate the solidus temperatures into high-melt and low-melt compositions. A mixture of these two powder compositions allows full-density sintering at a temperature between the two solidus temperatures. For these experiments, the two powders were nickel-based alloys, where the low-melt powder contained boron. The mixed powders were sintered at temperatures above the solidus of the low-melt powder to form a transient liquid that promoted rapid densification of the mixture. Microstructure evolution during sintering was assisted using quenching experiments. Variables in this study included the heating rate, peak temperature, hold time, and powder ratio. Interdiffusion between the two powders controls microstructure evolution, with a dominant role associated with boron diffusion and reaction. The transient liquid phase responsible for densification is linked to boron diffusion and subsequent compound precipitation.     

Grinding behavior of WO3, NiO,Fe2O3 by ultrasonic milling parameters control and preparation of nanocomposite powder

Tungsten-based alloys have been widely applied in various industries due to their excellent mechanical properties. Tungsten-based alloys have a high sintering temperature due to the high melting point of tungsten, so the coarse particles negatively affect the mechanical properties of the alloy. This problem can be solved by increasing the densification by reducing the sintering temperature and time by adding nanoparticles with high surface energy. Herein, we fabricated nanoparticle-sized metal oxides by ultrasonic milling to minimize the influx of impurities to improve the densification of tungsten alloys. The main parameters of the ultrasonic milling experiments were ball density and ball layer. Metal oxides prepared by ultrasonic milling showed an average particle size distribution of less than 200 nm, and metal composite powders prepared through subsequent hydrogen reduction also showed nanoparticle size distributions. We believe that this approach will enable the production of improved sintered tungsten-based alloys.     

放电等离子烧结制备AlCoCrFeNi高熵合金的组织演变与力学性能

采用放电等离子烧结方法(SPS)制备了AlCoCrFeNi高熵合金。通过差热分析、密度测试、X射线衍射、扫描电镜及力学性能测试,研究了SPS烧结温度对AlCoCrFeNi高熵合金的致密化行为、组织演变及力学性能影响。结果表明,随着SPS烧结温度的升高,材料的致密度与抗压缩强度明显提高。1200℃烧结后,AlCoCrFeNi高熵合金的致密度达到99.6%,抗压缩强度达到2195MPa,屈服强度达到1506MPa。在SPS烧结过程中,高熵合金从双相结构(BCC+B2)转变为三相结构(BCC+B2+FCC)。     

钼铜复合粉末的致密化及性能

对微波辅助法制备的钼铜复合粉末进行压制烧结,研究其致密化行为及复合材料性能。结果表明:烧结温度是控制钼铜复合材料成分、微观组织及综合性能的关键因素。1100℃下烧结的钼铜复合材料Cu含量最接近设计含量,过高的烧结温度将引起铜的损耗。在较低的烧结温度下(≤1100℃),复合材料的力学性能和物理性能随温度的升高而升高,但是过高的烧结温度(1200℃)会引起铜相的大量损失及颗粒异常长大,从而导致复合材料密度、硬度、导电率及导热率的降低。通过优化实验参数,1100℃下的复合材料具有理想的微观结构,铜相损失较少,复合材料成分接近设计成分,钼铜两相分散较为均匀,力学性能及物理性能优异,复合材料的密度、硬度、抗弯强度、电导率及热导率分别为9.79g/cm^3,229.1HV,837.76MPa,24.97×10~6S·m^-1和176.57W·m^-1·K^-1。     

电流直加热动态热压烧结制备SiCp/Fe复合材料

用电流直加热动态热压烧结法制备SiCp/Fe复合材料,研究了工艺参数对其性能的影响.结果表明,材料的性能随着热压压力、加载电压、烧结时间和间歇电流循环次数的增大而明显提高.该工艺热效率高,升温速率快,制备时间短,放电点的弥散分布,能实现均匀加热并使颗粒表面活化,使材料组织细小均匀.用此工艺可快速制备出均质、高致密和高质量的SiCp/Fe复合材料,其最好性能为致密度99.9%,布氏硬度416HB,抗拉强度838 MPa.     

颗粒弥散和核-壳共存的TiCN基金属陶瓷的制备

为了制备具有良好综合力学性能的TiCN基金属陶瓷，研究了烧结温度对TiCN-HfN陶瓷微观结构和力学性能的影响，构建了颗粒弥散和核-壳共存的微观结构模型，揭示了材料的致密化机制、增硬机制、增韧补强机制。结果表明:在1 500℃下所制备的TiCN-HfN材料具有颗粒弥散与核-壳共存的微观结构，其中弥散的颗粒为HfN，核为TiCN，壳主要为(Ti, Hf, Mo)CN固溶体；材料具有较好的性能，其相对密度为99.7%、硬度为20.6 GPa、抗弯强度为1 682.5 MPa、断裂韧度为8.5 MPa·m1/2；其致密化机制主要为颗粒和金属液相填充到烧结颈实现致密化，增硬机制主要为致密化和颗粒钉扎强化增硬，增韧补强机制主要为颗粒弥散和颗粒钉扎增韧、骨架结构和颗粒钉扎增强。      

Effect of particle size on densification of pure magnesium during spark plasma sintering

The effect of particles size ranges (<38 μm, 75–150 μm, 270–550 μm) of atomized magnesium powders on densification mechanisms during spark plasma sintering (SPS) process was investigated. The intrinsic driving force, local pressure and current of Mg powders with different particle sizes were analyzed by theoretical calculation. The results obviously indicate that the densification of pure magnesium can be improved by the reduction of particle size, suggesting the intrinsic driving force, local pressure and current intensity are enhanced significantly by a decrease in the particle size at the same sintering conditions, which can promote shrinkage of pores, formation of the sintering neck and mass transportation in the SPS process. Not only that, rapid densification is also interpreted in term of mechanical movement of particles, Joule heating effect and plastic deformation. However, the mechanical movement of the large particles is higher than that of small particles due to high punch displacement, and plastic deformation, detected by scanning electron microscopy, plays a main role in densification for large particles in the case during the sintering. Joule heating effect is the key factor for densification of small Mg particles, and high densification degree can be obtained by sintering small particles.     

Relation between microstructure,properties and spark plasma sintering (SPS) parameters of pure ultrafine WC powder

A combined experimental/numerical methodology is developed to fully consolidate pure ultrafine WC powder under a current-control mode. Three applied currents, 1900, 2100 and 2700 A, and a constant pressure of 20 MPa were employed as process conditions. The developed spark plasma sintering (SPS) finite-element model includes a moving-mesh technique to account for the contact resistance change due to sintering shrinkage and punch sliding. The effects of the heating rate on the microstructure and hardness were investigated in detail along the sample radius from both experimental and modeling points of view. The maximum hardness (2700 HV10) was achieved for a current of 1900 A at the core sample, while the maximum densification was achieved for 2100 and 2700 A. A direct relationship between the compact microstructure and both the sintering temperature and the heating rate was established.