还原回转窑中的粉末黏结特性及其固结机理

为了解决或延缓还原回转窑结圈问题,分析了粉末的黏结特性,包括粉末的软熔特性、固结强度,同时分析了还原回转窑中的粉末固结的原因与形成机理。研究结果表明:还原气氛越强、煤灰掺量越高,粉末的软熔温度越低,越容易形成液相固结;焙烧温度升高、煤灰的掺量增加,粉末固结强度提高,越易黏附固结在回转窑窑壁上;随着焙烧时间延长,粉末的固结强度先显著上升,再显著下降,然后又上升。焙烧温度升高、煤灰掺量增加,粉末固结强度增加的原因是促进了粉末中铁橄榄石和钙铁辉石等物质形成,产物使粉末黏结更紧密;焙烧时间造成粉末固结强度变化是固相固结和粉末还原过程晶形转变共同导致的结果:在焙烧初期,固相固结和还原同时进行,粉末固结强度上升;在还原焙烧中期,固相固结过程基本结束,还原膨胀效果显现,粉末的固结强度迅速下降;在焙烧后期,Fe2O3—Fe3O4—Fe O阶段基本结束,金属铁大量生成,粉末的体积收缩,其强度上升。     

WCu合金钨“网络”骨架的制备及其组织结构分析

在自制的设备上,通过化学镀正交试验法获得最佳的铜包覆钨复合粉末,再制成钨网络骨架,用类注射成型法也制得钨网络骨架,采用SEM与XRD手段与传统钨骨架制备技术进行了对比,结果表明:化学镀包覆粉和类注射法能够获得孔隙均匀、数量可控的钨网络骨架。而且影响钨粉化学镀包覆铜的因素较多,特别是钨粉粒径存在一最佳的尺度范围。     

Porous NiTi by creep expansion of argon-filled pores

NiTi powders are densified in the presence of argon gas, whose initial pressure is varied between 1 and 33 atm, to create NiTi billets containing isolated Ar-filled pores. Upon vacuum annealing, the pressurized pores expand by creep of the surrounding NiTi matrix at rates which are in agreement with a simple analytical model up to 16% porosity. Beyond this porosity, foaming becomes very slow, as pores connect with each other and with the specimen surface where the gas escapes. This is due to failure of previous NiTi powder boundaries weakened by oxides insoluble in NiTi; this mechanism does not occur in Ti foams which dissolve their oxides at high temperature, allowing higher levels of pore expansion and foam porosity. NiTi with 10–16% porosity exhibits Young's moduli of 48–57 GPa, and may be useful for high-strength, low stiffness biomedical implants with superelastic or shape-memory properties.     

Analysis of workability behavior of Al–SiC P/M composites using backpropagation neural network model and statistical technique

This paper presents an artificial neural network (ANN) model for predicting and analyzing the workability behavior during cold upsetting of sintered Al–SiC powder metallurgy (P/M) metal matrix composites (MMCs) under triaxial stress state condition which is the multifaceted technological concept, depending upon the ductility of the material and the process parameters. The input parameters of the ANN model are the preform density, the particle size, the percentage of reinforcement and the applied load. The output parameters of the model are the axial stress, the hoop stress, the axial strain, the hoop strain, the instantaneous strain hardening index, and the instantaneous strength coefficient. This model is a feed forward backpropagation neural network and is trained and tested with pairs of input/output data. A very good performance of the neural network, in terms of good agreement with the experimental data has been achieved. As a secondary objective, quantitative and statistical analyses were performed in order to evaluate the effect of the process parameters on the workability and the plastic deformation behavior of the composites.     

齿轮粉末锻造的变形力分析及其过程数值模拟

应用粉末烧结材料广义塑性理论,分析和计算了齿轮粉末锻造成形镦粗、复压的变形力和密度,运用MARC有限元数值模拟了粉末锻造齿轮的成形过程,讨论了数值模拟和理论计算结果。     

水雾化铁粉轧制试验研究

对自制的设备进行控制系统的改装,使得轧制参数便于调整.进行水雾化铁粉轧制试验,确定了随机轧制时带材相对密度和粉末松装相对密度及厚度的关系,分析了初始辊缝大小和摩擦系数对带材性能的影响.试验表明,对于150mm轧辊,当初始辊缝为0.475mm时,可轧制出最厚为1.22mm带材.     

Friction of PM ferritic stainless steels at temperatures up to 300 °C

Two ferritic stainless steels (409Nb and 434L) manufactured through powder metallurgical techniques were wear tested at different temperature conditions (up to 300 °C). Two sliding speeds were used, and tests were carried out against a wrought austenitic stainless steel. Materials’ wear performance was characterized through friction coefficients and analysis of wear tracks was carried out through scanning electron microscopy. Results have shown an adhesive wear mechanism. Oxidized ferrite particles have also been found on wear tracks.     

Amorphous and humidity caking: A review

Caking of products is a common and undesired phenomenon in food, chemical, pharmaceutical, and fertilizer industries which leads to extra cost and irregular quality. In general, caking processes could be identified as amorphous caking or humidity caking. In this review, history of studying caking, formation, methods, and prospects of these two caking processes are summarized and discussed. The relevant studies from the 1920 s to today are mentioned briefly. According to the different properties(i.e. hygrocapacity, hygrosensitivity, mechanical properties, and diffusion behavior) of amorphous powders and crystals, the conditions and mechanisms of amorphous and humidity caking are discussed. It is summarized that glass transition, moisture sorption, quantitative methods characterizing caking, accelerated caking tests, and simulation of caking behaviors are the main aspects that should be studied for a caking process. The methods for these five aspects are reviewed. Potential research points are proposed including caking of mixed particles, caking with phase transition or polymorph transition,non-homogenous caking, and simulation of caking.     

Designing a novel functional-structural NiTi/hydroxyapatite composite with enhanced mechanical properties and high bioactivity

Clinical applications require porous biomaterials, however, higher porosity levels and hydroxyapatite (HA) content hampers the mechanical properties like superelasticity. Here, a functional-structural composite consisting of a central NiTi shape memory alloy core with an outer macro-porous NiTi/HA layer was fabricated by spark plasma sintering (SPS). The central NiTi alloy provides desirable mechanical properties like high strength and superelasticity, while the outer layer with controllable pore size and bioactive HA, which strongly boosts the bioactivity. This work might provide a strategy for designing and fabricating multifunctional biocompatible materials that could be promising for bone implants.     

发动机连杆材料的研究现状

汽车连杆的强度、刚度和质量对提高发动机的动力性和可靠性至关重要,为满足发动机大功率、轻量化的设计要求,其中一个关键是连杆材料要有优越的综合性能。本为介绍了现阶段先进连杆材料的研究现状。