Effects of lubricant''''s friction coefficient on warm compaction powder metallurgy

1　INTRODUCTIONWarm compaction is a relatively simple and e conomical process that can produce sintered partswith density up to 94% of the theoretical pore freedensity[1 3], and its potential is tremendous. Withminor modification on the conventional powdermetallurgy equipment and approximately 20%higher cost than conventional cold compaction,green compact density of 7.5 g/cm3 can be obtainedby single press. The only difference between thewarm compaction and th…     

二次温压对铜粉和镍粉反应的影响

研究了铜和镍混合粉经冷压和一次冷压、二次温压两种压制方法成型后的烧结体的显微组织以及密度和硬度。结果发现，在铜粉和镍粉反应过程中，二次温压对烧结体显微组织、密度和硬度有重要的影响。二次温压较冷压有利于Cu-Ni单相固溶体的形成，可以提高铜粉和镍粉烧结体的密度和硬度。     

Influence of alloying additions on microstructure and thermal properties in compact graphite irons

Abstract

Nineteen compacted graphite cast irons were investigated to determine how alloying additions affect the thermal transport properties and microstructure. All melts were based on one chemical composition and alloying elements were added to obtain melts with variation in magnesium, silicon, carbon, copper, tin, chromium and molybdenum. Increasing amounts of magnesium resulted in a further compaction of the graphite particles, reducing the thermal conductivity. Large amounts of silicon resulted in a fully ferritic metal matrix. Silicon also formed solid solution with iron which had a deteriorating effect on the thermal conductivity, i.e. the larger amount of silicon the lower the thermal conductivity. Copper and tin promoted formation of pearlite that had worse thermal properties compared to ferrite. Increasing amount of ferrite generally had a positive influence of the thermal conductivity. Chromium and molybdenum were carbide forming elements and carbides had a negative influence on the thermal conductivity.     

KF-KCl熔体中电沉积TiB2镀层

在铝工业中TiB2是一种非常有前途的阴极内衬取代材料.本研究首先通过热力学分析验证了在Ti-B-C体系生成TiB2的可能性,然后在K2TiF6和KBF4作为活性物质的KF-KCl熔体中以石墨为基体通过直流电沉积(CCP)和周期断开电流电沉积(PIC)技术制备了TiB2镀层,并且研究了电流密度和电镀技术对镀层表面平整度、致密度和晶粒尺寸的影响.结果表明,当电流密度为0.8 A/cm2时,能够得到厚度均匀且和基体具有良好附着的TiB2镀层;和CCP相比,采用PIC技术制备的TiB2镀层表面平整度和致密度都得到明显改善,并且晶粒也更为细小.XRD分析表明镀层由相对纯净的TiB2组成,并且镀层择优取向均为(001)面,这和二维晶核理论的预测相吻合.     

石墨及其混合物料的磨矿动力学行为

借助于分批磨矿动力学模型，分别研究了鳞片石墨磨矿及其作为混合物料的一个组分参与磨矿时的动力学行为。结果表明：不管是天然鳞片石墨组分还是混合物料总体，其磨矿动力学行为均是非线性的。只有鳞片石墨在单独磨矿时，其动力学行为才是线性的。初步分析了这一变化产生的原因，同时研究了石墨单独磨矿的碎裂参数特性     

Warm compacting behavior of stainless steel powders

The warm compacting behaviors of four different kinds of stainless steel powders, 304L, 316L, 410L and 430L, were studied. The results show that warm compaction can be applied to stainless steel powders. The green densities and strengths of compacts obtained through warm compaction are generally higher than those obtained through cold compaction. The compacting behaviors in warm compaction and cold compaction are similar.Under the compacting pressure of 700 MPa, the warm compacted densities are 0.10 - 0.22 g/cm3 higher than the cold compacted ones, and the green strengths are 11.5%-50% higher. The optimal warm compacting temperature is 100 - 110℃. In the die wall lubricated warm compaction, the optimum internal lubricant content is 0.2%.     

Study of the cold compaction of composite powders by the discrete element method

We present numerical simulations of the cold isostatic and close die compaction of mixtures of soft and hard powders. The simulations use the discrete element method with periodic boundary conditions on packing of 4000 spherical monosize particles. The two mechanisms that are generally put forward to explain the retarding effect of hard particles on the compaction have been analysed. First, we have studied in which condition the hard particles form a cluster that hinders the homogeneous distribution of the load. Friction between particles is shown to affect significantly the formation of such a cluster. Second, the additional deformation that soft particles must undergo in the presence of hard non-deformable particles has been evaluated. Related to this last issue, the importance of including hardening effects in the constitutive equation of the soft phase is demonstrated.     

再探蠕虫状石墨的形成机理

通过对不同冷速下结晶蠕铁的液淬试样进行分析观测，对蠕墨铸铁的一次结晶及蠕墨的形成机理进行了一些探讨，并进一步阐述了石墨中倾斜孪晶的作用。     

无定形石墨砂在铜合金铸造中的应用研究

石墨砂是一种新型的铸造用砂，研究了石墨砂对铸铜合组织与性能的影响，并将石墨将应用于青铜阀体铸件生产中，取得了良好的效果。     

铝-7石墨复合材料的半固态加工

采用电磁机械复合搅拌法制备了铝-7石墨的半固态浆料,研究了常规铸造条件下浆料的固相率对铸锭中石墨颗 粒分布的影响,得到了合理的铝-7石墨复合材料半固态加工工艺条件。     

石墨—铝基复合材料的制备及耐磨性能

用复合铸造及压铸法制备了石墨颗粒铝基复合材料。研究了在制备过程中石墨的烧损率及石墨含量对复合材料磨损特性的影响。结果表明,石墨的烧损率在48%左右;石墨的加入可降低摩擦系数和磨损时的温升,且少量的石墨可以提高材料的耐磨性;石墨含量较高时,会破坏基体强度,导致剧烈的磨损率。     

Crystallography of graphite spheroids in cast iron

To further understand graphite growth mechanisms in cast irons, this study focuses on the crystal structure of a graphite spheroid in the vicinity of its nucleus. A sample of a graphite spheroid from a commercial cast iron was characterised using transmission electron microscopy. The chemical composition of the nucleating particle was studied at the local scale. Crystal orientation maps of the graphite spheroid revealed misorientations and twist boundaries. High-resolution lattice fringe images showed that the basal planes of graphite were wavy and distorted close to the nucleus and very straight further away from it. These techniques were complementary and provided new insights on spheroidal graphite nucleation and growth.     

Effects of lubrication and aspect ratio on the consolidation of metal matrix composites under cyclic pressure

The effects of powder compaction under cyclic load were compared to traditional single-cycle compaction. The effect of interparticle friction as modified by lubrication and compact aspect ratio received particular attention. Mixtures of Al and Al₂O₃ were consolidated at room temperature in contained uniaxial consolidation experiments. The experiments showed that in static compaction, lubrication aids densification at low pressures but can inhibit consolidation at high pressures. Enhanced densification was observed following pressure cycling. These improvements were more pronounced in compacts having smaller aspect ratios. The efficiency of pressure cycling was reduced by the lubricant. Lubrication also decreased the effects of aspect ratio in both the static and cyclic compaction cases. Although lubrication did increase density uniformity, the resulting compact green strength was much lower. Both single and double action compaction were studied and the best green strength and density distribution were obtained with double-action compaction under cyclic pressure without lubricant.     

石墨形态对铸铁热疲劳性能的影响

主要研究了石墨形态对铸铁热疲劳性能的影响,为高速列车制动盘的合理选材提供依据。试验结果表明:蠕墨铸铁的耐热疲劳性能最好,球墨铸铁次之,灰铸铁最差。     

脉中电场对渗碳体第一阶段石墨化过程的影响

通过试验研究了脉冲电场对球墨铸铁高温退火过程中渗碳体第一阶段石墨化的影响,结果表明,随脉冲频率的增加渗碳体分解加快,新生石墨数量增多.分析认为,脉冲电场通过增加奥氏体中石墨的数量,从而缩短渗碳体转变为石墨过程中碳原子的扩散距离来加速渗碳体的第一阶段石墨化过程.     

Effect of co-intercalated organic solvents in graphite on electrochemical Li intercalation

Electrochemical properties of graphite in propylene carbonate based electrolytes containing various organic solvents have been studied by cyclic voltammetry and charge–discharge measurements. Good correlation between solvent co-intercalation and electrochemical lithium intercalation into graphite was found. Effect of co-intercalated organic solvents in graphite on electrochemical Li intercalation was discussed.     

Effect of Compaction Load and Sintering Temperature on Tribological and Mechanical Behavior of Ni/SiC/MoS<Subscript>2</Subscript> Composites

In the present investigation, the effects of compaction load and sintering temperature on the tribological and mechanical behavior of Ni/20%SiC/7%MoS₂ hybrid composites was studied. The density, compression strength, and hardness of the composites were evaluated and compared. The wear properties of the composites were evaluated for the test condition of 1 m/s speed and 10 N load using a pin-on-disk tribometer. The braking performance of the composites was evaluated in a subscale dynamometer for the 500 kJ energy condition. The microstructure and wear surface morphology of the composites were analyzed by stereo, optical, and scanning electron microscopes. From the results, the following important conclusions are drawn: (1) the compaction load of 1400 kN and sintering temperature of 900 °C are optimum to obtain the best combination of tribological and mechanical properties; (2) the properties such as density, compression strength, hardness, wear, and friction increase up to a critical sintering temperature, and then decrease later; (3) the composition and thickness of the interface reaction product phases (Ni₂Si, Ni₃Si, and graphite) play a key role in deciding the strength of Ni/SiC interface that consequently affects the mechanical and tribological properties of the composites; (4) the abrasive wear is found to be the main wear mechanism in the highly densified composites, whereas the delamination wear and the third-body wear are major wear mechanisms in the poorly densified composites; and (5) the better braking performance of the highly densified composites is attributed to the absence of third-body wear, controlled flow of solid lubricant, and lower porosity.     

球墨铸铁件表面片状石墨层的应用

球墨铸铁具有较佳的高温强度,灰口铸中片状石墨对铝合人具有抗蚀性;利用片状石墨可防止铝液侵蚀金属基体的特性,设计制作表面为灰口铸件材质的热电偶保护,使控温热电偶不因熔液溶穿保护管而损坏。     

A Comparison of Chemistry and Inclusion Distribution and Morphology Versus Melting Method of NiTi Alloys

NiTi alloys are produced by three melting methods. The first method requires compaction of nickel and titanium raw material into sections that can be joined together for melting in a Vacuum Arc Remelt unit (VAR). This ingot is melted two or more times in a VAR. The second method utilizes a Vacuum Induction Melting (VIM) unit to alloy the nickel and titanium, with the use of a graphite crucible. The resulting ingot is prepared and remelted in a VAR. The third method begins with primary melting in a vacuum Induction Skull Melter (ISM). The ISM produces ingots that are assembled into an electrode for VAR melting. For each of the melting methods, the final product depends on the quality and handling of the raw materials, the control of the process at each unit, and the preparation of the intermediate ingots for further processing. The melting method influences the final chemistry as well as the type and number of inclusions present in the final product. This study compares the chemistry and microcleanliness of product manufactured by each method to determine the appropriate melting technique that produces NiTi with the lowest residual elements, such as carbon, as well as the lowest size, and number of inclusions.     

氮对灰铸铁中石墨组织的作用

本文研究了氮在灰铸铁中的分布及含氮灰铸铁石墨组织结构,结果表明,氮在石墨与基体界面上的吸附和在石墨中的固溶是氮使石墨组织形态发生变化的主要原因。