Influence of Lubricants on Dimensional Changes and Mechanical Properties of Sintered Ferrous Compacts

Abstract

The influence of admixed zinc stéarate on the shrinkage of uniaxially pressed iron powder compacts has been studied. For pressing conditions which caused inhibition of compaction the removal of the stéarate during sintering produced an increase in shrinkage parallel to the pressing axis and in direct proportion to lubricant content. Additions of stearic acid (varying particle size), zinc stearate, lithium stearate, stearamide, and Cosmic 64 wax were used to investigate the influence of lubricant on mechanical properties of green and sintered iron powder compacts. Green strength was reduced relative to unlubricated material only by lubricants whose physical and chemical properties enabled them to produce and maintain extensive interparticle films during pressing. Vapour from the rapid initial decomposition of lubricants which reduced green strength could have a deleterious physical influence on the tensile strength of dewaxed or sintered Fe compacts. Decomposing lubricants also produced undesirable chemical effects. These arose from reactions between lubricant decomposition products and the matrix or by these products interfering with reactions between matrix and sintering atmosphere.     

Low Dielectric Loss Ceramics of AlN Fine and Nanopowders

The dielectric properties of ceramics pressurelessly sintered from nano (10-100 nm) and fine (0.8-1.0 μm) aluminum nitride powders have been studied. High-purity aluminum nitride sintered from nanopowder of nearly-theoretical density has been found to exhibit a low dielectric constant ε = 6.3 and low loss, tgδ = 0.011 at 3.32 GHz. Ceramics sintered from a fine aluminum nitride powder doped with yttrium oxide have revealed ε = 7.7 and tgδ = 0.021 at 3.23 GHz. The dielectric properties have allowed us to use ceramics sintered from fine aluminum nitride powder as a material for microwave windows for the diagnosis and treatment of tumors of the larynx and breast.     

Characterization,Physical and Mechanical Behavior of Sintered Atomized Iron–Zinc Stearate Composite

Powder metallurgy is an effective method to process the iron component in near net shape. In this paper, the influence of particle size, lubricant and compaction load on the physical and mechanical properties of the sintered iron–zinc stearate composite sample has been investigated. Atomized iron powders of particle size 100–200 and 200–300 mesh with zinc stearate 2.5, 5.0 and 7.5 wt% were used for preparing the samples. Green samples were prepared by cold compaction at various loads of 200, 180 and 160 KN and the sintering is done at 500 °C. The physical properties and the mechanical properties such as density, hardness and compression strength have been measured for the sintered samples. Scanning electron microscope was used to characterize the atomized iron powders and the sintered samples. It were confirmed that the shape of atomized iron powder particles were irregular, dendritic and acicular. Energy dispersive spectroscopy was used to identify the elemental compositions of powders and the sintered samples. Taguchi (L₁₈) method was effectively used to develop the regression model and describe the contribution of the input parameters in compressive strength, density, and hardness. The highest effect on density was powder particle size followed by compaction load and lubricant wt%. The Hardness value increased with increase in the powder particle size and compaction load and decreases with increase in the lubricant wt%. The compression strength increased with increase of compaction load and decrease of lubricant wt% and particle size.     

A lubricant for pressing aluminum powder

Studies have been made on the effects of some organic compounds produced in the CIS countries on the technological behavior of aluminum powders with various grain sizes. The purpose has been to establish the best lubricant for pressing them. The effects of the lubricants have been examined on the density, fluidity, and shaping capacity of the powders, as well as the pressing forces needed. The organic compound edamid PS has been found to be in no way inferior to acrawax in its technological characteristics, the latter being the compound used in aluminum powder metallurgy in the USA. Siberian Technical Physics Institute, Institute for Strength Physics and Materials Science, Siberian Division, Russian Academy of Sciences, Tomsk, and Yakutsk State University, Russia. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 78–85, January–February, 1999.     

用温压制造高密度材料的关键参数

温压技术是由在加热的阴模中压制预热的粉末组成[1],已知温压有助于零件密实,从而改进烧结件的性能[2,3]。温压需要在适合温压的温度范围内进行。特别是,粉末混合粉应具有好的流动性,同时对阴模模壁有良好润滑性,以减小脱模力。在试验室和工业生产中都研究了用粘结剂处理的和未经粘剂处理的用温压技术制造的材料的性状与性能。为了确定和定量各种关键生产参数,诸如压制压力,粉末温度与阴模温度,生产速率及零件大小对生坯和烧结件特性和零件脱模力的影响,进行了专门的试验研究。依照粉末流动性与松装密度的稳定性,压制压力与温度以及压制零件的重量与密度讨论了温压的工艺性。     

Study of warm compaction of Alumix 123 L

Abstract

Although powder metallurgy (PM) material is dominated by ferrous alloys, there is a growing interest in Al PM. The usage of Al PM in automotive applications depends on the development of higher density and improved dynamic properties. Several approaches have been proposed to increase density of sintered parts. Warm compaction process of Al powder was used to achieve high density. In this study the authors focused on the effect of warm compaction on Alumix 123 L (ECKA Granules) powder blend. It has been found that warm compaction at 110°C led to a reduction in the ejection force by 27·9%, increased green density to 94% of theoretical density and increased sintered strength to 315 MPa as compared to those pressed at room temperature.     

润滑剂对Fe基粉末冶金材料温压工艺的影响

通过扫描电子显微镜观察和性能测试研究了硬脂酸锌、乙烯基双硬脂酰胺(ethylene bis stearamide,EBS)、复合润滑剂以及压制温度对Fe基粉末冶金材料温压工艺的影响规律。结果表明:当润滑剂加入量(质量分数)超过0.4%后,Fe基粉末的流动性和松装密度均随润滑剂加入量的增加而降低,其中加入单一EBS润滑剂的影响更大。添加润滑剂后增加了Fe基粉末冶金生坯的致密度,其中添加硬脂酸锌和复合润滑剂的Fe基粉末冶金生坯断口颗粒间结合更为紧密。润滑剂对提高Fe基粉末冶金试样生坯密度、烧结密度及抗弯强度的作用顺序为复合润滑剂硬脂酸锌EBS,Fe基粉末冶金材料的密度和力学性能均随温压温度的升高而增加。在最佳润滑剂加入量0.4%时,120℃温压Fe基粉末冶金试样密度比室温压制Fe基粉末冶金试样的密度提高了0.14~0.21 g/cm~3,硬度和抗弯强度提高了40%~65%。     

New technological approach to fabrication of high density PM parts by cold pressing sintering

Abstract

A new technological approach to the fabrication of high density powder metallurgy (PM) parts via single pressing sintering, allowing cold compaction to be performed without admixed lubricants, has been studied. The influence of in pore gas on the compacts' green density and their sintered properties were evaluated. A mathematical expression relating in pore gas pressure in the compacts to the green density was developed. The expression showed that in order to reduce the negative influence of gases trapped in the pores it is necessary to ensure effective air drainage from the compaction zone. In order to ensure sufficient air evacuation during cold compaction, a new design of porous die was developed. The behaviour of powder mixes with different lubricants during cold compaction in porous die was investigated. All the test conditions were evaluated in terms of green and sintered properties, including the ejection force, green and sintered densities, tensile strength and surface hardness. In the context of the experimental work, compaction in porous die promoted the improved combination of green and sintered properties compared with compaction in conventional dies.     

Effect of Zinc Stearate on Apparent Density,Mixing, and Compaction/Ejection of Iron Powder Compacts

Abstract

The behaviour of zinc stéarate (0–4 wt-%) during mixing with iron powder has been studied by monitoring changes of apparent density and comparison with powder prepared by depositing zinc stéarate from solution onto the iron particles. Apparent density was increased by the development of thin surface films at low lubricant contents but was decreased by the formation of thick layers and free lubricant at high contents. Pressure/density data were obtained from floating-die compaction of cylindrical iron powder compacts containing deposited zinc stéarate with and without die-wall lubrication to determine the relative significance of interparticle friction, particle/die-wall friction, and compaction inhibition. An optimum lubricant addition minimized interparticle friction during compaction. This was greater than the optimum observed for loose packing owing to the more arduous conditions prevalent in compaction. Compaction pressure losses associated with interparticle friction were lower than those caused by die-wall friction. The latter was only minimized by lubricant additions which also caused undesirable compaction inhibition. The forces required to overcome particle/die-wall friction were similar for both compaction and ejection.     

Production and properties of metal-PTFE antifriction materials from atomized bronze powders

Conclusions An investigation into the sinterability of loosely poured atomized bronze powders has established that the porosity of resultant sintered bronze skeletons depends on the particle size and shape. The shape of the bronze powder particles has some effect on the antifriction characteristics of a metal -PTFE material, but its coefficient of friction and wear resistance are affected more strongly by the composition of a solid lubricant introduced into the pores of its sintered skeleton. Using a nonspherical rather than spherical bronze powder gives a bronze saving of 15–20% without affecting the good antifriction properties of metal-PTFE materials, by increasing the porosity of their skeletons. Replacing molybdenum disulfide with graphite substantially increases the wear resistance of two-layer metal-PTFE materials and markedly decreases their cost, since the price of molybdenum disulfide is more than 20 times that of graphite.Translated from Poroshkovaya Metallurgiya, No. 9(273), pp. 30–34, September, 1985.     

The properties of tungsten processed by chemically activated sintering

Two tungsten powders have been treated with small concentrations of sintering activators to provide for enhanced low temperature sintering. The experimental study focused on the determination of the processing effects on properties such as sintered density, grain size, hardness, and strength. Variables in the plan included tungsten particle size, type of activator, amount of activator, compaction pressure, and sintering temperature. The sintered density is found to have a dominant effect on strength and hardness. The various processing variables are analyzed in terms of their effects on density. At high sintered densities, grain growth acts to degrade the strength. Additionally, the nature of the sintering activator influences the fracture strength. In this study optimal strength occurred with a 0.7 μm tungsten powder treated with 0.29 wt pct Ni, sintered at 1200 °C for one hour. The resulting density was 18.21 g/cm³, with aR _A hardness of 69 and a transverse rupture strength of 460 MPa.     

Investigation of warm compaction and sintering behaviour of aluminium alloys

Abstract

The effects of warm compaction on the green density and sintering behaviour of aluminium alloys were investigated. Particular attention is paid to prealloyed powders, i.e. eutectic and hypereutectic Al-Si alloys, regarding their potential applications in the automotive industry. The effects of chemical composition, alloying method, compacting temperature and the amount of powder lubricant were studied. The compaction behaviour was examined by an instrumented die enabling simultaneous measurement of density, die wall friction coefficient, the triaxial stresses acting on the powder during the course of compaction and ejection pressure. The sintering behaviour was studied via dilatometeric analysis as well as normal batch sintering. The results show that warm compaction could be a promising way to increase the green density of aluminium alloys, especially prealloyed powders, and to decreased imensional instability during sintering. Moreover, it reduces the sliding friction coefficient and the ejection force during the powder shaping process. This paper presents the significant advantages and drawbacks of using the warm compaction process for commercial PM aluminium alloys.     

温压工艺的研究进展

温压工艺在制造低成本、高密度、高强度、高精度异形复杂的粉末冶金零件方面具有巨大的优势。因而，详细介绍了该工艺所具有的诸如压坯密度大、强度高，烧结密度高、密度分布均匀，脱模压力低，制造成本低等技术与经济特点；分析了其关键技术，如温压用粉末制备、新型润滑剂和温压系统；总结了其致密化机理，即颗粒重排和塑性变形，并概括了其应用状况。最后指出发展我国温压工艺的意义。     

Development and Processing of Novel Aluminum Powder Metallurgy Materials for Heat Sink Applications

The objective of this research was to design aluminum powder metallurgy (PM) alloys and processing strategies that yielded sintered products with thermal properties that rivaled those of the cast and wrought aluminum alloys traditionally employed in heat sink manufacturing. Research has emphasized PM alloys within the Al-Mg-Sn system. In one sub-theme of research, the general processing response of each PM alloy was investigated through a combination of sintering trials, sintered density measurements, and microstructural assessments. In the second, the thermal properties of sintered products were studied in detail. Thermal conductivity was first determined using a calculated approach through discrete measurements of specific heat capacity, thermal diffusivity, and density and subsequently verified using a transient plane source technique on larger specimens. Experimental PM alloys achieved >99 pct theoretical density and exhibited thermal conductivity that ranged from 179 to 225 W/m K. Thermal performance was largely dominated by the amount of magnesium present within the aluminum grains and, in turn, bulk alloy chemistry. Data confirmed that the novel PM alloys were highly competitive with even the most advanced heat sink materials such as wrought 6063 and 6061.     

还原铁粉对Fe-1.1Ni-0.5Mo-0.5Cr合金组织与性能的影响

在惰性气体雾化法制备的Fe-1.1Ni-0.5Mo-0.5Cr预合金粉末中添加1.5％的Cu粉和0.6％的C粉(均为质量分数)以及还原铁粉(添加量分别为0、10％、20％和30％),混合均匀后在600 MPa压力下模压,在1 180℃烧结1h.烧结合金经180℃/1h回火处理后,进行密度、硬度、拉伸力学性能检测以及显微...     

Liquid-phase sintering of TiN-enriched T15-grade high-speed steels and their mechanical properties

The present investigation is an attempt to develop composites based on high-speed steel through liquid-phase sintering route using a powder metallurgical technique. Water-atomised annealed T15-grade HSS powder, lubricant and various mass percents of TiN (0–8%) were blended and axially compacted into green pellets at 850 MPa at room temperature. During sintering studies carried out in vacuum (10^?2 torr), optimum temperature for full densification was determined for each composition. Only full dense sintered samples (density ≥98% theoretical) were selected for further heat treatment and the evaluation of mechanical properties. Mechanical properties like hardness, transverse rupture strength and hot compressive yield strength were evaluated. Both qualitative and quantitative metallographic studies were carried out and chemical analysis of various phases in sintered as well as heat-treated composites were determined using SEM-EDX. The results confirm that fully dense composites containing up to 2% TiN exhibit equivalent mechanical properties, although some differences in service behaviour e.g. wear resistance are to be expected.     

LUBRICATION EFFECTS IN THE COMPACTION OF SPONGE-IRON POWDER AT LOW AND HIGH SPEEDS

Abstract

The effects of the amount and method of lubrication have been investigated when compacting Höganäs sponge-iron powder, NC100-24, at both low and high speeds. Pressing characteristics, ejection loads, and the final properties of the sintered compacts were markedly affected by both the amount and the method of lubrication. From the results obtained, an optimum amount of admixed zinc stearate is recommended for both low and high-speed conditions.     

固体自润滑减摩材料的研制和应用

为了满足某些工业用保持架材料的性能要求,采用粉末冶金工艺,以雾化青铜粉或Cu-Sn预混合粉为原料,添加适量的固体润滑剂,经混合、成型、烧结,制得了以青铜为基体并使润滑剂弥散分布于其中的固体自润滑减摩材料。测定了材料的密度、硬度、抗拉强度、摩擦系数和热膨胀系数,观察了金相组织,探讨了某些工艺参数对材料力学性能和物理性能的影响。结果表明,所研制的材料具有优良的加工性能,可成功地加工成保持架,其力学性能和物理性能已达到使用要求,在实际应用中获得了良好效果。     

Development of environmentally oriented processes for obtaining articles from aluminum powders by powder metallurgy: Report 2. Development of environmentally safe technology for compaction of finely dispersed aluminum powders

It is shown that the introduction of liquid film-forming lubricant into aluminum and the use of “warm” compaction make it possible to increase the environmental safety of powder metallurgy processes of aluminum via decreasing the dusting ability of finely dispersed powders, increasing the transportable properties of pressings, and excluding the operation of removing the grease lubricant from the pressing volume at the sintering stage.