A statistical analysis of the effect of a mixture component on the rheology of alumina feedstocks

A statistical analysis based on the McLean-Anderson design method was carried out in studying the influence of each formulation component on the flow properties of alumina feedstocks. The formulations were composed of alumina powder (AL), polypropylene resin (PP), paraffin wax (PW), and stearic acid (SA). Fourteen different formulations were designed and their viscosities were measured using a capillary viscometer. The corresponding rheological parameters,i.e., fluidity, pseudoplasticity, and flow energy (ΔE) were evaluated and the effects of each ingredient in the mixture on them were analyzed. The studied ranges of AL, PP, PW, and SA were 87 to 89, 5 to 9.25, 3 to 7.25, and 0.75 to 1.5 wt pct, respectively. The results indicated that the lower alumina content or higher binder content would improve the fluidity of feedstocks. The order of increase in fluidity is SA > PW > PP. An increase of either AL or SA or a decrease of either PP or PW would cause less shear thinning in the resulting mixtures. Polypropylene resin is more effective than PW in enhancing pseudoplasticity. Finally, ΔE of feedstocks first decreases, reaches a minimum value at AL of about 87.7 wt pct, and then increases with powder loading. Increasing SA or decreasing either PP or PW would make ΔE smaller.     

Optimisation of eco-friendly binary binder system for powder injection moulding

Abstract

In recent years, many efforts have been made to obtain more environmentally acceptable powder injection moulding processes. In this sense, the purpose of this study is to optimise an eco-binder based on polyethylene glycol (PEG) as a water soluble component and cellulose acetate butyrate (CAB) as a natural backbone polymer derived from cellulose for powder injection moulding of zirconium silicate powders until a solvent debinding stage. Four different feedstocks have been investigated. As well as, a volume fraction of PEG and CAB 70/30 (vol.-%) and a solid loading of 57·5 (vol.-%) were maintained, molecular weights of polymers were combined in order to minimize distortion during binder solvent extraction. Water solvent debinding was carried out at three temperatures stepwise during 5 h. As a result, efficient removal of the PEG as well as free defects samples were obtained after solvent debinding for binder systems based on low molecular weight of PEG.     

Effect of nickel boride and boron additions on sintering characteristics of injection moulded 316L powder using water soluble binder system

Abstract

A new metal injection moulding system for 316L stainless steels has successfully been derived and tested. A mixture of small water atomised powder (average size 15 µm), larger gas atomised powder (average size 75 µm), and sintering additives has been coupled with a new water soluble binder system for economical powder injection moulding. The details for each process step and the effect of sintering additives are described. The binder system consists of poly (2-ethyl-2-oxazoline) as the leachable polymer, polyethylene as the backbone, and stearic acid as a surfactant and plasticiser. This binder system provides satisfactory mixture stability, excellent mouldability, and reasonably fast water leaching and thermal debinding rates. The optimum powder/binder compositions were determined using torque and capillary rheometry. Densification was by persistent liquid phase sintering through additives, such as nickel boride and boron. This 316L powder system was sintered to 7·9 g cm ^-3 (98·75% of theoretical) at 1285°C using nickel boride addition and at 1245°using boron addition. nickel boride additions are particularly effective at increasing the tensile strength and ductility. In contrast, the boron additions only increase the tensile strength and decrease ductility. Based on microstructure evaluations, this effect is traced to a continuous boride phase on the grain boundaries of the boron doped samples and a discontinuous boride phase on the grain boundaries of the nickel boride samples.     

Metal injection moulding of bronze using thermoplastic binder based on HDPE

Abstract

In the present work, the injection moulding process of a Cu–10Sn bronze has been studied. Different formulations of binders based on high density polyethylene, paraffin wax and polyethylene glycol have been used. The optimisation of the metallic load is based on torque measurements and rheological studies. The optimum powder loading was 60 vol.-%. The moulding parameters are selected to obtain homogeneous specimens with three different geometries and without distortions. The green parts have an adequate strength for handling. The organic binder was eliminated by thermal debinding under N₂/10%H₂ atmosphere. The debinding process has been designed by means of thermogravimetrical analysis of binder and feedstock and considering the maximum heating rates at which the samples do not present cracks. The specimens were sintered at temperatures between 875 and 950°C in the same reducing atmosphere.     

Microstructural characterisation of nickel rich areas and their influence on endurance limit of sintered steel

Abstract

Nickel is an often used alloying element in powder metal steel to achieve high hardenability. However, when nickel is added, the slow diffusion rate between iron and nickel leads to the formation of nickel rich areas (NRAs). Two steel alloys were studied: a Fe–6·4Ni–0·7Mo–0·7C with standard sized nickel powder additions and a Fe–2·4Ni–0·7Mo–0·7C with a finer sized nickel powder. Microstructural characterisation of the parts revealed that sufficient hardenability was achieved for both materials, but that NRAs were observed when standard sized nickel is used. X-ray energy dispersive spectrometry and electron diffraction show that the NRAs are composed of martensite and austenite under rapid cooling conditions. Three-point bending fatigue tests were carried out on both alloys to evaluate the effect of these soft austenitic areas on the fatigue properties of powder metal steel parts. The analysis of the endurance limit results shows that NRAs are not a governing factor.     

Some Mechanical Properties of Powder-Forged Iron/Alloy Mixtures

Abstract

An investigation was made of the feasibility of producing alloy forgings (nominal composition Fe–0·5C–0·6% Mn), from a powder prepared by mixing the alloying additions with iron powder. The carbon was added as microcrystalline graphite and the manganese as elemental powder and as ferro-manganese powder. Additions of copper and ammonium chloride powders were also made for the purpose of assisting the manganese to alloy with the iron. The copper addition improved the tensile strength but lowered the ductility. The ammonium chloride had little effect except for an apparent lowering of hardness. It was found that useful mechanical properties could be obtained in forgings made from mixtures of the alloying ingredients.     

不同铁矿粉替代澳洲低铝矿粉对烧结黏结相高温行为的影响

澳洲某低铝矿粉具有低Al₂O₃、粗粒度、强同化性等优点,是国内钢铁企业进口矿石的主要来源之一,而该低铝矿粉已濒临枯竭,故寻求其他铁矿粉进行替代现已成为迫切需求。采用微型烧结等方法,考察不同铁矿粉替代该低铝矿粉后黏结相高温行为的变化。研究表明,当配加南美矿粉OA后,黏结相同化性减弱,液相流动性增强,铁酸钙含量降低;当配加北非铁矿OB粉后,黏结相同化性和液相流动性均增强,但硅酸钙含量有所增加;当配加2种澳洲铁矿粉OC和OD后,黏结相的同化性减弱,高铝脆性矿物含量增加。基于此,通过澳洲铁矿粉OC搭配北非铁矿粉OB共同替代该低铝矿粉的方式,增强黏结相同化性和流动性,提高铁酸钙含量,抑制了劣质矿物的生成。     

Effect of boron on vacuum carburising depth of iron powder metallurgy compacts

Abstract

The work was aimed at determining the effect of boron on vacuum carburising of iron compacts with density over 7·2 g cm^–3. An attempt was made to determine the effectiveness of boron on carbon diffusion rate into the material of compacts with no additional effect of interconnected porosity. Vacuum carburising of compacts made of iron powder with an addition of boron was carried out at 1050°C in a laboratory vacuum furnace.

The effect of boron content within 0·005 to 0·02% on the vacuum carburising depth was analysed. It was found that the boron addition up to 0·01% increased the carburising depth by ～0% in comparison with the compacts of pure iron.     

PRACTICAL EXPERIENCE IN THE PRODUCTION OF HIGH-DENSITY COMPONENTS TO ACCURATE DIMENSIONS FROM FINE POWDERS

Abstract

The paper traces the dependence of consistent quality in high-density components on the preparative history of the powder used in fabrication, taking uranium dioxide as an example. Consistent dimensions imply consistent densities, microstructures, &c., and the influence of powder quality on these properties is discussed. The chemistry of uranyl nitrate precipitation with ammonia is described with reference to the powder characteristics of the product and the way in which these are modified by subsequent thermal and mechanical treatments, such as hydrogen reduction and micronizing.

In the high-throughput production of uranium dioxide solid cylinders for nuclear fuel elements, automatic presses. are used; the requirements for granulation and binder addition to ensure a smooth and consistent feed to the presses are considered, together with the precautions necessary in removal of the binder to avoid subsequent distortion of the pellet on sintering.

In the U.K.A.E.A., such pellets are made on the ton scale and the typical dimensional spread on as-sintered pellets is ± 1% on components of ～0·5 in. dia.; this is a considerable achievement, considering that the shrinkage of a component on sintering is some 40 vol.-%. Final sizing, for instance on centreless grinders, reduces the dimensional spread to ± 0·0005 in.

The experience gained in studying uranium dioxide fabrication is translatable to other special (i.e. non-silicate) ceramics and to metal powders, as illustrated by work at Springfields on beryllia and alumina.     

Thixotropic properties of multi-functional binder and compaction behaviour of the low alloyed binder-treated powder

A new multi-functional binder with adhesive and lubricant effect was designed, and the thixotropic properties of the binder components and the resulting binder, the adhesive effect and compaction behaviour of the binder-treated powder were investigated. The results demonstrate that the thixotropic components in the binder are polyethylene wax and microcrystalline wax. With the increase of polyethylene wax content, the critical solid–liquid shear stress of binders decreases gradually. The main lubrication components in the low-pressure and high-pressure stages during the compaction process are found to be polyethylene wax and microcrystalline wax, respectively. The fine metal or graphite additives are effectively bonded on the surface of iron particles and filled in the pits. The green density reaches 7.25?g?cm^?3 at 600?MPa when the content of polyethylene wax is 30%. From 400 to 750?MPa, the content of polyethylene wax corresponding to the minimum ejection pressure decreases from 20 to 0%.     

Influence of Powder Type and Density on Pore Closure and Surface Hardness Changes Resulting from Steam Treatment of Sintered Iron

Abstract

Two types of Höganäs iron powder – sponge, and atomized with very high compressibility (ASC), after compaction to densities of 6·0, 6·4, and 6·8 Mg m^?3 and sintering under standard conditions were subjected to steam oxidation at 450, 525, and 600°C. The progress of oxidation was studied by measurement of weight gain and hardness. X-ray methods were used to determine the type of oxide present after treatment. During steam oxidation the type of powder has an important influence on the extent of pore closure and on the morphology of the oxide produced. The kinetics of oxidation were always faster for sponge iron than for atomized iron and there was a corresponding increase in the rate of pore closure and in surface hardness. For effective sealing of surface pores components should be of high density and be steam treated at 600°C but for attainment of maximum hardness components should be of low density and be steam treated at 525°C.     

Sintering parameters and mechanical properties of injection moulded aluminium powder

Abstract

This paper describes the microstructural and mechanical properties of injection moulded aluminium powder. Gas atomised aluminium powder was injection moulded with wax based binder. The critical powder loading for injection moulding was 62·5 vol.-% for feedstock. Binder debinding was performed in solvent and thermal method. After debinding, the samples were sintered at different temperatures and times in high purity N₂. Metallographic studies were conducted to determine the extent of densification and the corresponding microstructural changes. The results show that gas atomised aluminium powder could be sintered to a maximum 96·2% of theoretical density. Maximum density, tensile strength and hardness were obtained when sintered at 650°C for 60 min.     

Effect of Compacting Pressure and 0·5%Mo on Properties of Sintered Iron Powder and Manganese Steels

Abstract

An investigation has been carried out on the effect of compacting pressure, in the range 150–600 MPa, and of the addition of 0·5%Mo on the properties of sintered Hametag iron powder and manganese steels. Higher sintering activity compared with standard iron resulted in higher density and higher mechanical properties in the presence of manganese vapour. The addition of 0·5%Mo in the form of ferromolyb-denum caused an increase in density and strength properties in the Fe–C and Fe–Mn–C steels. PM/0157     

Microstructural and mechanical properties of injection moulded gas and water atomised 17-4 PH stainless steel powder

Abstract

This paper describes the microstructural and mechanical properties of injection moulded 17-4 PH stainless steel gas and water atomised powder. Gas and water atomised stainless steel powders were injection moulded with wax based binder. The critical powder loading for injection moulding were 62·5 and 55 vol.-% for gas and water atomised powders respectively. Binder debinding was performed using solvent and thermal method. After dedinding the samples were sintered at different temperatures for 1 h in pure H₂. Metallographic studies were conducted to determine to extend densification and the corresponding microstructural changes. The results show that gas atomised powder could be sintered to a maximum (98·7%) of theoretical density, and water atomised powder could be sintered to a maximum (97·08%) of theoretical density. Maximum tensile strength was obtained for gas atomised powder sintered at 1350°C. The tensile strength of the water atomised powder sintered at the same temperature was lower owing to higher porosity. Finally, mechanical tests show that the water atomised powder has lower mechanical properties than gas atomised powder.     

Dilatometric analysis of thermal debinding of injection moulded iron compacts

Abstract

The less than desired tolerance control of powder injection moulded compacts is a result of inconsistent dimensional changes in the compacts accumulated during moulding, debinding, and sintering. This study investigated the in situ length changes and their causes during thermal debinding on compacts which have been solvent debound. The dilatometric analysis showed that the specimen shrank in the early stage between 250 and 370°C, not because of sintering, but through the loss of N, C, and O in the carbonyl iron powder. At temperatures between 370 and 450°C, the specimen expanded owing to the carburisation of the iron powder. The length change was also influenced by the heating rate, debinding atmosphere, and the amount of the backbone binder. These dilatometric results are helpful in establishing the guidelines in designing binder compositions and debinding schedules.     

PERMANENT MAGNETS FROM ELONGATED SINGLE-DOMAIN PARTICLES

Abstract

A process is described for producing elongated single-domain (ESD) fine-particle magnets. The 150-Å. ESD iron or iron–cobalt alloy particles are prepared by controlled electrodeposition into mercury, followed by thermal growth and treatment with a third metal to attain optimum particle shape and magnetic properties. The particles are then aligned by a magnetic field, compacted under pressure, freed of mercury by vacuum distillation, and embedded in a suitable matrix. This is ground to a coarse powder and fed into automatic presses for realigning and compacting to the final magnet shape. The factors controlling each step of the process are discussed, and the advantages of magnets with artificial microstructures synthesized by this approach are pointed out. The process described produces commercial ESD iron and iron–cobalt magnets with energy products of 2·2 and 3·5 million gauss-oersteds, and laboratory ESD iron and iron–cobalt magnets of 4·2 and 5·0 million gauss-oersteds.     

Separation behaviour of zinc dross from hot dip galvanising melts of different aluminium concentrations by alternating magnetic field

Abstract

Dross in zinc pots is the most important factor that impairs the surface quality of hot dip galvanising automobile steel sheet. Separation behaviour of zinc dross from galvanising melts of different Al concentrations (0·12, 4·5 and 55·0 wt-% by an alternating magnetic field has been investigated in order to reduce the dross defects on steel sheets. The properties of different zinc drosses were investigated by means of EDAX and the quantitative metallographic method and the conductivities were measured by physics property measurements system. The experimental results show that the zinc dross in different hot dip galvanising melts has different morphologies, compositions and structures, and the average particle size of the dross increases with the Al concentration. In the case of extra iron (above the solubility limit) in the zinc melt, zinc dross quantity also increases with the Al concentration. All of the three types of zinc dross particles >5 μm can be successfully separated when the magnetic frequency is 17·5 kHz, effective magnetic flux intensity is 0·05 T, imposed time is 15 s and the cross-section of the ceramic square pipe is 5 × 5 mm.     

Recyclability assessment of Al 7075 chips produced by cold comminution and consolidation using spark plasma sintering

A solid-state recycling route for processing aluminium alloy 7075 chips is proposed. This process involves pulverizing the chips using an industrial scale comminution line to produce a broad particle size distribution of granulated products and powders. Upon sieving, the ?140 mesh fraction of the pulverised material was consolidated by spark plasma sintering into fully dense compacts, i.e. >99%. The properties of the pulverised powders and compacts were compared to commercially available aluminium alloy 7075 powder used in industrial press-sinter applications. The comminution line produced powder particles which possessed a 7·9?±?0·6-nm thick native oxide layer with adhering exogenous contaminants, and aluminium oxide particles dispersed throughout the powder. The presence of the oxide layer and exogenous contaminants was found to be deleterious to the powder consolidation and mechanical properties. A flexural strength and strain and hardness of 94·7?±?7·2?MPa, 2·1?±?0·3% and 69·3?±?5·2 HV were obtained, respectively.     

INFLUENCE OF IRON POWDER TYPE ON THE PROPERTIES OF SINTERED IRON AT VARIOUS DENSITY LEVELS

Abstract

The properties of various commercial and experimental iron powder types and of compacts made from them in the density range 6·8–7·87 kg/dm³ by single-pressing, double-pressing, and hot-forging techniques have been determined. It was shown that the ductility in all cases was more adversely affected than the tensile strength by the presence of porosity. However, it was also shown that at any particular density level or with a given processing schedule the mechanical properties varied widely, depending on the iron powder used. On the basis of the mechanical-property results, the powder types to be preferred at different density levels are indicated.