Compacted Iron Research Articles

Density improvement of carbonyl iron compacts by addition of titania powders: Y.C.Lu, K.S.Hwang. (Taiwan National University, Taipei, Taiwan.) Powder Metall., vol 42, no 3, 1999, 257–262

Density improvement of carbonyl iron compacts by addition of titania powders: Y.C.Lu, K.S.Hwang. (Taiwan National University, Taipei, Taiwan.) Powder Metall., vol 42, no 3, 1999, 257–262

Improved densification of carbonyl iron compacts by the addition of fine alumina powders

An investigation of the effect of alumina particles on the sintering behavior of a carbonyl iron powder compact was carried out in this study. Two different-sized alumina, 0.05 and 0.4 µm, were added to the iron compact at amounts up to 1.2 wt pct. When 0.4 µm alumina particles were added, no sintering enhancement was observed. But, in contrast to previous results reported in literature, the addition of 0.1 to 0.2 wt pct of 0.05 µm alumina particles was found to improve the densification. With 0.1 wt pct, the sintered density increased from 7.25 to 7.40 g/cm3 after the compact was sintered at 1350 °C for 1 hour in hydrogen. Dilatometric curves showed that alumina impeded the early-stage sintering of iron in the α phase, but improved densification in the γ phase at high temperatures. These results, along with microstructural analysis, suggested that alumina particles exhibit dual roles; their physical presence blocks the diffusion of iron atoms, thus causing inhibition of sintering, while their grainboundary pinning effect prevents exaggerated grain growth of iron and helps densification. It follows that, depending upon the amount and size of the alumina powders, either an increase or decrease in the final sintered density can be obtained.

Microstructural modelling of electrical conductivity and mechanical properties of sintered ferrous materials

The role of microstructure on mechanical properties of sintered ferrous materials was studied using a method based on electrical conductivity measurement. The method was accompanied by quantitative fractography to evaluate the dewaxing and sintering process in iron compacts. The effects of manufacturing parameters, such as compacting pressure in the range of 150–800 MPa, sintering temperature from 400 to 1300°C, sintering time up to 8 h, and lubrication mode were investigated. Several mathematical models were checked to obtain the best one for prediction of electrical conductivity changes as a function of manufacturing parameters. The mechanical properties of the sintered compacts were also evaluated to establish a relationship between conductivity, total porosity, pore morphology, and mechanical behaviour. The results show that the electrical conductivity/resistivity of sintered materials is closely related to its microstructure, so that measuring these properties can replace destructive test methods for prediction of mechanical strength of sintered materials with homogeneous matrix microstructure. The application of the method is shown for sintered Fe, Fe–0·8%C, and Fe–1·5%Mo–0·7%C compacts.

Dilatometric analysis of thermal debinding of injection moulded iron compacts

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.

Electrical conductivity and microstructure of sintered ferrous materials: sintered iron

The viability of electrical conductivity as a tool for describing the microstructure of sintered iron compacts was investigated, the sintering temperature being varied from dewaxing to high temperature sintering. The relationships between formation of sintered contacts, presence of lubricants, and mechanical properties were evaluated through determination of conductivity and effective load bearing cross-section Ac . The latter parameter was measured via quantitative fractography of specimens impact fractured at 77 K. The role of porosity and sintering temperature on grain growth in iron was also evaluated using quantitative metallography. It was found that the conductivity of pressed compacts increases during the dewaxing stage, while the effect of the sintering parameters at higher temperatures is less conspicuous. In any case, the conductivity can be related to the load bearing cross-section by a logarithmic equation. Using the already established relationships between Ac and the mechanical properties, the latter can be predicted by using the conductivity, which might be helpful in quality control of PM components.

Influence of process parameters on cold forgability of iron powder compacts: J.N.Das et al. (Regional Engineering College, Durgapur, India.)

Influence of process parameters on cold forgability of iron powder compacts: J.N.Das et al. (Regional Engineering College, Durgapur, India.)

Magnetic Sintering of Ferromagnetic Metal Powder Compacts

Magnetic sintering of ferromagnetic metal powder compacts has been carried out aiming at precise control of microstructures in polycrystalline materials. Powder compacts of carbonyl iron and cobalt were subjected to magnetic sintering in a direct-current magnetic field ranging up to 1.2 MA/m at temperatures in both the ferromagnetic and the paramagnetic regions. We have found that a magnetic field can enhance the densification and grain growth of iron powder compacts in the ferromagnetic state and in the paramagnetic one. The higher became the magnetic field strength, the more the densification during sintering proceeded. The observed magnetic field effects seemed to he most significant in the intermediate stage of sintering. The observations suggested that a magnetic field was responsible for an increase in the driving force for grain boundary migration that would play an important role in the densification during sintering. In contrast to iron powder compacts the densification of cobalt powder compacts were suppressed by a magnetic lield.

温間成形における鉄系粉末の圧密化挙動に及ぼす潤滑剤の影響

The effect of the lubricant on the compaction behavior in warm compaction of iron powder was examined by using Cooper-Eaton equation. Particle rearrangement depends on the lubrication effect between powder particles and is more dominant on its compaction behavior than the plastic deformation of powder particles until 423K. The total fractional volume compaction calculated by this method corresponds to the measured density of the green compact. Therefore, this analytical method is available to evaluate the warm compaction behavior quantitatively.

Density Gradients in Multilayer Compacted Iron Powder Parts

The use of multilayer compaction to form powder metal (P/M)components, is encouraging. With this process, a part is formed by successively compacting layers of powder. The formation of parts with larger than conventional height to diameter ratios is possible. Multilayer compaction also reduces the density gradients normally observed in large parts from conventional double action compaction. Optimization of the layer thickness based on the powder characteristics can lead to greatly reduced density gradients. The physical properties of multilayer compacted components are investigated as a function of layer thickness. The research has been performed with two iron powders of varying characteristics. The compressibility of the powder versus the layer thickness is discussed and related to the density distribution in the component.

Prediction of fracture generated by elastic recoveries of tools in multi-level powder compaction using finite element simulation

Fracture initiated in a compact by the difference between the amounts of elastic recovery of tools during the unloading process of multi-level powder compaction is predicted from calculated results by finite element simulation. The loading and unloading processes in the compaction are simulated by the rigid-plastic and elastic finite element methods, respectively. In these simulations, elastic tools are modelled as springs connected with the nodal points on the interfaces between the powder material and tools. This modelling leads to simple treatment of coupling of the tools and compact. The initiation of fracture is evaluated from the maximum principal stress, and the critical stress is measured by means of bending and shearing tests. Two-level compaction operations are simulated by the finite element methods to predict the initiation of fracture. The predicted critical values of relative density for the occurrence of fracture are in good agreement with the experimental ones for iron powder compacts.

Strength and microstructure during warm compaction of iron powders: K.Pischang et al. (Dresden University of Technology, Dresden, Germany.)

Strength and microstructure during warm compaction of iron powders: K.Pischang et al. (Dresden University of Technology, Dresden, Germany.)

Precipitation of graphite during sintering iron powder compacts with boron: Y.Nakano et al. (Kawasaki Steel Corp, Chiba, Japan.) J. Jpn Soc. Powder Powder Metall., Vol 44, No 9, 1997, 870–875. (In Japanese.)

Precipitation of graphite during sintering iron powder compacts with boron: Y.Nakano et al. (Kawasaki Steel Corp, Chiba, Japan.) J. Jpn Soc. Powder Powder Metall., Vol 44, No 9, 1997, 870–875. (In Japanese.)

Copper infiltration of iron compacts for high performance magnetic components: R.F.Krause et al. (Magnetics International Inc, USA.)

Copper infiltration of iron compacts for high performance magnetic components: R.F.Krause et al. (Magnetics International Inc, USA.)

The Institute of Materials Science and Engineering, National Taiwan University

The addition of fine titania powders increases the sintered density of carbonyl iron compacts from 6·91 to 7·28 g cm-3 when the compacts were sintered at 1200°C for 1 h in hydrogen. Analysis of dilatometric curves and microstructures indicated that titania inhibited the early stage sintering owing to the blocking of the diffusion path of iron atoms. However, the titania powders helped prevent the exaggerated grain growth that usually occurs during the α → γ phase transformation. As the compact reached 950°C, a small part of the titania was reduced by hydrogen, and the reduced titanium dissolved into the iron matrix and enhanced sintering. Meanwhile, the remaining titania coarsened, and its effect on sintering inhibition diminished. The retardation of the grain growth, coarsening of the titania at high temperatures, and the diffusion rates enhanced by the reduced titanium resulted in improved final sintered densities of carbonyl iron compacts.

Effect of Magnetic Field on Sintering of Iron Powder Compact

The present work has been performed to study the effect of application of direct current (DC) magnetic field on sintering of pure iron powder compacts. DC magnetic field up to 15kOe was applied during sintering for 100h at 973K in ferromagnetic region below the Curie temperature. The material used here was 99.9% pure carbonyl iron powder compacts with a cylindrical shape of 10mm in diameter and 10mm in length. Microstructural changes during sintering have been examined. In particular, we paid attention to change in the distributions of grain size, grain orientation and the grain boundary character distribution (GBCD). The determination of the size and the orientation of grains and the GBCD was performed with a FE-SEM-EBSP/OIM on-line analyzing system. Measurement of the density was also carried out to reveal the effect of magnetic field on sintering. It has been found that the application of magnetic field can enhance densification and grain growth in the cross sections both parallel and perpendicular to the magnetic field. In addition, it has been found from the GBCD analysis that the frequency of low angle boundaries and low Σ coincidence boundaries was increased by the DC magnetic field sintering.

Effect of lubricants on iron compacts for low frequency AC applications : C.Gelinas et al. (Quebec Metal Powders Ltd, Canada.)

Effect of lubricants on iron compacts for low frequency AC applications : C.Gelinas et al. (Quebec Metal Powders Ltd, Canada.)

Effect of heat treatment on iron compacts for low frequency ac applications : C.Gelinas et al. (Quebec Metal Powders Ltd, Canada.)

Effect of heat treatment on iron compacts for low frequency ac applications : C.Gelinas et al. (Quebec Metal Powders Ltd, Canada.)

Mechanical properties in tension of mechanically attrited nanocrystalline iron by the use of the miniaturized disk bend test

The mechanical properties of warm compacted nanocrystalline (nc) iron powder compacts of near theoretical density in the grain size range between 8 and 33 nm were investigated. The elastic and plastic behavior were characterized by miniaturized disk bend tests and hardness measurements. Light and scanning electron microscopy (SEM) were used to document the deformation and fracture morphologies. The Young's modulus of the nc Fe was essentially the same as that of coarse grained Fe. All samples failed in a macroscopically brittle manner. Local plasticity in shear bands was observed in the samples with the larger grain sizes (>20 nm). An increasing failure stress with increasing grain size is probably due to a processing effect on the flaw controlled failure of the samples. The results are discussed in the context of the deformation and fracture behavior of micrometer grain size metals and alloys.

Formation of free graphite during sintering of iron compacts containing carbon and boron

Formation of free graphite during sintering of iron compacts containing carbon and boron

Prediction of Crack Induced by Elastic Recoveries of Tools in Multi-Level Powder Compaction Using Finite Element Simulation.

The initiation of fracture induced in a compact by the difference between the elastic recoveries of tools during the unloading process of multi-level powder compaction is predicted from calculated results by finite element simulation. The loading and unloading processes in the compaction are simulated by the rigid-plastic and elastic finite element methods, respectively. In these simulations, elastic tools are modeled as springs connected with the nodal points on the interfaces between the compact and tools. This modeling leads to simple treatment of coupling of the tools and compact. The initiation of fracture is evaluated from the maximum principal stress, and the critical stress is measured by means of bending and shearing tests. Two-level compaction operations are simulated by the finite element method to predict the initiation of fracture. The predicted critical values of relative density for the occurrence of fracture are in good agreement with the experimental ones for iron powder compacts.