Compacted Iron Research Articles

Influence of Nickel on Reactive Sintering of Iron—Aluminium Intermetallics

Reactive sintering of rolled compacts consisting of elemental iron and aluminium powders has been studied. The results demonstrate that the addition of nickel can inhibit the swelling of sintered iron and aluminium powder compacts and promote densification of the sintered samples. Reactive sintering of rolled compacts of the powder mixture is an efficient method of obtaining high final densities (> 99% theoretical). Reactive sintering produces a two phase structure. It was found that where pores exist, they are formed in the intermetallic Fe 3 Al compound phase and that these pores largely disappear when nickel is added

鉄系焼結材料の疲労き裂進展挙動

The behavior of fatigue crack growth of sintered iron and steel compacts were investigated in comparing with that of the nodular graphite cast irons for various stress ratios and specimen thickness by using 1/2 compact type specimens, prepared by single pressing, sintering and machining.The results obtained were summarized as follows:1) Under the constant stress ratio, the relationship between fatigue crack growth rate(da/dN) and stress intensity factor range(ΔK) of sintered compacts was dependent on the density and the structure. However, the relationship between da/dN and ΔK/E normalized by Young's modulus(E) was linear independently of the density in the sintered iron compacts. Under the same ΔK, da/dN of the sintered compacts was slightly bigger than that of the nodular graphite cast irons.2) As the stress ratio is increased, the fatigue crack growth curves of sintered compacts were shifted to the lower stress intensity factor range. The threshold in stress intensity factor(ΔKth) was decreased with an increase in the stress ratio.3) Effects of specimen thickness on the fatigue crack growth in sintered compacts did not appear in the range of 10.0mm to 12.5mm.

Flow compaction of iron powders

Flow compaction of iron powders

Effects of graphite content on diffusion bonding of iron powder compacts with applied pressure: H. Iwasaki and E. Shorakui, (Himeji Inst, of Technology, Shosha Himeji, Japan), J. Japan Soc. Powder and Powder Metallurgy, Vol 39, No 1, 1992, 33–38. (In Japanese)

Die freie Bildungsenthalpie der im System Fe-W auftretenden intermetallischen Phasen Fe2W und Fe3W2 sowie des ternären Oxids FeWO4 im System Fe-W-O wird durch Messung elektromotorischer Kräfte an galvanischen Festkörperketten mit ThO2-Elektrolyt bestimmt. Zwischen 1180 und 1330 K ergibt sich: Die freie Bildungsenthalpie des im System Fe-W-C auftretenden ternären Carbids Fe3W3C (η-Phase) wird mit Hilfe dieser Ergebnisse und isothermer Schnitte im Phasendiagramm berechnet. Bei 1300 K ergibt sich: The Gibbs energies of formation of the intermetallic phases Fe2W and Fe3W2 existing in the Fe-W system and of the ternary oxide FeWO4 in the Fe-W-O system were determined by e.m.f. measurements on solid galvanic cells using a ThO2 electrolyte. The following results were obtained between 1180 and 1330 K: The Gibbs energy of formation of the ternary carbide Fe3W3C (η phase) in the Fe-W-C system was estimated using the experimental results and isothermal sections of the phase diagram. The following result was obtained at 1300 K:

鉄系圧粉体の加圧拡散接合に及ぼす黒鉛量の影響

Diffusion bonding between iron powder compacts was carried out to investigate an effect of graphite content in powder on bonding strength at several bonding temperatures and bonding pressures. The results are as follows:(1) Shear strength of both inside and joi t of iron powder compact subjected to diffusion bonding has a maximum value at graphite content of 0.2 wt% at overall bonding temperatures from 973 to 1273 K and bonding pressures from 10 to 60 MPa.(2) Subsequent sintering at a temperature of 1323 K and for a time of 3.6 ks remarkably improves the shear strength of both inside and joint, which increases linearly with increasing graphite content.(3) Critical bonding condition to obtain 100% of joint efficiency is a temperature of 1073 to 1173 K and a pressure of 20 to 40 MPa for all graphite contents up to 0.8 wt%.

The reduction of iron oxides during sintering of iron compacts: L.J. Cuddy, G.R. White, (Pennsylvania State Univ, Pennsylvania, USA)

The reduction of iron oxides during sintering of iron compacts: L.J. Cuddy, G.R. White, (Pennsylvania State Univ, Pennsylvania, USA)

Formation of nitride phases in the nitriding of porous iron

When sintered iron with a certain porosity (14–20%) is saturated with nitrogen, the amount of absorbed N2 and the depth of the nitride layer increase jumpwise. If we regard the porous material as a biphase mixture (of pores and iron particles), such a phenomenon can be associated with the jumpwise increase of the effective diffusion coefficient at a certain quantitative ratio of the phases (the so-called percolation effect of diffusion). When porous iron is nitrided, a peculiar morphological form of the nitride phases forms in the diffusion layer; this, in distinction to the acicular nitrides, which are typical of the nitriding of compact iron, has a comparatively equiaxial shape and sinuous phase boundaries.

Ultrasonic and magnetic analyses of porosity in iron compacts : Metallugical Transactions A, Vol. 20A, No. 4, pp. 571–578 (Apr. 1989)

This study showed that the tensile stress-strain behavior and ductility of porous iron compacts containing nearly spherical pores could be related solely to the initial poosity of the iron. Results are presented for these compacts on the use of ultrasonic wave propagation procedures for measuring porosity and on the effect on porosity on magnetic behavior, magnetization, and acoustic and magnetic Barkhausen signals. The successes, failures, and limitations of these nondestructive evaluation procedures for characterizing porosity and, therefore, the strength and ductility of porous iron are discussed. Wave velocity measurement techniques appear the most promising for characterizing porosity in porous iron compacts.

Magnetic properties of porous iron compacts : Journal of Nondestructive Evaluation, Vol. 6, No. 3, pp. 119–127 (1987)

Magnetic hysteresis measurements, magnetoacoustic emission, and the Barkhausen effect have been used to investigate the magnetic properties of six porous iron compacts with porosities in the range 0.3–6.2% and pore sizes in the range 1.6–13.2 µm. Coercivity and maximum permeability varied with pore size, showing respectively a maximum and a minimum for pore areas in the range 50–100 (µm)2, corresponding to pore diameters 8–11 µm. Significant correlations were found between several of the magnetic parameters including a fundamental relationship between coercivity, initial permeability, and maximum differential permeability. There were also indications of a correlation between magnetic properties and the initial molding pressure, although these were not conclusive. However, none of the magnetic properties was found to vary in a progressive manner with percentage porosity, although it is conceivable that if all other variables, such as pore size and grain size, remained constant, that changes in magnetic properties with porosity could be detected from magnetic measurements.

Effects of cold rolling and annealing on the damping capacity (internal friction) of Pb infiltrated sintered iron compacts: M Yokota, et al, J. Japan Soc. Powder and Powder Metallurgy, Vol 37, No 4, 539–545 In Japanese

Effects of cold rolling and annealing on the damping capacity (internal friction) of Pb infiltrated sintered iron compacts: M Yokota, et al, J. Japan Soc. Powder and Powder Metallurgy, Vol 37, No 4, 539–545 In Japanese

Relationships between microstructure and properties of unalloyed compacted graphite cast irons

Austempered cast irons have been the subject of much attention in recent years because of their excellent mechanical properties. The hardness, ultimate tensile strength and dynamic elastic modulus are presented for a commercially available unalloyed compacted iron (C.E. 4.31) and correlated with different matrix microstructures (as-cast, ferritized, normalized and austempered). For this study, two isothermal temperatures for the austempering treatment were chosen: 400°C and 300°C. The influence of a ferritizing treatment prior to normalizing and austempering has been evaluated, the results indicating that no advantages are obtained with this additional treatment. The influence of microstructure on properties and on the resulting fracture surfaces in tensile tests are discussed.

Effect of hydrostatic pressure on deformation, damage evolution, and fracture of iron with various initial porosities

This study evaluated the effects of superimposed hydrostatic pressure (138 to 1104 MPa) on densification and plastic flow behavior of porous iron (0.3 to 11.1 % porosity). Pressurization alone caused densification of the porous iron with the effect being most pronounced when the porosity was greater than 3.7% and the pressure above 276 MPa. For the porosities studied, densification as a result of pressurization increased with hydrostatic pressure and initial porosity. The 0.3% porosity iron was the only one whose density did not increase with pressurization or deformation under pressure. The effect of hydrostatic pressure on the flow stress of porous iron was small when densification resulting from pressurization was not a factor. The ductility was found to increase linearly with pressure and the effect of pressure on fracture strain increased with the initial porosity of the iron. Evaluation of the effect of hydrostatic pressure on development of porosity and growth during tensile deformation was limited to hydrostatic pressures of 138 and 276 MPa and iron compacts with initial porosities of 0.3, 1.5, and 3.7% because of the pressurization effects. It appeared that the porosity at fracture was similar in these compacts at both pressures but it was much larger than that observed at 0.1 MPa. The greater ductility of the iron compacts tested under hydrostatic pressure results from a decrease in the growth of pores with deformation and from a greater damage tolerance prior to fracture. As observed for porosity, the average maximum pore diameters at fracture for the compacts tested under pressure were similar but larger than those observed at 0.1 MPa. It appears that a general model of ductile fracture for porous materials cannot be based solely on a critical degree of dilation or on maximum pore extension as a fracture criterion.

Thermal shock resistance test for cast iron used in casting environments

The thermal shock resistance test was conducted for grey cast iron and a compacted cast iron for use in casting environment. The test consisted of a specimen partially immersed in a molten salt bath of 55% Na2C03 and 45% CaC03 at 1000 ° C for 4.5 min, followed by plunging into water. The test results from laboratory and field indicated that the grey cast iron is superior to the compacted cast iron. In the laboratory test, the thermal shock resistance of the cast iron can be judged from the summation of crack length and crack patterns in the specimen after a certain number of thermal shock cycles. The inferior thermal shock resistance of the compacted cast iron is mainly attributed to the more extensive martensite formation after the thermal shock cycling compared with the grey cast iron.

Densification of iron compacts with various initial porosities under hydrostatic pressure

This study evaluated the effects of hydrostatic pressures up to 1104 MPa on densification of porous iron containing 0.3–11.1% porosity. For the porosities studied, densification as a result of pressurization increased with hydrostatic pressure and initial porosity. The 0.3% porosity iron was the only one whose density did not increase with pressurization up to 1104MPa. Current deformation models of ductile porous materials based on Gurson's yield criterion and rigid-plastic FEM analysis predicted much faster densification with pressurization than observed for porosity contents of 6.2% or less. A reason proposed for this behavior is the omission in the models of an internal pressure which builds up in the pores during the compaction process. A modification is introduced to Gurson's model to take account of internal pressure effects. The modified model exhibited excellent agreement with the experimental observations and provides a constitutive relation for the simulation of compaction and forming processes of P/M parts.

Intensity and effectiveness of sintering of iron powder compacts

Intensity and effectiveness of sintering of iron powder compacts

Nondestructive evaluation of elastic parameters of sintered iron powder compacts

A systematic study of the variation of elastic moduli and Poisson's ratio of sintered iron compacts of porosity (up to 21.6%) has been carried out by measuring longitudinal and shear ultrasonic velocities. The variation of these parameters with porosity is compared with predictions of elasticity and scattering theories. Further, a linear relationship was observed between the elastic moduli and the ultrasonic velocities and the use of ultrasonic velocity as a predictor of elastic moduli is therefore recommended for porous materials.

鉄粉焼結体の緻密化と機械的性質におよぼすBの影響

The effect of addition of master alloy powders containing B on the densification, microstructure and mechanical properties of atomized iron powder compacts has been studied.The results are summarized as follows.(1) The Ni-B master alloys activated the sintering process through the formation of eutectic liquid. However, there was limitation to sintered density that was attained by those alloys.(2) Densities of the order 99% theoretical were readily achieved with addition of the Fe- Ni-B master alloy powders. Volume fraction of liquid phase was increased during the sintering process by addition of these additives.(3) Rapid densification occured at 1403 K in iron powder compacts from 16 μm and at 1423 K from 80 μm, but in compacts from 45 μm having large pore size distribution occurred above 1433 K.(4) Sintered strength increased with the amount of master alloy powders. With 5% additive, the tensile strength of 400 MPa was obtained. Maximum elongation of 30% occurred at 2% addition.(5) Elongation was closely related to the forming process of the eutectic phase and decreased as it became continuous since a fracture occurred along the eutectic structure.

Model for Hot Compaction of Metal Powders

A mathematical model is proposed to describe the variation with time of pressure, relative density, and temperature for metal powders during hot compaction. The model includes instantaneous response, equilibrium response, and creep response and is based on a micromechanical (hollow sphere) analysis. However, the development is mostly empirical, based on experimental data from hot compaction of iron powder. The instantaneous and equilibrium responses are described by linear response laws, whereas time dependent densification is described by a power law creep response. The experimental data support these assumptions. Agreement between theoretical curves and experimental data is very good. PM/0500

Nondestructive monitoring of fabrication parameters of sintered iron powder compacts using ultrasonics

Ultrasonic characterization of sintered iron powder compacts made with different fabrication parameters (compaction pressure, sintering time and temperature) has been carried out. Longitudinal and shear velocities of samples up to a pore volume fraction of 0.216 were measured to study the effect of porosity. The measured values were compared with the values predicted by scattering and elasticity theories. This study shows that the longitudinal velocity of the sintered compacts may be used for monitoring the basic production parameters.

The urea nitrocarburizing of cast irons with various graphite morphologies

The urea nitrocarburizing of nodular and compacted graphite cast irons has been investigated. Optical microscopy, EDAX analysis and hardness measurements have shown that a thick compound layer with high contents of nitrogen and silicon is formed, and a greater hardness in the area around the graphite beneath the surface is observed. The compacted cast iron with interconnected graphite has been found to exhibit a smaller effective diffusion zone, and formed Si3N4 precipitates within the hardened area. The nitrided nodular cast iron exhibited a higher fatigue strength increment and a smaller elongation decrement than that of compacted cast iron. Most fracture surfaces of compacted cast iron were found to be granular whereas the nodular cast iron was characterized as transgranular cleavage.