Sintered Iron Compacts Research Articles

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.

Effects of Porosity on Elastic Moduli and Poisson's Ratio of Sintered Irons.

A systematic study of the variation of elastic moduli and Poisson's ratio of sintered iron compacts of porosity (up to 0.6) has been carried out by measuring longitudinal and shear wave velocities. In this study, new equations of Young's modulus (E), shear modulus (G) and Poisson's ratio (v) as function of porosity (P) were proposed as follows ; E (P) = (-KE·P+E0)·(1-P) G (P) = (-KG·P+G0)·(1-P) v (P) =0.5 (-KE·P+E0)/(-KG·P+G0)-1 where KE and KG are experimental constants of Young's modulus and Shear modulus, respectively. And E0 and G0 are Young's modulus and shear modulus at P=0, respectively. In these equations, KE, KG, E0 and G0 at P&lnE;0.2 are different from those at P<0.2. Because the results of Poisson's ratio against porosity of sintered iron compacts show that downtrend of Poisson's ratio at P>0.2 was different from at P&lnE;0.2. The downtrend change is caused by pore connection as connecting pores increase and closed pores decrease at P&lnE;0.2. The fitting data of Poisson's ratio by these equations correspond with the measurement data by comparison with the published equations of many researchers.

In Situ Observation of Sintered Iron and Carbon Steel Compacts Using a Low-Temperature Acoustic Microscope

Sintered iron compacts and carbon steel compacts (0.3 mass% carbon) were observed in situ using a low-temperature acoustic microscope (LTSAM). The effects of structure, pore distribution, tensile load and testing temperature were evaluated by using the acoustic images. Before the tensile test was conducted, initial inner defects, such as pores and cracks, existed in the specimens and the conditions of the defect distribution were different for each specimen. As the tensile load increased, the newly generated defect area was extended where expansion, deformation and connection of pores occurred. As the testing temperature was lowered, the area became more localized. In different structures, for example, in ferrite and in ferrite-pearlite, the trend of the acoustic images also differed, and the defect area of the latter was sharper than that of the former. These results are consistent with elongation data obtained by tensile tests and observations using an optical microscope. Therefore, the LTSAM is useful for understanding the low-temperature brittleness of sintered iron and carbon steel compacts.

Equations for copper infiltration into sintered iron compacts: T. Watanabe et al. (Waseda University, Tokyo, Japan). J. Japan Soc. Powder Powder Metall., vol 41, no 10, 1994, 1261–1264. (In Japanese.)

Equations for copper infiltration into sintered iron compacts: T. Watanabe et al. (Waseda University, Tokyo, Japan). J. Japan Soc. Powder Powder Metall., vol 41, no 10, 1994, 1261–1264. (In Japanese.)

Effect of substrate porosity on the corrosion behaviour of electro less nickel-phosphorus coated powder metallurgy iron compacts and strip

Powder metallurgy (PM) sintered iron compacts having 2-9% porosity, and full density PM iron strip were electro less coated successfully with nickel-phosphorus alloy from baths containing sodium hypophosphite. Corrosion behaviour of such specimens in l·0M HCl was investigated. It was shown that anodic and cathodic polarisation plots of such PM iron specimens, irrespective of substrate porosity exhibit Tafel behaviour. Corrosion rates of PM iron compacts of 2-9% porosity and full density strip coated with electro less nickelphosphorus alloy for shorter periods, of the order of 0·5 h increase with substrate porosity. However, the corrosion rate of such PM iron compacts and strip coated for more than 0·5 h, first increases with substrate porosity and then remains practically constant.

Effect of substrate porosity on the corrosion behaviour of electro less nickel-phosphorus coated powder metallurgy iron compacts and strip

Powder metallurgy (PM) sintered iron compacts having 2-9% porosity, and full density PM iron strip were electro less coated successfully with nickel-phosphorus alloy from baths containing sodium hypophosphite. Corrosion behaviour of such specimens in l·0M HCl was investigated. It was shown that anodic and cathodic polarisation plots of such PM iron specimens, irrespective of substrate porosity exhibit Tafel behaviour. Corrosion rates of PM iron compacts of 2-9% porosity and full density strip coated with electro less nickelphosphorus alloy for shorter periods, of the order of 0·5 h increase with substrate porosity. However, the corrosion rate of such PM iron compacts and strip coated for more than 0·5 h, first increases with substrate porosity and then remains practically constant.

Infiltration of silver into sintered iron compacts : H-N, Huang, T. Watanabe (Waseda University, Tokyo, Japan), J.Japan Soc. Powder and Powder Metallurgy, vol 40, no 9, 1993, 919–922. (In Japanese)

Infiltration of silver into sintered iron compacts : H-N, Huang, T. Watanabe (Waseda University, Tokyo, Japan), J.Japan Soc. Powder and Powder Metallurgy, vol 40, no 9, 1993, 919–922. (In Japanese)

Electroless Nickel Coating of Sintered Iron Compacts

Sintered iron specimens with a 9% porosity level were successfully coated by electroless nickel deposition using a hypophosphite bath. The problems encountered during the deposition process are discussed. Some important deposit characteristics such as composition, thickness, hardness, and adhesion strength of the deposit are also reported for both as deposited and coated specimens heat treated at 400°C for 1 h in a vacuum. PM/0650

鉄焼結体への銅溶浸による溶浸一般式の検討

鉄焼結体への銅溶浸による溶浸一般式の検討

ＨＩＰ処理した鉄系焼結材料の疲労き裂進展に及ぼす組織の影響

Fatigue crack growth of the sintered ferrous materials by HIP has been investigated taking the microstructures and the pattern of fractured surfaces into account.The results obtained are summarized as follows:(1) In the case of constant stress ratio, the fatigue crack growth rate(da/dN) of sintered materials by HIP with diffusion alloyed powder had a tendency to become slower than that of sintered materials by HIP with prealloyed and mixed elemental powders under the same stress intensity factor range(ΔK). The material constant value (m) in da/dN=C(ΔK)m was found in the range of 3.8 to 5.3, which was the same as that of wrought materials. Sintered iron compacts showed higher da/dN and m values than those of sintered materials by HIP.(2) The ΔKth(da/dN<10-9m/cycle) of sintered iron compacts was higher than that of sintered materials by HIP. The influence of stress ratio was recognized with the relationship between da/dN and ΔK of any sintered materials by HIP.(3) Fatigure crack grew preferentially in the ferrites as forming the slip bands close together. The behavior of fatigue crack growth was distinctly dependent on the microstructures, the cracks propageted linearly through the pearlites, and the cracks penetrated through or bypassed the cementites.(4) The fractured surface reflected the local intergranular fracture in the region of low crack growth rate(da/dN<10-9m/cycle). On the other hand, the striation like pattern was mainly observed in the region of high crack growth rate(da/dN=10-7-10-9m/cycle). As the stress ratio was increased, unevenness of the fractured surface was more distinguished.

鉄系焼結材料の強度評価

The tensile strength of sintered iron and alloyed iron compacts have been analyzed statistically by using three types of iron powders produced by different process. The results obtained were summarized as follows:(1) The tensile strength of all sintered iron compacts were scattered according to the normal distribution curves in spite of difference in material and the sintered density.(2) Sintered iron compacts produced by fine powder showed the highest tensile strength. The coefficient of variation in tensile strength had a tendency to become high as the iron powder particle size is increasing and the density of sintered compact is decreasing.(3) The tensile strength and its coefficient of variation in sintered compacts produced by blended iron powder were similar to those of compacts produced by single powder.(4) The coefficient of variation in tensile strength of sintered alloyed iron compacts was increased with addition of Cu, while the addition of Ni had slightly influence on the coefficient of variation.

Changes in pore structure of sintered iron compacts of diffusion in of alloy elements: T.-W. Lim and K. Hayashi (University of Tokyo, Tokyo, Japan), J Japan Inst of Metals, Vol 56, No 7, 1992, 828–832. (In Japanese)

Changes in pore structure of sintered iron compacts of diffusion in of alloy elements: T.-W. Lim and K. Hayashi (University of Tokyo, Tokyo, Japan), J Japan Inst of Metals, Vol 56, No 7, 1992, 828–832. (In Japanese)

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.

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

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.

ＣＶＤ処理した多孔質鉄焼結体の特性

The sintered iron compacts will be able to be applied to selflubricating porous bearing, filter and metallic mold for casting, etc., because they have useful porosity. However, they do not have oxidation resistance, wear resistance and good mechanical properties. The chemical vapor deposition process (CVD process) is expected to give them good oxidation resistance and wear resistance. In this paper, the properties of the porous sintered iron compacts coated with TiC and Al2O3 by CVD process were investigated. The results obtained are as follows:The CVD coatings of the porous sintered iron compact are thinner from the surface forward the inside. The TiC coatings are smooth throughout the sintered compact, while the laminated coatings of TiC and Al2O3 are smooth in the surface part and granular toward the inside. The granular products on coatings are Al2O3. The hardness and the transverse rupture strength of the porous sintered iron compacts are remarkably increased and the intercommunicating porosity is decreased by the CVD treatment. The oxidation resistance is improved when the laminated coating of TiC and Al2O3 is repeated more than twice. The transverse rupture strength is not decreased and the intercommunicating porosity is decreased by oxidation.

気孔球状化処理を施した焼結鉄のヤング率測定による気孔形状の評価

The author reported previously that the Young's modulus of sintered iron compacts measured by the resonance method was affected by the pore shape, rather than by the pore size and number. The purpose of this study is attempts to express quantitatively the effect of pore shape on Young's modulus and evaluate the degree of spheroidizing of pores in sintered iron compacts added by alloying elements such as P and Si. The results are summarized as follows:Using the proposed pore shape factor, η, which is mainly based upon the Hashin's elastic theory, the relation between Young's modulus of compacts, E, and the porosity, s, can be simply and successfully expressed as E/E0=(1-e)/(1 +ηe), where E0 is Young's modulus of bulk material. In the case of sintered iron compacts, the value of η takes about 1 for the spherical shape of pores, and 2 to 3 for the pores with rounded edges. Thus, the value of η increases as the pore shape becomes irregular and angular.For a given amount of porosity, Young's modulus of Fe-P compacts sintered above 1050°C (eutectic temperature of Fe-Fe3P) is higher than that of Fe compacts alone, which is due to the appearance of spheroidized pores by the liquid phase sintering. Addition of 3 wt%Si to atomized iron powders is somewhat effective on the spheroidization of pores as compared to that of 0.4 wt%P for the same sintering conditions, e.g. 1150°C×1hr.Young's modulus of Fe-2.5%Si-0.3%P compact increases with increasing sintering temperature, and the elastic behavior of the specimen sintered at 1200°C for 1 hr is comparable with that of the carbonyl sintered iron, and the value of η of the former reaches nearly 1. Moreover, it was found that sintered iron compact treated by the gas sulfurizing shows a considerably spheroidized pore structure.

The Flow and Fracture Behaviour of Sintered Iron

The tensile fracture strength of sintered iron compacts cannot be simply related to the original pore content as proposed by many previous investigators. In a well-sintered compact, plastic flow precedes fracture and is localized at ligaments to a degree which increases as the sintered density decreases within the range of practical interest. Most ligaments deform without necking; some rupture to allow local pore coalescences. These effects cause the original pores to grow anisotropically. Fracture occurs when general plastic instability leads to internal necking and rupture of many ligaments, i.e. to the rapid coalescence of pores across a section of the compact. No macroscopic necking can be expected. Calculations reveal that pore growth due to the flow which precedes fracture may account for a large reduction in the effective load-carrying cross-section of the matrix.In lightly-sintered compacts, little macroscopic strain is seen, and fracture is concentrated at interparticle contacts. Microscopically, fracture may involve ductile coalescence of fine pores within the contacts, brittle grain-boundary separation, or a mixture of both mechanisms. Again, fracture strength cannot be related simply to pore fraction.

The Flow and Fracture Behaviour of Sintered Iron

AbstractThe tensile fracture strength of sintered iron compacts cannot be simply related to the original pore content as proposed by many previous investigators. In a well-sintered compact, plastic flow precedes fracture and is localized at ligaments to a degree which increases as the sintered density decreases within the range of practical interest. Most ligaments deform without necking; some rupture to allow local pore coalescences. These effects cause the original pores to grow anisotropically. Fracture occurs when general plastic instability leads to internal necking and rupture of many ligaments, i.e. to the rapid coalescence of pores across a section of the compact. No macroscopic necking can be expected. Calculations reveal that pore growth due to the flow which precedes fracture may account for a large reduction in the effective load-carrying cross-section of the matrix.In lightly-sintered compacts, little macroscopic strain is seen, and fracture is concentrated at interparticle contacts. Microsco...

焼結鉄の疲労強さに及ぼす研削加工及び研削後の焼なましとバフ仕上の影響

This work was made to clarify the influences of grinding, annealing after grinding and buff-finishing on fatigue strengths of electrolytic and carbonyl iron powder compacts sintered at 1123 and 1423 K for 3.6 ks.The results obtained were as follows:(1) The plastic flow induced by the grinding occurred on the surface layers of sintered iron compacts toward the grinding direction and the worked surface layers were formed in the region about 10μm thickness under the surfaces of them. The pores near the surface of specimens were collapsed to the grinding direction and became a linear-like microcrack.(2) From X-ray residual stress measurement, the residual stress in the surface layer of as-sintered specimen was slight, but that of as-ground specimen induced a very higher tensile and compressive stress, respectively, in parallel and transverse to the length of specimens. In the other specimens, the tensile residual stress disappeared and varied to compressive side.(3) In all fatigue strengths of specimens prepared by various processes, that of annealed specimen after grinding was the largest. This was caused by the reduction of the residual stress, the formation of some surface layers without pores and the nucleation of a few fine grain due to the recrystallization during annealing process.