Effect of Binder Composition on Rheology of Iron Powder Injection Moulding Feedstocks: Experimental Design

Abstract

A statistical analysis based on the McLean-Anderson design method was conducted to study the influence of each binder component on the flow properties of iron feed stocks for powder injection moulding. The formulations were composed of carbonyl iron powder (FE), polyethylene resin (PE), polyethylene wax (PEW), and stearic acid (SA). The viscosities of 15 different formulations were measured using a capillary viscometer. Fluidity and pseudoplasticity were evaluated and the effect of each component on these properties was analysed. The studied composition ranges of FE, PE, PEW, and SA were 90—92, 3—4·5, 2—4, and 0—1·5 wt—% respectively. It was found that lower iron powder content or higher binder content improved the fluidity of the feedstock. The relative effectiveness of binder ingredients in increasing fluidity is SA>PEW>PE and in enhancing pseudoplasticity PE > PEW > SA. Feedstocks with binder phases containing about 50 wt-%PE have the greatest fluidity with flow index n in the range 0·6—0·8. PM/0699     

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.     

Solute segregation behavior in spray-atomized Pd-Rh-V(Co) powders

In the present study, two palladium-based ternary alloys, with nominal compositions of Pd-4.9 wt pct Rh-0.72 wt pct V and Pd-5 wt pct Rh-1 wt pct Co, were spray atomized into micron-sized powders using a high-energy gas atomization technique. Solute segregation in the spray-atomized powders was systematically investigated. It was found that, as the powder size decreases, the solute segregation level decreases, either in terms of standard deviation of solute content from the average value, or in terms of the percentage of segregation-free regions in the powder, or in terms of the maximum (Rh)/minimum (Co, V) solute content in the powder. Moreover, theoretical analyses were carried out to evaluate the percentage of segregation-free regions, as well as the maximum/minimum solute content, in each powder. The theoretical analysis indicated that, among the different mechanisms governing the solute segregation behavior, undercooling levels experienced by the droplets, both prior to and after nucleation, played the most important role in decreasing the solute segregation level as the powder size decreased.     

Structure of a Fe-Cr-Mn-Mo-N alloy processed by mechanical alloying

Elemental Fe, Cr, Mn, and Mo powders were processed by mechanical alloying to develop a nanostructured Fe-18Cr-11Mn-5Mo alloy under a N₂ atmosphere. It was found that the nitrogen contents in the as-milled powder mixture increased up to 1.6 wt pct after 190 hours processing time. The as-milled powders were then annealed under vacuum at either 1173 or 1473 K to promote the formation of the resultant equilibrium phases. In the annealed powder mixtures, depending on the temperature and nitrogen content, the phases identified by X-ray diffraction were either austenite, ferrite, or chromium nitrides. Annealing at 1173 K promoted the development of γ-Fe, α-Fe, and Cr₂N for all the nitrogen contents considered (0.5 to 1.6 wt pct). The volume fractions of the various phases formed were found to be strongly influenced by the nitrogen content and annealing temperature. In addition, the levels of nitrogen absorbed during processing were retained after annealing. Finally, the outcome indicates that a fully austenitic structure can be obtained by annealing powder mixtures at 1473 K with maximum nitrogen contents of up to 1 wt pct.     

PW-EVA-SA金属注射成形粘结剂流变性能和热解行为的研究

对不同比例组成的PW-EVA-SA金属注射成形粘结剂进行了粘度测量并比较了其流变性能。对粘结剂、粘结剂各组元和注射料进行了TGA和DTA实验,对其热解行为进行了分析。     

Solubility of some transition metal oxides in cryolite-alumina melts: Part II. Solubility of TiO2

The solubility of TiO₂ in cryolite-alumina melts at 1020 °C was measured; it decreased with increasing alumina concentration up to ∼3.5 wt pct total oxide and then increased at higher alumina concentrations. The solubility was found to be 3.1 wt pct Ti in cryolite, and 2.7 wt pct Ti in an alumina-saturated melt. Modeling indicated that the most probable titanium species are TiOF₂ and Na₂TiO₃, which coexist in the solution; the former dominates at low alumina concentrations and the latter at high alumina concentrations. Additional unknown amounts of fluoride may also be associated with these species. Determination of the solubility of TiO₂ in alumina-saturated melts as a function of temperature showed that the solubility increased from 1.9 wt pct Ti at 975 °C to 2.8 wt pct Ti at 1035 °C, the apparent partial molar enthalpy of dissolution of TiO₂ being 88±4 kJ mol⁻¹.     

Preparation of submicron titanium nitride powder by vapor-phase reactions

The United States Bureau of Mines continued research on the preparation of titanium nitride powder for potential use as a substitute for imported tungsten used in metal cutting tools and wear-resistant applications. Major emphasis was directed toward improving the purity of the powder produced by vapor-phase reaction of titanium tetrachloride with magnesium in the presence of nitrogen or anhydrous ammonia at 1000 °C. Modifications were made in powder collection, handling, and purification procedures that significantly reduced the oxygen content of the product from > >5 wt pct to <<1 wt pct oxygen. Powder samples contained oxygen contents as low as 0.23 wt pct and exhibited a median particle size of 0.28 micrometer.     

Effect of magnesium on the aging behavior of Al-Zn-Mg-Cu/Al2O3 metal matrix composites

The effect of magnesium content on the aging behavior of Al-Zn-Mg-Cu alloy reinforced with alumina (A1₂O₃) was studied by using the differential scanning calorimetry (DSC) technique and hardness measurement. The magnesium contents were studied in the range from 1.23 to 2.97 wt pct. The addition of magnesium was found to increase the coherent Guinier-Preston (GP) zones in com-posites. The apparent formation enthalpy of GP zones of composites (0.1V _f) was 0.932 cal/g for 1.23 wt pct magnesium content and 1.375 cal/g for 2.97 wt pct magnesium content. The precipitation time to achieve the maximum hardness in the composites depends on the magnesium content. The time changed from 12 to 48 hours as the magnesium content increased from 1.23 to 2.97 wt pct. Both Vickers microhardness and Rockwell hardness increased with increasing magnesium content. The maximum hardness occurred in the composites that contained maximum amounts of GP zones and η′ precipitates. However, the microhardness of the composites was always lower than that of monolithic alloys due to the alumina fibers which caused the suppression of GP zones and η′ for-mation in the composites.     

Spreading and interlayer formation at the copper-copper oxide/polycrystalline alumina interface

Spreadability and reaction layer growth rates of copper-oxygen alloys on polycrystalline alumina were measured above the melting point of copper to better understand the direct bonding process. Spreading was measured as a function of composition and temperature by monitoring the diameter of molten droplets as a function of time. As the oxygen content of the melt increased from 0 to 3 wt pct, the spreading diameter increased linearly, at fixed time and temperature. Constant diameters were observed for oxygen compositions between approximately 3 and 6 wt pct. The diameters again increased linearly for oxygen concentrations greater than 7 wt pct. This behavior was explained by reference to the copper-oxygen binary phase equilibrium. An interfacial product was identified to be the complex oxide, CuA10₂. A detailed investigation of the interlayer growth kinetics was performed to understand the fundamental phenomena controlling the spreading rates. The growth rate of the CuAlO₂ phase and the spreading rate were simultaneously measured for alumina in contact with a copper-2 wt pct oxygen alloy drop as a function of temperature. The reaction layer thickening was found to be diffusion controlled, with an apparent activation energy of 309 kJ/mol, and the spreading rate did not correlate with the thickening rate. Formerly Research Associate, Center for Welding and Joining Research, Department of Metallurgical and Materials Engineering     

Dissolution of carbon from alumina-carbon mixtures into liquid iron: Influence of carbonaceous materials

Due to their excellent thermal shock and wear resistance at high temperatures, alumina-carbon based refractories are used extensively in the steel industry. A clear understanding of factors affecting the dissolution of carbon from refractories is of crucial importance, as carbon depletion from the refractory can significantly deteriorate refractory performance and metal quality. Atomistic simulations on the alumina-graphite/liquid iron system have shown that nonwetting between alumina and liquid iron is an important factor inhibiting the penetration of liquid metal in the refractory matrix and limiting carbon dissolution. This study investigates the role played by the carbonaceous material in the dissolution of carbon from the refractory composite. Two carbonaceous materials, namely, petroleum coke and natural graphite, respectively, containing 0.35 and 5.26 pct ash, were used in this study. Substrates were prepared from mixtures of alumina and carbon over a wide concentration range. Using a sessile drop arrangement, carbon pickup by liquid iron from alumina-carbon mixtures was measured at 1550 °C and was compared with the carbon pickup from alumina-synthetic graphite mixtures. These studies were supplemented with wettability measurements and microscopic investigations on the interfacial region. For high alumina concentrations (>40 wt pct), carbon dissolution from refractory mixtures was found to be negligible for all carbonaceous materials under investigation. Significant differences however were observed at lower alumina concentrations. Carbon dissolution from alumina-petroleum coke mixtures was much lower than the corresponding dissolution from alumina synthetic graphite-mixtures and was attributed to poor wettability of petroleum coke with liquid iron, its structural disorder, and the presence of sulfur. Very high levels of carbon dissolution, however, were observed from alumina-natural graphite mixtures, with carbon pickup by liquid iron from mixtures with up to 30 wt pct alumina reaching saturation. A sharp reduction to near zero levels was observed in the 30 to 40 wt pct alumina range. Along with implications for commercial refractory applications, these results are discussed in terms of material characteristics, interactions between ash impurities and alumina, and formation of complexes in the interfacial region.     

Fatigue crack propagation in aluminum-base copper alloys

Fatigue crack propagation ratesda/dN in binary Al alloys with 3.6 wt pct Cu and 6.3 wt pct Cu and commercial 2024 aged at 21°C were compared with 99.95⁺ wt pct aluminum. Omitting an anomalous region at lowΔK, the extrapolated rates for “pure” aluminum are more than 100 times greater than those in the three alloys at the same ΔK. The data for the alloys fit into a single scatter band of a factor of three. It was suggested thatda/dN varies inversely with the square of the strength of the alloy but that another parameter related to the fatigue crack propagation energy per unit area is also important. Theda/dN vs ΔK curves were determined for 3.6 wt pct Cu single crystals aged seven days at 21°C which containGP zones and two and seven days at 160°C which contain mixtures ofθ′ andθ′’. No systematic variation of (da/dN _Δ with crystallographic orientation was discerned, but the naturally aged specimen had a strong orientation dependence on crack initiation. At low ΔK 21°C aged specimens gave the lowestda/dN while at high ΔK the warm aged specimens gave the lower values ofda/dN. Measurement ofda/dN vs ΔK curves were conducted on specimens of 3.6 wt pct Cu with 1 mm equiaxed grains aged for various times at 130°C, 160°C, and 190°C. All warm aged specimens experienced brittle intergranular fracture at sufficiently high ΔK. The transition ΔK where intergranular fracture first appears is inversely proportional to the aging temperature. The change of fracture mode from intra to intergranular occurs gradually over a broad range of ΔK which shifts to lower ΔK with increase in aging temperature.     

Effect of alumina diluent on the fabrication of in-situ Al2O3-Ti/ZrB2 composite by self propagating high temperature synthesis dynamic compaction

A detailed investigation of the effect of alumina diluent on the Al₂O₃-TiB₂/ZrB₂ composite by self propagating high temperature synthesis (SHS) dynamic compaction was carried out. A dense composite could be obtained and microstructure could be tailored and controlled by adding alumina as diluent during the SHS reaction. The microhardness values decreased for 5 and 10 wt pct additions of alumna but increased for 15 and 20 wt pct additions. Hardness is influenced by the different phases present and the grain size.     

The effect of aluminum content on the corrosion behavior of Fe-Al alloys in reducing environments at 700 °C

The high-temperature corrosion behavior of monolithic Fe-Al alloys, with 0 to 20 wt pct Al, was investigated at 700 °C in a reducing atmosphere (p(S₂) = 10⁻⁴ atm, p(O₂) = 10⁻²⁵ atm) for up to 100 hours. Postexposure characterization of the corrosion reaction products consisted of surface and cross-sectional microscopy, in combination with energy dispersive spectroscopy, electron probe microanalysis, and quantitative image analysis. From the kinetic data, three stages of corrosion behavior (i.e., inhibition, breakdown, and steady state) were found with the observance and/or duration of each stage directly related to the aluminum content of the alloy. The first stage, labeled the inhibition stage, was characterized by low weight gains and the absence of rapid degradation of the alloy. Typically observed for compositions with 10 to 20 wt pct Al, protection was afforded due to the development of a thin, continuous alumina scale. For alloys with 7.5 wt pct A1, the ability to maintain the initially formed alumina scale was not observed, resulting in the breakdown stage. Localized corrosion product nodules, containing iron sulfide (Fe_1-x S) and the spinel-type tau phase (FeAl₂S₄), developed through the alumina scale due to sulfur short-circuit diffusion. These growths were accompanied by relatively high corrosion rates. Further decreasing the aluminum content to 5 wt pct and below lead to the formation of a continuous sulfide scale whose growth was controlled by iron and sulfur diffusion through the previously formed product. The alloy wastage rates in the steady-state stage were relatively high when compared to the previous two regions.     

Cast aluminum alloys containing dispersions of zircon particles

A process for preparing Al-alloy castings containing dispersions of zircon particles is described. Composites were prepared by stirring zircon particles (40 to 200 μm size) in commercially pure Al (99.5 pct)* and Al-11.8 pct Si melts and subsequently casting these melts in permanent molds. It was found to be necessary to alloy the above two melts with 3 pct Mg to disperse substantial amounts of zircon particles (25 to 30 pct). Further, it was possible to disperse up to 60 wt pct zircon by adding up to 5 pct Mg; however, the melts containing above 30 wt pct zircon showed insufficient fluidity for gravity diecasting and had to be pressure diecast. Microstructural studies of cast composites indicated the presence of a reaction zone at the periphery of zircon particles, and electron probe microanalysis showed concentrations of Mg and Si at the particle-matrix interface. Hardness, abrasive wear resistance, elastic modulus, 0.2 pct proof stress, and tensile strength of cast Al-3 pct Mg alloy were found to improve with the dispersions of zircon particles. Scanning electron micrographs of abraded and fractured surfaces did not show any evidence of particle pull-outs or voids at the particle matrix interface, indicating strong continuous bonding.     

Numerical simulation of macrosegregation: a comparison between finite volume method and finite element method predictions and a confrontation with experiments

Micro-macrosegregation calculations have been performed for a rectangular cavity containing either a Pb-48 wt pct Sn alloy or a Sn-5 wt pct Pb alloy. The numerical results calculated with a finite volume method (FVM) and a finite element method (FEM) are compared with experimental results previously obtained by Hebditch and Hunt. The two methods are based on the same average conservation equations governing heat and mass transfer and the same assumptions: lever rule, equal and constant density of the solid and liquid phases (except in the buoyancy term), permeability of the mushy zone given by the Carman-Kozeny relation, and no transport of the solid phase. Although the same parameters are used in both calculations, small differences are observed as a result of the different formulations. In particular, the instabilities appearing in the mushy zone (channels) of the Sn-5 wt pct Pb alloy are more pronounced with the FVM formulation as compared with FEM, whereas the opposite trend is observed for the Pb-48 wt pct Sn alloy. Nevertheless, the final segregation maps at the end of solidification compare fairly well with the experimental findings.     

The solubility of aluminum in cryolite-alumina melts and the mechanism of metal loss

The solubility of aluminum in cryolite-alumina melts has been determined in laboratory experiments by analyzing rapidly-quenched samples of the melt after equilibration with metal at temperatures between 960 and 1060°C. The solubility in pure cryolite increases from 0.085 at 1020°C to 0.12 wt pct Al at 1060°C. The addition of alumina decreases the solubility at 1020°C to 0.081 with 5 pct A1₂O₃ and to 0.073 wt pct Al in melts saturated with alumina. Quenched samples have been taken from operating 130 kA prebake cells at different heights above the metal pad, both in the center channel and beneath the anodes. Within about 10 mm of the cathode the metal content is close to the equilibrium value obtained in the laboratory but above this level it decreases rapidly. It is suggested that oxidation occurs in a central zone of the electrolyte. Mechanisms of metal loss and implications for current efficiency are discussed.     

Study on the Role of Stearic Acid and Ethylene-bis-stearamide on the Mechanical Alloying of a Biomedical Titanium Based Alloy

The present study examines the influence of different contents and types of process control agent (PCA), i.e., stearic acid (SA) and ethylene-bis-stearamide (EBS), on the microstructural evolution and characteristics of Ti-16Sn-4Nb (wt pct) alloy powders and bulk samples. The characterization of the powders and bulk samples was carried out by using chemical analysis, optical microscopy, scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS), and X-ray diffractometry. Results indicated that the powder recovered from the ball milling containers increased with increasing amounts of SA and EBS. Furthermore, adding more SA or EBS to the powder mixture resulted in a considerably smaller particle size, with a flaky-shaped morphology for the given ball milling time. Also, a slightly higher effectiveness was found for EBS when compared to SA. Meanwhile, the addition of both SA and EBS led to a delay in the alloy formation during mechanical alloying (MA) and caused contamination of the material with mainly carbon (C) and oxygen (O). An optimum amount of 1 wt pct PCA led to a good balance between cold welding and fracturing, and thus favored the formation of the titanium alloy. The microstructural observation of the bulk alloy showed a homogeneous distribution of fine Nb-rich β-phase colonies within the α-Ti matrix with the addition of PCA less than 1 wt pct.     

Fluidity of aluminum-silicon-alumina composite

Fluidity of Al-11.8 pet Si alloy containing up to 5.5 wt pet dispersed ν-A1₂O₃ particles has been studied. Spiral fluidity of Al-11.8 pet Si alloy decreases with an increase in the amount of dispersed alumina particles (for a given size) and decrease in the particle size (for a given weight percent). The spiral fluidity(F) of Al-11.8 pet Si-Al₂O₃ composite correlates well with the total surface area of dispersed A1₂O₃ particles and it can be expressed by the equation of the typeF = a − bx wherex represents the total surface area of alumina particles present in unit weight of the composite and, a and b are constants. Part of the observed decreases in fluidity could be attributed to expected increases in the effective viscosity of composite melts due to the presence of dispersed A1₂O₃ particles. However, the fluidity of Al-11.8 pct Si-5.5 pet A1₂O₃ (60μm) composite poured at 740 °C is at the same level as of Al-11.8 pet Si alloy poured at 700 °C. Hence, the fluidity of Al-11.8 pet Si alloy containing up to 5.5 wt pet A1₂O₃ particles is adequate to make variety of castings at 740 °C. Formerly with the Indian Institute of Science, Bangalore, India     

Synergistic effects of wear and corrosion for Al2O3 particulate-reinforced 6061 aluminum matrix composites

Wear corrosion of alumina particulate-reinforced 6061 aluminum matrix composites in a 3.5 wt pct NaCl solution with a revised block-on-ring wear tester has been investigated. The studies involved the effects of applied load, rotational speed, and environments (dry air and 3.5 pct NaCl solution) on the wear rates of materials. Also various specimens with Al₂O₃ volume fractions of 0, 10, 15, and 20 pct were employed in this work. Electrochemical measurements and electron micrographic observations were conducted to clarify the micromechanisms of wear corrosion in such metal matrix composites. Experimental results indicated that the wear rate of monolithic 6061 Al in either dry wear or wear corrosion was reduced by adding alumina reinforcements. However, the effect of volume fraction on wear rate is only minor in dry wear, while it is significant in the case of wear corrosion. Wear-corrosion tests also showed that the corrosion potential shifted to the active side and the current density for an applied potential increased with the decrease of Al₂O₃ volume fraction in the materials and the increase in applied load and rotational speed. Although the incorporation of reinforcement in these aluminum matrix composites was deterimental to their corrosion resistance, the influence on wear corrosion was favorable.