Journal of Powder Materials

Volume 6(1); February 1999

In-situ Structure Modification of W powder Skeleton and related Cu Infiltration Kinetics in W-Cu: J Korean Powder Metall Inst. 1999;6(1):36-41.

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Abstract PDF: The present work has attempted to investigate the dependence of Cu infiltration kinetics on in-situ structure modification of W powder skeleton in W-Cu system. In-situ structure modification of W skeleton by addition of 0.3wt%Ni-P eutectic alloy was designed to proceed during heat-up of the W compact for Cu infiltration process. It was found that the Ni-P added W skeleton underwent remarkable stucture change only during heating-up. its structure was composed of large necks of W particles above 0.5 in the ratio of neck to particle size and smooth pore channels. The infiltration experiment showed that the infiltration kinetics for the W-Ni-P followed well the linear relationship of h vs. t1/2 the rate constant K of which was in good agreement with the theoretical value. On the other hand, in case of the pure W skeleton a lower K value by 20% than the theoretical one was obatined. Such discrepancy is discussed in terms of skeleton structure induced infiltration mechanics.

Formation Behaviour Al-Ti Intermetallic Compounds by Ball milling methods: J Korean Powder Metall Inst. 1999;6(1):42-48.

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Abstract PDF: Three mixtures of elemental powders of Al-25at.%Ti, 48at.%Ti and 70at.%Ti were offered to ball milling process for the formation of intermetallic compounds of Al_3Ti, AlTi and Ti_3Al. Ballmilling or attrition process were carried out at the condition of rotaing speed of 110 or 350 rpm at 10-3 torr vacuum or argon atmospheres. Al_3Tiphases were fully obtained by heat treatment for 1 hors at 600°C with Al-25at.%Ti composition mixtures milled by 100 hours. The amorphous phase was completely formed at the composition of Al-48at.%Ti mixed powders by milling 100hours at the 50 to 1 weight ratio of ball to powder, and AlTi compounds were obtained by heat treament. In the case of Al-70at%Ti mixed powders milled for 100 hours, Ti_3Al and Al_3Tiintermetallic compounds were formed by heat treatment for 1 hour at 600°C. By attrition milling of 350rpm for 10 hours, Ti_3Al phase was formed completley after heat treatment for 1 hour at 600°C.

Evaluation of Elevated Temperature Strength of Al-Cr-Zr Alloys Strengthened by Nanostructured Crystallines and Intermetallic Compounds (I): J Korean Powder Metall Inst. 1999;6(1):49-55.

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Abstract PDF: Al-Cr-Zr nanocomposite metal powders were prepared by mechnical alloying (MA) in order to develop aircraft structure materials with lighter weight and lower cost than the conventional Ti and Ni alloys. The morphological changes and microstrutural evolution of Al-6wt.%Cr-3wt.%Zr nanocomposite metal powders during MA were investigated by SEM, XRD and TEM. The approximately 50mum sized Al-Cr-Zr nanocomposite metal powders has been formed after 20 h of MA. The individual X-ray diffraction peaks of Al, Cr and Zr were broadened and peak intensitied were decreased as a function of MA time. The observed Al crystallite size by TEM was in the range of 20 nm, which is a simliar value calculated by Scherrer equation. The microhardness of Al-Cr-Zr nanocomposite metal powders increases alomost linearly with increase of the processing time, reaching a saturation hardness value of 127 kg/mm2 after 20 h of processing. The intermetallic compound phase of Al_3Zr_4 in the matrix was identifed by XRD and TEM.

Extrusion Behavior and Finite Element Analysis of Rapidly Solidified Al-Si-Fe Alloys: J Korean Powder Metall Inst. 1999;6(1):56-61.

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Abstract PDF: The plastic deformation behaviors for powder extrusion of rapidly soildified Al-Si-Fe alloys at high temperature were investigated. During extrusion of Al-Si-Fe alloys, primary Si and intermetallic compound in matrix are broken finely. Additionally, during extrusion metastable delta phase(Al_4SiFe_2) intermetallic compound disappears and the equilibrium beta phase(Al_5FeSi_2) is formed. In gereral, it was diffcult to establish optimum process variables for extrusion condition through experimentation, because this was costly and time-consuming. In this paper, in order to overcome these problems, we compared the experimental results to the finite element analysis for extrusion behaviors of rapidly solidified Al-Si-Fe alloys. This ingormation is expected to assist in improving rapidly solidified Al-Si alloys extrusion operations.

The Effects of Carbon and Mo_2C Content on the Microstructure and Hardness of TiC-Ni_3Al cermet: J Korean Powder Metall Inst. 1999;6(1):62-68.

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Abstract PDF: The effects of the carbon content ranging from 17.5 to 21.0 wt.% in TiC-30vol.% Ni_3Al cenmet and the Mo_2C content raging from 0 to 30 wt.% in TiC-20 vol.% Ni_3Al cermet were investigated in the relation to the microstures and harbness. The speciment were sintered at 1400°C, 1430°C and 1450°C for 60minutes. The results were summarized as follows; 1) The shrinkages and relative densitites of the specimens were incrased up to 20.0 wt.% C and then decreased. 2) The grains of TiC were almost the same size with the different content of carbon. Free carbons were appeared on the microstrures when carbon was added over 20.5 wt.% while TiC and Ni_3All were formed when carbon was added below 20.0 wt.%; 3) The lattice parameters of the Ni_3Al and TiC phases were increased up to 20.5 wt.% C, and then saturated. 4) The hardess was increased up to 20.0 wt.% C, and then decreased. 5) The Mo_2C made the TiC grains fine and the surrounding structure around TiC gains. 6) The micropores were decreased with increasing the binder and the sintering temperature. 7) The lattice parameter of the Ni_3All ana TiC were almost the samp up to 10 wt.% Mo_2C and then decreased. 8) The hatdness was increased up to 5wt.% Mo_2C and then decreased owing to the micrpores. 9) The more the binder phase, the higher the relative density and the proper Mo_2C amount of TiC-Ni_3Al cermets were obtained.

A Study on the Microstryctural Evoulution of the Reagion Aheas of Craters Created by Copper and W-Cu Shaped Charge Jets: Seong Lee, Moon-Hee Hong, Woon-Hyung Baek; J Korean Powder Metall Inst. 1999;6(1):69-74.

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Abstract PDF: The microstructure of the reagion of carters, created by Cu and W-Cu shaped charge jets, in a 1020 mild steel target has been intestiaged. The region ahead of the crater created by the Cu shaped charge jet, reveals dramatic grain refinement implying the occurrence of a dynamic recrystallization, while that of W-Cu one dose a martensitic transformation indicative of heating up to an austenitic region followed by rapid cooling.The impacting pressure calculated when the W-Cu shaped charge jet encounters the target is higher than that of the Cu one. The micro-hardness of the region ahead of the crater created by the W-Cu shaped charge jet is also higher than that of the Cu one. The microstructure of W-Cu slug remained in the inside of the craters depicts the occurrence of the remarkable elongation of W particles during the liner collaphse. From these results, the microstructural variation of the region ahead of the crater with Cu and W-Cu shaped charge jets is discussed in trems of the pressure dependency of the transformation region of ferrite and austenite phases.

The Effect of the Precursor Delivery Rate on low Pressure Flame Synthesis of n-TiO_2 Powder: J Korean Powder Metall Inst. 1999;6(1):75-80.

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Abstract PDF: The formation of n-TiO_2 powder by oxidation of Ti-ethoxied vapor in a flat flame burner reactor maintained under 20 torr has been studied. The produced powder were characterized in terms of crystal structure, chemical composition by XRD and TEM. The results showed that the powder consisted of loose agglomerated anatase and rutile particles and their size were about 10 nm and 20 nm, respectively. In the course of synthesis, changes of the flame color were happened to each condition during heating up the bubbler. The flame color transition phenomena reveled that a critical precursor delivery rate was needed for the powder formation (obtainable powder yield). The critical precursor delivery rate was estimated by a simple function of the bubbler temperature and the carrier gas flow rate. The critical precursor delivery rate was reviewed as an important variable of the nanopowder synthesis.

Pore Filling Theory of Liquid Phase Sintering and Microstrcture Evolution: J Korean Powder Metall Inst. 1999;6(1):81-87.

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Abstract PDF: Based on the pore filling theory, the microstructure evolution during liquid-phase sintering has been analyzed in terms of interrelationship between average grain size and relative density. For constant liquid volume fraction, the microsturucture trajectories reduced to a single curve in a grain size(x)-density(y) map, regardless of grain growth constant. The slope of curves in the map was inversely proportional to average pore size, while it increased fapidly with liquid volume fraction. Increase in pore volume fraction retarded the densification considerably, but showed marginal effect on the slope. The activation energy of densification was predicted to be the same as that of grain growth as long as the liquid volume fraction is constant for any temperature range studied. The present analyses on microstricture evolution may demonstrate the usefulness of pore filling theory and provide a guideline for process optimization of liquid-phase sintering.

WC-Co Milling Inserts Manufactured by Powder Injection Molding: J Korean Powder Metall Inst. 1999;6(1):88-95.

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Abstract PDF: The purpose of this study is to investigate the manufacturing feasibility of WC-Co milling inserts via Powder Injection Molding (PIM) process. WC-Co is used in a wide variety of cutting tools due to its high hardness, stiffness, compressive strength and wear resistance properties. WC-Co parts for a high stress application were conventionally produced by the press and sinter method, which were Iimited to 2 dimensional shapes. Manufacturing WC-Co parts for a high stress application by PIM implies that tool efficiency can be highly improved due to increased freedom is design. P30 grade WC powder (WC-Co-TiC-TaC system) was mixed with RIST-5B133 binder and injection molded into milling inserts (Taegu Tech. Model WCMX 06T 308). The mean grain size of the powder was about 0.8mum. Injection molded specimens were debound by solvent extraction and thermal degradation method at various conditions. The specimens were sintered at 1400°C for 1 hr in vacuum. Carbon content, weight loss, dimensional change, and macro defects of the specimen were carefully monitored at each stage of the PIM process. PIMed WC-Co milling inserts reached 100% full density after sinteing. Its mechanical properties and micro-structures were comparable with the press and sintered milling insert. Carbon content of the sintered WC-Co insert was mainly determained by the atmosphere of thermal debinding. By controlling powder loading and injection molding condition, dimensional accuracy could be obtained within 0.4%. We confirm that PIM can not only be an alternative manufacturing method for WC-Co parts economically but also provide a design freedom for more effieient cutting tools.

Microstructure and Wear Behaviour of Rapidly Solidified Al-20Si-5Fe-zPb(x=2, 4, 6wt.%) Alloys: J Korean Powder Metall Inst. 1999;6(1):96-102.

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Abstract PDF: The effect of Pb addition on microstructure and wear resistance was studied in rapidly solidified Al-20Si-5Fe-xPb(x=2, 4, 6 wt.%) alloys. The R/S Al-20Si-5Fe-xPb (x=2, 4, 6 wt.%) alloys showed a fine and homogeneous microstructure and an improved wear property compared with Al-20Si-5Fe alloy, while no significant change in UTS (Ultimate Tensile Strength) was shown. Contribution of the dispersoids on the wear property was discussed by showing the plastic deformation layers formed during wear track.

Effect of Degrees of Powder Mixing on the Synthesis of Ti_3Si and TiSi_2 by Mechanical Alloying: J Korean Powder Metall Inst. 1999;6(1):103-110.

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Abstract PDF: Different sizes of Si powder and milling medium materials (steel and partially stabilized zirconia (PSZ)) were used to synthesize Ti_3Si and TiSi_2 by mechanical aollying (MA) of Ti-25.0.at.%Si and Ti-66.7at.% Si powder mixtures. the formation of each titanium silicide did not occur even after 360 min of MA of as-re-ceived Si and Ti powder mixtures due to the lack of homogeneity. Ti_3Si, however, was synthesized after 240 min of MA of Ti and 60 min-premilled Si powder mixture. alpha-TiSi_2 and TiSi_2 were produced by jar milling of Ti and 60 min-premilled Si powder mixture for 48 hr and high -energy PSZ ball-milling in a steel vial for 360 min. The formation of each titanium silicide was characterized by a slow reaction rate as the reactants and product(s) coexisted for a certain period of time. The formation of Ti_3Si and TiSi_2 and the reaction rates appeared to be influenced by the Si particle size, the homogeneity of the powder mixtures and the milling medium materials.

A Study of Production, Hot Consolidation, Secondary Recrystallization and Mechnical Property Assesment of Mechanically Alloyed NiAl-Fe-AiN-Al_2O_3: J Korean Powder Metall Inst. 1999;6(1):111-118.

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Abstract PDF: Ni(Fe)Al powders containing a homogeneous distribution of the in-situ formed AIN and Al_2O_3 dispersoids have been produced by mechanical alloying process in a controlled atmosphere using high energy attrition mill. The powders have been successfully consolidated by hot extrusion process. The phase information investigated by TEM and XRD analysis reveals that Fe can be soluble up to 20% to the NiAl phase (beta) at room temperature after MA process. Subsequent thermomechanical treatment under specific condition has been tried to induce secondary recrystallization (SRx) to improve high temperature properties, however, the clear evidence of SRx was not obtained in this material. Mechanical properties in term of strength at room temperature as well as at high temperatures have been improved by the addition pf AIN, and the room temperature ductility has been shown to be improved after heat treatment, presumably due to the precipitation of second phase of alpha in this material.

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