Journal of Powder Materials

Powder Metallurgy in Defense Industry: J Korean Powder Metall Inst. 1994;1(1):1-3.

69 View
3 Download

PDF

Effects of Ce on the Mechanical Alloying Behavior and Thermal Stability of Al-8wt.%Fe Powder: J Korean Powder Metall Inst. 1994;1(1):4-14.

47 View
1 Download

Abstract PDF: The effects of Ce on the mechanical alloying behavior and the thermal stability of Al-8wt.%Fe were investigated. The steady states of Al-8wt.%Fe and Al-8wt.%Fe-4wt.%Ce powders with 1.5 wt.% stearic acid as a process control agent were reached after mechanical alloying for 1000 minuties and 1300 minuties respectively at the conditions of the impeller revolving velocity of 300 rpm and the ball to powder input ratio of 50 : 1. The hardness of Al-8wt.%Fe specimen hot extruded and isothermally aged at various temperatures for up to 1000 hours decreased rapidly at 500°C and its high temperature ultimate tensile strength began to decrease at 400°C with increasing aging time. The decrease in the hardness and ultimate tensile strength of the specimen were reduced substantially by addition of Ce. It was thought to be due to the formation of thermally stable A14Ce and All3Fe3Ce intermetallic compounds.

Sintering Behavior of TiB_2-SiC Composites: J Korean Powder Metall Inst. 1994;1(1):15-20.

52 View
1 Download

Abstract PDF: The effect of SiC addition on sintering behaviors and microstructures of TiB2 ceramics were studied. The sintering of TiB2 was limited due to the surface diffusion and rapid grain growth at high temperature. However the addition of SiC to TiB2 ceramics improved the densification to above 99% of the theoretical density. The sintering of TiB2-SiC composite starts at 1200°C with the melting of the oxides in particle surface as impurities. After the reduction of the oxide by additional cabon at above 1400°C, the grain boundary diffusion through the interface of TiB2-SiC play an important role. TEM observation showed neither chemical reactions nor other phases formed at the TiB2-SiC interfaces but the microcracks were observed due to the mismatch of thermal expansion between TiB2-SiC.

Aluminum Coating on A12O3 Powders in Fluidized Bed Reactor at Atmospheric Pressure: J Korean Powder Metall Inst. 1994;1(1):21-26.

49 View
2 Download

Abstract PDF: Aluminum was deposited on aluminum oxide powders using a fluidized bed reactor at atmospheric pressure. The aluminum oxide powders were irregular flakes with acute angles and the average particle size was 26 mutextrmm. The fluidized bed was formed by flowing argon gas at the velocity of 60 cm/sec. The optimal fluidization condition was obtained with the reactor designed to be tapered so that the fluid velocity decreases as the fluidizing gas goes up along the reactor. Aluminum was deposited by flowing TiBA(Triisobutylaluminum) evaporated at250°C through the fluidized bed reactor heated to 350~450°C. The result from the analysis by XRD and EDAX confirmed the coating of aluminum and an SEM micrograph showed the conformality.

Microstructures and Heat-treatment of Sintered Steels Using Iron Powder Coated with 0.45% Phosphorus: J Korean Powder Metall Inst. 1994;1(1):27-34.

47 View
1 Download

Abstract PDF: Commercial pure iron powder and iron powder of coated 0.45% phosphorus were mixed with graphite powder in dry mixer to control carbon content from 0 wt% to 0.8 wt%. Mixed powder was pressed in the mould under the pressure of 510 MPa. Compacts were sintered at 1180°C for 40 min. in cracked ammonia gaseous atmosphere. Some of these sintered specimens were quenched in oil, and tempered in Ar gas. All of these specimens were investigated for microstructure, density and hardness in relation to coated phosphorus and carbon content. The results obtained were as follows: (1) The microstructure of the sintered speciments revealed that the amount of pearlite was increased with increasing C content but decreased by P-addition. (2) The P-addition affected the microstructure of pores in which the pore shape became round and its mean size was decreased by P-addition. (3) After tempering of sintered specimens the structure of pearlite was changed from fine structure to coarse one in P added specimen. (4) Hardness was higher in P added specimens.

High Temperature properties of Mechanically Alloyed Al-Ni System: J Korean Powder Metall Inst. 1994;1(1):35-41.

51 View
1 Download

Abstract PDF: Mechanical alloying process of Al-8wt.% Ni powder was investigated for the various milling time in order to get the steady state powder. High temperature deformation behaviors of the sintered specimens were investigated by activation energy calculated after high temperature compression tests at the strain rates of 2.5times10-3 s-1, 2.5times10-2 s-1 and 2.5times10-1 s-1 at the temperature range between 350°C and 450°C. The steady state was obtained after 1000 minutes of milling with the PCA of 1.5 wt.% stearic acid under the condition of grinding media to powder weight ratio of 50 : 1 and impeller rotating speed of 300 rpm. True activation energy of Al-8wt.% Fe alloy was estimated to be 181 kJ/mole at the temperature range of 350~ 400°C and 265 kJ/mole at the range of 400~450°C.

A Study on the Microstructures and Properties of Al-SiC)_p Metal Matrix Composites Fabricated by Spray Forming Process: J Korean Powder Metall Inst. 1994;1(1):42-51.

80 View
1 Download

Abstract PDF: 6061Al-SiCP metal matrix composite materials(MMCs) were fabricated by injecting SiCP particles directly into the atomized spray. The main attraction of this technique is the rapid fabrication of semi-finished, composite products in a combined atomization, particulate injection(10 mutextrmm, 40 mutextrmm, SiCP) and deposition operation. Conclusions obtained are as follows; The microstructure of the unreinforced spray formed 6061Al alloy consisted of relatively fine(50 mutextrmm) equiaxed grains. By comparision, the microstructure of the I/M materials was segregated and consisted of relatively coarse(150 mutextrmm) grains. The probability of clustering of SiCP particles in co-sprayed metal matrix composites increased it ceramic particle size(SiCP) was reduced and the volume fraction was held constant. Analysis of overspray powders collected from the spray atomization and deposition experiments indicated that morphology of powders were nearly spherical and degree of powders sphercity was deviated due to composite with SiCp particles. Interfacial bonding between matrix and ceramics was improved by heat treatment and addition of alloying elements(Mg). Maximum hardness values [Hv: 165 kg/mm2 for Al-10 mutextrmm SiCp Hv--159 kg/mm2 for Al-40 mutextrmmSiCp] were obtained through the solution heat treatment at 530°C for 2 hrs and aging at 178°C, and there by the resistance were improved.

The Effect of W Particle Volume Percent on the Residual Stress of W Heavy Alloy: J Korean Powder Metall Inst. 1994;1(1):52-59.

78 View
0 Download

Abstract PDF: Since the coefficient of thermal expansion (CTE) of matrix phase is larger about 4 times than that of W particle in tungsten heavy alloy, the thermal stresses due to the CTE difference between the two phases are induced in the alloy during heating and cooling processes. In the present study, a series of W heavy alloy containing various W particle volumes of 0 to 90% is made to investigate the residual stress taking place during cooling process. The CTE and residual stress of the series of alloy are measured by dilatometer and X-ray diffractometer. The residual stress of W particle is in compressive stress irrespective of W particle vol% and tends to increase with decreasing W particle vol% while that of the matrix phase is in tensile stress. The measured residual stress of W particle is about a third of calculated thermal stress. The influence of W particle vol% on the residual stress of W heavy alloy is discussed in terms of the deformation behaviors of W particle and matrix phase.

The Effect of Elastic Anisotropy on the Shape of a Liquid Precipitate in a Wear-Resistant Fe-Base Alloy(Fe-5Cr- lMo-2Cu-0.5P-3C): J Korean Powder Metall Inst. 1994;1(1):60-65.

98 View
2 Download

Abstract PDF: When a commercial prealloyed Fe-powder(Fe-5Cr-lMo-2Cu-0.5P-3C) is liquid phase sintered at 1160°C, liquid precipitates with various shapes form within solid grains during the initial stage of sintering. The shape of a liquid precipitate changes pith the increment of their size from sphere(with radius<0.3mutextrmm), a transient polyhedron with more than 7 faces(1~2 mutextrmm), cuboid(3~5 mutextrmm), and finally to sphere(>5 mutextrmm). The shapes of liquid precipitates closely resemble the growth shapes predicted on the basis of solid-liquid interfacial energy and the coherency strain energy with anisotropic elastic constants in the diffusion zone around the precipitates.

Fabrication of Rapidly Solidified Al-20wt%Si-5wt%Fe Alloy Powder and Mechanical Properties of its Extrudates: J Korean Powder Metall Inst. 1994;1(1):66-71.

61 View
1 Download

Abstract PDF: Optical microstructures and mechanical properties of Na gas atomized Al-20Si-5Fe alloying powder and its hot extrudates were studied on 3 different types of powder size distribution. This powder showed the size distribution of 10~210 mutextrmm. Also the microstructures of alpha-Al, primary and eutectic Si and needle shaped intermetallic compounds were observed by optical microscope. These needle shaped intermetallic compounds were identified as deltaAl_4FeSi_2- by XRD and EDX analysis. The ultimate tensile strength(UTS) of these alloy extrudates was increased from 324 to 390 MPa with decreasing powder size range from 120~210 mutextrmm to 10~64 mutextrmm. A value of Micro-vic-kers hardness was simillar to the result of UTS. These extrudates showed better wear resistance than those of Al-20Si-2X(X : Ni, Cr, Zr), although they are insensitive to the size distribution. These results indicate that the presentation of deltaAl_4FeSi_2 intermetallic compounds contributed to the wear resistance improvement.

Preparation and Characterization of Uranium Silicide Dispersion Nuclear Fuel by Centrifugal Atomization: J Korean Powder Metall Inst. 1994;1(1):72-78.

46 View
0 Download

Abstract PDF: Two kinds of U_3Si powders and U_3Si dispersed nuclear fuel meats have been prepared by conventional comminution process and a newly developed rotating disk atomization process. In contrast to angular shape and broad size distribution of the conventionally processed powder, the atomized powder was spherical and showed narrow size distribution. For the atomized powder, the heat treatment time for the formation of U_3Si by a peritectoid reaction was reduced to about one tenth, thanks to microstructure refinement by rapid cooling of about 5times104 K/s. The extruding pressure of atomized U_3Si powder and Al powder mixture was lower than that of comminuted U_3Si and Al powder mixture. The elongation of the atomization processed fuel meats was much higher than that of the comminution processed fuel meats and remained over 10% up to 80wt.% of U_3Si powder fraction in the fuel meats. It appears therefore that the loading density of U_3Si in fuel meat can be increased by using atomized U_3Si powder. The atomized spherical particles were randomly distributed, while the comminuted particles with angular and longish shape were considerably aligned along the extrusion direction. Along the transverse direction of the extraction the electrical conductivity of the atomization processed fuel meats was appreciably higher than that of comminution processed fuel meats. This tendency became pronounced as U_3Si content increased. Because the thermal conduction which is believed to be proportioned to the electrical conduction in the nuclear fuel meats occurs in radial direction, the atomization processed fuel can be better used in research reactors where high thermal conductivity is required.

The Role of Grain Boundary Diffusion in the Activated Sintering of Tungsten Powder: J Korean Powder Metall Inst. 1994;1(1):79-84.

94 View
0 Download

Abstract PDF: The mechanism of activated sintering of tungsten powder was discussed in terms of diffusion and segregation of activator atoms at W grain boundaries. Shrinkage behaviours of W-0.2wt.% Ni, W-0.2wt.% Cu or pure W powder compacts during sintering at low temperatures of 900~ 1200°C were investigated. It was found that the Cu additive inhibits sintering process causing lower densification than pure W compact while remarkable shrinkage occurred in the Ni added W powder. Such contrary effect was explained by comparing self diffusion processes along Ni or Cu segregated W boundaries in which Ni segregants enhance but Cu atoms retard the migration of W atoms at W boundaries.

Thermal History Analysis and Solid Fraction Prediction of Gas-Atomized Alloy Droplets during Spray Forming: J Korean Powder Metall Inst. 1994;1(1):85-94.

94 View
0 Download

Abstract PDF: In order to predict droplet velocity and temperature profiles and fractional solidification with flight distance during spray forming, the Newtonian heat transfer formulation has been coupled with the classical heterogeneous nucleation and the specific solidification process. It has been demonstrated that the thermal profile of the droplet in flight is significantly affected by process parameters such as droplet size, initial gas velocity, undercooling. As the droplet size and/or the initial gas velocity increase, the onset and completion of solidification are shifted to greater flight distances and the solidification process also extends over a wider range of flight distances. The amounts of solid fractions formed during recoalescence, segregated solidification and eutectic solidification are insensitive to droplet size and initial gas velocity whereas those are strongly affected by the degree of undercooling. There are good linear relations between the undercooling and the corresponding solid fractions generated during recoalesced, segregated and eutectic stages.

PM 기술의 국제동향: J Korean Powder Metall Inst. 1994;1(1):95-96.

80 View
0 Download

PDF

ADVANCED CERAMICS의 시장전망: J Korean Powder Metall Inst. 1994;1(1):97-98.

77 View
0 Download

PDF

Previous issues