Journal of Powder Materials

Principle and Applications of Spray Casting Technology: J Korean Powder Metall Inst. 1996;3(3):143-152.

Effect of Copper on the Properties of ZSM-5 Catalyst Fabricated by Mechanical Alloying Method: J Korean Powder Metall Inst. 1996;3(3):153-158.

Abstract PDF: The exhaust gas from vehicle engines and industrial boilers contains considerable amount of harmful nitrogen monoxide(NO) which causes air pollusion and acid rain. To remove NO catalytic reduction processes using Cu ion exchanged ZSM-5 zeolite have been widely studied. In this study, an attempt was made to fabricate Cu/zeolite catalyst by using high energy ball mill. The catalytic performance of ball milled Cu/ZSM-5 zeolites is analyzed and optimum copper contents was determined. The processing variables were reaction temperature and copper contents. Complete removal of NO gas was obtained at the temperature of 553 K on 10wt.% CU/ZSM-5 mechanically alloyed composite powders. Mechanically alloyed CU/ZSM-5 catalyst showed homogeneous distribution of Cu in ZSM-5.

Fabrication of Aluminium Flake Powder by Ball Milling Process: J Korean Powder Metall Inst. 1996;3(3):159-166.

Abstract PDF: A series of test were undertaken in order to estabilish the effect of different milling variables on dimension and quality of aluminium flake powder. Milling conditions such as initial powder size, milling container rotation speed, milling time, and ball size were varied to produce aluminium flake powder. Flake powder could then be obtained with size range from 15 mum to 40 mum with a maximum specific surface area of 5 m2/g by controlling milling conditions. Diameter of milled powders with different milling container rotation speed and ball size were compared with that obtained from theoretical model. The best flake powder was obtained in milling condition of initial powder with average size of 19 mum, mill container rotation speed of 80 rpm, balls of 9.5 mm diameter, and milling time of 40 hours.

Sintering Behavior of Ball Milled MoSi_2 Powders: J Korean Powder Metall Inst. 1996;3(3):167-173.

Abstract PDF: The effect of ball milling on the pressureless sintering of MoSi_2 was investigated. Ball milling was conducted at 70 rpm for 72 hours using different balls and vessels: one used tungsten carbide balls in a plastic vessel(referred as B-powder) and the other stainless steel ball in a stainless steel vessel(referred as C- powder). The powder was compacted with 173MPa and subsequently sintered at the temperature range of 1150 °C and 1450 °C in H_2, atmosphere. Sintered density was measured and scanning electron micrograph was observed. Over 90% of the theoretical density was attained at 1250 °C within 10 minutes for C-powders, while the similar densification required a sintering temperature of 1450 °C for B-powders. Such a difference in sinterability between B and C-powders was discussed in terms of the effect of particle size reduction and activated sintering caused by Ni and/or Fe introduced during ball milling.

Phase Changes of Mechanically Alloyed TiNi Powders by Heat-treatment and Microstructural Properties in the Al/TiNi Sintered Materials: J Korean Powder Metall Inst. 1996;3(3):174-180.

Abstract PDF: Microstructure and phase transformation of mechanically alloyed TiNi powders added to aluminium matrix for enhancing the damping properties were studied. Four compositions between 48.5 and 51.5 at% Ti intermetallic compounds were selected to control the fraction of martensite phase. Mechanically alloyed TiNi powders were heat-treated at vacuum of 10-6 torr for crystallization. Ball milled AI/TiNi composite powders were swaged at room temperature and rolled at 450 °C. After mechanical alloying for 10 hours, Ti and Ni elements were alloyed completely and amorphous phase was formed. Amorphous phase was crystallized to martensite (Bl9') and austenite(B2) after heat treating for 1 hour at the temperature of 850 °C, and TiNi_3, intermetallic compound was partially formed. Considerable amount of martensite phase was remained after swaging and rolling.

Ball Milling and Sintering Behavior of High Speed Steel Powders Containing VC and Co: J Korean Powder Metall Inst. 1996;3(3):181-187.

Abstract PDF: Cobalt and VC powders were ball milled with M2 grade high speed steel powders under various ball to powder ratios. The powders milled under higher ball to powder ratio become finer, more irregular and have a broader size distribution, and thus possess a lower compressibility and a better sinterability regarding densification. Increasing the ball to powder ratio lowered the sintering temperature to obtain the density level necessary to isolate all the pores. Lowering the sintering temperature is very critical to maintain fine microstructure since grain and carbide coarsening are accelerated by higher sintering temperature due to more liquid phase formation. The powders obtained by ball milling at 20 to 1 ratio has the lowest compressibility but has the best sinterability, almost compatible to unmilled pure M2 powders. A sintered body over 97% theoretical density with fine microstructures having average grain size of ~10 microns was obtained from the powder by sintering at 1260 °C for 1 hour in vacuum. XRD results indicate that two types of carbides are mainly present in the sintered structure, MC and M_6C type. The MC type carbides are more or less round shaped and mainly located at the grain boundaries whereas the M_6C type are angular shaped and mainly located inside the grains.

EHect of Carbide Addition on Riping and Wear Properties of HSS: J Korean Powder Metall Inst. 1996;3(3):188-195.

Abstract PDF: In recent times the potential application of the high speed steel produced by HIP process for wear resistant and cutting materials are increasing. In this work the microstructure of Anval 30 produced by HIP process was investigated and the effect of WC, TiC addition on microstructure formation and wear properties were studied. After HIP process at 1150 °C, the original feature of spherical raw powders was not removed and consequently, nonuniform microstructure was formed. However the WC added by simple powder mixture incereased the sinterbility of high speed steel and uniform microstructure formed. The wear characteristics of Anval 30 with carbide addition were tested at RT and 600°C. The uniform microstructure played an more important role in wear resistance as compared with the hardness.

Motion of WC Grains in the Liquid Matrix during Liquid Phase Sintering of WC-Co Alloys: J Korean Powder Metall Inst. 1996;3(3):196-200.

Abstract PDF: The dispersion of WC grains Into the interior of an eutectic liquid has been studied by superimposing the eutectic WC-85wt.%Co liquid on the top surface of presintered WC-l0wt.%Co alloy compacts. The heavy WC grains diffused into the interior of liquid from the WC-l0wt.%Co compacts. According to increasing the treating temperatures and times, the dispersion distance from WC-l0wt.%Co substrates increased. The fine WC grains diffused into the liquid faster than the coarse WC grains. The high microstructural stability of WC-Co alloys having the heavier WC grains dispersed in a lighter Co-rich liquid was attributed to Brownian motion of WC grains in liquid. The motion of WC grains in the liquid appears to be same with the colloid(the disperse phase) in a dispersing medium. The dihedral angle of 0 degree of WC-Co at. toy seems one of key parameters, which enables the WC-Co alloys to have high structural stability without settling the WC grains during liquid phase sintering.

Previous issues