Journal of Powder Materials

차량 부품용 Al 합금 분말의 제조 및 분말 압출: J Korean Powder Metall Inst. 1995;2(3):193-200.

Variation of Mechanical Properties with Powder Spraying Conditions in Mo and Co Alloy: J Korean Powder Metall Inst. 1995;2(3):201-207.

Abstract PDF: In general, the characteristics of plasma spray coating are strongly dependent on process conditions. In this paper, Mo and Co alloy coating layers were made by plasma spraying with different spray parameters and characterized using X-ray diffraction, scanning electron microscopy(SEM), hardnass test, and wear test. It was found that the coating characteristics were mainly affected by phase composition of the powder, spray distance, arc current, and gas flow rate.

Aging of Melt Spun Ribbons in Cu-Based Shape Memory Alloys at High Temperature: J Korean Powder Metall Inst. 1995;2(3):208-215.

Abstract PDF: The aging effects on the characteristics of the melt spun Cu based shape memory alloys have been investigated by the microhardness test, X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. After aged for specific times, hardness of the ribbons began to increase and shape memory capacity diminished. At the initial stage of aging the austenitic transformation temperatures increased gradually, but at last became nearly constant: That is, the aging deteriorated the thermal stability. The increase in hardness was due to the formation of the gamma_2 precipitates. The loss in the shape memory capacity was due to the decrement of solute atoms in the matrix by the formation of the gamma_2 precipitates. In this study, it was confirmed that Mn is an effective element for Improving the thermal stability.

Microstructures and Mechanical Properties of SiC/TiB_2 Composites: J Korean Powder Metall Inst. 1995;2(3):216-222.

Abstract PDF: SiC/TiB_2 composites of varying TiB_2 content from 0 to 52 vol.% were prepared by pressureless sintering. When these composites were sintered at 2150°C the mechanical properties such as elastic modulus, strength and toughness increased with increasing TiB_2 content. On the other hand, at a sintering temperature of 2200°C, the mechanical properties reduced gradually with increasing TiB_2 content. The main reason was deduced from the onset of spontaneous microcracking and the critical particle size for microcracking was calculated approximately 5.6 mutextrmm.

Effects of Mn, Co Additions and Microporosities on the Thermal Expansion Coefficient of powder Rolled Fe-36Ni Invar Strip: J Korean Powder Metall Inst. 1995;2(3):223-230.

Abstract PDF: The effects of Mn and Co additions up to 0.6 and 2.0 wt% respectively and the amount of cold-rolled reduction on the thermal expansion coefficient (TEC) of powder rolled Fe-Ni Invar strips were investigated. The compacted strips were sintered, homogenized and cold-rolled to the final thickness of 0.8 mm, 0.65 mm and 0.4 mm. All the strips reached full density except the case of 0.8 mm sample which has a very few porosities. The interstitials which are well known to increase TEC were minimized to the level of 10 rpm C,5 and N,0 by the processing. TEC was found to decrease by increasing the cold reduction. The Mn content had little effect on the TEC. But in Fe-Ni-Co system, TEC decreased with Co content up to 0.4 wt% and then increased, yielding the minimum value of 0.2 times 10-6/°C at 0.4 wt% Co. This value is much lower than that of commercial Invar product. Such effect of Co is considered to be related with the maxiumum spontaneous- magnetostriction effect.

Synthesis and Mechanical Properties of Ti_25Cr_8Al_67 Alloy by Mechanical Alloying: J Korean Powder Metall Inst. 1995;2(3):231-237.

Abstract PDF: The powder mixtures of Al, Ti and Cr were mechanically alloyed to obtain nanocrystalline powders of Ti_25Cr_8Al_67 composition. Both FCC phase and undissolved metal chromium formed by MA. During the annealing of the MA powders, the phase transition from FCC to ordered Ll_2 started at ~300°C and was completed below 600°C. As a result of the high-temperature compressive test for the MA powder compacts, the stress-strain curves showed serrated yielding behavior at 400 and 600°C, and softening phenomenon below the strain rate of 5times10-3s-1 at 800°C. The compressive yield strength as a function of test temperatures showed the nature of the positive-temperature dependence which has the peak temperature around 600°C.

Improvement of Mechanical Properties of P/M Processed 2XXX Al-SiC_w Composites: J Korean Powder Metall Inst. 1995;2(3):238-246.

Abstract PDF: The purpose of this study is to establish powder metallurgy (P/M) fabrication processes for high performance 2XXX Al composites reinforced with SiC whiskers. Rapidly solidified 2XXX Al powders produced by commercial atomization technique were mixed with SiC whiskers. The results of mixing processes indicated that fluidized zone mixing technique was considerably effective for the large scale production of the mixture of Al powders and whiskers. In order to consolidate these Al-SiC_w mixtures into Al-SiC_w composite billets, a vacuum hot press was set up, and hot processing variables were investigated. Using the hot pressing temperature of 620°C under the pressure of 50 MPa, good quality Al-SiC_w composite billets having relatively homogeneous microstructure and sound Al/sic interfacial bonding were obtained. Composite billets were then extruded to bars having relatively homogeneous microstructures at the extrusion temperature of 450~500°C under the extrusion pressure of 700~ 1000 MPa. Mechanical properties of the extruded bars were found to be comparable with those of the composite processed by Advanced Composite Materials Corp. To improve mechanical properties of the composites, elimination of coarse intermetallic compounds, uniform distribution of reinforcements, and minimization of whisker breakage are suggested.

The Thermal Stability of Mechanically Alloyed Quaternary Al-8wt.%(Ti+V+Zr) Alloys: J Korean Powder Metall Inst. 1995;2(3):247-254.

Abstract PDF: The theoretical optimum quaternary composition for improving the thermal stability of Al-Ti alloy was recently proposed. On the basis of the suggestion, quaternary Al-Ti-V-Zr alloy powders corresponding to the optimum compositions, one of which belongs to the region of the smallest lattice misfit between the matrix and the precipitates and the other belongs to the region of the smallest rate constant of coarsening, were prepared by mechanical alloying and the powders were vacuum-hot-pressed at 430°C under the pressure of 800 MPa. The thermal stability of the specimens was evaluated by hardness testing after isothermal aging up to 400 hrs at various temperatures. The decrease of hardness of Al-Ti-V-Zr alloys was smaller than that of Al-Ti alloys. It was considered to be due to the formation of Al_3Zr type andAl_3Ti type quaternary precipitates having smaller lattice misfit than Al_3Ti and the increase of volume fraction of All0v during the isothermal aging. The quaternary Al-Ti-V-Zr alloys corresponding to the smallest lattice misfit showed the most improved thermal stablilty and it was mainly considered to be due to the formation of All0v.

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