발간논문

Home > KJMM 논문 > 발간논문

The effect of degassing treatment on statistical properties of SiC_p/2024Al composites fabricated by powder extrusion was studied in terms of Weibull distribution probability. The degassed powders and powders degassed at 450℃ were extruded at 500℃. The tensile strength and elongation of the degassed composites were superior to those of the undegassed composites. This may be due to the fact that the degassing treatment inhibited the formation and growth of oxides at interface between the SiC and aluminum matrix. Weibull parameter, m, of the undegassed composites was lower than that of the undegassed composites. It was suggested that the oxides, especially MgO, at interface acts as a crack initiation site during tensile loading. Therefore, it is believed that the degassing treatment is necessary to improve of the tensile properties and reliability in composites.

keyword :

Mechanical properties of (SiC_w+SiC_p) (15Vol.%) AA2124 hybrid composites subjected to aging treatment were studied. The hybrid composites with different SiC_w : SiC_p ratios of 1 : 1, 1 : 2, and 1 : 3 were fabricated by powder metallurgy and were solution treated followed by aging treatment at 190℃ from 0 to 48 hours. In order to build a basis for comparison, an identical aging treatment for the monolithic AA2124 alloy was also conducted. The peak aging time for both the hybrid composites and monolithic AA2124 alloy was determined from the measurement of matrix hardness. The strength, ductility, and work hardening rate of the hybrid composites were evaluated from the result of tensile stress-strain curves. Accelerated aging occurred in the hybrid composites compared to the monolithic AA2124 alloy and the peak aging time of all the composites showed 3-5 hours. The hybrid composite with SiC_w : SiC_p =1 : 1 showed the highest ultimate tensile strength compared to that of the hybrid composites with SiC_w : SiC_ =1 : 2 and 1 : 3. For the under-aged hybrid composite with SiC_w : SiC_p =1 : 1, the work hardening rate was higher than that of the over-aged hybrid composite.

keyword :

Samples of Tm^(3+)-doped YTa_7O_(19) were prepared using the conventional solid state reaction method and the solid state reaction method induced co-decomposition nitrates as starting materials to investigate their photoluminescence characteristic. The samples were identified by XRD and SEM, and the optical measurement was also carried out. Under 359㎚ excitation, YTa_7O_(19) doped with Tm^(3+) exhibited a narrow-band blue emission, peaking at about 455㎚. The maximum of relative emission intensity of Y_(1-x)Tm_xTa_7O_(19) using co-decomposition nitrates was obtained at x=0.1. This revealed the concentration quenching of emission.

keyword :

The effect of metalloids on the crystallization temperature(T_x) and the melting point(T_m) has been investigated in Fe_(100)-○Si_xB_y, (2.5≤20, 2.5≤25, 10≤x+y≤35) alloy wires. The atomic size difference and heat of mixing of the alloys increased with increasing metalloid content. Conversely, the electron concentration decreased with the content. T_x of the Fe-Si-B amorphous alloy wires increased with the increasing values of the underlined three factors up to a maximum at a certain value of each factor. Then, the T_x decreased with those factors after the maximum. It is assumed that the change of T_x results from the variation of the relative stability of an amorphous phase with the heat of mixing which depends on the atomic size and electron concentration in alloys. The stability relies upon the elastic energy in a solid solution and the structural stability. The latter comes from the electron concentration effect, the former the atomic size difference. In contrast to T_x, T_m initially decreased with the three factors, then increased with them after showing a minimum although the relation showed much more divergence than that of T_x. Since the maximum of T_x and the minimum of T_m occur at the nearly same values of heat of mixing, T_x/T_m(glass forming ability) has a maximum in the vicinity of these heat of mixing values.

keyword :