발간논문

Home > KJMM 논문 > 발간논문

The effect of process variables on the formation of amorphous wires has been investigated in the Fe_(77. 5)Si_(7. 5)B_(15) alloy. The in-rotating-water spinning process was used for the wire forming method. The longest amorphous wire was made when the V_I/V_w ratio was 0.85, where V_I is the velocity of the melt jet ejected from a nozzle and V_w is the speed of rotating cooling water. The V_I/V_w ratio should be in the range of 0.85±0.02 for the formation of a continuous wire longer than 5 m in length. The velocity of the melt jet increased with the square root of the pressure in a crucible. The stability of the melt jet increased with the pressure and decreased with the melt temperature. The continuity of the jet decreased with the increasing flying distance from a nozzle. Since the jet lost its characteristics of continuous flow at the flying distance of 4∼8 ㎜, the gap between a nozzle and water surface should be kept lower than that distance to obtain a continuous wire. It was found that the optimum melt temperature was 70∼80℃ higher than the melting point of the alloy in this spinning process.

keyword :

The glass forming ability. GFA, has been investigated experimentally and predicted from the transformation kinetics in Fe-Si-B alloy wires. The critical diameter for the formation of an Fe-Si-B amorphous wire increased with the metalloid content up to the amount of 25 at%, then decreased over that content. The amorphous alloy wire with the largest critical diameter has shown the highest value of crystallization temperature at the composition of Fe_(15)Si_(10)B_(15). The larger the diameter of an amorphous wire was, the lower the critical cooling rate that was predicted from the transformation kinetics. The kinetic approach for the prediction of the glass forming ability was successful in view of a good agreement of the measured GFA with the predicted one.

keyword :

InSb thin films with electron mobility as high as 49,000 ㎠/V·sec were formed by heat treatment at 535℃ for 5 minutes of multi-layered(Al₂O₃/In(9,000A˚)/Sb(1 ㎛)) thin films. And it was found that the annealing time and temperature margins to get InSb films of high electron mobility were much narrow. InSb formation mechanisms of In/Sb multi-layered thin films were proposed on the base of In-Sb phase diagram.

keyword :

Co_(68)Fe₄Cr₄B_(11)Si_(13) amorphous ribbon was fabricated by PFC(Planar Flow Casting) process. The effect of PFC parameters on the thickness and surface defects of amorphous ribbon was examined. The thickness of amorphous ribbon is proportional to the square root of melt ejection pressure and nozzle to roll distance, gap, but inversely proportional to the wheel speed and melt temperature. Gap is closely related with the increase of internal pressure in melt puddle. Surface defects of amorphous ribbon are classified into droplet, oxide film, air pocket and wave pattern. These surface defects result from entrapped air in puddle, poor wettability between liquid metal and cooling wheel, and instability of melt puddle. The increase of ejection pressure or decrease of gap size reduced surface defects, because increase of puddle internal pressure makes melt puddle more stable. Decreasing of gap size was the most effective method to reduce thickness and improve surface quality of amorphous ribbon.

keyword :

In this paper, the theoretical analysis is presented to relate the film crack patterns, developed during tensile uniaxial loading of brittle film on ductile substrate, to interface adhesion strength. If the shear stress, developed at the interface due to different deformation properties of two materials with uniaxial loading, exceeds the critical shear strength τ_d, interfacial adhesion is lost by shear breakage of interface bonding. This stress analysis describes the biaxial stress state in near-interface in terms of external strain and crack spacing. With loading the number of parallel cracks increases until the interface separation occurs, and finally no additive film cracks generate. Therefore, the interface shear strength can be estimated from the external strain ε_s and crack spacing λ_s at the onset of saturation through the proposed analysis model. The interface adhesion evaluation of DLC/Al shows the increase by a factor of 1.6 in a 30min Ar-plasma etching compared to no etching. It was found that ε_s increases, conversely λ_s decreases with Ar-plasma etching time, which means that interface adhesion increases. Such strong dependencies of ε_s and λ_s on interface adhesion indicate that the experimentally measured parameters, ε_s and λ_s can be used as a rough estimate of interfacial adhesion in a given system.

keyword :

Creep properties of the lamellar structured Ti-46.6Al-1.4Mn-2Mo(at%) alloy, which is made by hot extrusion of a blended elemental powder mixture, are investigated in air environment over the temperature range from 1023K to 1173K at constant stress levels ranging from 100MPa to 250MPa. The average activation energy for creep within the temperature range from 1048K∼1173K at stress level 150MPa and 200MPa is found to tie 384kJ/㏖. The value of the stress exponent n in the range of 3.8∼4.3 was obtained within the stress range from 150MPa to 250MPa and 1.3 between 100MPa and 150MPa at 1073K. Microstructural studies conducted on creep fractured specimen showed the secondary cracks along the lamellar grain boundaries and the secondary cracks are assumed to be formed by pore nucleation, growth and coalescence during the tertiary stage.

keyword :

In this study, microstructural influence on the anisotropic fatigue properties of Al-Li 8090 alloy has been investigated in relation to the intrinsic and extrinsic nature. For all three(L-T, T-S and S-T) orientations fatigue resistance of δ` microstructure was higher than that of S`+δ` microstructure, mainly due to the higher levels of crack closure in δ` microstructure. In the early stage of crack growth, fatigue resistance of -T and T-S specimens was considerably higher than that of S-T specimen. lntergranular delamination susceptible to occur in the S-T specimen was found to be responsible for the highest crack growth rate. However, overall fatigue properties of T-S specimen were estimated to be poor due to the frequent catastrophic fracture occurring in the direction of vertical intergranular boundaries. Fatigue resistance of S-T specimen was not largely affected by the introduction of S` phase in the δ` microstructure.

keyword :

This study was to investigate the effect of alloying elements i.e, nitrogen and copper on the low temperature tensile and impact properties of duplex stainless steels. Four kinds of specimens, which are the 0wt.%N, 0.13wt.% N, 0.17wt.%N and 0.19wt.%N+1.5wt.%Cu additions to the base composition of 22wt.%Cr-5.5wt.%Ni-3wt.%Mo duplex stainless steel, were prepared. From the room temperature tensile testing, it was found that the tensile strength and elongation increased with increasing the volume fraction of austenite. Tensile strengths increased with the addition of N and Cu, while for the specimen of Cu addition, the lowest elongation was shown with increasing the volume fraction of austenite. Low temperature tensile tests showed the increase in tensile strength with the addition of N and Cu. Elongation decreased after showing the maximum peak value at -50℃ and -100℃ for the nitrogen free and 0.13wt.%N alloyed specimens, respectively. On the other hand, the elongation increased continuously with decreasing the test temperature for the specimens containing 0.17wt.%N alloyed and Cu alloyed specimen. From the observation of ferrite and austenite phase after tensile deformation, the dislocations in the ferrite region were entangled leaving a relatively dislocation free region, while the extensive stacking fault and deformation twining created α` martensite in the austenite region. The volume fraction of transformed α` martensite increased with decreasing testing temperature. The N and Cu alloyed specimens appeared to decrease the volume fraction of α` martensite with decreasing the test temperature. The maximum elongation peak could be obtained when the volume fraction of α` martensite was higher than 88%.

keyword :

Fe-Cr-C hardfacing stainless steels were deposited on S45C carbon steel using a submerged arc welding process. The effects of C and Cr contents on the as-welded structures of Fe-(12-17)%Cr-(0.19-0.32)%C hardfacing stainless steels have been studied by microstructural observation and mechanical testing. The variation of as-welded structure as a function of C and Cr contents was compared with the microstructure predicted by the Schaeffler diagram. In Fe-12%Cr-(0.19-0.32)%C stainless steels, carbon solute atoms were primarily segregated in the interdendritic regions. And Cr-rich carbides tends to precipitate along the interdendritic regions in the stainless steels having C contents higher than 0.2%C. This explains why that the abrupt decreases of mechanical properties and the cleavage fracture surfaces appear in the stainless steels having C contents higher than 0.20%. The sliding wear mechanism varied from the adhesion to tribochemical reaction with increasing hardness of weld metal. However, the wear resistance tends to be affected by the introduction of abrasion. wear mode due to the hard carbide particles. This can be confirmed by the fact that its wear resistance increases with the increase of matrix hardness of weld metal.

keyword :

The changes in the damping properties of the Fe-5%Al and Fe-28%Mn alloys have been studied when they are bonded in parallel. When they are not bonded, the specific damping capacities (SDC) of the Fe-5%Al and Fe-28%Mn alloys have been found to be higher than 40% at a strain of 0.05% and more than 10% over 0.05% strain, respectively. In the case of Fe-5%Al alloy surface strain and applied magnetic field decrease the damping property to some extent. As the bonding volume ratio of Fe-5%Al to Fe-28%Mn was varied from 1:1 to 3:1, the tendency of measured SDC vs strain curves follows the theory for composite alloys at all three volume ratios. So the bonded alloy shows damping properties of both Fe-5%Al and Fe-28%Mn alloys.

keyword :