AISI 304L 스테인리스 강의 크리프-피로 상호작용에 미치는 인 (P) 의 영향

위당문,남수우,윤영철,김중재 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.11

Effect of phosphorus on the creep-fatigue interaction of 304L stainless steel was investigated at the test temperature of 823K. The microstructural observation was very distinctive. As the content of phosphorus increases, the density of grain boundary carbide decreases. The results of creep-fatigue test for the three materials show that the effect of phosphorus is beneficial for the fatigue life under creep-fatigue loading condition. Since the segregation of phosphorus on grain boundary lowers grain boundary diffusivity and the density of grain boundary carbides, the nucleation site and growth rate of cavity is considered to be decreased as the content of phosphorus increases. Therefore, the addition of phosphorus to 304L stainless steel is believed to prolong the creep-fatigue life.

금속간화합물 TiAl 의 고온산화거동 및 기계적성질에 미치는 Al-21Ti-23Cr 코팅의 효과

위당문,오명훈,이호년,박정용 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.1

Ti-48Al specimens were coated with Al-21Ti-23Cr film at 200W, 0.8Pa and 573K by RF magnetron sputtering. The oxidation behavior of the coated specimens was investigated through isothermal and cyclic oxidation tests, and the tensile deformation properties of the uncoated and the coated specimens were also investigated before and after oxidation. The isothermal and cyclic oxidation curves showed that the AI-21Ti-23Cr film was very effective in decreasing the oxidation rate of the Ti-48Al at 1273 K. This excellent oxidation resistance is attributable to the formation of a protective Al₂O₃, layer on the surface of the Al-21Ti-23Cr film. From the tensile test, it was found that the protective Al₂O₃, layer on the surface of the Al-21Ti-23Cr film enabled the Ti-48Al to maintain its tensile properties in an oxidizing environment. Moreover, from the microhardness test, it was also found that the Al-21Ti-23Cr film suppressed the embrittlement of the Ti-48A1 during oxidation. Although extensive cracking with a transverse direction was observed on the surface of the film, the delamination of the film from the substrate and the spallation of the Al₂O₃ scale were not observed. Thus, it is suggested that the adhesion of the Al₂O₃ scale on the Al-21Ti-23Cr film and the Al-21Ti-23Cr film on the Ti-48Al is excellent before and after oxidation.

금속간화합물 TiAl 의 고온산화거동 및 기계적성질에 미치는 Yttrium 첨가 Ll2 (Al, Cr) 3Ti 코팅의 효과

위당문,오명훈,이호년,박정용,박진민 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.4

The oxidation behaviors and the mechanical properties of TiAl alloys coated with the Al-21Ti-23Cr and the Al-21Ti-23Cr-0.lY films were investigated. A small addition of yttrium to the coating material was, effective in the improvement of the oxidation resistance of the Ti-48Al. From the scratch test, specimen coated with the Al-21Ti-23Cr-0.1Y film had better adhesion between the Al₂O₃ scale and the coating layer than one coated with the Al-21Ti-23Cr film. And AFM study showed that the Al₂O₃,surface of the Al-21Ti-23Cr-0.1Y coating is more smooth than one of the Al-21Tr-23Cr coating after isothermal oxidation; Thus, it is suggested that this excellent oxidation resistance is attributable to the excellent adhesion between the Al₂O₃ scale and the Al-21Ti-23Cr-0.1Y film and the smooth Al₂O₃ surface of the Al-21Ti-23Cr-0.1Y coating. From the tensile test, it was found that AI-21Ti-23Cr-0.1Y coating enables the TiAl to maintain more effectively its tensile properties in an oxidizing environment than the Al-21Ti-23Cr coating. Moreover, the specimen coated with the Al-21Ti-23Cr-0.1Y film showed lower creep rate and longer time to rupture than the specimen without coating, under the constant stress of 200 ㎫ at 1123 K in air. Therefore. it could be assumed that the Al-21Ti-23Cr-0.1Y alloy was prospective as an oxidation-resistant coating material for TiAl alloys.

Cu-Ni 고용체 합금의 정적 및 반복응력 Creep 변형에 미치는 용질원자의 영향

위당문,남수우,이상인 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.1

Four kinds of Cu-Ni alloys(90Ni-Cu, 78Ni-Cu, 10Ni-Cu) were crept to investigate the effect of solute atom on the creep behavior of these alloys over the temperature range of 558-676K(0.4T_m where T_m is the absolute melting temperature) and at the stress levels from 127 to 256 ㎫. Results show Chat the static and cyclic creep deformation behaviors are affected by the thermodynamic factor, 1-(d ln γ_i/d lnX_i), Where γ_i and X_i are activation coefficient and compositional concentration, respectively. Cyclic creep acceleration is observed for 40Ni alloy under the stress of 197 ㎫, and it can be explained that the excess vacancies generated mechanically under cyclic creep assist the recovery process with dislocation climb. To illustrate the above results, a proper creep equation is proposed as, ε˚=K(1/b²)(γ/Eb)³(D₁.+f_PD_P)(σ/E)³(T.F.), where E is Young's modulus, b is Burgers vector, r is stacking fault energy, D_L is lattice diffusion coefficient, D_p is pipe diffusion coefficient and T.F. is thermodynamic factor.

Seed 를 이용한 일방향 응고법에 의한 TiAl 합금의 층상경계방향제어

위당문,오명훈,이호년,Johnson, D . R .,건청행,산구정치 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.11

The thermal stability of the lamellar microstructure and the orientation control of the lamellar microstructure in a cast TiAl alloys with Mo and C were investigated. The lamellar stability of the seed material up to the melting temperature is important in the orientation control of the lamellar microstructure by the directional solidification. First, the partial liquidus surface was constructed for TiAl-C ternary and TiAl-1.5Mo-C quaternary systems. The lamellar stability was determined by quickly heating specimens to a temperature just below the melting temperature, holding, and then cooling to room temperature. Ti-46Al-1.5Mo-0.2C alloy was found to be a promising composition as a seed materials and ingots with a lamellar microstructure aligned along the growth direction were successfully grown by directional solidification process using the seed alloy. From the result of tensile and compression tests, directionally solidified Ti-46Al-1.5Mo-0.2C (at.%) ingots were found to exhibit a high yield stress together with a reasonably good tensile elongation at room temperature and a high compression stress up to 1000℃.

일방향응고에 의한 TiAl 합금의 상평형

위당문,이재현,오명훈,김민철,정인수 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.4

TiAl 합금의 코팅재료로서 Al-Ti-Cr 2상합금의 장시간 산화특성

위당문,이재경,이호년,오명훈 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.8

Both Al-21Ti-23Cr(L1₂+Cr₂Al) and Al-37Ti-12Cr(γ+TiAlCr) two-phase alloys have been accepted to be the most pertinent coating materials in Al-Ti-Cr alloy system to improve the high-temperature oxidation resistance of TiAl alloy taking into consideration of the oxidation properties, the resistance to thermal stress and the chemical compatibility. In this study, the analysis on thermal stress through a thermal expansion coefficient, a tensile and compressive test and reaction properties with TiAl alloy by means of bonding coating materials and TiAl substrate was performed. This elucidates the long-term oxidation properties in L1₂-based and γ-based alloys. The difference from a short-term oxidation resistance between L1₂-based alloy and the γ-based alloy was not observed because both alloys could form a stable Al₂O₃ layer. However, although both alloys show similar resistance to thermal stress, it was confirmed that the L1₂-based two-phase alloy has much better oxidation resistance than γ-based two-phase alloy in a long-term oxidation behavior considering the interface reaction properties with TiAl alloy.

β-안정화 원소가 첨가된 TiAl 합금의 특성 : 1. 고온 상변태 1. Phase Transformation at Elevated Temperatures

위당문,오명훈,정인수,장홍섭 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.8

The phase transformation of TiAl-X (X = Mo, W, Re) system at elevated temperatures was investigated by analyzing the dendritic morphologies of TiAl-X alloys and by constructing pseudo-binary phase diagrams of TiAl-2X ternary alloys. It was found that the addition of β stabilizers such as Mo, W, Re shifted the high temperature region of the binary Ti-Al phase diagram to the high Al composition side so that β phase forms as a primary crystal even at higher Al composition compared with the binary Ti-Al system. It also appeared that those β stabilizers shifted melting temperature and β phase region to low temperature and high Al composition side comparing the TiAl-2X (X = Mo, W, Re) pseudo binary phase diagram with the binary TiAl phase diagram. From the partial liquidus projections and pseudo-binary phase diagrams, the degree of 'β stabilizing effect' was found to be in the following order : W$gt;Re≥Mo.

일방향응고된 2상 TiAl 합금의 층상경계 방향제어

위당문,이재현,오명훈,김민철 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.11

The effect of Al concentration and third element addition on the directionally solidified (DS) TiAl alloys were systematically investigated in order to get a basic conception for control of lamellar boundary orientation. DS ingots have been grown by the arc melted unidirectional solidification equipment without seed materials. Some β stabilizing elements such as Mo, Nb and Cr have been added in order to increase phase field in the binary system. In the case of Ti-46Al-2Mo, Ti-96Al-2Mb and Ti-46Al-2Cr DS ingot grown at a growth rate of 90㎜ hr, it has been found that the lamellar orientation was aligned nearly 0˚ to 45˚ to the growth direction. Therefore, it could be suggested that there has been great possibility to align lamellar orientation by adding β stabilizing elements such as Mo, Nb and Cr. In the case of Ti-47.5Al-2.5Mo DS ingot grown at a growth rate of 180㎜/hr and 360㎜/hr, the lamellar boundary was nearly perpendicular to the growth direction. However, when the directional solidification was performed at a growth rate of 90㎜/hr, the lamellar boundary orientation of Ti-47.5Al-2.5Mo DS ingot was nearly parallel to the growth direction. These results indicate that lamellar boundary orientation of DS ingot may been affected by the growth rate as well as composition.

다결정 TiAl + Mo 합금의 인장변형특성 및 층상조직의 제어

위당문,김민길,오명훈,이재현 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.1

The effect of Mo additions on the microstructure and the room temperature deformation behavior of directionally solidified (DS) and polycrystalline forms of two-phase TiAl alloys were systematically investigated. Tensile elongation as large as 6.5% was observed for a polycrystalline specimen with duplex structure, but it varied with the strain rate and the test environments. In case of the fully lamellar structure, however, tensile elongation lover than 1% was obtained both in polycrystalline and in DS specimens. It was found from directional solidification studies that the lamellar boundary orientation in DS ingot has been affected by the growth rate and Mo contents. In case of Ti-48.5at.%Al-0.6at.%Mo DS ingot grown at a growth rate of 300 ㎜/hr, the lamellar boundary was nearly perpendicular to the growth direction. However, the lamellar boundary orientation of Ti-47.5at.%Al-2.5at.%Mo DS ingot was nearly parallel to the growth direction when the directional solidification was performed at a growth rate of 90 ㎜/hr. These results have shown that solidification procedures of TiAl with a nearly stoichiometric composition has been affected by Mo addition and, therefore, the lamellar boundary orientation in DS ingot could be controlled by changing the growth rate and the content of Mo additions.