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Al/Graphite 합금 복합재료의 마모특성에 미치는 흑연의 영향
천병선,홍순직,김홍물 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.7
In the present investigation, P/M method and extrusion process have been used to manufacture Al6061/graphite composite materials. The graphite particles were distributed uniformly within the Al6061 alloy matrix. The results showed that tensile properties and hardness of the composites reduced with increasing graphite volume and a comparison of experimental and calculated results was compatible to the tensile strength behavior. The wear behaviour of the 6061/graphite composites was also studied as a function of speed and distance with reference to different values of the matrix hardness. The obtained wear data were interpreted on the basis of the analysis of the surface and subsurface damage to the composites. As the hardness of the materials increased, their specific wear rate also decrease.
고분해능 전자현미경에 의한 SiAiON-SiC 복합재료의 미세구조와 파괴 특성
천병선,최경식,이병택,평가찬이 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.12
Microstructure and fracture behavior of pressurelessly-sintered SiAlON-SiC composite containing different SiC contents was investigated using high-resolution electron microscopy(HREM) and micro-indentation fracture(MIF) technique. The SiAlON-6%SiC composite showed the highest Vickers hardness and fracture toughness. The composite contained nanometer-size SiC particles dispersed homogeneously both in SiAlON grains and at grain boundaries. The grain boundary were formed with a 1-2㎚ thick amorphous layer regardness of the SiC content. The interface between SiAlON and SiC embedded in the grain, however, were formed without any amorphous layer. The typical fracture mode of the monolithic SiAlON was intergranular. That is, cracks propagate along The SiAlON grain boundaries with amorphous layers. In SiAlON-6wt%SiC, mixed mode of intergranular and transgranular fracture was observed, which seems to be caused by the nanometer-size SiC distributed in the SiAlON grains. In SiAlON-12wt%SiC, cracks propagated more straight through the SiAlON grains with submicron-size SiC particles, and the typical fracture mode was transgranular.
Ti-Ni-Cu 형상기억 합금의 상변태 및 열 싸이클에 의한 피로특성
천병선,이오연,남궁정,조광희 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.2
Martensitic transformation and effects of thermal fatigue cycles on the transfer mation temperature and shape recovery of Ti-Ni-Cu alloys were investigated by means of electrical resistance measurement, thermal fatigue tests and transmission electron micros copy. Thermo-mechanical treatment at 600℃ for one hour after cold rolling showed the best shape recovery effect irrespective of Cu concentration. Substitution of a small amount of Cu for Ni in the equiatomic composition of Ti-Ni showed folling results ; Ms-temperature of the Ti-Ni-Cu alloy increased slightly with the increase of Cu content, The range of transformation temperature for Ti_(50)Ni_(40)Cu_(10) alloy(i.e., T_(Mf-Af)) was reduced to 7℃. After stress relief treatment at 750 ℃ for one hour, the Ti_(50)Ni_(45)Cu_5 alloy showed good two-way memory effect. Change of the M_s temperature was observed to a certain number of thermal cycles, and it became nearly constant after a critical number of thermal fatigue cycles.
정응력하에서 Ti50NI35Pd15 형상기억합금의 변형거동에 관한 연구
천병선,이갑호,오현숙,홍석균 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.9
The B₂⇔ B_(19) transformation behaviours in a ternary Ti_(50)Ni_(35)Pd_(15)(at.%) alloy were investigated by means of electrical resistivity measurements, differential scanning calorimetry and constant load thermal cycling tests and they were compared with the B₂⇔ R and B₂⇔ B_(19) transformations in a thermo-mechanically treated binary Ti-50.2Ni alloy. The transformation start temperature of B₂→ B_(19) transformation and transformation finish temperature of B_(19) → B₂ transformation increased lineary with increasing applied stress. The stress dependence of the transformation start temperature, transformation elongation and hysteresis of the B₂⇔ B_(19) tranformations in the ternary alloy were 10.0MPa/K in the reciprocal form(dσ/dT) where σ in the critical stress for inducing the transformation, 2.1% and 25K, respectively. The B₂→ B_(19) transformation in the ternary Ti-Ni-Pd alloy lies between the B₂→ R and B₂B_(19)' transformation in the binary Ti-Ni alloy. And the transformation elongation associated with the B₂⇔ B_(19) transformation increased rapidly for stresses less than 80MPa and slowly above 80MPa with increasing applied stress.
텅스텐 중합금의 냉간가공 및 Ageing 효과에 관한 연구
천병선,송흥섭,김은표,이성,노준웅,백운형 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.3
Tungsten heavy alloys are successful combinations of strong W grain and ductile Ni base matrix. Its high density and strength combined with excellent ductility are the principal advantages of these alloys. The purpose of this study was to understand the effects of cold working and post-ageing treatments on the mechanical properties using the classical approach of sintering compacts from a mixture of 93W-4. 9Ni-2.1Fe system. By using the ageing treatment, the strength and hardness were increased with ageing temperatures and showed maximum strength at 600℃ for the 15% cold worked specimens; whereas, ductility was minimum. Strengthening by the ageing treatment might be attributed to the very fine dispersed precipitates in W grains.
Ti-Ni-X (X = Cu, Al) 형상기억합금의 의탄성 및 내식성에 관한 연구
천병선,한철호,이형란,홍석균 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.6
Pseudoelasticity behaviour and passivetion treatment on the shape memory alloys are known to have a great deal of influence on the stability of transformation temperature, shape recovery and improvement of corrosion resistance characteristics in their practical applications. The present work was aimed to examine the pseudoelasticity characteristics by tensile test, and corrosion resistance characteristics by corrosion test in Ti-Ni-X(X-Al, Cu) alloys with/ without passivation treatment. The results of this study are as follows, 1. The results of tensile test for Ti-Ni-X(X-Al, Cu) alloys show that the shape recovery is nearly perfect in martensite state and critical stress for slip is increased with increasing strain. Also, the pseudoelasticity behaviour appears in Ti_(50.0)Ni_(40.0)Cu_(10.0) alloy by unloading at temperature above Af and Ti_(50.0)Ni_(49.0)Al_(10.0) alloy by cold working over 25%. 2. The results of the anodic polarization corrosion test show that the corrosion resistance characteristics of Ti-Ni based alloys can be increased by application of passivation treatment and Ti-Ni-X(X=Al, Cu) alloys has better corrosion resistance characteristics than Ti-Ni equiatomic composition alloy.
Al-Li-Cu-Zr 합금의 기계적 성질에 미치는 저온 시효 열처리의 영향
천병선,김종희,이용연 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.2
The effects of low temperature aging on the impact toughness and mechanical properties of Al-1.9%Li-3.0%Cu-0.15%Zr alloy have been investigated. It shows that the impact absorption energy and elongation are increased in the order of over-aged, peak-aged and under-aged specimen at the various aging temperature, and these values in the specimen peak-aged at lower aging temperature are increased. In the specimens aged at 120℃ and 140℃, dimples are observed in the matrix and around the grain boundary. Intergranular fracture has been observed noticeably in the 160℃ peak aged specimen. These results are attributed to the microstructural changes by the low temperature aging treatment that forms more dense and homogeneous distribution of T₁ phases on the dislocations within the matrix and more narrow precipitate free zone in the grain boundary at 120℃ and 140℃ than at 160℃.
천병선,이철로,류광현,임승택 대한금속재료학회(대한금속학회) 1987 대한금속·재료학회지 Vol.25 No.9
A bimetal was produced by a welding method. Its base metal was carbon steel containing 0.53 wt% C and the weld metal was pure copper containing 1 wt% Sn which was added as a deoxidizer. The yield strength and the ultimate tensile strength of the bimetal bonding were 6.8 ㎏/㎟ and 21.5 ㎏/㎟, respectively. The Charry V-notch impact absorption energy of the bimetal was 41.8 J/㎠ and the fracture was found to take place in copper near the interface indicating relatively high interface strength. The elastic-plastic fracture toughness value under static load, Jic, was 1.1 ㎏/㎜ and the mode of fracture was similar to that in the Charpy impact test, The wear resistance of the base metal was superior to that of SUS 304 stainless steel.