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김동환(D. H. Kim),권혁무(H. M. Kwon),김택기(T. K. Kim),김희태(H. T. Kim),김윤배(Y. B. Kim) 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.5
The nitrogenation process and magnetic properties of Sm₂Fe_(17)Nx (0 ≤ x ≤ 3) were investigated. During the initial nitrogenation process, the nitrogen content had linear relation with the square root of nitrogenation time, and the activation energy for the process was calculated to be 102.4 kJ/㏖. The magnetic properties of Sm₂Fe_(17)Nx were strongly dependent on the nitrogen content and the composition having Sm₂Fe_(17)N_(2.8) showed optimum magnetic properties with a Curie temperature of 450 oC. The intrinsic magnetic properties of the nitride at room temperature were Ms = 1147 emu/㎤, K₁ = 4.6 × 10^7 erg/㎤, K₂ = 6.0 × 10^7 erg/㎤ and H_A = 290 kOe, respectively.
장충근,김기원,권혁무 충남대학교 자연과학연구소 1979 學術硏究誌 Vol.6 No.2
Studies on the X-ray stress measurement have been made in various kinds of nitrided iron specimens. The relation between the hardness measured mechanically and the stress measured by X-rays is Considered. The main results observed are: (1) Nitrided pure iron has the tendency of increaing residual stress with, the increasing time duration of nitriding, (2) Carbon steel has the tendency of decreasing residual stress with the increasing time duration of nitriding treatment. (3) Both of the above cases showed the same results that the hardness increases with the time duration of nitriding treatment.
(Sm0.5RE0.5)Fe₁₁ Ti 화합물의 구조 및 자기특성
김희태(H.T.Kim),김윤배(Y.B.Kim),김창석(C.S. Kim),김택기(T.K. Kim),권혁무(H.M. Kwon) 한국자기학회 1993 韓國磁氣學會誌 Vol.3 No.3
(Sm_(0.5)RE_(0.5))Fe₁₁ Ti compounds have tetragonal ThMn₁₂-type structure and show the uniaxial magnetocrystalline anisotropy with the easy magnetization c-axis. Among the (Sm_(0.5)RE_(0.5)Fe₁₁Ti series, RE=Sm shows the highest anisotropy field of 11200 ㎄ / m(140 kOe). On the other hand, RE=Nd has the highest saturation magnetization of 122.3 Am² / ㎏ (122.3 emu / g) and RE=Gd the highest Curie temperature of 326 ℃.
권혁무,초천륭차 대한금속재료학회(대한금속학회) 1987 대한금속·재료학회지 Vol.25 No.2
Effects of graphite shape and pearlite ratio on thermal properties of a compacted vermicular graphite cast iron(CVGCI) were studied. Thermal expansion coefficients, thermal conductivities, specific heats and thermal diffusivities of flaky graphite cast iron(FGCI), CVGCI and spheroidal graphite cast iron(SGCI) were correctly measured. Thermal diffusivity decreases as the nodularity of graphite, temperature and the pearlite ratio in matrix increase. FGCI shows higher temperature dependency compared with CVGCI and SGCI. Linear correlation is obtained between thermal diffusivity(α) and the pearlite ratio in matrix(p) as α=α_0(1-4.3×10^(-3). p), where α_0 is thermal diffusivity of the ferrite matrix. (Received January 26, 1987)
金秀東,權赫茂,張忠根 충남대학교 자연과학연구소 1981 忠南科學硏究誌 Vol.8 No.1
The relation between phase transformation and optical micrograph differential thermal analysis and electrical resistivity in cu-Al alloys have been investigated as a function of temperature in the range of 400-750C at the composition range of 11.8-15.0 wt, pct. Aluminum. The electrical resistivity and D.T.A. results of the alloys were in good agreement with the phase transformations.
張忠根,崔勝平,權赫茂 충남대학교 1985 忠南科學硏究誌 Vol.12 No.1
Binary alloys containing up from 0% to 18% silicon at intervals of 3% we have been produced by casting. Each specimen was lathed, and had a dimension of 46㎜ length, 16㎜ diameter. Effect of silicon on the vibration damping of Al-Si alloys have been investigated using an impluse method which an iron ball, 1.95gr weight, 4.0㎜ diameter, was fallen from a height 150㎜ freely, and gave an impulse to middle of a specimen. The relation of frequencies-intensity (dB) from which its maximum natural frequency can be obtained was measured by both the condenser microphone(B & K #4165) and the digital frequency analyser(B & K # 2131C). A decrease in quantity of the relative logarithmic decrement δ_Re concerning to each percentage silicon increase in Al-Si alloys was 5.4×10 gm^-1 sec. The effect of vibration damping relying on the Si contents in the Al-Si alloys was negligible.
박헌범,권혁무 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.8
To investigate the effects of graphite contents on the mechanical and vibration damping properties, through manufacturing Al/Gr. composites by compacting and extruding Al and graphite powders, rolling its specimen up to 80%, and testing the specimen for its hardness, tensile strength, vibration damping, etc. The followings are the results as; microstructure observation showed that the Al/Gr. composites are uniformed distribution, which means its adequacy for composites. When Al/Gr. composites was rolled, the graphite shape was modified to plate shape at the parallel side to the rolling direction. According to the result of hardness tests on graphite, the more the graphite content and the smaller the rolling ratio, the less the hardness. The result of tensile strength tests show that the tensile strength increase as the graphite content deceases or the rolling ratio increases. The more the graphite content or the smaller the rolling ratio, the bigger the vibration damping coefficient. When Al contains graphite up to 15%, the tensile strength decreases by 27%, whereas, the vibration damping coefficient increases by 80%, which means inverse proportional relationship between the two.
순 AI 과 순 Cu 의 진동 특성에 미치는 시편 크기의 영향
장충근,권혁무,박헌범 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.4
The vibration properties of the pure Al plate and pure Cu plate, 12 ㎜ wide and 164∼254 ㎜ long, were investigated by cantilever beam and RFDA to get the following results. (1) The results by cantilever beam method and RFDA show that the resonance frequency decreases as the specimen length increases or the thickness decreases. (2) When measuring the vibration by the cantilever beam method, the vibration damping coefficients are stable at the specimen with 184 ㎜ or higher length. (3) When measuring the vibration damping coefficient by the cantilever beam method, the mean vibration damping ratio of Al specimen 1.6∼0.8 ㎜ thick is 3.1×10^(-2) and 4.0×10^(-2) in Cu specimen of 2.0∼1.2 ㎜ (4) When measuring the vibration damping properties by the RFDA, vibration damping coefficients are similar regardless of the length and thickness of a specimen and the mean vibration damping ratios of Al and Cu were 2.1×10^(-2) and 2.7×10^(-2), respectively. (5) As a result of (3) and (4), The relationship, between the vibration damping ratio measured by the cantilever beam method and it by the RFDA was founded as g_s=(δ_o/δ_r)×(1/1.5).
(Fe, Co) 73.5 Nb3Cu1Si13.5B9 합금의 초미세결정립형성 및 연자기적 특성
조성석,김택기,권혁무,조용수,이갑호 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.10
Ribbon-shaped amorphous Fe_(73.5-X),Co_XNb₃Cu₁Si_(13.5)B9(0≤X≤25, ΔX=5 at%) alloys prepared by rapidly quenching technique were annealed above their crystallization temperatures. The annealed Fe_(73.5-X)Co_XNb_₃Cu_₁,Si_(13.5)B_9 alloys tranformed into nanocrystalline in all range of X. Nanocrystalline Fe_(73.5-X)Co_XNb₃Cu_₁Si_(13.5)B_9 alloys annealed under optimum condition show the highest saturation magnetization and the lowest AC coercive force(f=1 ㎑, Ha=5 Oe) and core loss(f=100 ㎑, B_m0.5T) at X=5, But the initial permeability(f=1 ㎑, Ha=1 mOe) shows maximum value at X=0. An average grain size of α-Fe(Si) showing excellent soft magnetic properties is around 10 nm and increases with Co content. The degradation of soft magnetic properties during the intial crystallization process is due to the Fe-rich amorphous phase retained at grain boundary.