• 한국분말재료학회지
• /
• 제29권4호
• /
• pp.325-331
• /
• 2022

Beta-titanium alloys are used in many industries due to their increased elongation resulting from their BCC structure and low modulus of elasticity. However, there are many limitations to their use due to the high cost of beta-stabilizer elements. In this study, biocompatible Ti-Mo-Fe beta titanium alloys are designed by replacing costly beta-stabilizer elements (e.g., Nb, Zr, or Ta) with inexpensive Mo and Fe elements. Additionally, Ti-Mo-Fe alloys designed with different Fe contents are fabricated using powder metallurgy. Fe is a strong, biocompatible beta-stabilizer element and a low-cost alloying element. The mechanical properties of the Ti-Mo-Fe metastable beta titanium alloys are analyzed in relation to the microstructural changes. When the Fe content increases, the tensile strength and elongation decrease due to brittle fracture despite a decreasing pore fraction. It is confirmed that the hardness and tensile strength of Ti-5Mo-2Fe P/M improve to more than 360 Hv and 900 MPa, respectively.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2022년도 봄 학술논문 발표대회
• /
• pp.93-94
• /
• 2022

The presence of chloride (Cl-) ions in environments causes localized corrosion resulting decrease the durability of the structures. In this study, 5% Mg containing Al alloys (Al-5Mg) wire used vis-à-vis compared its corrosion resistance with pure Al in 3.5wt.% NaCl solution with exposure periods. Initially both wires exhibited identical open circuit potential (OCP) attributed to the presence of native oxide film on the surface but with the exposure periods it shifted towards active direction owing to the dissolution of oxide film. The pure Al continuously shifted the OCP towards active direction while Al-5Mg shows stabilization of OCP after 8 days of exposure. The OCP of Al-5Mg is slightly higher compared to pure Al wire owing to the activeness of Mg. The total impedance of the Al-5Mg alloy is almost three times greater than pure Al with exposure periods in 3.5 wt.% NaCl solution. It might be formation of Al-Mg LDH (layered double hydroxide) thin film onto the surface.

• Archives of Metallurgy and Materials
• /
• 제66권3호
• /
• pp.759-763
• /
• 2021

The effects of the sintering holding time and cooling rate on the microstructure and mechanical properties of nanocrystalline Fe-Cr-C alloy were investigated. Nanocrystalline Fe-1.5Cr-1C (wt.%) alloy was fabricated by mechanical alloying and spark plasma sintering. Different process conditions were applied to fabricate the sintered samples. The phase fraction and grain size were measured using X-ray powder diffraction and confirmed by electron backscatter diffraction. The stability and volume fraction of the austenite phase, which could affect the mechanical properties of the Fe-based alloy, were calculated using an empirical equation. The sample names consist of a number and a letter, which correspond to the holding time and cooling method, respectively. For the 0A, 0W, 10A, and 10W samples, the volume fraction was measured at 5.56, 44.95, 6.15, and 61.44 vol.%. To evaluate the mechanical properties, the hardness of 0A, 0W, 10A, and 10W samples were measured as 44.6, 63.1, 42.5, and 53.8 HRC. These results show that there is a difference in carbon diffusion and solubility depending on the sintering holding time and cooling rate.

• 한국재료학회지
• /
• 제4권4호
• /
• pp.483-490
• /
• 1994

AI-Ti합금의 열적 안정성에 미치는 V첨가의 영향에 대하여 조사하였다. AI-8wt.%Ti 분말과 Ti과 V의 원자비를 3:1, 1:1로 달리한 AI-8wt.%(Ti+V)분말을 기계적 합금화 방법으로 준비하였으며 16시간의 기계적 합금화 후 모든 조성에 대해 정상상태의 혼합 분말을 얻을 수 있었다. 기계적 합금화한 분말은 진공열간압축하여 성형하였다. 열적 안정성을 평가하기 위하여 $400^{\circ}C$, $480^{\circ}C$, $550^{\circ}C$에서 최고 1000시간까지 등온열처리후 경도시험을 행하였다. AI-Ti합금에 V을 첨가함으로써 $Ai_{3}Ti$의 조대화가 억제되어 열적 안정성이 증가하였음을 확인하였다.

• 한국재료학회지
• /
• 제28권10호
• /
• pp.539-543
• /
• 2018

We report the structural, morphological and magnetic properties of the $Ni_{70}Mn_{30}$ alloy prepared by Planetary Ball Mill method. Keeping the milling time constant for 30 h, the effect of different ball milling speeds on the synthesis and magnetic properties of the samples was thoroughly investigated. A remarkable variation in the morphology and average particle size was observed with the increase in milling speed. For the samples ball milled at 200 and 300 rpm, the average particle size and hence magnetization were decreased due to the increased lattice strain, distortion and surface effects which became prominent due to the increase in the thickness of the outer magnetically dead layer. For the samples ball milled at 400, 500 and 600 rpm however, the average particle size and hence magnetization were increased. This increased magnetization was attributed to the reduced surface area to volume ratio that ultimately led to the enhanced ferromagnetic interactions. The maximum saturation magnetization (75 emu/g at 1 T applied field) observed for the sample ball milled at 600 rpm and the low value of coercivity makes this material useful as soft magnetic material.

• Corrosion Science and Technology
• /
• 제12권6호
• /
• pp.274-279
• /
• 2013

Flow accelerated corrosion (FAC) of the carbon steel piping in nuclear power plants (NPPs) has been major issue in nuclear industry. During the FAC, a protective oxide layer on carbon steel dissolves into flowing water leading to a thinning of the oxide layer and accelerating corrosion of base material. As a result, severe failures may occur in the piping and equipment of NPPs. Effect of alloying elements on FAC of pipe materials was studied with rotating cylinder FAC test facility at $150^{\circ}C$ and at flow velocity of 4m/s. The facility is equipped with on line monitoring of pH, conductivity, dissolved oxygen(DO) and temperature. Test solution was the demineralized water, and DO concentration was less than 1 ppb. Surface appearance of A 106 Gr. B which is used widely in secondary pipe in NPPs showed orange peel appearance, typical appearance of FAC. The materials with Cr content higher than 0.17wt.% showed pit. The pit is thought to early degradation mode of FAC. The corrosion product within the pit was enriched with Cr, Mo, Cu, Ni and S. But S was not detected in SA336 F22V with 2.25wt.% Cr. The enrichment of Cr and Mo seemed to be related with low, solubility of Cr and Mo compared to Fe. Measured FAC rate was compared with Ducreaux's relationship and showed slightly lower FAC rate than Ducreaux's relationship.

• 대한기계학회논문집
• /
• 제9권1호
• /
• pp.40-46
• /
• 1985

본 연구에서는 제 1보에 밝힌 바 있는 용접 HAZ조직의 파괴인성에 영향을 주 는 PWHT 유지시간과 가열속도에 이어, 용접 HAZ의 불안정포성파괴에 미치는 용접잔유 응력의 영향을 상세히 밝히기 위하여 일층 용접을 실시하고, 이 용접재의 용접HAZ에 단축상태의 일정한 응력을 작용시켜 주면서 소정의 열처리를 실시함으로써 용접후 열 처리시 용접HAZ에 작용된 응력의 크기가 파괴인성에 어떠한 영향을 미치는지를 COD파 괴인성시험, 미소경도시험, 파면관찰을 통하여 고찰하고자 한다.

• 한국주조공학회지
• /
• 제34권6호
• /
• pp.194-199
• /
• 2014

The effect of $Al_2Ca$ on the oxidation resistance and tensile property of Al-5Mg alloys was investigated. According to the TGA (Thermogravimetric analysis) result at $550^{\circ}C$ after 24hrs, the Al-5Mg alloy showed parabolic behavior with weight gain. On the other hand, there was almost no difference in the weight changes of the $Al_2Ca$ added Al-5Mg alloys during the oxidation. It was thought that the improvement of oxidation resistance in $Al_2Ca$ added Al-5Mg alloys might be due to the formation of a protective oxide layer with CaO and MgO on the surface. The microstructures of the alloys showed grain refinement with an increasing $Al_2Ca$ content. From the tensile test, the yield strength of the alloys were improved with an increasing $Al_2Ca$ content. The 0.07 mass%$Al_2Ca$ added Al-5Mg alloy showed similar elongation and increased strength, simultaneously. It was considered that the addition of $Al_2Ca$, which was superior in the oxidation resistance of Al, reduced the formation of Mg oxides and inclusions during the alloying. This, partly led to the improvement of tensile properties.

• 한국재료학회지
• /
• 제25권5호
• /
• pp.215-220
• /
• 2015

The effect of Al content on the processing of reaction-bonded $Al_2O_3$ (RBAO) ceramics using 40v/o ~ 80v/o Al-Zn-Mg alloy powder was studied in order to improve traditional RBAO ceramic processes that use ~ 40v/o pure Al powder. The influence of high Al content in starting $Al_2O_3$-Al alloy powder mixtures on its particulate characteristics, reaction-bonding, microstructure, physical and mechanical properties was revealed. Starting $Al_2O_3$-Al alloy powder mixtures with 40v/o ~ 80v/o Al alloy powder were milled, reaction-bonded, post-sintered, and characterized. With an increasing Al alloy content, the milling efficiency of Al alloy powder was lowered, resulting in a larger particle size after milling. However, in spite of the larger particle size of Al alloy powder, the oxidation, i.e., reaction-bonding, of the Al alloy was successfully completed via solid and liquid state oxidation, in which the activation energy of the oxidation was nearly the same regardless of Al alloy content. After reaction-bonding and post-sintering at $1600^{\circ}C$, RBAO ceramics from 80v/o Al alloy content showed a relative density of ~97% and a flexural strength of 251 MPa compared to ~ 96% and 353 MPa for RBAO ceramics from 40v/o Al alloy content, respectively. The lower flexural strength at 80v/o Al alloy content was due to the weak spinel phase that formed from Zn, Mg alloying elements in Al.

• 한국재료학회지
• /
• 제12권3호
• /
• pp.182-189
• /
• 2002

The Zr-0.2Sn-0.8Nb-X(X = 0~200ppm Si, 0~0.4wt.% Mo and Mn respectively) ingots for test specimens were manufactured by a vacuum arc re-melting method to find out the effect of Si, Mo, and Mn on the corrosion characteristics of the Zr-0.2Sn-0.8Nb alloy. After being heat-treated and rolled repeatedly out to be flat materials, they were finally heat-treated at 51$0^{\circ}C$ for three hours and used as the specimens for corrosion tests. The corrosion behavior of the specimens was studied in both 40$0^{\circ}C$ steam for 200 days and in aqueous 70 ppm LiOH solution at 36$0^{\circ}C$ for 90 days. From the study it was found that Si from 80 to 200 ppm contributed to increasing the corrosion resistance of Zr-0.2Sn-0.8Nb alloy in both steam and LiOH solution. This study also showed that Mn from 0.1 to 0.4% caused to go up the corrosion resistance, whereas Mo played a apart in improving the corrosion resistance only between 0.05 and 0.2 wt.%.