Oxidation of Titanium Matrix Composites Reinforced with (TiB + TiC) Particulates

Young‑Jig Kim,Poonam Yadav,Junhee Hahn,Xiao Xiao,Dong Bok Lee 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3

Titanium matrix composites reinforced with (5, 10, 20) vol% (TiB + TiC) particulates were in situ synthesized using melting-investment casting method by reacting Ti with B4Cpowder. Their oxidation behavior was studied at 800–1000 °C inair. Formed scales consisted of transient TiO3and stable rutile-TiO2. More dispersed (TiB + TiC) particulates had higheroxidation resistance due to strong Ti–B and Ti–C bonding which required higher activation energy for oxidation comparedto Ti–Ti bonding in the matrix. However, such increment in oxidation resistance was limited by the formation of semiprotectivetitanium oxides, volatile B2O3,and CO2gas. With increment of (TiB + TiC), scales progressively became thinner,thus improving scale adherence.

AZ91D Mg 합금의 반용융 성형가공성에 미치는 액상율 및 압출속도의 영향

김영직 成均館大學校 科學技術硏究所 1994 論文集 Vol.45 No.2

This study describes the influence of the liquid fraction and the extrution rate on the formability of AZ91D Mg alloy prepared by semi-liquid extrution process. Surface roughness and innerdefects of forming products are also evaluated Net-shape forming of AZ91D Mg alloy products with the thickness of 1 mm is possible by optimization of forming conditions, such as liquid fraction and extrusion rate. Surface roughness of parts produced by semi-liquid process is developed in comparison with that of ordinal melt forming products. And also defects, such as blow hole, are decreased remarkably because of linear filling behavior of slurry.

AZ91HP/SiC_p+SiC_w Hybrid Mg복합재료의 반용융 가압성형

김명균,김영직 成均館大學校 科學技術硏究所 2000 論文集 Vol.51 No.2

Thixoforming process is a novel forming process that has some advantages compared to conventional die-casting. In the present investigation, material characterization of hybrid magnesium composites in terms of reinforcement fraction, forming temperature, hybrid ratio was obtained at the semi-solid state through thixoforming process. Moreover, silicon carbide particulate and whisker reinforced AZ91HP magnesium composites were manufactured by Rotation-Cylinder Method. The fulfilling behaviors of the hybrid magnesium composite slurries with thixotropic microstructures showed that the fluidity of them was dependent on the amount of whisker, whose fulfilling was not achieved over 6.7% hybrid ratio. The tensile strength of hybrid magnesium composites was compared to that of silicon carbide only particulate reinforced magnesium composites owing to strengthening effect of whisker in spite of agglomeration defect in hybrid magnesium composites. The wear properties of them were dependent not on hybrid ratio but on the fraction of reinforcement.

急速凝固한 高純度 Fe―C―Si合金중의 Carbide共晶의 過冷却凝固 시뮬레이션

김영직,서수정,안현모 成均館大學校 科學技術硏究所 1991 論文集 Vol.42 No.1

This paper decribes a study of the solidification simulation with supercooling of levitation melted and rapidly solidified high purity Fe--C-Si alloys with emphasis on carbide eutectic. Newly designed growth model of carbide eutectic is proposed. From the simulation model, calculated cooling curves are derived by means of a personal computer, and compared with experimental data. The results calculated are influenced remarkably by coefficient of heat tranfer(h), latent heat of solidification(L), growth rate constant(n) and range of temperature of mushy zone. After suitable choice of h, L, n and especially temperature range of mushy zone as 100K, experimental cooling curves are duplicated by calculated. As the cooling rate exceed about l0^3K/s, graphite crystal is not formed in the high purity Fe -C-Si melts.

Ti 정밀주조 계면반응생성물 규명에 관한 연구

성시영,김명균,김영직 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.9

The aim of the present study is to investigate the alpha-case formation mechanism between titanium melts and Al₂O₃mold during investment casting of titanium alloys. The metal/mold reaction products of titanium castings were investigated by optical microscope, microhardness profile, EPMA and XRD analysis. In this study, the mechanism of alpha-case formation was verified with thermodynamic calculations. The reaction of only TiO₂interstitial alpha-case formation could not occur spontaneously, on the basis of thermodynamic calculations. From the results of the experimental and thermodynamic calculations, the alpha-case is the reaction products of interstitial oxygen and the substitutional atoms dissolved from the mold materials with titanium, and then this reaction is spontaneous process.

Compocasting 법에 의한 AZ91D/SiC_pMMCs(metal matrix composites)제조

이경태,김세광,구형찬,김달식,김영직 成均館大學校 科學技術硏究所 1994 論文集 Vol.45 No.2

Metal matrix composites have toughness, machinability and heat conductivity, which can be obtained in metals, as well as hardness, high temperature stability, which can be obtained in ceramics. The purpose of this study is to find the optimum production condition of a compocasting method which is composed of stirring SiC particles inside a matrix which is presented as a solid or liquid state. During the compocasting method. SiC particles are mechanically incorporated into the matrix. From this study, sound AZ91D/SiC_p composites were obtained when stirring the matrix for 60minutes between 583-588℃.

Bimodal SiC 입자강화 AZ91D 마그네슘 복합재료의 유동성 및 기계적 특성 평가

裵徹洪,金世光,金永稷 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.7

The objective of this study was to investigate the influence of bimodal reinforcement on the fluidity and mechanical properties of SiC particle reinforced AZ91D Mg composites. The fraction of bimodal SiC particles was fixed at 20 wt% and the mixing ratios of 5 ㎛ to 50 ㎛ SiC particles were 0:1, 1:2, 1:1, 2:1 and 1:0. The results clearly showed that the fluidity and mechanical properties of the composites with bimodal reinforcement were dependent on mixing ratio. In terms of molten state fabrication and tailored mechanical properties, it was obtained that the proper mixing ratio seems to be 1:2.

Al-7%Si-0.3%Mg 合金의 衝擊靭性에 미치는 Zn添加의 影響에 관한 硏究

尹義博,金永稷 成均館大學校 1981 論文集 Vol.29 No.-

熱處理, Sb添加條件, Zn含量이 機械的 性質에 미치는 영향에 대해 조사하였다. 共晶Si의 크기와 형태는 적절한 熱處理에 依해 微細·球狀化하였다. 760℃에서 Al-7%Si合金에 0.15%Sb를 添加함으로써 共晶Si의 改良處理가 되었으며, 그 後 0.3%Mg를 添加시키면 强度와 伸率은 向上되었다. 356合金에 Zn이 0.2%에서 2.0%까지 添加되면 引張强度, 降伏强度는 增加하나 伸率은 오히려 減少하는 데, 이것은 Mg_2Si및 Zn_2Mg相이 粒界 및 粒內에 석출되기 때문이라고 생각된다. 또, 흡수에너지는 1.3%Zn까지는 급격히 減少하나, 그 以上에서는 거의 一定하게 되었다. Effects of heat treatment, addition of Sb, and Zn contents on the mechanical properties were examined. The size and shape of eutectic-Si particles is refined and spherodized by the optimum heat treatment. Adding of 0.15% Sb to the Al-7% Si alloy at 760℃, it is obtained modification of eutectic-Si particles, and moreover addition of 0.3% Mg contributes to promote strength and ductility. When the Zn content in increases up to 2% in Al-7%Si-0.3%Mg alloy, ultimate and yield strength increases, while ductility decreases because of precipitation of Mg_2Si, Zn_2Mg in matrix and between grain boundaries. The toughness (absorbed energy) decreases rapidly up 1.3% Zn, but become-nearly constant above 1.3% Zn.

Compocasting 법으로 제조된 AS91D/SiC_p composite 의 특성 평가

이경태,김세광,김영직 成均館大學校 科學技術硏究所 1994 論文集 Vol.45 No.2

The properties of SiC particle reinforced metal matrix composites(MMCs) of magnesuim alloy were investigated. MMCs was produced by compocasting method and specimens were fabricated by pressing of slurry. These specimens were evaluated in tensile strength, hardness, wear resistance, oxidation properties. The hardness and tensile strength were increased with SiC_p contents. Up to 5 % addition of SiC_p the wear resistancewas improved. It was deteriorated however above 5 % addition because of adhesive wear. Under isothermal oxidation conditions, oxidation resistance was improved with SiC_p.

A7003 합금의 환경친화적 압출공정을 위한 Mg조성 및 공정비교 연구

조훈,조형호,한명근,김영직 한국전과정평가학회 2002 한국전과정평가학회지 Vol.4 No.1

최근 수송기계 경량화 추세에 부응하여 door impact beam, seat side rail 및 hood support와 같은 자동차 부품등에 Al-Mg-Zn계 중경질 A7003 합금소재의 적용이 검토되고 있는 실정이다. 그러나 이들 합금소재의 적용을 위해서는 제품의 용도와 특성을 만족함과 동시에 압출성이 높은 합금소재의 개발이 선행되어야 한다. 본 연구에서는 A7003 합금소재의 압출성을 향상시키기 위하여 합금원소 첨가량이 미세조직, 압출성 및 기계적 특성에 미치는 영향을 조사하였다. Mg조성 제어에 의해 기계적 강도의 저하없이 A7003 합금의 압출성을 향상시킬 수 있었다. 또한 MLCA 기법을 적용하여 A7003 합금중의 Mg 첨가량 및 빌렛가열공정 변화에 따른 에너지 소비량 및 환경오염부하물질 배출량을 산정하였다. A7003 합금중 Mg의 첨가량을 제어하여도 압출재 생산에 소요되는 에너지의 소비량은 거의 같음을 확인하였으며 CO₂와 같은 대기오염물질을 저감시키기 위해서는 유도가열에 의한 빌렛가열공정의 적용이 가장 효과적임을 알 수 있었다. A7003 alloy has characteristics of their excellent weldability, high corrosion resistance and superior plastic working however the broadening of application for the alloy has been hampered by the lower extrudability associated by Mg content. For improvement of extrudability and enhanced recovery efficiency during Al scrap recycling, it has been generally practiced to reduce Mg content in A7003 alloy. Therefore, it is necessary to investigate the influence of Mg content on mechanical strength and extrudability of A7003 alloy. For efficient material processing which has small amounts, material life cycle assessment(MLCA) is evaluated. The quantitative analysis of energy requirements and CO₂ emission for production of A7003 extruded bar are estimated with different Mg content and billet pre-heating process (heating source by light oil or LPG). In particular, the estimation of energy requirements was performed within shipping and gating range (except the mining and extraction stages) to investigate the influence of the variables on energy requirements and CO₂ emission in detail. As Mg content increased, the flow stress and the extrusion pressure for A7003 alloy increased. It has been thought that an increment in extrusion pressure with increasing Mg content is caused by the solid solution hardening of Mg atoms in the matrix and increment in volume fraction of intermetallic compound, Mg2Si. The extrudability and the tensile strength are equal to, or above that of conventional A7003 alloy even the content of Mg varied from 1.1wt.% to 0.5wt.%.alloy. This means that minimizing the content of Mg in A7003 alloy can enhance recovery efficiency during Al scrap recycling. It can be quoted that rather than Mg content energy source for billet heating is a prime factor to determine the atmospheric CO₂ emission.