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The effects of the modification and silicon contents on the pitting corrosion of the aluminum silicon alloys in the solution of Na₂SO₄ and NaCl were studied by the electrochemical methods. Pits were found to be initiated at theboundary region between the aluminum matrix and the silicon precipitates in the eutectic structure. The modification and silicon contents of the alloy did not affect the mechanism of pitting reaction, but affect the critical pitting corrosion potentials, pitting induction times and protective potentials. It is concluded that the resistance to the pitting corrosion of the alloys was dependent on the ratio of the eutectic structure and the particle size of the silicon precipitates.
The mechanisms of the liquid metal formation at Ni/B/Ni (Ni: base metal, B: insert material) joint, which could be characterized as liquid phase diffusion bonding, has been investigated. Fine boron (B) powders (under 300 mesh) were coated on the elaborately polished bonding surfaces as an insert material. The specimen packed in quartz tube under 5×10^(-3) torr vacuum was heated in a induction furnace to 1283K-1473K. It is observed that inserted material B was diffused into base metal, and that liquid metal was formed by the reaction of B and Ni. Liquid metal was formed preferentially at the grain boundaries. The state of phases was analyzed to depend on B content because of the fact that content of B on the liquid layer was higher than the solid state base metal.
Ni was bonded by liquid phase diffusion using pure boron (B) as an insert material, and bonding mechanism and its application to other metals were studied. B powder, under 300 mesh, was coated on the polished bonding surface. Bonding specimen was packed in a quartz tube under 1.6×10^(-1) Pa vacuum atmosphere, and heated to 1433-1473K. As results, at the bonding temperature of 1433K, 1453K and 1473K, initial width of liquid layer was 87 ㎛, 81 ㎛, 80 ㎛, and maximum width of liquid layer was 138 ㎛, 146 ㎛ and 158 ㎛ respectively with the thickness of insert material of 25 ㎛. Bonding mechanism was similar to conventional TLP bonding except the formation of liquid metal on the joint and initial width of liquid layer. Other metals such as Cu, AISI304 steel, Alloy713C and Rene80 superalloy were also liquid phase diffusion bonded by using pure B.
The dielectric layers for plasma panel display device were prepared from two series of glass-ceramics, namely, P₂O_5-ZnO-BaO and SiO₂-ZnO-B₂O₃ glass-ceramics containing filler. The nucleation and crystallization process of glassceramics for dielectric layer have been examined by differential thermal analysis, X-ray diffraction and light and electron microscopy. Optical, thermal and electrical properties of the dielectric layer were evaluated by means of spectrophotometer, dilatometer and LCR meter. From this research, it was found that these glass-ceramics are useful materials for dielectric layers in plasma panel display device, as those have a similar thermal expansion to soda-lime glass plate, high reflectance, low sintering temperature. Also the addition of Al₂O₃ and TiO₂ as fillers to these glass-ceramics is considered to be suitable for acquiring good properties of dielectric layer for PDP device.
The corrosion behaviors with grain refinement were investigated on the AZ91D magnesium alloy. The grain size was controlled by the inoculation and the change of pouring temperature, the use of cone-type permanent mold. The salt spray test was conducted for 480 hours following ASTM B 117 specification. And the corroded surface and corrosion products were analyzed by SEM and XRD, respectively. Both the corrosion rate and the corrosion depth were markedly decreased by the fine distribution of second phase due to the grain refinement. The relationship between corrosion rate and grain size in the present study could be well predicted the corrosion rate of as-cast AZ91D alloy that have a range of grain size in commercial castings. The corrosion products were consisted of Mg(OH) ₂ and chlorides mainly.
The effects of the modification and silicon contents on the pitting corrosion of the aluminum-silicon alloys in the solution of Na₂SO₄ and NaCl were studied by the electrochemical methods. Pits were found to be initiated at the boundary region between the aluminum matrix and the silicon precipitates in the eutectic structure. The modification and silicon contents of the alloy did not affect the mechanism of pitting reaction, but affect the critical pitting corrosion potentials, pitting induction times and protective potentials. It is concluded that the resistance to the pitting corrosion of the alloys was dependent on the ratio of the eutectic structure and the particle size of the silicon precipitates.
化學組成을 一定하게 하고 Mg로서 球狀化處理한 後 各種 應力下에서 凝固시킨 鑄鐵을 黑鉛化시켰을 때 黑鉛化速度에 미치는 應力의 影響을 調査한 結果는 다음과 같다. (1) 應力增加에 따라 第一段 黑鉛化는 促進되며 硬度測定値로 미루어 보아 黑鉛化에 미치는 stress의 영향은 아니링溫度가 높을수록 현저하다. (2) 應固時應力을 0∼4.83×10^6 dyne/㎠ 範圍內에서 變化시켰을 때의 黑鉛核生成에 要하는 活性化 에너지는 33,000∼22,000 ㎈/㏖ 이며 黑鉛核成長에 要하는 活性化 에너지는 29,000∼20,000 ㎈/㏖ 이다. (3) 應力이 增加할수록 鑄放狀態의 硬度는 增加한다. (4) 應力이 增加할수록 微細한 free cementite 粒子가 基地組織에 散在하여 있고 pearlite의 層狀간격도 좁다. The effects of stress on the first stage graphitization have heen studied by using nodular cast irons solidified under three levels of stress of approximately 1.38×10^6, 2.45×10^6, and 4.83×10^6 dyne/㎠ The results obtained ara as follows. (1) The first stage graphitization of the cast iron is accelerated with stress level, and the higher the annealing temperature, the greater the effect of stress on the graphitization. (2) The activation energies for graphite nucleation and graphite growth decrease from 33,000 to 22,000 ㎈/㏖ and from 29,000 to 20,000 ㎈/㏖ respectively as the stress level is increased up to 4.83×10^6 dyne/㎠. (3) As-cast hardness of the cast iron increases with increasing stress level. (4) Free cementite particles distributed in the as-cast structure and the pearlite lamella spacing in the matrix become smaller at the higher stress level.