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AL-Li-Cu-Mg-Zr alloy powders were manufactured by gas atomizer and then extruded. The microstructures and mechanical properties of alloy powders and extruded bars were studied. The microstructures were typical cellular structure and icosahedral phases were crystallized out on the cell boundaries in Al-3Li-3Cu-1Mg-0.3Zr, Al-3Li-3Cu-1Mg-0.1Zr and Al-4Li-3Cu-1Mg-0.1Zr alloy powders. But increasing Li/Cu ratio, icosahedral phase and T_B, phase were crystallized out simultaneously. In Al-3Li-3Cu-Mg-Zr alloy extruded bars, almost the precipitates were icosahedral phase and Type 1 phase appeared. In Al-3Li-1.5Cu-Mg-Zr alloy extruded bars, the precipitates were almost R phase. In Al-3Li-1Cu-Mg-Zr alloy extruded bars, the precipitates were almost C phase. Therefore, In AI-Li-Cu-Mg-Zr alloy extruded bars, precipitation mode is Icosahedral phase → Type 1 → Type 2 → R → C phase appeared according to increasing Li/Cu ratio.

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To understand the role of a nickel(Ni) activator during sintering of tungsten(W), the densification behaviors of pure W and Ni-doped W compacts have been observed. The densification of the Ni-doped W compacts occurred rapidly at 1000℃. The W compacts containing 0.2% Ni by weight (more than the solubility limit) were densified up to 90% relative density at 1500℃, while the W compacts containing 0.037% Ni(less than the solubilty limit) were densified to 75% at 1290℃ and stopped being densified above 1290℃. In the plateau of the temperature between 1290℃ and 1800℃, neither grain growth nor densification was observed. The starting temperature of the plateau was lowered when the compacts were sintered longer time at each temperature. Above 1800℃, the 0.037% Ni-doped W compacts started to be densified again and their densification behavior was similar to that of the pure W compacts. The roles of the Ni activator on the densification of the W compacts were interpreted in two different ways. One is to provide a fast diffusion path for W atoms, which can result rapid densification due to rapid polygonization of the elongated W grains. The other is to form an elongated W grain structure formed by the grain boudary migration during alloying of Ni into W phase. The elongated grain structure is considered to be a prerequisite microstructure for subsequent rapid shrinkage. The activation energy of the alloying by grain boundary migration induced by diffusion of Ni in W was estimated to be about 234 kJ/mol; this value is within the range of previously estimated values of activation energy for densification of W-Ni powder compacts.

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Microstructural change and its effect on mechanical properties were studied for Ti-(49-45) Al-(1-5) Cr (in at.%) intermetallic compounds under various heat treatment conditions. Various microstructures such as nearly lamellar, duplex and nearly γ were obtained depending on Cr-content and heat treatment temperature. The best compressive ductility value was shown when microstructure was consisted of the lamellae of small volume fraction (about 20%) and γ matrix. The best bending ductility value was shown when the duplex structure consisted of γ and lamellae was presented. Some alloys could be deformed to true strain of 0.7 in compression at 700℃ without crack initiation.

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To predict the nearest-alumina reaction product between alumina and titanium (for solid pure Ti and liquid Cu-l0at%Ti alloy) thermodynamic calculation was carried out, and its result was compared with experimental observations. Joining experiments were performed using Ti-containing alloy (Cu-Ag-Ti), 99.9% titanium sheet and titanium coat at 1193-1393 K for 1.2-3.6 ks by vacuum brazing (〈10^(-5)Torr) and diffusion bonding (〈10^(-4)Torr). At 1193 K, the Al-Ti-O ternary phase diagram for reaction products between alumina and solid titanium was proposed. With the temperature and oxygen mole fraction, the Cu-Al-Ti-O quaternary phase diagram was proposed for reaction products between alumina and liquid Cu-l0at%Ti alloy. The redox reaction product is varied with the application method of titanium, i.e. from TiO [nonstoichiometric TiO_(1±x(x=0.1))] to TiAl and Ti₃Al. That is because the behavior of aluminium and oxygen decomposed form alumina by titanium is varied with the application method (according to whether solid or liquid) and a volume of titanium. These experimental results were well agreed with the thermodynamic prediction.

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The purpose of the present study was to investigate the fracture behavior of low carbon steels during wire drawing. In ferrite-pearlite steels, cracks were initiated at the interfaces of pearlite nodules and ferrite-pearlite, and at cementite precipitated along the grain boundaries. In steel containing martensite, cracks were initiated by decohesion of ferrite-martensite interface and by shear fracture of martensite particle. Crack initiation behavior appeared to be related to the degree of plastic deformation of constitutent phases, i.e. ferrite, pearlite and martensite. During wire drawing, cracks initiated at ferrite-martensite interface were propagated as characteristic conical shape by the coalescence of small cracks, resulting in final failure of cuppy fracture.

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This paper describes the results on the fabrication of the iron-nitriding powders using the pickling acid of steel. The fabrication of iron-nitriding powders is easily proceeded when the ultra fine (75 angstrom) magnetite precipitated at pH 12, Fe^(2+)/Fe^(3+)=0.5 mol ratio in the pickling acid are reacted with the mixing gases of H₂ and NH₃. 1) Fe₄N powder was formed at 500℃ with the mixing ratio H₂/NH₃ of 1.0/0.2 to 1.0/0.4. Mixed Fe₄N and Fe₃N powders were obtained at 500℃ with the mixing ratio H₂/NH₃ of 1.0/0.6 to 1.0/0.8. 2) Iron-nitriding powders were fine sizes less than 0.3㎛ and nodular shape. 3) Maximum saturation magnetization among the iron-nitriding powder under this experimental is 178emu/g when Fe₄N formed at 590℃. The value of saturation magnetization is equivalent to 96% of theoretical Fe₄N.

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The nitrogen reaction between steel and slag was studied by using CaO-Al₂O₃-TiO₂ slag system which has good ability for denitrogenization. The experimentally determined activity of Al₂O₃ increases with increasing TiO₂ content. The nitride capactiy, C_N to quantify the equilibrium nitrogen solubility in the slag increases with increasing TiO₂ content, but decreases with increasing slag basicity. The nitrogen reaction between CaO(BaO)-Al₂O₃-TiO₂ slag and steel may be interpreted by the Network model describing the behavior of oxygen and nitrogen ions in slag. The effect of the addition of BaO for replacing CaO on the nitride capacity was found to be very sensitive to the oxygen potentials. The nitrogen distribution ratio between CaO(BaO)-Al₂O,-TiO₂ slag and 304 stainless steel increased with decreasing Cr content and increasing temperature. Based on the results, the equilibrium nitrogen content in 304 stainless steel can be estimated when the denitrogenization is carried out using the slag investigated.

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An attempt was made to reduce Nd₂O₃ electrolytically in a fluoride bath. Neodymium metal was electrodeposited on the iron cathode to produce the Fe-Nd eutectic alloy in a liquid state at operating temperatures. Graphite was adopted for the anode and pure iron for the cathode. The Nd₂O₃ feed was prepared by dissolving into cryolite to increase the solubility of Nd₂O₃ in fluoride electrolyte. The premelt thus made had the composition of Na₃AlF_6 50wt.%, AlF₃ 34wt.% and Nd₂O₃ 16wt.% The constituents of fluoride electrolyte were NdF₃, LiF and BaF₂ which were electrochemically very stable. All the experiments were carried out in the absence of oxygen, as well as H₂O. Analysis of alloy product showed Nd 87.6wt.% Fe 11.6wt.% and Al 0.14wt.% in an optimum operating condition with the feed rate of 3.25g/hr at the temperature of 900℃ and cathode current density 3.0A/㎠. Experimental results proved that the cryolite based premelt was suitable for the electrolysis of rare earth oxide in a fluoride bath due to their prominent solubilities.

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The behaviors of physico-chemical and metallurgical properties of CaO-MgO-Fe_tO-SiO₂-∑M_xO_y slags which are saturated with MgO and in equilibrium with molten iron were investigated according to the change of MnO content from 2 to 30wt% in the temperature range of 1550 to 1700℃, and discussed in terms of the concept of the optical basicity. The results obtained were summarized as follows; 1) The activity of iron oxide was found to be maximized when the basicity B"=(CaO+MgO+MnO)/(SiO₂+P₂O_5) is 2. And, the activity coefficient of iron oxide approached to unity above 7 of B". 2) The activity of iron oxide was hardly affected by the temperature and the molar ratio of manganese oxide to the sum of basic oxides (MnO)/(CaO+MgO+MnO). 3) The empirical optical basicities of pure FeO, Fe₂O₃ and MnO were derived from the magnesia capacity and the ratio of Fe^(3+)/Fe^(2+) in these stags. The values of those were 0.65, 0.58 and 0.75, respectively. 4) The magnesia capacity, the value of Fe^(3+)/Fe^(2+), the activity coefficient of iron oxide in these stags were expressed by the following equations. log C_(Mg)^(2+)=4.039/Δ(2)-954/T-4.083 log Fe^(3+)/Fe^(2+)=5.085Δ(2)+1367/T-5.194 log γ_(Fe10)=-1.959Δ(5)-2124/T+2.955

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Effect of Precipitation free zone(PFZ) width on the fracture toughness and stress corrosion cracking(SCC) of 7475 aluminum alloy has been studied. The different PFZ width was obtained by controlling the cooling rate following solution treatment in the thermomechanical treatment of this study. PFZ width was also varied by aging treatment of different stages. By increasing the PFZ width stress intensity factor, K_(lc) has been increased in the under-and peak-aged conditions. Over-aged state has shown lower value of K_(lc) than the under-and peak-aged state when compared in the same level of PFZ width. However, when compared in the same over-aged condition, increased PFZ width resulted increased fracture toughness. The effect of PFZ width on the SCC has been studied in the under-aged condition by the crack-growth-rate test. Increased PFZ width resulted increased K_(lscc) and lower plateau velocity, which denotes the decrease of SCC sensitivity.

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