Anisotropic Dimensional Change Research Articles

反応焼結におけるＴｉＡｌ（Ｍｎ）金属間化合物の寸法変化

We report the dimensional change of powder mixture of titanium and aluminum alloy during reactive sintering in hot isostatic pressing(HIP) . The powder mixture of titanium and aluminum alloy were prepared by using powder extrusion process with various extrusion ratio. The hot pressed material showed a swelling during reactive sintering because of the pore formation. The materials with extrusion ratio over 5.4 exhibited a volumetric shrinking at the ratio of 0.96. However, these materials exhibited anisotropic dimensional change. The materials that had a extrusion ratio from 17.6 to 295 showed the expansion at the ratio of 1.1 for longitudinal direction of extruded direction and the shrinkage at the ratio of 0.93 for radial direction of extruded direction. This anisotropy is due to the fibrous structure developed by extrusion.

Ｔｉ／Ａｌ素粉末混合圧粉体の燃焼合成における寸法変化

Stoichiometric mixtures of titanium hydride and atomized aluminum powders for TiAl are pressed uniaxially into compacts, 10mm×10mm×10 or 5mm in size, and sintered in argon.Differential thermal analysis curves demonstrate the decomposing endothermic reaction of the titanium hydride into titanium and hydrogen, and exothermic synthesizing reactions of compounds. The synthesizing reactions begin before the exothermic peak in a DTA curve and proceed through the peak. A subsequent holding at a high temperature for a long time is necessary in order to complete homogenization. The exothermic peak appears immediately after the melting of aluminum. The peak is attended with a rapid decrease in density of the compact. A subsequent heating to higher temperatures gives rise to a slow densification. Both swelling and shrinkage appear earlier in the compacting direction than in the lateral one.The slower is the heating rate in the reaction temperature range, the less are the swelling and the anisotropic dimensional change. The finer particle size gives less swelling and anisotropy in dimensional change and more densification and independency of heating rate.

Ｔｉ‐５０ａｔ％Ｎｉ混合圧粉体の焼結中における寸法変化の異方性

The reaction process of Ti and Ni during sintering process of the Ti-50 at%Ni binary mixed powder compacts was investigated by the model experiment using the synthetic compacts of φ300 μm Ti wire and carbonyl Ni powders, and also the dimensional changes were examined by the dilatometric method both in the press direction and that perpendicular to it.The results obtained are as follows: The width of growth layers of intermetallic compounds, such as Ti2Ni, TiNi and TiNi3 produced in the press direction by the interdiffusion between Ti and Ni during sintering was thick, while in the direction perpendicular to it, it was thin, and some pores which are thought to he one of the main factors for the expanding phenomenon were observed in the Ni side of the interface between Ti wire and carbonyl Ni powders. On the other hand, the anisotropy of dimensional change was observed by the dilatometric method; i.e., the continuous shrinkage in the press direction and the great expansion especially in the temperatures higher than 955°C of eutectic reaction in the direction perpendicular to it. Judging from the above mentioned results of model experiment, it was confirmed that this anisotropy of dimensional change was deeply related to (1) the contracting phenomenon due to the appearance of thick layer of the intermetallic compounds in the press direction, and (2) the expanding phenomenon due to a reaction between the eutectic liquid and the intermetallic compounds being greater in the direction perpendicular to it where the width of Ti2Ni phase contacting with the eutectic liquid is thin.

Dimensional Changes of Acrylonitrile Copolymer During Coagulation

Anisotropic dimensional changes in uniaxially oriented acrylonitrile copolymer film during coagulation were investigated isothermally by varying the NaSCN concentration. Anisotropic dimensional change occurs when the swollen acrylonitrile films are im mersed in a strong nonsolvent (e.g., 35% NaSCN) or the degree of orientation prior to cross-linking at an adequate level, and swelling is high enough. The former phe nomenon is due to skin (semipermeable membrane) formation and nonuniform coagula tion; the latter phenomenon is due to spontaneous elongation, and the wide-angle x-ray diffraction measurements show that it occurs with crystal-liquid transformation in accordance with the previously reported theory that reversible contractile processes are related to these transformations.