Ternary Eutectic Structure Research Articles

Ａｌ‐Ｓｉ‐Ｓｒ３元系状態図の研究

The aluminum corner of Al-Si-Sr ternary alloy system was investigated by means of inverse rate thermal analysis, identification by X-ray diffraction, EPMA analysis and microscopic observation.A ternary compound SrAl2Si2, named "T", exists in this ternary system and Al-T line is considered as a quasibinary system with a eutectic point at 1.1%Si, 2.4%Sr, 645°C. The aluminium corner is divided into two regions by the Al-T quasibinary system. A ternary eutectic point was determined to locate at 575°C, 13.1%Si, 0.03% Sr, which is very close to the Al-Si binary eutectic point. The modification effect of small amount of strontium addition on Al-Si alloys can be regarded to be due to the formation of fine ternary eutectic structure. In the Al-SrAl4-T region, a ternary eutectic point was found to locate at 643°C with 1.7%Si, 2.4%Sr.

The structures expected in a simple ternary eutectic system: Part II. The Al-Ag-Cu ternary system

Ternary alloys of various compositions from the aluminum rich corner of the Al-Ag-Cu system were directionally solidified at several different growth rates ranging from 6.4 × 10−1 mm·S−1 to 5.6 × 10−3 mm· s−1. The region of two phase coupled growth between α-Al and CuAl2 was determined at a growth rate of 6.4 × 10−1 mm· s−1. The composition range over which a fully ternary eutectic structure formed was investigated for several different growth rates. The results are found to be consistent with the predictions of the competitive growth model set out in Part I,1 and it would seem that the ternary eutectic composition of the published phase diagram may be incorrect. Scanning electron microscopy, using the backscattered electron signal, was used, together with optical microscopy, to study the microstructures formed. The ternary eutectic between α-Al, Ag2Al, and CuAl2 was found to be semiregular, and the unusual morphology of the two phase dendrites between α-Al and Ag2Al is explained.

Microstructure and mechanical properties of unidirectionally solidified Al-Si-Ni ternary eutectic

Al-10.98 pct Si-4.9 pct Ni ternary eutectic alloy was unidirectionally solidified at growth rates from 1.39μm/sec to 6.95μm/sec. Binary Al-Ni and Al-Si eutectics prepared from the same purity metals were also solidified under similar conditions to characterize the growth conditions under the conditions of present study. NiAl3 phase appeared as fibers in the binary Al-Ni eutectic and silicon appeared as irregular plates in the binary Al-Si eutectic. However, in the ternary Al-Si-Ni eutectic alloy both NiAl3 and silicon phases appeared as irregular plates dispersed in α-Al phase, without any regular repctitive arrangement. The size and spacing of NiAl3 and Si platelets in cone shaped colonies decreased with an increase in the growth rate of the ternary eutectic. Examination of specimen quenched during unidirectional solidification indicated that the ternary eutectic grows with a non-planar interface with both Si and NiAl3 phases protruding into the liquid. It is concluded that it will be difficult to grow regular ternary eutectic structures even if only one phase has a high entropy of melting. The tensile strength and modulus of unidirectionally solidified Al-Si-Ni eutectic was lower than the chill cast alloys of the same composition, and decreased with a decrease in growth rate. Tensile modulus and strength of ternary Al-Si-Ni eutectic alloys was greater than binary Al-Si eutectic alloy under similar growth conditions, both in the chill cast and in unidirectionally solidified conditions.