Solidification behavior of IN-100 and effect of alloying elements on it were investigated by means of differential thermal analysis (DTA), microstructural observation, X-ray diffraction, and EPMA analysis.
In alloy IN-100, it was revealed that six phase reactions took place successively during cooling from melt. These reactions and the onset temperatures were as follows, 1)
L→γ(1 329°C), 2)
L→γ+MC(D) (1319°C), 3)
L→γ+MC(ID) (1 310°C), 4)
L→γ+γ' (1 259°C), 5)γγ'→(1 210°C), and 6)
L→γ+M
3B
2 (1 200°C), where
L is melt, γ is fcc phase. MC(D) and MC(ID) denote MC carbides formed among dendrite arms and interdendritic regions, respectively. γ' is Ll
2 type ordered phase and M
3B
2 denotes boride phase.
The occurrence of two kinds of carbide reactions ((2) and (3)) and M
3B
2 eutectic reaction ((6)) was identified for the first time in this study. SEM observation on the carbides, which were embossed on the γ matrix by an electrolytic etching, showed that the carbides had three types of morphology. These were blocky, lattice-like and flaky in shape. It was found that the blocky carbides were contained in MC(D), while the lattice-like and flaky carbides were frequently found in MC(ID). The influence of C, Al, Ti, and B on the above phase reactions and solidified structure was also clarified.
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