Fe₄₀Ni₄₀B₂₀共晶合金深过冷凝固组织演化的温度曲线及高速摄影分析

The temperature curves and the images of solidification for Fe₄₀Ni₄₀B₂₀ (at%) eutectic alloys were detected and recorded by using the infrared pyrometer and the high speed video (HSV). Combining with the previous DSC results,three evolution regions can be deduced for the microstructure with initial melts undercoolings (ΔT): ΔT=170~230K, the rod eutectic colonies of metastable phase (Fe,Ni)₂₃B₆ and γ-(Fe,Ni) forms initially which gives birth to the first recalescence in temperature curve and HSV Images. Subsequently, the stable phases γ-(Fe,Ni) and (Fe,Ni)₃B solidify from remaining melts and the metastable phases remelt which causes the second recalescence; ΔT=230~260 K, the rod eutectic colonies or near uncoupled two phases with metastable phase solidify from undercooled melts initially and transform into stable phases during further cooling, the stable phase form epitaxially from the matrix phase of the initial colonies almost simultaneously. Therefore only one sharp recalescence peak can be obtained from temperature curve which corresponding to one brightening process from HSV. ΔT=260~300 K, The uncoupled growth between γ-(Fe,Ni) and (Fe,Ni)₂₃B₆ appears and forms the anomalous eutectic structure. The severe decomposition of metastable give rise to the inflexion on the temperature curve and the second recalescence in HSV images. The solidification rates of metastable phase were calculated by using BCT model which coincide with the rates first recalescence in the region of medium and large ΔT. With further increasing ΔT, the recalescence rates deviate from the model results and keep almost steady values due to uncoupled growth of two phases.