Geleneksel sinterleme ve spark plazma sinterleme yöntemlerinin nanokristal yapılı CoCrFeNi yüksek entropili alaşımın mikroyapısal özellikleri ve sertliği üzerine etkilerinin araştırılması

In the present study, CoCrFeNi HEAs were prepared in nanocrystalline structure and consolidated via conventional sintering and spark plasma sintering. Investigation of microstructures were implemented by using x-ray diffraction (XRD), focused ion beam microscopy (FIB), and transmission electron microscopy (TEM) with respect to sintering type and temperature. The findings have showed that the as-milled single-phase face centered cubic (fcc) crystal structure was retained after conventional sintering at 1000 and 1100°C, whereas spark plasma sintering yielded additional phase (Cr7C3) at the same temperatures. The as-milled grain size was increased from 10 nm to 450 nm and 1.5 µm after conventional sintering at 1000 and 1100°C, respectively, revealing that the nano-structured CoCrFeNi alloy does not remain thermally stable after long exposures at elevated temperatures. On the other hand, the grain size was retained around 353 nm after spark plasma sintering at 1100°C, which is dramatically smaller than that of conventional sintering. Accordingly, the hardness of mechanically alloyed CoCrFeNi HEA reduced from 4.6 GPa to 2.1 GPa after conventional sintering at 1100°C due to the significant grain growth, whereas the enhanced hardness of 3.6 GPa was maintained after consolidation at the same temperature with spark plasma sintering. [ABSTRACT FROM AUTHOR]