On the phase formation of CoCrFeNiX high entropy alloys

• Main Authors: An-Chen Fan, 范恩誠
• Other Authors: 蔡銘洪
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/99273497616861057019

碩士 === 國立中興大學 === 材料科學與工程學系所 === 103 === Despite the vast numbers of reported high entropy alloys (HEAs), our understanding of the composition-phase relationship of HEAs is far from satisfactory. One of the main problems that hinder our progress is that most works study the effect of alloying by adding different elements into different base alloys. Because there can be substantial difference between base alloys, it becomes difficult to understand the effect of the alloying elements themselves. Here, we add ten different alloying elements to the same base alloy CoCrFeNi. The alloying elements are varied systematically from IIIB to VIB elements (X = Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W), leading to ten CoCrFeNiX alloys. Except for the cast ingots, the ten alloys have been processed by four heat treatments conditions. We try to understand that the results in the alloys with different adding elements by analysing the structures of these alloys with different conditions. We realize that existing phase formation theories often fail to explain the behavior of the CoCrFeNiX alloys. Besides, we find that atomic size difference is the key factor to the selection of intermetallic phase type. In this research, we create an idea to predict the possible main intermettallic phase in the CoCrFeNiX cast alloys by checking the binary phase diagrams. In other conditions, we find that most of the ten alloys have no phase transformations during 1100°C Homogenizing and 500°C annealing. However, most of the ten alloys have phase transformations during 900°C and 700°C annealing, and the common phase transformation in thes ten alloys during annealing is the formation of the σ phase.