Perpustakaan Digital ITB

High-entropy alloys (HEAs) as a new concept of alloy design has been studied intensively these past decades due to the possibility of this alloys for exhibiting excellent properties. CoCrFeMnNi HEAs, which have a single FCC crystal at high-temperature has been verified to exhibit good combination of strength and ductility. Considering its low stacking fault energy, which twinning is favorably formed thus could affecting the mechanical properties, a study to investigate the annealing twin and deformation twin behavior in this alloy subjected to different annealing treatment was conducted and correlates the behavior to the mechanical properties, therefore give more knowledge about the nature of this novel alloy. A CoCrFeMnNi HEAs rod sample was fabricated by arc-melting process was used in this study. After homogenization for 3 days at 1200°C and cold-rolling until 70% thickness reduction, isochronal annealing for 1 h at different temperature, which are 800,900, 1000, 1100°C, and different heating rate, which are 1,5,25, and 50°C/s to 900°C, were conducted to observe the annealing twin behavior. Deformation twin behavior were observed on the uniformly deformed area of the tensile specimen which prior annealed at different temperature then subjected to tensile test. SEM-EBSD was used to characterized annealing and deformation twin behavior, in addition hardness test was conducted to observe the mechanical properties of the alloys after annealing treatment and different area in the grain. The result shows fully recrystallized microstructure obtained from all annealing treatment. With increased of annealing temperature, increased of grain size with change of modality of grain size distribution were observed. Increased of heating rate led to slight increase of grain size with no change of grain size modality. Annealing twin density were exhibited to have inverse correlation with grain size, due to mechanisms during grain growth. With increased of grain size, hardness and strength were decreased, in expense of increased ductility. Annealing twin boundary was shown to be less efficient as grain boundary, with 4.46% of deficiency. Deformation twin could be observed, and qualitatively the density increased with increased of grain size. Fractography showed ductile dimple structure from all tensile specimens, with larger facets obtained by higher annealing temperature. Deep dimples were observed from all specimens subjected at each annealing temperature could be associated with twin bundle acted as crack deflector.