Microstructure and Mechanical Properties of Precipitate Strengthened High Entropy Alloy Al10Co25Cr8Fe15Ni36Ti6 with Additions of Hafnium and Molybdenum

Abstract

High entropy or compositionally complex alloys provide opportunities for optimization towards new high-temperature materials. Improvements in the equiatomic alloy Al17Co17Cr17Cu17Fe17Ni17 (at.%) led to the base alloy for this work with the chemical composition Al10Co25Cr8Fe15Ni36Ti6 (at.%). Characterization of the beneficial particle-strengthened microstructure by scanning electron microscopy (SEM) and observation of good mechanical properties at elevated temperatures arose the need of accomplishing further optimization steps. For this purpose, the refractory metals hafnium and molybdenum were added in small amounts (0.5 and 1.0 at.% respectively) because of their well-known positive effects on mechanical properties of Ni-based superalloys. By correlation of microstructural examinations using SEM with tensile tests in the temperature range of room temperature up to 900 °C, conclusions could be drawn for further optimization steps.

Hierarchical microstructure strengthening in a single crystal high entropy superalloy

“…With further ageing at 1,023 K for 200 h, the metastable FCC particles would mostly be eliminated by diffusing FCC formers into the surrounding FCC matrix, eventually, the whole system would reach the equilibrium state. Figure 4a shows the tensile yield strength versus temperature plot, which includes HESA, some advanced superalloys 30,[33][34][35] and some conventional HEAs 17,18,23,36 23 . By contrast, HESA in HT-1 state could achieve a yield strength of 880 MPa at 298 K and 954 MPa at 1,023 K, both were higher than those of CoCrFeMnNi and other HEAs, approaching the yield strength level of advanced superalloy such as CMSX-4 (888 MPa at 298 K and 913 MPa at 1,023 K) 33 .…”

“…However, the elevated temperature tensile strength of HEA could be limited by insufficient fractions and relatively low solvus of strengthening phases in HEAs 11 . One of the highest reported tensile yield strength of HEAs at 1,023 K was 473 MPa for cast-type Al 10 Co 25 Cr 8 Fe 15 Ni 36 Ti 6 , which contained a FCC matrix with 46% L1 2 and 5% B2 phases by volume fractions 23 , although its yield strength could surpass those of solid solution type superalloys such as 800H and Inconel617, it was weaker than advanced precipitation strengthened cast-type superalloys 24 . Alloy design for higher L1 2 phase fraction and solvus temperature are required to further improve the high temperature tensile strength of HEAs.…”

New Advances in High-Entropy Alloys

“…It seems that alloying with Ti leads to an increase in microstructural heterogeneity. Similarly aimed at the Al-Co-Cr-Fe-Ni-Ti alloy after the composition adjustment, Manzoni et al [ 29 ] studied the microstructure and properties of the Al 10 Co 25 Cr 8 Fe 15 Ni 36 Ti 6 alloy and Haas et al [ 30 ] studied those of the Al 10 Co 25 Cr 8 Fe 15 Ni 36 Ti 6 alloy. Both kinds of alloy showed beneficial particle-strengthened microstructures.…”

Structure and Phase Composition of a W-Ta-Mo-Nb-V-Cr-Zr-Ti Alloy Obtained by Ball Milling and Spark Plasma Sintering

“…The interest in these alloys is due to unique combinations of mechanical properties that they can offer when properly designed. Research in this area is aimed at finding new promising compositions [1][2][3][6][7][8][9], characterizing the microstructure and mechanical properties [10][11][12][13][14][15][16], studying the mechanisms of plastic deformation [4,17], or determining the phase composition and phase stability of the alloys [18][19][20][21][22][23][24][25][26][27][28][29].…”