High temperature deformation behaviour of as-cast Al0.4Co0.9Cr1.2Fe0.9Ni1.2(Si, Ti, C, B)0.375 complex concentrated alloy during tensile and compression tests

Abstract

The deformation behaviour of as-cast Al0.4Co0.9Cr1.2Fe0.9Ni1.2(Si, Ti, C, B)0.375 complex concentrated alloy (CCA) in the temperature range from 700 up to 900 • C during tensile and compression tests was studied. The as-cast alloy was prepared by vacuum induction melting in a ceramic crucible followed by a tilt casting to a graphite mould. Highly anisotropic microstructure of tensile and compression specimens taken from the as-cast ingot consisted of 89 vol.% of columnar FCC(A1) (face-centred cubic crystal structure A1) dendrites and 11 vol.% of the multiphase interdendritic region where ordered phases as Cr2B, TiC, BCC(B2) (ordered body-centred cubic crystal structure B2) + BCC(A2) (disordered body-centred cubic crystal structure A2), and lamellar eutectic composed of FCC(A1) + G -(Ni,Co,Fe)16(Ti,Cr)6(Si,Al)7 (cubic face-centred crystal structure) phase were formed during solidification. Columnar FCC(A1) dendrite grains were oriented at an angle ranging from 60 • to 90 • to the longitudinal axis of the test specimens.The value of 0.2 % offset yield strength decreases with increasing applied temperature, at 700 • C tension and compression, it was measured to be about (429 ± 3) MPa and at 900 • C it decreased to the value of about (90 ± 5) MPa. The alloy during tensile deformation at 700 • C shows the strain hardening stage up to fracture. The tensile deformation true strain-true stress curves at 800 • C and compression deformation true strain-true stress curves at temperatures from 700 to 800 • C show the strain hardening stage at initial strains. After reaching the peak values, the strain softening stage is typical for the alloy. The strain softening stage results from partial dynamic recrystallisation of FCC(A1) dendrites and fracture of brittle high elastic modulus phases in the interdendritic region. The compression and tensile curves at the temperature of 900 • C show a short area of the strain hardening stage, followed by a steady-state deformation at a constant flow stress. The finite element analysis (FEA) of the 3D distribution of local equivalent strains corresponds qualitatively to the observed structural changes within the necked and barrelled specimens. K e y w o r d s : complex concentrated alloys, microstructure, numerical modelling, mechanical properties, fracture