抄録
An investigation is made on the homogenization of microstructures and the improvement of elevated temperature tensile properties in the Ni-base superalloy containing 6.74%Co, 11.15%Cr, 3.12%Mo, 3.25%W, 3.98%Al, 2.74%Ti, 3.93%Nb and Bal.Ni by rheocasting with the rotation of a stirrer at a speed in the range of 20 to 70 rev/s. The results are as follows:
(1) When the superalloy is agitated at 70 s−1 from the start of solidification to above the volume fraction of solid of 0.42, the columnar dendrites are broken up and equiaxed grain structures are formed. However, when the rotation of a stirrer immersed in the alloy at a speed of 10 or 70 s−1 is interrupted at the fraction of solid of 0.19, equiaxed dendrites will grow from the primary solid particles in the subsequent process of solidification.
(2) When the fraction of solid at the end of stirring is increased from 0.42 to 0.95, the average primary solid particle size is slightly decreased.
(3) The primary solid particle sizes in the alloy agitated from the start of solidification to the fraction of solid of 0.95 at the stirrer speeds of 20, 30, 40, 50, 60, 65 and 70 s−1 are 87±21, 80±16, 75±18, 73±15, 76±14, 72±13 and 66±14 μm.
(4) The elongation values are 91% for the strain rate of 1.67×10−4 s−1 at 1373 K and 70% for the strain rate of 0.83×10−4 s−1 at 1323 K in the alloy agitated at 70 s−1 from the start of solidification to the fraction of solid of 0.42 and subsequently solidified without stirring.
