抄録
An investigation is made on the homogenization of microstructure 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 follows:
(1) The torque value remains almost unchanged during the solidification of the alloy with the rotational stirring except its initial stage. The level of torque values increases with the increase in stirrer speed.
(2) When the alloy 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 rotational stirring of the alloy at 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.
(3) When the fraction of solid at the end of the rotational stirring is increased from 0.42 to 0.95, the average primary solid particle size is slightly decreased.
(4) The primary solid particle sizes in the alloys 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, respectively.
(5) 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 the speed of 70−1 from the start of solidification to the fraction of solid of 0.42 and subsequently solidified without stirring.
