Effect of thermomechanical treatment on recrystallization of boron doped nickel aluminide

The major difficulty with polycrystalline Ni3Al for engineering application s is its extremely low ductility and brittle intergranular fracture at ambi ent temperatures. This problem can be reduced either by microalloying or by performing thermomechanical treatment, (TMT). In this investigation the ca st Ni -24 at%Al -0.1 at%B has been deformed to different extents (i.e. 25, 30, 35 and 50%) by rolling, and recrystallisation studies have been carried out for different extents of time, i.e. 25, 55 and 90 min at 1000 degrees C. It is observed that the volume fraction of recrystallised grains increas es with time of annealing as observed by other investigators. At a particul ar time of annealing, the volume fractions of recrystallised grains have be en found to be greater for the intermetallic with higher plastic deformatio n. For the intermetallic deformed to 50%, the whole material has been obser ved to recrystallise in 55 mins during annealing at 1000 degrees C. It is s een that the percentage elongation is highest at about 17% for the average grains of the size similar to 15 mu m (and this could be even higher at gra in size <15 mu m). The percentage elongation seemed to decrease with the in crease in grain size. It is found that the variation of percentage elongati on, e, with average grain size, d, in the grain size range of 10-35 mu m ob eys the following equation, e = -0.044d(2) + 1.4d + 5.6. (C) 1999 Elsevier Science Ltd. All rights reserved.