Effect of thermomechanical treatment on recrystallization of boron doped nickel aluminide

The major difficulty with polycrystalline Ni3Al for engineering applications is its extremely low ductility and brittle intergranular fracture at ambient temperatures. This problem can be reduced either by microalloying or by performing thermomechanical treatment, (TMT). In this investigation the cast 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°C. It is observed that the volume fraction of recrystallised grains increases with time of annealing as observed by other investigators. At a particular time of annealing, the volume fractions of recrystallised grains have been found to be greater for the intermetallic with higher plastic deformation. For the intermetallic deformed to 50%, the whole material has been observed to recrystallise in 55 mins during annealing at 1000°C. It is seen that the percentage elongation is highest at about 17% for the average grains of the size ∼15 μm (and this could be even higher at grain size <15 μm). The percentage elongation seemed to decrease with the increase in grain size. It is found that the variation of percentage elongation, e, with average grain size, d, in the grain size range of 10–35 μm obeys the following equation, e=−0.044d2+1.4d+5.6.