The effects of third elements on the kinetics of order change in Ni3Al under HVEM irradiation

The effects of boron, cobalt or titanium additions on the kinetics of order changes in Ni3Al under irradiation were investigated in a HVEM. The long-r ange order (LRO) parameter was determined by measuring the intensities of s uperlattice spots on the diffraction patterns. Order-variation kinetics was investigated by using a previously proposed theoretical model. The number of replacements per displacement epsilon and the steady-state LRO parameter S infinity were directly deduced by fitting a kinetic law to experimental data; a good agreement was generally found. A weak effects of the above thi rd elements on the disordering efficiency was observed whereas the effect o f stoichiometry appeared to be more important. Reordering was found to be c ontrolled by long-range vacancy migration with a migration enthalpy of 0.9 to 1.0 eV ; this was deduced from a comparison between the experimental tem perature dependence of the steady - state LRO parameter with calculated cur ves. The effects of third elements on the reordering kinetics is clearly re vealed : compared to, binary alloys, a decrease of the effective reordering rate is generally observed.