Ion mass effects on bombardment-induced disordering of γ'-Ni3Si

The kinetics of disordering of the ordered compound γ'-Ni3Si during ion bombardment were investigated at a temperature of 2700C. The disordering followed first order kinetics and the rate constant was measured as a function of incident ion flux, ion energy, and ion mass. The rate constant varied approximately in direct proportion with the ion flux during bombardment with 1 MeV 84Kr+-ions: from approx.= 0.28 min-1 at approx.= 70 nA/cm2 to approx.= 50 min-1 at approx.= 4.4 μA/cm2. During bombardment with a flux of approx.= 1 μA/cm2 of 132Xe+-ions, the rate constant was directly proportional to the calculated near-surface damage rate. It varied from approx.= 50 min-1 for 200 KeV ions with calculated damage rates of approx.= 2.3x10-2 dpa/s to approx.= 1.8 min-1 for 3 MeV ions with damage rates of 2x10-3 dpa/s. The disordering rate was also observed to be directly proportional to the near surface damage rate for heavier mass ions (40Ar+, 84Kr+ and 132Xe+); the ratio of disordering rate to damage rate was approx.= 17. This ratio dropped to approx.= 3 for 20Ne+-ion bombardment, and to approx.= 0.4 for bombardment with 4He+-ions. The decrease in the ratio with decreasing mass is discussed in terms of cascade size, replacement-to-displacement ratio, and random recombination. (orig.)