Ion Beam Modification of Surface for Improved High Temperature Performance of Materials.

摘要

A novel experimental technique, 'Thin Film Calorimetry' (TFC), has been developed to determine the enthalpy of transformation from metastable to stable equilibrium structures in thin films. This technique has been applied to investigate metastable stable transformations occurring in thin films of nominal composition NiAl3. Elemental Ni and Al are codeposited directly onto the surface of a pure Al calorimeter sample pan to form a 0.75 solid solution of NiAl3. The as-deposited microstructure in this case is a metastable configuration, and the reaction heat accompanying its transformation to the stable, equilibrium NiAl3 phase is measured directly in the calorimeter. The mean change in enthalpy, DeltaH, for a series of such measurements, is -4.16 kcal/mole. A second approach involves annealing the as-deposited film to form the epsilon phase, then irradiating the as-annealed film, using 1.5 MeV Ni++ ions, to form an amorphous structure. The enthalpy associated with the transformation of this structure to the equilibrium is then measured in the DSC. The mean DeltaH found for this reaction is -5.02 kcal/mole. Keywords: Metastable materials; Phase transformation; Calorimetry; Codeposition; Ion beam mixing. (js)