THE THERMAL DIFFUSIVITIES OF NANOSTRUCTURED NIAL ALLOYS MEASURED BY USING PHOTOACOUSTIC TECHNIQUE

The thermal diffusivities of nanostructured NiAl (n-NiAl) alloys with different relative densities and the polycrystalline NiAl alloy are me asured by using photoacoustic technique in which the signal is detecte d at the front surface while the rear-surface is excited. It is shown that the values of thermal diffusivity of the nanostructured NiAl allo y are lower than that of the polycrystalline NiAl alloy. The thermal d iffusivities of n-NiAl alloys decrease with the decrease of their rela tive densities when they are over 70%. When the relative density of n- NiAl alloys is lower than 70%, an anomalous increase of thermal diffus ivity is observed, which indicates there exists a critical excess volu me Delta V-c (or critical relative density) in n-NiAl alloys near 70%. The results are discussed.