THERMAL-EXPANSION BEHAVIOR OF NANOCRYSTALLINE NI-P ALLOYS OF DIFFERENT GRAIN SIZES

Nanocrystalline (NC) Ni-P alloy samples with average grain sizes rangi ng from a Sew to 127 nm have been produced by crystallizing the amorph ous Ni-P alloy at various annealing temperatures. The linear thermal e xpansion coefficients (alpha(I)) of these NC samples were accurately m easured in a temperature range of 300-400K. Experimental results showe d that alpha(L) is heavily dependent on the grain size and decreases f rom about 20.7x10(-6) to 15.5x10(-6) K-1 with an increase in the avera ge grain size from 7.5 to 127 nm. From the alpha(L) dependence of grai n size in these NC samples and the at value of the as-cast coarse-grai ned polycrystalline Ni-P sample we deduced that the difference in ther mal expansion coefficients of the interfaces and ofthe nm-crystallites decreases with a reduction of grain size.