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By means of the positron annihilation techn ique (PAT), superfine TiC powders obtained by ball-milling pro cess were characterized. The results showed that there was a clear correlation between the change in TiC powders and that in the PAT parameters. In the high energy ball-milling process, TiC powders were severely deformed, which caused large increase in the amount of defects and severe distortion of lattice. On the other hand, the extreme refinement of grain size of powders resulted in the increase of grain boundary area and enhancement of system free energy. The spacing be tween deformed domains in 96 h milled samples is somewhat smaller than those in 48 h milled samples, indicating the size of Type Ⅱ defects in 96 h milled samples is somewhat smaller than that in 48 h milled samples.