Grain boundary and triple junction enthalpies in nanocrystalline metals - art. no. 134101

We calculate the contribution to the total enthalpy of nanocrystalline comp uter-generated samples coming from grain boundaries, (GB's) and triple join ts (TJ's). We show that the excess enthalpy per unit volume (excess enthalp y density) at the TJ is essentially the same as that found in the GB. This implies that TJ's and GB's are kinds of matter with equivalent departures f rom a perfect crystal structure, at least in the energetic aspect. By a pro per account of the amount of GB's and TJ's, we show that the reported obser vations on decreasing GB energy with decreasing grain size in nanocrystalli zed amorphous Se [K. Ln and N. X. Sun, Philos. Mag Lett. 75, 389 (1997)] an d negative TJ line tension from computer simulation results [S. G. Srinivas an et al., Acta Mater. 47, 2821 (1999)] are consequences of neglecting the relation between the grain boundary width delta and the grain size d, which in the nanophase regime may be of the same order of magnitude.