THE EFFECT OF GRAIN-SIZE ON THE YIELD STRENGTH OF FEAL AND NIAL

The yield strength, sigma-y, has been measured as a function of grain size, d, for a number of FeAl and NiAl alloys of different aluminum contents and the data fitted to the Hall-Petch relationship, sigma-y = sigma-0 + kd-1/2, where sigma-0 is the lattice resistance and k the Hall-Petch slope. For NiAl, both sigma-0 and k are a minimum at the stoichiometric composition and increase with decreasing aluminum content. For FeAl, sigma-0 and k are a maximum at the stoichiometric composition but show a minimum around the iron-rich composition Fe-45 at.% Al. The data do not indicate any relationship between k and the degree of (constitutional) disorder but suggest that k is simply proportional to sigma-0.