A .gamma.' precipitation strengthened nickel-base superalloy provided in powder metal or cast and wrought form and alloyed to minimize nucleation tendencies and control grain growth. The superalloy includes a fine dispersion of a second phase in sufficient amounts to prevent critical grain growth in the superalloy when the superalloy is subjected to temperatures above its .gamma.' solvus temperature. The superalloy preferably contains at least about 0.030 weight percent carbon or about 27 to about 2000 ppm yttrium in order to produce a volume fraction of the second phase which is sufficient to cover a minimum of about 10 percent of the grain boundary area. The fine dispersion of the second phase restricts the grain boundary motion of the alloy during supersolvus heat treatment, thereby preventing random grain growth during supersolvus heat treatment and yielding a microstructure whose grain size is uniform, for example, having a grain size range of about 2 to about 3 ASTM units and being substantially free of random grain growth in excess of about 2 ASTM units coarser than the desired grain size range.