The Influence of γ Precipitation upon the Creep of γ′ (Ni3 (Al, Ti)) Single Crystals

AbstractEarlier work by R. K. Ham, R. H. Cook, and G. R. Purdy (Metal Sci. J, 1972, 6, 73) has demonstrated that it is possible to produce a precipitate of the disordered nickel-rich terminal solid solution, γ, in a matrix of the ordered γ′ phase Ni3 (Al,Ti). The present paper shows that this precipitate increases the steady-state creep-resistance of the matrix and induces a prolonged initial stage of very low creep rate (‘nilcreep stage’). The end of the nil-creep stage was associated with loss of coherency of the γ precipitate and an increase in matrix dislocation activity. A model is proposed in which the particles are treated as attractive trapping sites for superlattice dislocations, so that measurable deformation can occur only when Ostwald ripening has increased the particle spacing to a level sufficient for Orowan looping of dislocations between the particles. This model accounts for many of the observed features of the nil-creep stage.