Precipitation sequence for simultaneous continuous and discontinuous modes in Cu–Be binary alloys

Abstract

The precipitation sequence of the discontinuous and continuous modes in Cu–0·9Be and Cu–1·4Be binary alloys (compositions in wt-%) has been studied primarily via metallographic observations and hardness measurements. A single C curve and triple C curves separated by two temperatures T₁ and T₂ (T₁>T₂) are obtained for the precipitation of discontinuous and continuous modes, respectively. The triple C curves correspond to the formation of γ, γ′, and Guinier–Preston (GP) zones. The precipitation sequence of these two precipitation modes and the cell growth behaviour are different for the following three temperature ranges defined by the triple C curves: (i) above T₁, discontinuous precipitation occurs before the continuous precipitation of γ phase, and the cell growth rate G decreases abruptly; (ii) between T₁ and T₂, the precipitation sequence is similar to that above T₁, but G decreases and interlamellar spacing increases progressively with aging time; (iii) below T₂, GP zones, fine γ″, and/or fine γ′ form before cell growth but the associated variation in G is not observed. The effect of continuous precipitation on the cell growth behaviour is discussed.

MST/1647