Interface morphology evolvement and microstructure characteristics of hypoeutectic Cu-1.0Â wt%Cr alloy during unidirectional solidification

Effect of unidirectional solidification rate on microstructure of hypoeutectic Cu-1.0%Cr alloy was investigated. The microstructure evolution of Cu-1.0%Cr alloy was noticed especially during the unidirectional solidification with the different solidification rates. It is shown that eutectic (α+β) and primary α(Cu) phase grew up equably in parallel to direction of solidification. A kind of fibriform microstructure will appear when unidirectional solidification rate is up to some enough high certain values. When temperature gradient was changeless, the interface morphology evolution of the primary α(Cu) phase underwent to a series of changes from plane to cell, coarse dendrite, and fine dendrite grains with increasing the solidification rates. Primary dendrite arm spacing λ1 of α(Cu) phase increases with increasing the solidification rate where the morphology of the solid/liquid (S/L) interface is cellular. However, λ1 decreases with further increasing the solidification rate where the S/L interface morphology is changed from cell to dendrite-type. Its rule might accord with Jackson-Hunt theory model. An experience equation obtained is as follows: λ1=−0.0052+0.061GL−1/2V−1/4. On the other hand, secondary dendrite spacing λ2 of primary α(Cu) phase will thin gradually with increasing the solidification rate. Moreover, secondary dendrite will become coarse in further solidification. Another experience equation about relationship among secondary dendrite arm spacing (λ2), temperature gradient GL and the velocity of the S/L interface (V) is that: λ2=−0.0003+0.0027(GLV)−1/3. In addition, the volume fraction of eutectic will decrease with the increase of solidification rate.