Dendritic growth of primary γ ′ precipitates in nickel based alloy

Abstract

Crystal growth from all three states of matter, i.e. vapour, liquid and solid, produces the dendritic morphology. A well known vapour case is the snowflake. Most liquid metal products solidify by forming dendrites. Crystal growth from an already crystalline matrix is also found to produce precipitates with a dendritic morphology. However, dendritic precipitates were scarcely observed to form from liquid state. In the present paper, a directionally solidified nickel based superalloy was designed to show the dendritic growth of precipitates from the liquid state. The formation of carbides led to the negative temperature gradient and constitutional supercooling in the residual liquid melts as a result of the release of latent heat and ejecting of forming precipitate elements respectively. This resulted in the formation of dendritic primary precipitates.