Study on the response of dendritic growth to periodic increase–decrease pressure in solidification via in situ observation using succinonitrile

Abstract A novel experimental apparatus for in situ observation of dendritic growth in directional solidification under dynamic pressure and thermal conditions was built, based on the principles of direct squeeze-casting, and the response of dendritic growth to an increase–hold–decrease pressure and a periodic increase–decrease pressure was investigated using succinonitrile. The results showed that, when continuous increase–hold–decrease pressure was applied, the dendrites underwent a growing and re-melting process where the dendritic re-melting phenomenon with fish-bone-like dendrites in the pressure decline stage was observed for the first time. When periodic increase–decrease pressure was applied, dendrites re-grew and were re-melted periodically owing to the change in effective undercooling, which is the difference between the equilibrium melting temperature under pressure T m P and the temperature at the dendrite tip T tip , as expressed by Δ T eff = T m P - T tip , whereas secondary dendrite arm spacing increased with the re-growth and re-melting cycle. The relationship of the velocity of the dendrite tip v with the effective undercooling Δ T eff and pressure change Δ P was derived and expressed as v = A Δ T eff + B Δ P 2 + C where the effective undercooling plays a primary role in determining the tip velocity.