STRUCTURE CHANGES OF DIRECTIONALLY SOLIDIFIED EUTECTIC Pb-Sn ALLOY UNDER VARYING GROWTH VELOCITY
变速定向生长条件下Pb－Sn共晶组织变化

The structure variety of directionally solidified eutectic Pb-Sn alloy under step and linear change of specimen displacement velocity was experimentally observed.The experiments were conducted on a directional solidification apparatus with an electronic varying velocity programmer for specimen displacement,which was designed and constructed by the authors.The experimental results show that,when the eutectic specimen moves with a slow and linear increase or decrease in velocity,the average laminar spacing of the directionally grown eutectic changes through progressive branching or merging of the eutectic laminae of both the two phases.The variation curves of the eutectic growth rates are approximately symmetric for the increase and decrease in the displacement velocity at the same acceleration.