快速定向凝固Cu_(50)Ni_(50)单晶

Single Crystal Solidified by Undercooled Cu_(50)Ni_(50) Melts

过冷单相合金熔体枝晶生长过程动力学分析结果表明 ,存在一个枝晶生长控制方式发生转变的临界过冷度 ΔTc→ t(溶质过冷度 ΔTc与热过冷度 ΔTt交点对应的过冷度 )。在临界过冷度两侧枝晶对生长过程中速度波动的响应不同。当 ΔT<ΔTc→ t时 ,枝晶生长主要受溶质扩散控制 ,任何波动引起生长速度提高 ,都将引起枝晶尖端 ΔTc增大 ,导致生长速度回落。当 ΔT<ΔTc→ t时 ,枝晶生长的控制性环节是热扩散 ,生长速度提高 ,溶质截留效应加剧 ,ΔTc降低 ,枝晶高速长入过冷熔体 ,形成定向生长的枝晶。根据这一理论预测 ,通过实验获得了快速定向凝固 Cu50 Ni50 块体单晶 ,并验证了枝晶生长过程动力学分析的正确性。

Based on dynamic analyzing of dendritic growth of undercooled single phase alloy,it is found a critical undercooling Δ T c→t , which is the point of intersection of solutal undercooling curve Δ T c and thermal undercooling curve Δ T t, exits.When melts' undercooling is less than the critical one of Δ T c→t , solutal undercooling is main factor which controls dendrite growth.Increasing of dendritic growth velocity by some disturbance will cause increase of solutal undercooling at dendrite tip. Consequently results in decrease of dendritic growth velocity.When melts'undercooling is greater than the critical one of Δ T c→t , thermal undercooling controls dendrite growth.Under this condition,increasing of dendritic growth velocity will increase solutal trap and thus cause Δ T c decrease.The growth dendrite can rapidly across undercooled melts in directional form.According to the dynamic analyzing,bulk single crystal of Cu 50 Ni 50 alloy was prepared.