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Ni基偏晶合金是一种优良的自润滑耐磨材料,其组织形成规律对力学性能的影响十分关键。在自由落体条件下,对不同成分二元Ni-Pb偏晶型合金的快速凝固进行了实验研究。随着液滴直径的减小,Ni-20%Pb亚偏晶合金中α-Ni枝晶生长经历“粗大枝晶→等轴晶→蠕虫状枝晶”的转变。Ni-31.4%Pb偏晶合金的凝固组织以偏晶胞为主,偏晶胞的体积分数随液滴直径的减小而增大。过偏晶合金的快速凝固过程中均发生液相分离。Ni-50%Pb过偏晶合金中L2(Pb)相平均尺寸和最大尺寸均随液滴直径的减小先增大后减小。当液滴直径小于400μm时,Ni-60%Pb过偏晶合金由壳核组织演变为L2(Pb)相分布在α-Ni相枝晶间的偏析组织。根据Borelius脱溶模型、Gibbs-Thomson关系和LSW(Lifshitz-Slyozov-Wagner)理论,分析了合金成分、液相分离时间和第二液相体积分数对凝固组织形成的作用机制。
Ni-based amorphous alloy is an excellent self-lubricating wear-resistant materials, the formation of the law of the mechanical properties of the impact of the key. In the free-fall condition, the rapid solidification of binary Ni-Pb amorphous alloys with different compositions was studied experimentally. With the decrease of droplet diameter, the growth of α-Ni dendrites in Ni-20% Pb sub-metastable undergoes the transformation of “coarse dendrite → equiaxed → wormlike dendrite”. Ni-31.4% Pb monotectic alloy solidification organization to the most for the unit cell, the unit cell volume fraction increases with the droplet diameter increases. Off-crystal alloy rapid solidification process occurs during the liquid phase separation. The average size and the maximum size of L2 (Pb) phase in Ni-50% Pb over-crystallite alloy firstly increase and then decrease with the droplet diameter decreasing. When the droplet diameter is less than 400μm, the Ni-60% Pb over-crystallized alloy evolves from the putamen to the segregation structure with L2 (Pb) phase distributed between the α-Ni phase dendrites. Based on the Borelius dissolution model, the Gibbs-Thomson relationship and the LSW (Lifshitz-Slyozov-Wagner) theory, the mechanism of the alloying composition, the liquid phase separation time and the second liquid phase volume fraction on the formation of solidified tissue was analyzed.