(西北工業(yè)大學(xué) 應(yīng)用物理系，西安 710072)
摘 要: 在自由落體條件下研究三元Ni62Pb30Cu8偏晶合金的相分離與快速凝固。XRD分析結(jié)果表明；凝固組織由固溶體(Ni)和(Pb)兩相構(gòu)成；隨液滴直徑減小，三元Ni62Pb30Cu8偏晶合金從殼核組織演變?yōu)?Pb)相顆粒分布在 (Ni)枝晶間的組織；在形成的殼核組織中，表面張力較小的(Pb)相始終占據(jù)最外層，有利于降低表面相和體系總吉布斯自由能。能譜測(cè)定發(fā)現(xiàn)，在固溶體(Ni)和(Pb)相中，溶質(zhì)截留效應(yīng)十分顯著。采用傳熱模型計(jì)算了不同直徑液滴的冷卻速率與過(guò)冷度，二者均隨液滴直徑的增大而減小。理論分析了合金液滴的內(nèi)部溫度梯度與第二相L(Pb)液滴的Maragoni遷移，發(fā)現(xiàn)第二相L(Pb)液滴充分實(shí)現(xiàn)二次相分離。在自由落體條件下，合金液滴的最終凝固組織由冷卻速率、表面偏析、Marangoni遷移和(Ni)枝晶生長(zhǎng)共同決定。
關(guān)鍵字: Ni-Pb-Cu偏晶合金；自由落體；快速凝固；殼核組織；表面偏析
free fall conditions
（Department of Applied Physics, Northwestern Polytechnical University, Xi’an 710072, China）
Abstract: The phase separation and rapid solidification of ternary Ni62Pb30Cu8 monotectic alloy were investigated under free fall conditions. X-ray diffraction analysis indicates that the solidified microstructure consists of (Ni) and (Pb) phases. With the decrease of droplet diameter, the morphology transforms from a triple-layer core-shell microstructure into (Ni) dendrite microstructure. In the triple-layer core-shell microstructure, the surface layer is (Pb) phase, which is favourable to reducing the surface Gibbs free energy. EDS analyses reveal that both (Ni) and (Pb) phases exhibit conspicuous solute trapping effect during rapid solidification. The calculated cooling rate and undercooling increase exponentially with the decrease of droplet diameter. Furthermore, the Maragnoni migration of the second liquid (Pb) phase was studied, which indicates that the L(Pb) phase droplets can migrate to the central part. Under free fall conditions, the cooling rate, surface segregation, Maragnoni migration and dendrite growth are responsible for the microstructure evolution.
Key words: Ni-Pb-Cu monotectic alloy; free fall; rapid solidification; core-shell microstructure; surface segregation
