(1. 西安理工大學(xué) 材料科學(xué)與工程學(xué)院， 西安 710048;
2. 西北工業(yè)大學(xué) 凝固技術(shù)國(guó)家重點(diǎn)實(shí)驗(yàn)室， 西安 710072;
3. 西安交通大學(xué) 機(jī)械工程學(xué)院， 西安 710049)
摘 要: 在高真空度下， 采用熔融玻璃凈化與循環(huán)過(guò)熱相結(jié)合的方法，在寬的過(guò)冷度范圍內(nèi)， 研究了Cu50Ni50合金凝固組織形態(tài)演化過(guò)程。結(jié)果表明， 隨著過(guò)冷度增大， 凝固組織發(fā)生了3次轉(zhuǎn)變。 其中， 當(dāng)120 K(ΔT2*)<ΔT<192 K(ΔT3*)時(shí)， 凝固組織發(fā)生第2次轉(zhuǎn)變，由粒狀晶演變?yōu)槎ㄏ蛏L(zhǎng)的深過(guò)冷枝晶。 通過(guò)組織觀察和過(guò)冷熔體枝晶生長(zhǎng)過(guò)程的計(jì)算發(fā)現(xiàn)， 快速凝固形成的枝晶在再輝和再輝結(jié)束后枝晶熟化過(guò)程被高度抑制是在該過(guò)冷度區(qū)間形成定向枝晶的原因。
關(guān)鍵字: 深過(guò)冷； Cu50Ni50合金；枝晶熟化； 定向凝固
（1. College of Material Science and Technology， Xi′an University of Technology， Xi′an 710048, P.R.China;
2. State Key Laboratory of Solidification Processing， Northwestern Polytechnical University， Xi′an 710072, P.R.China;
3. School of Mechanical Engineering，Xi′an JiaoTong University， Xi′an 710049, P.R.China）
Abstract:The evolution of solidification microstructuresin undercooled Cu50Ni50 melts was systematically investigated， by using glass fluxing technique combinedwith cycle superheating in high vacuum. Within the achieved wide range of undercoolings， three consecutive microstructural transitionswith the increase of undercooling are revealed. When the melt undercooled into the range of 120 K(ΔT2* )<Δ T <192 K(ΔT3* )， the second transition of microstructure from the first refined granular grain to coarse grained dendritic microstructure takes place. And in this undercooling range， directional dendritic solidification can berealized. Based on the microstructure observation as well as calculations of the solid/liquid composition and undercooling using BCT model of the dendritic growth， it is found that the ripping and remelting processes of dendrites are restrained, which causes the formation of directional dendrites.
Key words: superundercooling； Cu50Ni50 alloys； dendritic ripping; directional solidification
