液态五元Ni-Zr-Ti-Al-Cu合金快速凝固过程的高速摄影研究  

Rapid solidification mechanism of liquid quinary Ni-Zr-Ti-Al-Cu alloy investigated by high-speed cinematography

作　　者：徐山森[1] 常健[1] 吴宇昊[1] 沙莎 魏炳波[1] Xu Shan -Sen;Chang Jian;Wu Yu -Hao;Sha Sha;Wei Bing -Bo(MOE Key Laboratory of Space Applied Physics and Chemistry, Northwestern Polytechnical University, Xi’an 710072, China)

机构地区：[1]西北工业大学应用物理系

出　　处：《物理学报》2019年第19期218-228,共11页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:51771154,51327901);陕西省重点研发计划(批准号:2019GY-152)资助的课题~~

摘　　要：采用电磁悬浮和自由落体两种无容器熔凝技术,并借助高速摄影实时分析方法,研究了液态五元金的快速凝固组织由初生Ni3Ti相、次生Ni10Zr7相和(Ni10Zr7+Ni21Zr8)共晶组成.初生Ni3Ti相以枝晶方式生长,枝晶生长速度随熔体过冷度的增大以幂函数关系单调递增,最高可达 12 mm/s,同时其体积分数逐渐减小至 13.4%,并发生显著组织细化.在自由落体条件下,尽管合金液滴凝固组织的相组成并未发生变化,但随着过冷度的增大,初生 Ni3Ti 相的生长被抑制,凝固组织由晶态向非晶态转变,且非晶相的体积分数线性增大.当直径小于 275 m 时,合金液滴实现了完全非晶态凝固.The ability to undercool and solidification mechanism of liquid quinary Ni40Zr28.5Ti16.5Al10Cu5 alloy are investigated by electromagnetic levitation(EML) and drop tube(DT) technique.Under the EML condition,the maximum undercooling of levitated alloy can reach up to 290 K(0.21 TL).Under the DT condition,the alloy achieves higher undercooling than EML,and solidifies finally into metallic glass.At lower undercooling,the solidification structure of the alloy is composed of primary Ni3Ti phase,secondary Ni10Zr7 phase and eutectic(Ni10Zr7+Ni21Zr8) phase.With the rise of undercooling,the solidification structure displays the following evolution events:phase morphology refinement,primary phase inhibition,phase number reduction,and amorphous phase formation.By using the high-speed cinematography technique,three nucleation modes are distinctly observed on the levitated alloy melt surface at the beginning of solidification,that is,single-point nucleation,multi-point nucleation and annular nucleation.The levitation state corresponding to single-point mode nucleation is relatively stable,and the alloy undercooling is also relatively low.The annular nucleation only occursin the case with high rotation speed,and the undercooling is greater than 208 K.The discrepancy between nucleation modes is due to the He gas flow for forced cooling.The theoretical calculations indicate that the alloy droplets achieve high undercoolingand large cooling rate under the DT condition.The experimental results show that when the droplet diameter decreases to 498 μm,the amorphous phase begins to appear in the alloy particles.It is noteworthy that the amorphous phase is preferentially formed inside the droplet,but not on the outer surface.The morphology of solidification structure reveals that different regions of the droplet have various local undercoolings,which result in the distribution characteristics of amorphous phase.The volume fraction of amorphous phase increases linearly with the decrease of particle diameter.When the droplet diameter dec

关 键 词：电磁悬浮 自由落体 深过冷 快速凝固 

分 类 号：TG146.15[一般工业技术—材料科学与工程]