Chen Ruirun, Zheng Deshuang, Ma Tengfei, Ding Hongsheng, Su Yanqing, Guo Jingjie, Fu Hengzhi
School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China.
School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China.
Ultrason Sonochem. 2017 Sep;38:120-133. doi: 10.1016/j.ultsonch.2017.03.006. Epub 2017 Mar 7.
In spite of their high temperature and reactivity, the binary TiAl alloys are successfully imposed by the ultrasonic irradiation and the microstructure evolution, solidification behaviors and mechanical properties are elaborately investigated. After ultrasonic irradiation, a high quality ingot without shrinkage defects and element segregation is obtained and the coarse dendrite structure is well modified into fine non-dendrite globular grains. The coarse lamellar colony and lamellar space of Ti44Al alloy is refined from 685μm to 52μm and 1185nm to 312nm, respectively (similarly, 819μm to 102μm and 2085nm to 565nm for Ti48Al alloy). For Ti48Al alloy, the α peritectic phase is simultaneously precipitated from the melt as well as the β primary phase before the peritectic reaction and the solidification is transformed into the mixed α-solidifying and β-solidifying. Ultrasonic irradiation promotes the peritectic reaction and phase transformation completely and the phase constituent becomes more close to the equilibrium level. The compressive strength of Ti44Al and Ti48Al alloys are increased from 623MPa to 1250MPa and 980MPa to 1295MPa, respectively. The grain refinement and dendrite transformation enhance the grain boundary sliding improving the plastic deformation ability. Ultrasonic irradiation significantly accelerates the melt flow and solute redistribution and the main grain refinement mechanism is the cavitation-enhanced nucleation by inclusion activation and heightened supercooling.
尽管二元TiAl合金具有高温和高反应活性，但通过超声辐照仍成功制备了该合金，并对其微观结构演变、凝固行为和力学性能进行了详细研究。超声辐照后，获得了无收缩缺陷和元素偏析的高质量铸锭，粗大的枝晶结构被良好地改造成细小的非枝晶球状晶粒。Ti44Al合金粗大的片层晶团和片层间距分别从685μm细化至52μm，从1185nm细化至312nm（类似地，Ti48Al合金从819μm细化至102μm，从2085nm细化至565nm）。对于Ti48Al合金，包晶反应前，α包晶相与β初生相同时从熔体中析出，凝固转变为α凝固和β凝固混合模式。超声辐照促进了包晶反应和相变的完全进行，相组成更接近平衡态。Ti44Al和Ti48Al合金的抗压强度分别从623MPa提高到1250MPa和从980MPa提高到1295MPa。晶粒细化和枝晶转变增强了晶界滑动，提高了塑性变形能力。超声辐照显著加速了熔体流动和溶质再分布，主要的晶粒细化机制是通过夹杂物激活和过冷度增加实现的空化强化形核。
