冷坩埚定向凝固Ti-45Al-2Nb-2Mn组织及性能研究

发布时间：2018-05-29 10:44

  本文选题：冷坩埚 + 定向凝固　； 参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：Ti Al基合金因具有优良的高温性能和优异的抗氧化性能,在过去的20年里,Ti Al基合金在航空航天领域的应用引起了非常广泛的关注,因此对推动高温结构材料的发展起到了极大的作用,然而Ti Al基合金的室温塑性与断裂韧性不足,是限制扩大其实际应用的主要障碍。本课题首先采用水冷铜坩埚真空感应熔炼炉(ISM)制备Ti45Al2Nb2Mn母合金锭,再利用电磁冷坩埚对Ti Al合金进行定向凝固实验制备出表面质量和宏观定向组织良好的Ti45Al2Nb2Mn合金铸锭。对Ti-45Al-2Nb-2Mn合金经冷坩埚定向凝固,通过控制不同的抽拉速度(凝固速率)制备出了具有良好定向效果的铸锭;原始铸态组织中有缩孔产生,而定向凝固后缺陷消失。合金在电磁冷坩埚定向凝固过程中,固液界面形貌随着凝固速率的提高,呈枝状-胞枝状-胞状变化,随抽拉速度的增加,定向凝固区的晶粒减小。Nb属于β稳定元素,可以扩大β凝固区间,因此反应过程中β相始终为初生相,由于是二维照片,当先析出相为β时,部分α2/γ片层取向与生长方向并不严格呈45°或平行关系,进行XRD分析以及能谱分析发现,其组织主要是α2+γ的双相全片层组织,少量的B2相。相比于铸态组织,定向凝固组织力学性能均得到明显提高。Ti Al基合金在定向凝固后其压缩强度最高达到1654MPa,而原始铸态的合金压缩强度仅仅达到899Mpa。铸态合金在同等条件下的峰值应力仅为329MPa左右,而定向凝固后的合金峰值应力最高达到了479MPa左右,拉伸强度随着抽拉速度增加而提高。合金的柱状晶全片层组织断裂韧性均超过20MPa·m1/2。定向凝固条件下的合金显微硬度较原始铸态的提高了40%-70%。压缩断口断裂方式主要以撕裂断裂为主,同时混有穿层断裂;拉伸断口出现了阶梯状断裂形貌以及P型断口形貌;断裂韧性断口形貌均为典型的脆性解理断裂。
[Abstract]:Due to its excellent high temperature properties and excellent oxidation resistance, TiAl-based alloys have been widely used in aerospace industry in the past 20 years. Therefore, it plays an important role in promoting the development of high temperature structural materials. However, the lack of room temperature ductility and fracture toughness of Ti-Al-base alloys is the main obstacle to the expansion of their practical application. In this paper, Ti45Al2Nb2Mn master alloy ingot was prepared by water cooled copper crucible vacuum induction melting furnace (ISM), and Ti45Al2Nb2Mn alloy ingot with good surface quality and macroscopical directional structure was prepared by directional solidification experiment with electromagnetic cold crucible. Through directional solidification of Ti-45Al-2Nb-2Mn alloy by cold crucible, the ingot with good directional effect was prepared by controlling the different drawing speed (solidification rate), and the shrinkage holes were produced in the original cast structure, but the defects disappeared after directional solidification. During the directional solidification of the alloy in the electromagnetic cold crucible, the morphology of the solid-liquid interface changes as the solidification rate increases, and with the increase of the drawing speed, the grain size in the directional solidification zone decreases. NB is a 尾 stable element. The 尾 phase is always a primary phase in the reaction process. When the precipitated phase is 尾, the orientation of some 伪 2 / 纬 lamellae is not strictly 45 掳or parallel to the growth direction when the precipitated phase is 尾. The results of XRD analysis and energy spectrum analysis showed that the structure of 伪 2 纬 was mainly a two-phase full-lamellar structure with a small amount of B2 phase. Compared with the as-cast microstructure, the mechanical properties of the directionally solidified alloy were obviously improved. The compressive strength of the as-cast alloy reached 1654MPa after directional solidification, but the compressive strength of the as-cast alloy was only 899Mpa. The peak stress of the as-cast alloy is only about 329MPa under the same conditions, but the peak stress of the alloy after directional solidification reaches about 479MPa, and the tensile strength increases with the increase of the pulling speed. The fracture toughness of the columnar crystal layer of the alloy is higher than that of 20MPa m 1 / 2. The microhardness of the alloy under directional solidification is 40-70 higher than that of the as-cast alloy. The fracture mode of compression fracture is mainly tear fracture and mixed with penetrating layer fracture; the tensile fracture surface has ladder and P fracture morphology; the fracture toughness fracture surface morphology is typical brittle cleavage fracture.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.23;TG292
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本文编号：1950590