Quasi-Seeding Mechanism in Lamellae Alignment of TiAl Alloys During Directional Solidification
Quasi-Seeding Mechanism in Lamellae Alignment of TiAl Alloys During Directional Solidification
复制标题
TiAl合金定向凝固过程中片层排列的准晶种机制
DOI：
10.1007/s11661-019-05310-0
复制
发表时间：
2019-09-01
影响因子：
2.8
通讯作者：
Fu, Hengzhi
中科院分区：
文献类型：
--
作者：
Du, Yujun;Shen, Jun;Fu, Hengzhi
提出了一种新的准籽晶定向凝固机制，该机制中籽晶材料需满足以下两个条件，以实现TiAl合金定向凝固过程中片层组织的定向排列。首先，通过控制凝固条件，使准籽晶内的柱状晶凝固为包绕α相，而不是初生β相，从而获得具有合适层状取向的准籽晶。其次，当加热速率足够高时，单个γ晶粒的形核和长大受到限制，因此加热形成的高温α-II晶粒经历了α2/γ→α/γ→α的固相转变，而不是α2/γ→γ→α/γ→α的固相转变。结果表明，原始准籽晶锭中高温α-II晶粒的基面平行于α2/γ片层，热处理后的片层组织没有变化。基于这一机制，采用快速加热限制γ相形核和生长的Ti-47 Al-2Nb-2Cr合金准晶种，在不同生长速度下定向凝固，使同一合金的片层组织定向排列。结果表明，在10μm/s的速度下，获得的层状组织的抗拉强度为558 MPa，延伸率为6.2%。考察了不同取向的片层组织的断裂行为，并对相应的断裂机制进行了探讨。
A novel quasi-seeding mechanism, in which the seed material needs to meet the following two requirements, was developed to align the lamellar microstructures of TiAl alloys during directional solidification. First, by controlling solidification condition, columnar grains within the quasi-seed ingot are solidified as the peritecticαphase rather than the primaryβphase and thus the quasi-seed ingot with appropriate lamellae orientation is obtained. Second, the nucleation and growth of singleγgrains are restricted when heating rate is sufficiently high and thus the high-temperatureα-II grains that form upon heating have undergone the solid-phase transformation ofα2/γ→α/γ→αrather thanα2/γ→γ→α/γ→α. As a result, the high-temperatureα-II grains have the basal planes parallel to theα2/γlamellae within the original quasi-seed ingot and the lamellar microstructure remains unchanged after the heat treatment. Based on the mechanism, a quasi-seed of Ti-47Al-2Nb-2Cr alloy, in which the nucleation and growth of theγphase was restricted by a rapid heating procedure, was employed to align the lamellar microstructures of the same alloy during directional solidification at different growth velocities. The room-temperature tensile properties of the directionally solidified samples were measured and the results showed that the desired lamellar microstructure obtained at 10μm/s had a tensile strength of 558 MPa and an elongation of 6.2 pct simultaneously. The fracture behaviors of the lamellar microstructures with different orientations were checked and the relevant mechanisms were discussed correspondingly.