Selective evolution of secondary γ' precipitation in a Ni-based single crystal superalloy both in the γ matrix and at the dislocation nodes
Selective evolution of secondary γ' precipitation in a Ni-based single crystal superalloy both in the γ matrix and at the dislocation nodes
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DOI：
10.1016/j.actamat.2016.06.055
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发表时间：
2016-09-01
期刊：
影响因子：
9.4
通讯作者：
Han, Xiaodong
中科院分区：
文献类型：
--
作者：
Xiang, Sisi;Mao, Shengcheng;Han, Xiaodong
用铯校正高分辨透射电镜（HRTEM）和相应的X射线能谱分析揭示了一种镍基单晶高温合金中二次γ '相的两种不同演化过程。在高温下进行蠕变试验时，确定形成了大量的二次γ '沉淀物。发现沉淀物选择两种不同的形式和路线：一种是随机分散在γ基体中（2nd gamma '（gamma）），另一种是在位错网络的节点处形成规则阵列（2nd gamma'（d））。这两种类型的二次γ '沉淀物表现出不同的演化形态和机制。第二γ '（γ）沉淀物的形状从球形逐渐演变为长方体，然后演变为蝶形，平均尺寸也从11 nm逐渐增大到34 nm。第二种γ ′（d）沉淀物具有稳定的立方形貌，平均尺寸为30 nm。这些差异可归因于两种类型沉淀物的不同元素输运条件，即，第二种γ ′（γ）析出相为上坡扩散，第二种γ ′（d）析出相为位错网络管道输运。与第2 γ ′（d）沉淀相相比，第2 γ ′（γ）沉淀相显示出富γ ′元素Ni和Al的严重偏析以及贫γ ′元素Cr的缺乏。(C)2016 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
Two distinct evolutionary processes of secondary gamma' precipitates in a Ni-based single crystal superalloy were revealed by means of Cs-corrected high-resolution transmission electron microscopy (HRTEM) and corresponding X-ray energy dispersive spectroscopy analyses. Upon creep testing at elevated temperatures, it was determined that large quantities of secondary gamma' precipitates were formed. The precipitates were found to select two distinctive forms and routes: one randomly dispersed in the gamma matrix (2nd gamma'(gamma)), and the other formed at nodes of dislocation networks (2nd gamma'(d)) in regular arrays. These two types of secondary gamma' precipitates exhibited different evolutionary morphologies and mechanisms. The 2nd gamma'(gamma) precipitates progressively evolved in shape from spherical to cuboidal and then to butterfly-like shapes, and the mean size also increased gradually from 11 nm to 34 nm. The 2nd gamma'(d) precipitates exhibited stable cuboidal morphology and a mean size of 30 nm. These differences are attributable to the different element transport conditions for the two types of precipitates, i.e., an uphill diffusion for the 2nd gamma'(gamma) precipitates and a dislocation network pipe transportation for the 2nd gamma'(d) precipitates. The 2nd gamma'(gamma) precipitates show severe segregation of gamma'-rich elements of Ni and Al and deficiency of gamma'-poor elements of Cr compared with the 2nd gamma'(d) precipitates. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.