Microstructure and mechanical properties evolutions of alloy 718 during isothermal and thermal cycling over-aging
Microstructure and mechanical properties evolutions of alloy 718 during isothermal and thermal cycling over-aging
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DOI：
10.1016/j.matdes.2016.04.048
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发表时间：
2016-07-15
影响因子：
8.4
通讯作者：
Franchet, J. -M.
中科院分区：
文献类型：
--
作者：
Jouiad, M.;Marin, E.;Franchet, J. -M.
对718直接时效合金在650℃以上的温度下进行等温时效和非等温时效，以评估其在更高温度下的使用潜力。通过热循环获得了航空发动机部件的非等温老化条件。在650℃下进行布氏硬度和热拉伸试验，了解不同时效处理/条件对合金力学性能的影响。布氏硬度和热拉伸性能随时效时间的延长和时效温度的升高而降低。此外，发现热循环后与年龄相关的力学性能退化加速。通过高分辨透射电镜观察，所有时效样品均表现出γ′、γ′和δ相的粗化，同时γ′通过壁壁生长机制转变为有序的正交相δ。这种由热循环加速的转变是由相对于的γ”和/或δ相的取向控制的。基体和溶质原子在析出物-基体界面的位错辅助下的扩散。本研究阐明了在非等温条件下718合金γ - δ转变的机理，并指出该机制是导致合金力学性能加速损失的原因。(C) 2016 Elsevier Ltd.版权所有。
Direct aged alloy 718 was subjected to isothermal and non-isothermal aging at temperatures above 650 degrees C to assess its potential use at higher temperatures. Non-isothermal aging conditions were achieved by thermal cycling to represent the operating conditions of aero-engine components. The effect of different aging treatments/conditions on mechanical properties was understood by performing Brinell hardness and hot tensile tests at 650 degrees C. Brinell hardness and hot tensile properties were found to decrease with increasing aging time and higher temperature. Additionally, age related mechanical properties degradation was found to accelerate after thermal cycling. According to High Resolution Transmission Electron Microscopy, all aged samples showed coarsening of gamma', gamma '' and delta phases, in addition to the transformation of gamma '' into ordered orthorhombic phase delta by ledge growing mechanism. This transformation, which was accelerated by thermal cycling is controlled by the orientation of gamma '' and/or delta precipitates with respect to. matrix and also by the diffusion of solute atoms assisted by dislocations at the precipitate-matrix interface. This study elucidates the mechanism of gamma '' to delta transformation and suggests this mechanism is responsible for the accelerated loss of mechanical properties of alloy 718 under non-isothermal conditions. (C) 2016 Elsevier Ltd. All rights reserved.