单晶/多晶镍轴向拉伸力学性能的分子动力学模拟

Molecular dynamics simulation on the uniaxial tensile mechanical response of single crystal/polycrystalline nickel

摘要:

为提高航空发动机推重比采用整体叶盘新技术却带来了盘叶连接区域高风险失效问题。本文采用分子动力学对连接区单晶/多晶镍(SPSNi)的力学性能进行模拟,首先通过对比了不同晶态镍拉伸原子图。发现,由于单晶/多晶界面的存在使得拉伸后界面处的非晶化程度加剧,易于孔洞萌生,加剧了SPSNi突然断裂的风险。最后重点研究了单晶/多晶镍的应变率效应与温度效应。当应变率大于1í10_⁸s_^-1小于2í10_¹⁰s_^-1时,SPSNi对加载应变率几乎不敏感,屈服强度小幅上升。超过2í10_¹⁰s_^-1之后,其屈服强度随着应变率的增加而迅速下降。这是因为在高应变率下,SPSNi的FCC原子大规模迅速转变为无序的非晶结构,导致了晶体镍承载能力迅速下降。可以将应变率2í10_¹⁰s_^-1作为SPSNi拉伸变形的阈值。不同温度下,SPSNi屈服强度随温度的增大而线性下降。这是由于在温度的影响下,位错网络的初始镶嵌结构逐渐变得不规则,初始失配应力随着温度的升高而下降。

Abstract:

A new technology of the integral blisk was proposed recently to improve the thrust-to-weight ratio of the aero-engine, but which may result in high-risk failure near the disk-blade connection area. Therefore, here the molecular dynamics is used to simulate the mechanical properties of the single-crystal/polycrystalline nickel (SPSNi) in the joint zone. Firstly, the tensile atomic diagram of different crystalline nickels are compared. It is found that the degree of amorphization at the interface after tension is aggravated due to the presence of the single crystal/polycrystalline interface, which easily germinates void and exacerbates the risk of sudden fracture of SPSNi. Finally, the effects of the strain rate and temperature are especially investigated.When the strain rate is greater than 1í10_⁸s_^-1 and less than 2í10_¹⁰s_^-1, the tensile mechanical of SPSNi is almost insensitive to the loading strain rate, and the yield strength rises slightly.After exceeding 2í10_¹⁰s_^-1, the yield strength decreases rapidly with the increase of strain rate.This is because a large number of FCC atoms in SPSNi rapidly transform into disordered amorphous structure at high strain rate, resulting in the rapid decline of SPSNi carrying capacity. Strain rate 2í10_¹⁰s_^-1 can be used as the threshold of SPSNi tensile deformation. At different temperatures, the yield strength of SPSNi decreases linearly with increasing temperature, because the initial mosaic structure of dislocation network gradually becomes irregular, and the initial mismatch stress decreases with the increase of temperature under the influence of temperature.