600℃高温钛合金超高周疲劳早期损伤机理研究

In this project, experiments will be conducted to determine the effects of temperature, load frequency, stress ratio and low cycle fatigue (LCF) damage on very high cycle fatigue (VHCF) behavior of 600℃ high temperature titanium alloy for aeroengine. The mechanism of crack initiation and early growth for VHCF at elevated temperatures, frequency dependence, and VHCF behavior under operating environment will be investigated. The evolution law of local microstructure under the combined action of heating, loading with high frequency but low amplitude, and loading with low frequency but high amplitude will be further studied. In order to reveal the control parameters of VHCF properties, the relationship between cyclic stress and micro damage characteristics will be emphasized. Finally, models for crack initiation and early growth in VHCF regime will be proposed. This study is expected to establish theoretical basis for fatigue life prediction and reliability evaluation of key components for aerongine.

本项目以航空发动机用600℃高温钛合金为研究对象，拟从温度、加载频率、应力比和低周疲劳损伤对材料超高周疲劳行为影响规律的试验研究入手，对高温条件下材料超高周疲劳裂纹萌生和早期扩展机制、频率效应、模拟服役环境下的超高周疲劳行为进行深入的研究。重点探讨材料在热、高频低幅、低频高幅载荷耦合作用下局部显微组织的累积响应机理和退化规律，揭示显微组织调控对材料高温超高周疲劳性能的影响规律，建立基于显微组织的疲劳裂纹萌生物理模型和裂纹早期扩展的力学模型。为高温钛合金疲劳寿命预测奠定理论基础，并为航空发动机关键零部件的定寿和可靠性分析提供科学依据。

先进航空发动机高压压气机叶片面临着高温超高周疲劳失效的问题。本项目以双性能整体叶盘用600℃高温钛合金TA29为研究对象，开展了高温超高周疲劳性能测试、损伤机理分析和寿命预测模型等方面的研究工作。采用自主设计的高温超声疲劳测试装置，系统测试了双态和片层显微组织TA29在3个温度和2个频率下的超高周疲劳性能，获得了材料的超高周疲劳S-N曲线和P-S-N曲线；深入分析了温度、加载频率、低周疲劳载荷等因素对合金超高周疲劳性能和损伤机制的影响规律，温度对合金超高周疲劳性能有着显著的影响，在叶片振动频率范围内未发现明显的频率效应，一定程度的低周疲劳损伤反而起到了强化作用；高温下组织退化和长时氧化导致TA29超高周疲劳损伤机制转变，通过优化的间隔加载方法在超高周疲劳断口上获得了精细的有规律性的疲劳弧线，建立了疲劳裂纹早期扩展模型；建立了基于损伤力学的超高周疲劳寿命模型。本项目为叶片的疲劳可靠性分析提供了数据基础和理论依据。