鎳基合金激光噴丸誘導的殘余壓應力的高溫松弛規(guī)律研究

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摘 要
激光噴丸 (Laser Peening, LP)，是一種利用激光與材料相互作用產生的高幅沖擊波壓力實施材料表面改性的技術，其通過改變材料表面的殘余應力分布及微觀組織結構，大幅提升金屬結構件的機械性能和疲勞壽命。鎳基合金作為航天航空領域使用的重要材料，其關鍵零部件通常服役于高溫條件下，此時激光噴丸誘導的有益殘余壓應力將產生松弛現(xiàn)象，進而影響激光噴丸強化的力學性能增益。因此掌握激光噴丸殘余應力在高溫條件下的松弛特性，進而實現(xiàn)殘余應力松弛量和松弛速率的有效控制，是保證材料改性后性能增益和質量可靠性的關鍵。本文采用理論分析與試驗研究相結合的方法，系統(tǒng)研究IN718鎳基合金激光噴丸誘導的殘余應力的高溫松弛特性，主要工作如下：
（1）以高能短脈沖激光與材料相互作用誘導高幅沖擊波的物理機制為基礎，探討金屬材料激光噴丸殘余壓應力的產生機理，分析殘余壓應力的影響因素及其評價指標，引入殘余壓應力估算模型，在此基礎上，宏微觀相結合分析殘余壓應力在高溫條件下的松弛規(guī)律和松弛機理。
（2）實驗研究激光噴丸殘余壓應力在高溫條件下的松弛特性。選用GAIA Nd:YAG高功率激光器對典型IN718鎳基合金試樣進行激光噴丸試驗，SX2-4-10箱式電阻爐進行保溫試驗，通過X-350A型X射線衍射儀測量試樣表面的殘余應力，LEICA DFC420光學顯微鏡分析試樣微觀組織結構。通過不同溫度和不同保溫時間下殘余應力值和顯微硬度的測試，分析殘余壓應力在高溫下的松弛規(guī)律，通過激光噴丸和保溫試驗后鎳基合金表層的顯微組織形態(tài)觀察，探討激光噴丸對材料高溫穩(wěn)定性的影響機制。
關鍵詞：激光噴丸強化，殘余應力，高溫松弛，鎳基合金

Abstract
Laser peening is a surface modification technology, using high-amplitude shock wave pressure induced by the laser-material interaction. The mechanical properties and fatigue life of metal structures are significantly enhanced by changing its residual stress distribution and microstructure of the material surface.Nickel-based alloy is an important material used in aerospace field.The key components are usually served at high temperatures, and at this time the beneficial residual stress induced by laser peening will produce release phenomenon,thereby the gain of materials’ mechanical properties by laser peening are also affected. Therefore the key point to ensure the performance improvement and the quality reliability of the material modified is to grasp the release characteristics of residual stress induced by laser peening at high temperatures and effectively control the release rate of residual stress.In this study, the distribution of the residual stress induced by laser peening and its release characteristics under high temperatures of IN718 nickel-based alloy was researched with a combination of theoretical analysis and experimental methods, and the main works are as follows:
（1）Based on the physical mechanism of high amplitude shock wave induced by high-energy short-pulse laser-material interaction, the mechanism of the residual compressive stress of metal material induced by laser peening was explored, and the influence factor and eva luation was analyzed, and the estimation model of residual compressive stress was introduced. Then the rule and mechanism of the release of residual compressive stress under high temperature conditions were analyzed macroscopically and microscopically on this basis.
（2）The release characteristics under high temperature conditions of the residual compressive stress induced by laser peening was researched. The laser peening test of typical IN718 nickel-based alloy specimens was conducted by using a high power Nd: YAG GAIA laser. The thermal insulation test was conducted with the SX2-4-10 box-type resistance furnace. The residual stress distribution on the surface of specimen was measured with X-350A X-ray diffraction. The microstructure of the specimen was analyzed with LEICA DFC420 optical microscopy. The release patterns under high temperature conditions of the residual compressive stress was analyzed by testing the residual stress and surface hardness at different temperatures and holding time. And the impact mechanism of the laser peening to the high temperature stability of materials was explored by the observation of the microstructure morphology of nickel surface after the laser peening and thermal insulation test.
Key: laser peening, residual stress, thermal release, nickel-based alloy


目 錄

第一章 緒論 1
1.1 引言 1
1.2 激光噴丸強化技術 1
1.2.1 激光噴丸的基本原理及特點 1
1.2.2 激光噴丸強化工藝中的能量吸收層和約束層的選擇 3
1.2.3 激光噴丸強化的發(fā)展歷程及應用現(xiàn)狀 3
1.3 高溫下殘余應力松弛的研究現(xiàn)狀與進展 5
1.4 本課題選題研究意義及主要內容 7
1.4.1 研究意義 7
1.4.2 研究內容 7
第二章 激光噴丸誘導殘余應力松弛特性分析 9
2.1 激光噴丸殘余應力場理論 9
2.1.1 激光噴丸材料表層的塑性變形過程 9
2.1.2 激光噴丸誘導殘余應力場的產生與估算 11
2.1.3 殘余應力的測量 13
2.1.4 激光噴丸誘導殘余應力場的影響因素及其評價指標 14
2.2 殘余應力高溫松弛理論 15
2.2.1 殘余應力高溫松弛宏觀理論 15
2.2.2 殘余應力高溫松弛過程中晶粒尺寸與位錯密度的演變 16
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