复合喷丸提高等轴状TC4钛合金的疲劳性能

首先对等轴状TC4钛合金疲劳试样表面进行了不同时间的高能喷丸,制备出一定深度的纳米表层,然后采用小尺寸弹丸进行表面损伤修复喷丸,提高纳米表层质量,最后对不同喷丸状态的试样进行了疲劳试验。结果表明:复合喷丸使等轴状TC4钛合金的疲劳强度相比未喷丸状态提高了34%,在单纯高能喷丸纳米化方法的基础上进一步提高了12%;高能喷丸在试样表面形成的损伤阻碍了表层纳米化提高疲劳强度的效果,通过修复喷丸可以修复部分高能喷丸损伤。     

工业纯钛表面高能喷丸对溶胶-凝胶法制备羟基磷灰石涂层的影响

将表面抛光和高能喷丸处理的工业纯钛在8mol/L NaOH溶液中处理后,采用溶胶-凝胶(sol-gel)法在其表面制备羟基磷灰石(HAP)涂层.用扫描电镜(SEM)、X射线衍射仪(XRD)对涂层的表面、截面形貌及成份进行了分析;用拉伸试验机测试了涂层与基体之间的结合强度;动态凝血实验测试了涂层的血液相溶性;探讨了高能喷丸工艺对钛基体及涂层的影响.结果表明,通过sol-gel法,在两种基体表面制备了HAP涂层;高能喷丸工艺增加了基体的表面粗糙度和表面积,利于HAP的涂覆.提高了涂层与基体间的结合力,由抛光处理的10MPa提高到喷丸处理的30MPa;喷丸基体表面的涂层具有更好的抗凝血性.     

微粒子喷丸工艺对EA4T车轴钢表面性能和疲劳强度的影响

研究了不同微粒子喷丸工艺对EA4T车轴钢材料表面性能和疲劳强度的影响。基于9种不同喷丸强度或覆盖率(主要由喷丸时间决定)的微粒子喷丸工艺,探究了微粒子喷丸工艺对EA4T车轴钢表面的粗糙度、三维形貌、残余应力、半高宽(FWHM)和表面晶粒尺寸的影响。同时进行疲劳实验得出每种工艺的疲劳极限,并分析了试样断口的形貌。微粒子喷丸在材料表面引入了100μm左右的影响层。随着喷丸强度的增加,材料的表面粗糙度增加。在同一喷丸强度下,20 s喷丸表面粗糙度比10 s与30 s喷丸小。喷丸强度和覆盖率对残余应力最大值的影响较小,但对残余应力层深度的影响显著。喷丸后表面的FWHM最大并在深度方向逐渐减小,喷丸强度越大,喷丸对FWHM的影响层越深。随着喷丸强度和覆盖率的增加,微粒子喷丸试样表面晶粒尺寸减小。所有微粒子喷丸试样疲劳破坏均萌生自表面。不同微粒子喷丸工艺对EA4T车轴钢表面性能的影响不同,但是微粒子喷丸均使材料疲劳极限得到显著提高。     

激光喷丸强化对半圆孔件疲劳寿命的影响

为研究激光喷丸强化对7075-T6铝合金半圆孔件疲劳寿命的影响,对激光喷丸与未喷丸的试样进行了对比试验,利用X射线应力仪测定其表面残余应力,并对试样进行疲劳拉伸试验.用扫描电镜观察了两类试样疲劳断口的形貌,并采用数理统计方法对其疲劳寿命进行分析.研究表明:经激光喷丸处理区域,表面存在较大的残余压应力,幅值为310 MPa;未喷丸试样疲劳裂纹条带的宽度为0.7~0.8μm,而喷丸试样疲劳裂纹条带的宽度为0.3~0.4μm,说明喷丸试样裂纹扩展的速度比未喷丸试样慢很多;激光喷丸后半圆孔件的疲劳寿命比未喷丸的疲劳寿命提高了2.8~7.2倍.     

工业纯钛表面高能喷丸对仿生矿化合成羟基磷灰石涂层的影响

将表面抛光和高能喷丸处理的工业纯钛在5mol/L NaOH溶液中处理后,在模拟体液(SBF)中矿化生成羟基磷灰石(HAP)涂层.用扫描电镜(SEM)、X射线衍射仪(XRD)、电子探针(EPMA)和红外光谱仪(FT-IR)分析了涂层表面形貌和成分,探讨了表面高能喷丸工艺对钛基体及涂层的影响.结果表明,通过仿生矿化法,生成了钙磷比为1.30的碳酸化的HAP涂层;与抛光钛相比,高能喷丸工艺增加了钛基体的表面化学反应活性,从而加快了钛基体上HAP沉积速度;增加了表面粗糙度,提高了涂层与基体的结合力.     

45钢表面喷丸强化工艺的模拟分析

为了研究高压水射流喷丸的工艺效果,选择合适的水射流喷丸工艺参数,利用ANSYS有限元仿真软件进行模拟分析,以玻璃为喷丸材料,45钢为靶体材料,采用LS-DYNA软件,建立喷丸与靶体的有限元模型,通过模拟喷丸冲击靶体的动态过程,得到弹坑的深度及最大残余压应力的分布情况,绘制工艺参数对弹坑深度以及最大残余压应力的关系曲线。结果表明:弹坑深度及最大残余压应力随着弹丸速度的增加而明显增加,而弹丸入射角度对于弹坑深度及最大残余压应力的影响则比较平缓;该仿真结果与试验结果相近。     

高压水射流参数对材料表面强化性能的影响

高压水冲击强化是一种新的表面强化方法,通过改善零件的表面状态而提高疲劳寿命.本文通过淹没射流的方法,选用铝合金7075T651作为实验材料,研究了高压水射流工艺参数对冲击强化的影响规律,并测试了材料表面强化的效果.结果表明:试件经高压水冲击强化后,其拉伸疲劳极限比未强化和喷丸强化条件下分别提高了22%和6.6%.由于高压水强化比喷丸强化得到了更好的表面状态,强化后的表面轮廓连贯平滑、浅表层压应力高,因而能更大程度提高强化件的疲劳性能.     

镀铬/高能束复合表面处理研究进展

根据高能束对镀铬涂层及其界面强化机制的不同,镀铬/高能束表面复合技术可分为两类:高能束强化镀铬涂层复合技术和高能束预处理基体/镀铬复合技术.前者典型代表有激光表面强化或等离子体氮化/镀铬涂层;后者主要代表是激光预淬火基体/镀铬复合表面处理.综合阐述了上述3种典型的复合处理技术的原理、目的及实际综合效果;通过试验初步探讨了激光预淬火基体/镀铬复合技术延长镀铬身管寿命的主要机理.     

表面粗糙度对喷丸残余应力场的影响

为定性研究表面粗糙度对喷丸残余应力场的影响,采用余弦曲线模拟靶材粗糙表面,建立喷丸二维有限元模型,采用ABAQUS/EXPLICIT求解器对喷丸过程进行数值模拟,研究了表面粗糙度喷丸残余应力场的影响规律,分析了同一粗糙度下弹丸尺寸和喷射速度对喷丸残余应力场的影响规律,并与表面理想光滑时的情况进行了对比.结果表明,表面粗糙度的增加使残余压应力区变浅变薄,甚至使靶材表面产生残余拉应力,不利于喷丸强化件抗疲劳性能的提高,喷丸件表面应尽可能光滑以改善喷丸效果.     

高能喷丸预处理对钛表面组织及生物活性微弧氧化层的影响

为了提高钛表面的生物活性,利用微弧氧化工艺分别在普通粗晶钛和表面高能喷丸细晶钛上制备了多孔TiO2氧化层。经光镜和透射电镜观察,喷丸钛表面形成厚度40μm,直径100～200nm的等轴晶结构层。利用扫描电镜(带能谱分析)和X射线衍射仪对氧化层表面形貌、成分和相组成进行分析。结果表明,高能喷丸钛的表面生成的氧化层中含有α-Ca3(PO4)2相且钙磷百分含量提高。在粗糙的高能喷丸钛表面,微弧氧化速度在不同位置有所不同,氧化层与基体形成微机械咬合,基层结合力提高。     

Technical note A study on stress, reflection and double shot peening to inrease compressive residual stress

The technique of shot peening is commonly used to increase the fatigue limit of a steel. However, there are many practical difficulties in applying it to very high HV steel and complicated components. To overcome these problems, the authors proposed two new methods: stress double shot peening and stress reflection double shot peening. Both techniques were applied to quench and tempered steel (QT steel) and induction-heated steel (IH steel). The main results were as follows: (a) by double shot peening, the compressive residual stress near the sample surface was increased considerably; (b) by stress shot peening, the maximum compressive residual stress ( σ _max ) and the surface compressive residual stress ( σ _s ) were greatly increased; (c) by stress double shot peening, very high compressive residual stresses ( σ _max = −1710 MPa and σ _s = −1320 MPa) were successfully introduced into a hard steel (HV = 700); (d) in the new method (stress reflection double shot peening), very high compressive residual stresses ( σ _max = −1760 MPa and σ _s = −1460 MPa) were successfully introduced into a hard steel (HV = 700).     

大尺寸2024-T351铝合金喷丸成形曲率变化规律研究

目的 以喷丸成形工艺下的2024-T351铝合金平板件和单筋件为研究对象,分析弦向及展向曲率半径试验值与拟合值的变形规律。方法 针对试件厚度、喷丸压力、喷丸速度、预弯量4个参数进行喷丸成形操作的正交试验,通过测量成形后曲率的变化规律,分析不同参数组合对平板件和单筋件成形变化规律的影响。结果 在不考虑材料性能波动的情况下,随着平板件厚度和喷丸速度的增大,平板试件的弦向曲率半径和展向曲率半径均呈递增趋势;而随着喷丸压力的增大,平板试件的弦向曲率半径和展向曲率半径则呈现递减趋势,即当平板件厚度和喷丸速度增大时,喷丸成形对平板试件弯曲的影响程度有所增大,曲率半径减小;反之,喷丸成形对平板试验件弯曲的影响程度减小,曲率半径增大。结论 在忽略初始状态并将其假设为自由状态或给定预弯量状态的条件下,随着喷丸速度的增大,单筋试件的曲率半径递增,试验值与拟合值的变化趋势基本相符,二者最大偏差为11.2%。     

高能喷丸对AZ31镁合金耐腐蚀性及硬度的影响

采用高能喷丸对AZ31镁合金棒材端面进行表面自纳米化处理,利用失重法研究了AZ31镁合金喷丸试样和未喷丸试样在中性5%NaCl溶液中的腐蚀行为。利用扫描电子显微镜(SEM)、能量色谱仪(EDS)对塑性变形层腐蚀后的表面形貌、元素分布进行了表征,利用微观硬度计测试了由喷丸表面到基体的硬度变化。结果表明,喷完后AZ31镁合金试样的腐蚀速率明显大于未喷丸的试样,随着腐蚀时间的延长,喷丸试样的腐蚀率急剧减小,然后缓慢降低,在喷丸表面形成了1层厚度约150μm的塑性变形区,在喷丸表面有裂纹存在。晶粒细化显著提高了母材表面的微观硬度,喷丸表面的微观硬度最高达到135HV,是母材的2倍多。     

Effect of laser peening on fatigue performance in 300M steel

This study investigated and quantified the ability of laser peening to extend fatigue life and mitigate common fatigue crack nucleation mechanisms including foreign object damage and stress corrosion cracking in high strength, 300M steel. Residual stress was measured and fatigue tests were completed for as‐machined, shot peened and laser peened coupons tested under a variety of conditions including in a corrosive environment and with simulated foreign object damage. The results are compared to available reference data studying the application of another emerging surface treatment, low plasticity burnishing, to the same material (300M steel) and in similar coupons. Laser peening resulted in large stress‐life improvements in each condition, with a 54% increase in fatigue strength in an air environment for laser peened coupons at a lifetime of one million cycles. Additional fatigue testing in the 300M program showed that laser peening mitigated fatigue strength losses and improved the lifetimes (relative to as‐machined, air environment) for coupons subject to either a corrosive environment or simulated FOD. Performance of laser peened coupons under all conditions proved to be better than reference data for coupons treated with shot peening or low plasticity burnishing.     

Laser peening and shot peening effects on fatigue life and surface roughness of friction stir welded 7075-T7351 aluminum

The effects of laser peening, shot peening, and a combination of both on the fatigue life of Friction Stir Welds (FSW) was investigated. The fatigue samples consisted of dog bone specimens and the loading was applied in a direction perpendicular to the weld direction. Several laser peening (LP) conditions with different intensities, durations, and peening orders were tested in order to obtain the optimum peening parameters. The surface roughness resulting from various peening techniques was assessed and characterized. The results indicate a significant increase in fatigue life using LP compared to shot peening when tested on their native welded specimens.     

喷丸成形压力对7B50−T7751铝合金力学性能的影响

目的 研究7B50−T7751铝合金在不同喷丸成形压力下力学性能的变化规律,探究喷丸成形压力对材料表面形貌、疲劳寿命及静力性能的影响。方法 在不同的喷丸成形压力(0.42、0.50 MPa)下对7B50−T7751铝合金进行处理,分析材料的表面形貌。在此基础上,通过细节额定疲劳基准值和截止值进行计算,并进行压缩试验,结合铝合金材料在喷丸前后应变层的位错密度和形态,分析喷丸成形压力对合金材料疲劳寿命和静力性能的影响。结果 与未喷丸试件相比,在0.42 MPa的成形压力下,合金材料的疲劳寿命和静力性能均有所提高。喷丸成形之后,材料表层引入了一定深度的残余压应力层,形成位错密度较大的加工硬化组织,阻碍裂纹扩展,宏观上提高了材料的强度。在0.50 MPa的成形压力下,材料表面更加粗糙,裂纹易在晶粒连接薄弱处萌生,导致合金材料的疲劳寿命有所降低。结论 随着喷丸成形压力的增大,合金材料的疲劳寿命先增大后减小,抗压强度有所增大。在0.50 MPa的成形压力下,部分裂纹易于在弹坑边缘萌生,在一定程度上会降低合金材料的疲劳强度。     

Low cycle fatigue life prediction in shot‐peened components of different geometries – part II: life prediction

This study investigates the effects of shot peening on the low‐cycle fatigue performance of a low‐pressure steam turbine blade material. The finite element model incorporating shot‐peening effects, which has been introduced in part I, has been used to predict the stabilised stress/strain state in shot‐peened samples during fatigue loading. The application of this model has been extended to different notched geometries in this study. Based on the modelling results, both the Smith–Watson–Topper and Fatemi–Socie critical plane fatigue criteria have been used to predict the fatigue life of shot‐peened samples (treated with two different peening intensities) with varying notched geometries. A good agreement between experiments and predictions was obtained. The application of a critical distance method considering the stress and strain hardening gradients near the shot‐peened surface has been found to improve the life prediction results. The effects of surface defects on the accuracy of life predictions using the proposed method were also discussed.     

喷丸过程中的能量转化及残余应力分布研究

本文建立了喷丸表面强化过程的三维有限元模型,研究了靶材的力学性能及弹丸喷射速度对能量转化率和残余应力分布的影响规律。通过对有限元计算结果的分析发现,杨氏模量与屈服强度之比E/&;#61555;y较大,应变硬化率较低的靶材喷丸效率较高。屈服强度的提高使得最大残余压应力变大,残余压应力场深度变小。应变硬化率和喷丸速度的提高均会使最大残余压应力及其深度变大,同时会使表面残余压应力减小并向拉应力转变。本文的研究结果从能量转化的角度为喷丸强化件材料的选择提供了理论基础     

Low cycle fatigue life prediction in shot‐peened components of different geometries—part I: residual stress relaxation

In this study, the residual stress relaxation behaviour occurring during low‐cycle fatigue in shot‐peened specimens with either a flat or a notched geometry has been studied. A representative low‐pressure steam turbine material, FV448, was used. The residual stress and strain hardening profiles caused by shot peening were measured experimentally and were then incorporated into a finite element model. By allowing for both effects of shot peening, the residual stress relaxation behaviour was successfully simulated using this model and correlated well with the experimental data. Although more modelling work may be required to simulate the interaction between shot peening effects and external loads in a range of notched geometries, the model predictions are consistent with the specimens tested in the current study. The novelty of this study lies in the development of such a modelling approach which can be used to effectively simulate the complex interaction between shot peening effects and external loads in notched regions. Compared with the un‐notched geometry, the notched geometry was found to be more effective in retaining the improvement in fatigue life resulting from shot peening, by restricting the compressive residual stress relaxation during fatigue loading.