高能喷丸表层纳米化对纯钛旋转弯曲疲劳性能的影响

采用高能喷丸方法使工业纯钛疲劳试样的表层实现纳米化,并进行了疲劳试验。结果表明,高能喷丸后其表层组织发生严重塑性变形并实现组织纳米化,是提高弯曲疲劳寿命的主要原因。扫描电子显微镜分析发现,疲劳裂纹源的位置主要呈现为表层和次表层两种情况。在相同应力水平下,疲劳裂纹源在次表层时疲劳寿命较长,而疲劳裂纹源在表面时疲劳寿命很短,相应的疲劳试样的表面损伤也比较严重。     

再次喷丸周期对TC18钛合金疲劳寿命的影响

研究了再次喷丸对于经过预先喷丸的TC18钛合金残余应力和室温疲劳寿命的影响。使用X射线衍射仪和旋转弯曲疲劳机测定了再次喷丸后的合金的表面残余应力以及总疲劳寿命。结果表明,疲劳试验会使预先喷丸的TC18钛合金疲劳试样表面残余压应力松弛30%～50%,而再次喷丸可以使由于疲劳而松弛的表面残余压应力回复到疲劳试验前试样的50%～70%。此外,相比未经过再次喷丸的试样,选择合适的再次喷丸周期可使TC18钛合金的总疲劳服役寿命提高了75%。     

拉-拉疲劳载荷下钛合金湿喷丸的残余应力松弛及再次喷丸工艺EI北大核心CSCD

采用湿法喷丸强化工艺(wet shot-peening)对TC4钛合金表面进行处理,研究高、低周的拉-拉疲劳过程中合金残余应力松弛规律,探讨再次喷丸工艺(re-shot-peening,RSP)对疲劳寿命的影响。结果表明:在拉应力载荷状态下,残余压应力依然发生松弛现象。疲劳载荷水平对喷丸TC4钛合金残余压应力场(CRSF)的松弛速率、松弛程度和松弛范围具有重要影响。高周疲劳(HCF)过程中残余应力松弛主要发生在近表层0~30μm,松弛速率较慢。低周疲劳(LCF)过程中残余应力松弛发生在0~80μm,范围更大,速率更快。RSP周期对于TC4钛合金的疲劳寿命也具有较大影响。在25%和50%初始喷丸疲劳寿命进行RSP处理会显著提高疲劳寿命,而在75%初始喷丸疲劳寿命处进行RSP处理对于疲劳寿命基本没有影响。此外,RSP的强化效果与疲劳载荷水平相关,对于高周疲劳寿命提高明显。     

孔强化对TC18钛合金疲劳寿命的影响

为提高TC18钛合金带孔零件的疲劳寿命,使用基体和焊缝上开孔的TC18钛合金试样,研究孔挤压和孔喷丸强化前后的表面残余应力,孔强化工艺对试样疲劳寿命的影响以及试样疲劳断口.研究表明,对基体和焊缝上的孔进行喷丸强化处理后,孔表面残余压应力值达到-300MPa以上,由于残余压应力和表面完整性的作用,孔喷丸强化效果比挤压强化...     

陶瓷喷丸强化对TC4-DT钛合金疲劳性能的影响

为了探讨陶瓷丸喷丸强化对TC4-DT钛合金疲劳行为的影响,对TC4-DT钛合金进行了铸钢喷丸强化和陶瓷喷丸强化,采用表面轮廓仪、扫描电子显微镜、旋转弯曲疲劳、轴向疲劳等研究了2种喷丸介质对TC4-DT钛合金表面粗糙度、表面形貌、表面残余压应力、疲劳寿命、疲劳强度的影响。结果表明:陶瓷丸喷丸对TC4-DT钛合金疲劳极限影响不大,陶瓷丸喷丸后表面形貌和粗糙度明显优于铸钢丸喷丸表面,陶瓷丸喷丸强化效果优于铸钢丸喷丸,可提高疲劳寿命达20倍以上。对于薄壁零件喷丸强化,陶瓷喷丸强度不宜超过0.15 A,喷丸强度过高,强化效果不佳。     

发动机用TC17合金喷丸+微弧氧化涂层组织和疲劳性分析北大核心CSCD

通过实验研究了TC17钛合金的喷丸处理效果,利用微弧氧化方法来达到纳米晶过渡层组织结构重构的过程。通过实验测试的方式研究不同工艺涂层微观组织,硬度以及疲劳性能。研究结果表明:形成许多火山型微孔,孔洞尺寸也存在明显差异。对合金实施喷丸处理能够获得厚度更大微弧氧化层,引起了晶粒的明显细化,得到更加致密的组织结构。经过喷丸处理后,硬度为463HV0.1,表现为硬度提高。对不同深度区域的组织硬度进行对比发现,从表面过渡到基体中的范围内硬度呈现不断减小的变化趋势。当试样表面经喷丸处理后疲劳寿命可以达到15361周次,相对处理前的试样疲劳寿命延长了15%左右。对试样表面实施喷丸处理将会导致表面组织中产生众多疲劳源并进一步迁移到基体内,疲劳源范围也持续缩小,涂层表面存在众多微孔。     

X射线衍射分析高能喷丸后45钢的表层晶粒尺寸

首先对45钢试样表层进行了高能喷丸处理,然后采用X射线衍射仪(XRD)对喷丸后试样表层的组织结构进行了分析,给出了实测XRD谱和降噪后的XRD谱,通过半高宽分析了试样表层晶粒的大小,并计算了平均晶粒尺寸。结果表明:高能喷丸处理30 min后,45钢表层平均晶粒尺寸为64.847 8 nm,达到了纳米量级,说明采用高能喷丸方法可在45钢表层形成纳米层。     

喷丸强化对材料旋转弯曲疲劳强度影响的定量研究

以往的工作已经提出了金属表面及内部疲劳极限的新概念，成功地分析了喷丸对三点弯曲（应力比Ｒ＝０．０５）条件下材料疲劳强度的影响。本文采用３００Ｍ钢研究了喷丸强化对旋转弯曲疲劳强度的影响。结果表明，经适当表面强化后，疲劳裂纹萌生于试样的次表层，萌生疲劳裂纹的；陆界应力（称内部疲劳极限）为未经喷丸强化试样疲劳极限（称表面疲劳极限）的１．３９倍，表明内部疲劳极限理论在旋转弯曲条件下仍然有效。     

先进喷丸表面改性技术研究进展

综述了先进喷丸表面改性技术研究现状及应用,阐述了微粒子喷丸、激光喷丸、超声/高能喷丸、高压水射流喷丸的基本原理,与传统喷丸对比发现,微粒子喷丸可提高材料的耐磨性,激光喷丸可精确控制定位,超声/高能喷丸可实现材料表面纳米化,高压水射流喷丸可承受半柔性冲击并减少应力集中.此外,对各种喷丸技术综合分析并进行对比,认为超声喷丸、复合喷丸(高能-微粒喷丸,激光-机械喷丸)综合性能最佳,并展望了未来应重点开展的工作.     

喷丸强度对不同粗糙度表面超高强度钢疲劳性能的影响

不同方式加工的高强度钢零件具有不同的表面状态,对其采用相同的喷丸工艺是否合理尚不明确。对不同表面粗糙度23Co14Ni12Cr3Mo E超高强度钢作不同强度的喷丸强化。采用扫描电镜及白光干涉仪观察了喷丸试样的表面形貌,采用金相显微镜观察喷丸试样的表面组织,采用旋弯疲劳试验机测试了喷丸试样的疲劳性能,采用X射线衍射残余应力测试仪测试喷丸试样的残余应力。研究了喷丸强度对不同表面粗糙度超高强度钢的表面组织、形貌、残余应力场及疲劳性能的影响。结果表明:喷丸过程可以细化表面组织,引入残余压应力场,改变表面形貌特征,从而引起表面应力集中状况的改变,其改善效果与原始表面状态有关;对于初始表面粗糙度Ra≤0.4μm的表面,喷丸强化过程能有效提高材料的疲劳寿命,促使疲劳裂纹源内移;随表面粗糙度的提高,当应力集中状况过于严重时,表面组织细化和残余压应力对疲劳性能的提升作用会被抑制,喷丸工艺对疲劳寿命的提升效果大幅下降,疲劳裂纹源均位于表面。     

Effects of Shot‐Peening on Fretting Fatigue Crack Growth Behavior in Ti‐6Al‐4V

Abstract: The effects of shot‐peening on fretting fatigue crack growth behaviour in titanium alloy, Ti‐6A1‐4V were investigated. Three shot‐peening intensities: 4A, 7A and 10A were considered. The analysis involved the fracture mechanics and finite element sub‐modelling technique to estimate crack propagation lives. These computations were supplemented with the experimentally measured total fretting fatigue lives of laboratory specimens to assess the crack initiation lives. Shot‐peening has significant effect on the initiation/propagation phases of fretting fatigue cracks; however this effect depends upon the shot‐peening intensity. The ratio of crack initiation and total life increased while the ratio of the crack propagation and total life decreased with an increase of shot‐peening intensity. Effects of residual compressive stress from shot‐peening on the crack growth behaviour were also investigated. The fretting fatigue crack propagation component of the total life with relaxation increased in comparison to its counterpart without relaxation in each shot‐peened intensity case while the initiation component decreased. Improvement in the fretting fatigue life from the shot‐peening and also with an increase in the shot‐peening intensity appears to be not always due to increase in the crack initiation resistance from shot‐peened induced residual compressive stress.     

Nitriding duration reduction without sacrificing mechanical characteristics and fatigue behavior: The beneficial effect of surface nano-crystallization by prior severe shot peening

Generally a clear beneficial effect of nitriding duration on resultant mechanical characteristics is reported in the literature. Considering the high energy cost in the competitive business environment, this work explores any opportunities to reduce nitriding duration while not sacrificing the resultant mechanical characteristics and fatigue behavior. To this end prior shot peening is applied with particularly severe parameters to generate ultra-fine grains and nano-structures in the surface layers. It was recently shown that the local fatigue strength improvement by combination of severe shot peening and 15 h nitriding could not eventually contribute in further increasing the fatigue limit of high strength low alloy steel smooth specimens as compared to only 15 h nitriding. In the present research combination of severe shot peening with nitriding at 7.5 h is assessed. It is affirmed that improvement by hybrid treatment can be actively exploited in the form of duration reduction. The characterization is carried out by optical and scanning electron microscopy observation, micro-hardness test, surface roughness measurement and X-ray diffraction measurement of residual stress. Fatigue limit of the treated specimens is experimentally determined. A critical comparison between the hybrid process with 50% nitriding duration reduction and the original nitriding process is presented. Based on the result of this study, nitriding duration can be successfully reduced without losing improvements in mechanical characteristics and fatigue behavior if a suitable prior severe shot peening, aimed to surface nano-crystallization, is performed.     

Effects of laser peening on the fatigue strength and defect tolerance of aluminum alloy

The effects of laser peening (LP) on the bending fatigue strength of the 7075‐T651 aluminum alloy were investigated. Accordingly, the defect tolerance of the aluminum alloy subjected to LP is discussed on the basis of fracture mechanics. The results indicate that a deeper compressive residual stress was induced by LP compared with the case of shot peening (SP). The fatigue strengths increased when both peening types were used. Semicircular slits with depths less than 0.4 and 0.1 mm were rendered harmless on the basis of the applications of LP and SP, respectively. The apparent threshold stress intensity factor range ΔK_th,ap increased by approximately five and two times owing to LP and SP, respectively. The increase of the ΔK_th,ap was caused by the compressive residual stress induced by the peening. The Kitagawa‐Takahashi diagram of the laser‐peened specimens shows that the defect tolerance of the aluminum alloy was improved by LP.     

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。     

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.     

Fatigue assessment and failure analysis of shot‐peened leaf springs

The paper deals with the fatigue and failure analysis of serial shot‐peened leaf springs of heavy trucks emphasizing on the influence of thermal treatment and shot peening on fatigue life. Experimental stress–life curves are determined by investigating smooth specimens subjected to fully reversed rotating bending conditions. These test results are compared to corresponding ones determined from cyclic three‐point bend tests on shot‐peened serial leaf springs in order to reveal the influence of the applied thermal treatment and shot peening process on the fatigue life of the high‐strength steel used for leaf spring manufacturing, dependent on the load level. Microstructure, macro‐ and micro‐hardness analyses are performed to support the analyses and explain the effects resulting from the certain shot peening process on the surface properties of the high‐strength spring steel under investigation. The assessment of the fatigue results reveals nearly no life improvement due to the manufacturing, emphasizing the necessity for mutual adjustment of shot peening and thermal treatment parameters to take account for life improvement.     

Influence of anodization on the fatigue strength of 7050-T7451 aluminium alloy

In recent years, with higher demand for improved quality and corrosion resistance, recovered substrates have been extensively used. Consequently residual stresses originated from these coatings reduce the fatigue strength of a component. Due to this negative influence occasioned by corrosion resistance protective coatings, an effective process like shot peening must be considered to improve the fatigue strength. The shot peening treatment pushes the crack sources beneath the surface in most of medium and high cycle cases due to the compressive residual stress field (CRSF) induced. The aim of this study was to evaluate the influence on the fatigue life of anodic films grown on 7050-T7451 aluminium alloy by sulphuric acid anodizing, chromic acid anodizing and hard anodizing. The influence on the rotating and reverse bending fatigue strength of anodic films grown on the aluminium alloy is to degrade the stress life fatigue performance of the base material. A consistent gain in fatigue life in relation to the base material was obtained through the shot peening process in coated specimens, associated to a residual stress field compressive near the surface, useful to avoid fatigue crack nucleation and delay or even stop crack propagation.     

Surface characteristics and fatigue performance of warm shot peened wrought magnesium alloy Mg–9Gd–2Y

Abstract

The surface characteristics and fatigue performance of the warm shot peened Mg–9Gd–2Y alloys were investigated. Compared to conventional shot peening (SP) at room temperature, warm shot peening (WSP) at 240°C induces higher subsurface hardening and larger maximum compressive residual stress in the subsurface of the specimens. The optimum Almen intensity of WSP is 0·15 mm N, whereas it is 0·10 mm N for SP. The main reason is that the surface of warm shot peened specimen is more plastically deformed but less damaged at the optimum Almen intensity due to the increase in plastic deformation ability of the tested alloys at elevated temperature. The fatigue strength of the tested alloy at 10⁷ cycles is increased from 125 to 175 MPa by optimum SP and to 185 MPa by optimum WSP.     

Influence of shot peening parameters on high‐cycle fatigue strength of steel produced by powder metallurgy process

In this study, the effect of shot peening parameters on fatigue strength of steel manufactured by powder metallurgy (PM) was investigated. Steel material obtained from Höganas ASC 100.29 in chemical composition of Fe–0.5% C–2% Cu was produced by using a single action press PM process. To determine the effect of shot peening parameters on fatigue performance, fatigue tests were performed on 20 unpeened and 80 shot‐peened samples, which were machined from sintered steel. Furthermore, shot‐peened samples were peened at different peening intensities, 100% and 200% saturation and full coverage conditions. Fatigue performance of steel, produced by PM process, was improved by surface peening process. For the studied PM steel, the best fatigue performance was obtained with the samples that were shot peened at 20 Almen intensity and 100% saturation. Fatigue strength and limit of the samples, however, were reduced after a certain cold work level. Higher intensity and saturation levels of peening process thus deteriorated the beneficial effect on fatigue strength and limit.