高强度钢喷丸强化处理的试验研究

喷丸强化是一种以小而硬的弹丸连续高速撞击金属零件表面而进行的一种特殊加工方法,零件通过喷丸可以大大提高材料的疲劳性能和抵抗应力腐蚀的能力。针对某型飞机上的喷丸强化零件,选取材料牌号为16Co14Ni10Cr2Mo高强度钢为研究对象,对两种厚度的试样进行不同喷丸强度的喷丸强化,对不同喷丸强度的试样进行疲劳寿命和残余应力场对比分析。     

前混合水射流喷丸强化表面力学特性及疲劳寿命试验

为获得前混合水射流喷丸强化增益效果,研究前混合水射流喷丸对2A 11铝合金和45钢的表面显微硬度、表面残余压应力和疲劳寿命的影响.采用显微硬度计和X射线应力分析仪分别测定喷丸表面显微硬度和表面残余应力,利用扫描电镜观察疲劳断口形貌,获得喷丸表面显微硬度和表面残余压应力随喷丸压力、扫描速度及靶距的变化规律,指出射流喷丸可以大幅度地提高2A11铝合金和45钢的疲劳寿命,当2A11铝合金和45钢的应力振幅分别为155.7 MPa和282MPa时,喷丸试样疲劳寿命比未喷丸试样疲劳寿命分别提高25.31倍和18.56倍,且未喷丸试样疲劳裂纹萌生于试样表面,喷丸试样疲劳裂纹有的萌生于试样表面,有的萌生于试样内部,当疲劳源在试样内部时,裂纹在夹杂物处萌生.因此,前混合水射流喷丸是一种提高金属零构件疲劳寿命的有效方法.     

AZ31B镁合金激光喷丸强化后疲劳裂纹扩展的数值模拟研究

激光喷丸(LSP)是一种先进的材料表面强化工艺,能有效提高零件的机械性能及其使角寿命.建立了以有限元软件ABAQUS和MSC.Fatigue为平台,面向抗疲劳制造的激光喷丸工艺有限元分析模型.结果表日月激光喷丸可以有效抑制疲劳裂纹扩展,延长疲劳寿命,喷丸次数的增加在一定程度上增大残余应力及疲劳寿命.残余应力抑制疲劳裂纹扩展的原因归结为最终断裂尺寸的增大以及裂纹扩展速度的减小.研究结果为LSP抗疲劳效果的预测提供了有效的方法,对于优化工艺参数,减少试验次数,降低成本具有指导意义.     

激光冲击强化与喷丸提高不锈钢疲劳性能对比研究

对不锈钢材料1Cr11Ni2W2MoV进行了激光冲击强化和喷丸强化后表面粗糙度和残余应力测试分析,与喷丸相比,激光冲击强化对试件表面形貌和表面粗糙度的影响更小,产生的残余压应力更大。对光滑试件和2种强化后试件的振动疲劳对比试验表明,激光冲击强化能显著提高不锈钢材料振动疲劳寿命,是喷丸的2倍以上。     

高强度喷丸对300M钢抗疲劳性能的影响

采用喷丸强度分别为0.424mm和0.576mm的两种工艺对300M钢进行高强度喷丸强化,从表面完整性、残余应力场、显微硬度及抗疲劳性能等方面研究了高强度喷丸对300M钢的强化效果。结果表明:喷丸强化处理后,300M钢试样喷丸面均被弹坑完全覆盖,表面粗糙度显著提高;喷丸后试样表层形成较高的残余压应力场,表面显微硬度得到提高;喷丸后试样疲劳寿命比喷丸强化前的有小幅提高,较高的表面粗糙度造成的应力集中以及微裂纹的产生是其疲劳寿命没有明显提高的主要原因。     

喷丸强化对2024铝合金疲劳性能的影响分析

以2024铝合金材料为研究对象,开展了表面喷丸处理对材料疲劳性能的影响研究。采用试验方法对比分析了2024铝合金试件在喷丸强化前后的疲劳性能。在此基础上采用ABAQUS有限元软件模拟分析了喷丸强化后试件的残余应力分布规律。两组疲劳试验数据对比分析表明:喷丸强化后2024铝合金材料的疲劳寿命可以提高(1.53~2.55)倍。有限元分析结果表明:喷丸强化在材料表层引入了残余压应力,从而提高了材料的疲劳性能。分析结果为定量研究喷丸强化对材料疲劳性能的影响提供了参考。     

喷丸强化对异物致损车轴钢疲劳性能的影响

高速铁路车轴长期服役中形成各种损伤,严重破坏了结构完整性.为此,首先采用喷丸处理(SP)对车轴钢试样进行强化,运用空气炮装置预制异物损伤(FOD),基于X射线衍射和纳米压痕仪得到喷丸强化试样表层的残余应力和微观硬度分布,开展高周疲劳试验分别获得未强化光滑试样(UnSPed+UnFODed)、强化处理的光滑试样(SPed+UnFODed)、未强化处理的FODed试样(UnSPed+FODed)和强化处理的FODed试样(SPed+FODed)的疲劳S-N曲线,同时考虑疲劳寿命数据的分散性,引入C95R95的概率评估方法得到上述各类试样的疲劳P-S-N曲线.最后,建立了伤损车轴材料的修正Kitagawa-Takahashi图.研究发现,异物损伤过程将会显著降低车轴钢试样的疲劳强度和寿命,然而由于残余压应力和硬化层的存在,喷丸强化能够有效提高受到FOD冲击试样的抗疲劳性能,具有重要的工程应用价值.     

喷丸表面强化处理Fe-2Cu-2Ni-1Mo-1C材料的弯曲疲劳性能及断口分析

由于孔隙的存在,粉末冶金材料的性能较差,尤其是疲劳性能,而喷丸后续处理工艺可显著降低材料表面的孔隙率,对疲劳性能起到明显的强化效果。因此,采用超声弯曲疲劳试验方法研究喷丸后续处理工艺对Fe-2Cu-2Ni-1Mo-1C粉末冶金烧结材料的疲劳性能的影响。结果显示,喷丸处理可以明显提高Fe-2Cu-2Ni-1Mo-1C烧结钢的疲劳性能,在106、107、108循环周次条件下,喷丸前试样的条件疲劳极限分别为424 MPa、311 MPa和229 MPa,喷丸后的分别为513 MPa、421 MPa和346 MPa,依次提高了21.0%、35.2%和51.0%。断口分析发现,喷丸处理对Fe-2Cu-2Ni-1Mo-1C材料的疲劳断口的影响主要在裂纹萌生阶段,未经过喷丸处理的试样裂纹源集中在应力最大的试样喷丸表面棱角处,喷丸强化后的试样疲劳裂纹在喷丸表面的亚表面萌生,裂纹源有向试样亚表面移动的趋势。     

表面喷丸工艺提高金属材料疲劳性能试验分析

在航空航天等领域,疲劳失效甚至占到所有零件失效的80％～90％,金属材料的表面强化技术,例如表面喷丸工艺成本较低且适用场景广泛而被工业界和研究人员关注.介绍了ZK60镁合金、Ti60钛合金以及0Cr13Ni8Mo2Al钢在喷丸处理前后疲劳寿命的对比,说明了喷丸技术对多种金属构件的疲劳性能的提升具有非常显著的效果.通过喷丸等表面强化技术可以很好地提高材料的疲劳寿命,从而避免危险事故的发生,节约经济成本.     

渗碳及渗碳喷丸齿轮轮齿弯曲疲劳极限的定量分析

跳出学科分工的局限性,对以齿轮为例的表面强化零件的表象疲劳极限进行综合分析。采用20CrMnTi钢制备三点弯曲小试样及齿轮试样。试样都经过同样的渗碳(并淬火及低温回火)处理,其中一半试样再经过表面喷丸强化。为了对比,还有一组小试样经过伪渗碳处理。测定了小试样表面层的残余压应力场。利用升降法确定了5×106周、应力比0.05条件下小试样和齿轮试样轮齿的弯曲疲劳极限载荷,并对各组试验中疲劳寿命最长的断口进行分析。建立有限元模型,并利用ANSYS软件计算齿轮根部的应力场。利用“疲劳源形成和疲劳极限的微细观过程理论”及“表面和内部疲劳极限”的概念对试验结果进行定量分析,并探讨根据小试样疲劳极限确定复杂零件(如齿轮)疲劳极限载荷的方法,以及表面强化工艺优化的问题。     

Effect of shot peening on rolling contact fatigue and lubricant film thickness within mixed lubricated non-conformal rolling/sliding contacts

The effect of shot peening on rolling contact fatigue (RCF) and lubricant film thickness within non-conformal rolling/sliding contacts operated under mixed lubrication conditions was observed in this study. Rolling contact fatigue tests and film thickness measurements were carried out using specimens with modified surface topography by shot peening process using glass beads having diameter between 0.07 and 0.11 mm. It has been shown that the effect of shot peening on RCF has no positive effect even if shot peened surface of the roller exhibited somewhat higher hardness in contrast to the grounded surface. The reduction of RCF may be caused due to asperities interactions because after shot peening the surface roughness of the roller was increased. Film thickness measurements confirmed that the contact is realized actually only between asperity peaks of shot peened ball and smooth disc.Conversely, no negative effect on RCF was observed when the shot peened surface of the roller was polished. The polish of asperity peaks causes the creation of lands and micro-cavities, which may be employed as lubricant micro-reservoirs. From film thickness measurements it has been observed that lubricant emitted by shallow micro-cavities can provide the local increase in lubrication film thickness, which thereby reduces asperities interactions. Similar results were obtained for start-up conditions where the squeeze lubricant enlarges film thickness and reduces surface interactions.From the obtained results, it can be suggested that properly designed surface topography modification could help to increase the efficiency of lubrication films leading to the enhancement of contact fatigue life of non-conformal mixed lubricated rolling/sliding contacts.     

喷丸残余应力场有限元模拟研究进展

喷丸强化处理工艺可以显著提高金属材料的抗疲劳和抗应力腐蚀等性能,这与喷丸后在金属表面层形成的残余应力场紧密相关,因此对喷丸残余应力的大小及分布进行预测具有重要意义。对近年国内外喷丸残余应力场的有限元模拟进行评述,总结出6种典型的残余应力分析模型,分别是二维轴对称模型、四对称面模型、三对称面模型、双对称面模型、单对称面模型和无对称边界条件的有限元模型,比较了不同模型的特点及应用现状。介绍了当前几种新的残余应力分析有限元模型:随机三维模型和周期性边界条件模型,根据其原理和特点认为其本质是无对称边界条件模型和对称边界条件有限元模型的延伸。针对空化水喷丸、激光喷丸和超声波喷丸等新工艺,新喷丸过程的数值模拟一般是以机械喷丸工艺的数值模拟方法为基础进行改进,主要采用弹丸撞击法和等效载荷法。对未来喷丸残余应力数值模拟研究进行了展望,认为从组织强化角度深入研究喷丸强化机理、建立更符合实际喷丸工艺的有限元模型、开发新算法以及将有限元法和离散元法进行结合是值得关注的研究方向。     

Effect of shot peening on the fretting wear of Ti–6Al–4V

In this paper, we report on the fretting wear behaviour of polished and shot peened Ti–6Al–4V specimens. For fretting experiments, due to micro-displacements at the interface between two contacting surfaces, two types of damage can be observed: crack initiation and debris formation. Shot peening, which is already well known for improving fatigue resistance of titanium alloys, is shown to have a beneficial effect on the crack initiation and propagation under fretting wear loading, as cracks observed on specimens after cylinder-on-flat fretting tests are shorter in shot peened specimens than in polished ones. It is also demonstrated that shot peening decreases the friction coefficient only at the beginning of the test, as long as the asperities induced by shot peening are not worn-off. The effects of displacement amplitude, normal force and test duration on the wear volume have been investigated: in all cases, shot peening has no significant impact on the wear process. The same amount of debris are formed and ejected for both polished and shot peened specimens. Moreover, it is found that, for both types of specimens, the linear relation, developed for steels and hard coatings, between wear volume and cumulated dissipated energy is not valid in the present case as different wear volumes are measured for the same cumulated dissipated energy, depending on the experimental conditions (normal force, displacement amplitude). Using the test duration as the variable parameter, energy wear coefficients are calculated for different experimental conditions.     

Effect of shot peening coverage on fatigue limit in round bar of annealed medium carbon steel

Shot peening is an effective and economical technique for improving the fatigue strength of metallic components by inducing compressive residual stress and hardening the layer near the surface. The effect is generally evaluated by main two parameters: coverage and peening intensity. However, the valuable coverage for improving the fatigue strength depends on the shape of the target material. In this study, the effect of coverage on fatigue limit in round bar of annealed medium carbon steel was experimentally studied. The fatigue limits for shot peened round bar specimens with 140–2300% coverage increased 14–25% by comparing those for non-peened round bar specimens. The valuable range of coverage was 280–60% in the used material and shot peening condition for improving the fatigue limit in short time. The result indicates that the valuable coverage of the round bar material is higher than full coverage to improve the fatigue limit of the material due to the effect of incident angle on round bar, even though the degree depends on the materials and shot peening conditions.     

A non-local fatigue approach to quantify Ti-10V-2Fe-3Al fretting cracking process: Application to grinding and shot peening

This paper presents an experimental study on the tribological behaviour and cracking response of a Ti-10V-2Fe-3Al titanium alloy under fretting loading with a cylinder on plane configuration. Three types of surfaces were investigated: a polished one considered as the reference, a ground one and a shot peened surface. Surfaces were compared with respect to residual stress, hardness and roughness. The first step of this study was to determine sliding conditions and coefficient of friction of the three contact types. Next, fretting tests under stabilized partial slip regime were carried out to investigate crack nucleation and propagation. Results show that whatever surface roughness or residual stress in the material, tribological behaviour is the same. These latter confirm that sliding condition and coefficient of friction in partial slip regime is due to material effect and not to roughness or surface hardness. Then, residual stress induced by grinding or shot peening have no influence on the crack nucleation threshold under fretting solicitation because crack nucleation is only induced by a sufficient tangential loading. The crack nucleation threshold is formalized by applying the Crossland criterion taking into account the stress gradient and the ensuing “size effect”. As expected, cracks propagation is influenced by residual stress under the surface. Compared to the reference case, for a same loading parameters set, residual stress induced by grinding is not sufficient to decrease the crack length reached whereas effects of shot peening decrease highly these latter. So, there is a threshold of residual stress from which residual stresses are useful against cracking.     

钛合金激光冲击强化层的残余应力及显微组织

对TC6钛合金进行了激光冲击强化(LSP),对强化层的残余应力分布进行了测试,应用透射电子显微镜对强化层的显微组织进行了观察。结果表明:TC6钛合金LSP的最佳功率密度为4GW.cm-2,LSP能在材料表层产生高的残余压应力场,表面残余压应力可达530.4 MPa;LSP可在钛合金表层产生高密度位错和纳米晶,纳米晶尺寸在10～100nm。     

The effects of laser peening and shot peening on fretting fatigue in Ti-6Al-4V coupons

This paper describes testing of Ti-6Al-4V coupons in fretting fatigue and compares the effects of mechanical surface treatments on performance. Fretting fatigue tests were performed using a proving ring for fretting load, bridge-type fretting pads, and applied tension-tension cyclic fatigue stress. As-machined (AM), shot peened (SP), and laser peened (LP) coupons were evaluated, and data generated to compare residual stress, surface condition, lifetime, and fractographic detail encountered for each. Near-surface residual stress in SP and LP coupons was similar. The layer of compressive residual stress was far deeper in LP coupons than in SP coupons and, consequently, subsurface tensile residual stress was significantly greater in LP coupons than in SP coupons. SP coupons exhibited a rough surface and had the greatest volume of fretting-induced wear. LP coupons exhibited a wavy surface and had a small volume of wear localized at wave peaks. SP coupons had the greatest fretting fatigue lifetime, with significant improvement over AM coupons. Lifetimes of LP coupons were similar to those for SP coupons at high fatigue stress, but fell between AM and SP coupons at lower fatigue stress. Fractographic evaluation showed that fractures of AM samples were preceded by initiation of fretting-induced cracks, transition of a lead fretting crack to mode-I fatigue crack growth, and crack growth to failure. SP and LP samples exhibited behavior similar to AM samples at high fatigue stress, but in coupons tested at low stress the lead crack initiated subsurface, near the measured depth of maximum tensile residual stress, despite the presence of fretting-induced cracks. The level of fatigue stress above which lead cracks were initiated by fretting was higher for LP than for SP, and was predicted with good accuracy using an analysis based on linear elastic fracture mechanics, the fatigue crack growth threshold stress intensity factor range, and superposition of measured residual stress and applied fatigue stress.     

曲面铝合金锤击平整技术研究

以曲面铝合金为例,利用工业机器人锤击的方式对曲面类零件表面进行平整,并探究各锤击工艺参数对其表面的粗糙度、硬度及表面形貌的影响。将锤击装置装夹到工业机器人上,控制工业机器人以矩形光栅式运动路径对曲面铝合金表面进行锤击加工,并对锤击后表面的粗糙度、硬度及表面形貌进行测量观察。结果表明:经锤击加工后的铝合金表面粗糙度可达0.5μm,表面硬度可以提升91%左右,且采用小的锤击节距及锤击进给速度,高的锤击频率可在减小表面粗糙度的同时提升其表面硬度,因此工业机器人锤击可用于曲面类零件表面的平整,且对铝合金表面具有很好的表面强化能力,是一种有效、无材料去除以及环保的表面平整方式。     

Impact of surface hardening treatment generated by shot peening on the fatigue life of brass alloy

Brass alloy is widely used because of some attractive properties such as high electrical and thermal conductivity. But its fatigue performance after surface treatment is not very well explored in literature. Thus, in the present work, particular emphasis was given to the influence of surface treatment by shot peening on the fatigue life of brass alloy, throughout surface roughness and microstructural evolution. Fatigue tests were performed on unpeened, peened and peened then polished specimens. Various times of surface hardening treatment as 30, 60 and 120 min were considered. Experimental results reveal that the fatigue life of peened brass alloy decrease for all studied hardening treatment conditions. Surface roughness and microstructural properties showed large sensitivity to the shot peening process of brass alloy.