喷丸强化对OCr13Ni8Mo2Al钢疲劳性能的影响

研究了表面喷丸强化后表面残余应力、表面粗糙度和表面层残余压应力场对0Cr13Ni8Mo2Al钢疲劳性能的影响.结果表明:0Cr13Ni8Mo2Al钢经喷丸强化后,在表面层残余压应力场的作用下疲劳裂纹源由表面被"驱赶"到表面强化层下,疲劳寿命得到显著提高.     

喷丸强化对0Cr13Ni8Mo2Al钢疲劳性能的影响

研究了表面喷丸强化后表面残余应力,表面粗糙度和表面层残余应力场对0Cr13Ni8Mo2Al钢疲劳性能的影响,结果表明：0Cr13Ni8Mo2Al钢经喷丸强化后,在表面层残余应力场的作用下疲劳裂纹源由表面被“驱赶”到表面强化层下,疲劳寿命得到显著提高。     

Influence of surface integrity on fatigue strength of 40CrNi2Si2MoVA steel

Influence of surface integrity (including surface roughness, residual stresses, and microstructure in surface) on fatigue limit of 40CrNi2Si2MoVA steel specimens is investigated comprehensively in this work according to a systematic consideration. The surface integrity of specimens is changed due to several widely used manufacturing procedures: heat-treatment, grinding, electro-polishing, hard chromium plating and shot peening. In comparison with specimen electro-polished after grinding, the specimen without polishing has 10% lower fatigue limit due to higher surface roughness; while shot peening improves the fatigue limit for about 36% due to inducing of compressive residual stress field in the surface and transferring the fatigue crack source from surface to interior. The fatigue limit of specimen with decarburized layer after grinding is lower about 13%, but the shot peening can eliminate its detrimental effect. Hard chromium plating decreases the fatigue limit dramatically. The shot peening carried before plating can improve the fatigue limit of specimen and cause it to get to a level even higher than that of specimen without plating.     

Shot peening of plasma nitrided steel for fretting fatigue strength enhancement

Abstract

The potential of fretting fatigue strength enhancement by a duplex surface engineering process involving shot peening of plasma nitrided steel, termed duplex SP/PN, is demonstrated. Specimens of 709M40 steel were individually plasma nitrided, shot peened, or duplex SP/PN treated. Fretting fatigue properties of the surface engineered specimens were evaluated. Surface roughness, residual stress, and hardening effect following the various surface treatments were examined and compared. It has been found that the duplex treatment can significantly improve the fretting fatigue strength of the investigated low alloy steel. Under the present testing conditions, the duplex SP/PN treatment increased the fretting fatigue strength (at 10⁷ cycles) of 709M40 steel by more than 70% relative to the nitrided, 120% to the shot peened, and 500% to the untreated steel. The improvement has been explained in terms of the significantly increased surface hardness and compressive residual stress in the near surface region following the duplex SP/PN treatment. By analysing the stress distributions in a shot peened surface, the influence of surface roughness on fretting fatigue strength is also discussed.     

Improvement of spring fatigue strength by new warm stress double shot peening process

Abstract

Shot peening technology plays a very important role in improving the fatigue strength of springs. In the present paper a new warm stress double shot peening (WSDSP) process developed by the authors is described. The authors have previously proposed a warm stress shot peening (WSSP) process, which is a combination of warm shot peening (WSP) and stress shot peening (SSP). Double shot peening (DSP) has been the method employed most widely for improved fatigue strength to date. The fatigue strengths resulting from these shot peening processes are compared in the present work. The new WSDSP process leads to significant improvement of spring fatigue strength because it includes an additional shot peening stage with small shot size (0.2 mm dia.), elevated temperature (300°C), and stressed condition (735 MPa), all not found in WSSP. After 300 000 cycles, the standard required life span, WSDSP results in a fatigue strength as high as 735 ± 590 MPa. In comparison, DSP gives a fatigue strength of 735 ± 300 MPa and WSSP of 735 ± 500 MPa. The WSDSP treated material gives the highest performance because the use of small shot size for the additional warm stress shot peening increases the compressive residual stress and hardness near the surface, and decreases the surface roughness.     

Effects of shot peening on bending fatigue strength of spring steel SS 2090

Abstract

The influence of prior surface condition and of a shot peening treatment on the bending fatigue strength of a standard Si–Cr spring steel (SS 2090) has been investigated. This steel was initially hardened and tempered to a hardness of 52–54 HRC. After shot peening, compressive residual stresses had been introduced into a surface layer of depth ~0·3 mm, with the maximum value of ~1000 MN m^?2 being found close to the surface. The effect of this treatment was to increase the fatigue limit by ~40% to 890 MN m^?2. Coincident with this increase was a change in the site of fatigue initiation from a surface to a subsurface location beneath the compressive residual stress layer. The initiating inclusions, which were 20–40 μm in size, were analysed and found to be Al₂O₃. At stress amplitudes greater than the fatigue limit, initiation was invariably found to occur at the surface and was not always due to inclusions. Inclusion initiated failure has been modelled using the size and spatial distribution of inclusions in the test bars in addition to the variation of applied and residual stresses through the section. A crack propagation criterion based on linear elastic fracture mechanics is used, assuming that propagation is controlled by stress intensity threshold value. It is assumed that small cracks exist at oxide inclusions from the beginning of the fatigue life and that failure is associated with the propagation of one of these cracks.

MST/1392     

Effect of surface properties on high cycle fatigue behaviour of shot peened ductile steel

Abstract

Experimental investigations into shot peened ductile steel have been carried out, applying three surface finishing conditions: as machined, standard shot peening using 100% coverage and severe shot peening with 1000% coverage (high exposure time). The properties of the shot peened surfaces were examined and characterised, and specimens were then submitted to three point bending tests. The fatigue limit was determined for each case. In this way, the dependence of fatigue behaviour on initial surface finishing properties was determined, and a relationship is suggested to describe and correlate fatigue limits with initial surface properties. A phenomenological approach is proposed to characterise and to correlate qualitatively and quantitatively the influence of local shot peened surface properties on fatigue limit of treated specimens. The Crossland multiaxial failure high cycle fatigue criterion is used in this approach to model the influence of each surface property.     

Survey about effects of shot peening conditions on fatigue performances of Ti–6Al–4V mechanical specimens featured by different cross-section geometries

Abstract

The present article provides a technical survey of the effects of shot peening conditions on the fatigue performance of Ti–6Al–4V specimens representative of the material (and the surface treatment) used in helicopter rotor hubs. As the effects of shot peening on non-plain surfaces have been fairly neglected in the scientific literature, the present work attempts to define the effects of shot peening on different specimens, featuring specific cross-section geometries, namely smooth and sharp edged specimens. Experimental tests also include measurements of the residual stress field caused by shot peening and the definition of the fatigue limit (by means of the ‘staircase method’) for all the tested specimen configurations. The present study proceeds with an optical and scanning electron microscopic investigation of the dynamics and causes of the different fatigue limits associated with the geometrical features. The present study conveys a strong correlation between specimen geometry and shot peening microstructural effects, resulting in different fatigue performances. The present work concludes that, whenever surface treatment is involved in the manufacturing process, the component’s design must be included, in addition to the required geometrical features for the operative conditions, an evaluation of how these provided features might affect the surface treatment outcome.     

Surface modifications induced by shot peening and their effect on the plane bending fatigue strength of a Cr-Mo steel produced by powder metallurgy

The effect of shot peening on the plane bending fatigue strength of a 7.1 g/cm³ sintered Cr-Mo steel was investigated. Shot peening provides surface densification, strain hardening, compressive residual stresses up to −700 MPa, without impairing the dimensional and geometrical precision of specimens. Plane bending fatigue strength increases of 30%, irrespective to the different residual stress profiles obtained by changing the shot peening parameters. The improvement is mainly due to the surface densification and strain hardening.     

42CrMo曲轴钢喷丸强化有限元模拟

喷丸强化能够有效提高42CrMo曲轴钢的抗疲劳性能,且喷丸数值模拟是制定喷丸工艺方案、评估喷丸后工件表面疲劳抗力的主要理论工具。为了体现喷丸过程中的随机性,利用MATLAB软件提供的Rand随机函数产生弹丸的位置,建立随机喷丸模型,并在此模型基础上研究弹丸直径、弹丸材料、冲击速度以及覆盖率与残余应力间的分布规律,进一步讨论喷丸工艺对42CrMo曲轴钢表面粗糙度的影响。研究发现:随着弹丸直径以及速度的增大,残余应力增大,抗疲劳性能提高,但粗糙度也相应增大;随着覆盖率的增大,残余应力增大,表面残余应力分布更加均匀,稳定性提高;同时弹丸强度越高,残余应力越大。通过喷丸试验对随机多弹丸模型进行验证,为喷丸工艺的精确控制提供了科学依据和理论基础。     

High- and very high-cycle plain fatigue resistance of shot peened high-strength aluminum alloys: The role of surface morphology

The present paper is aimed at investigating the effect of shot peening on the high and very-high cycle plain fatigue resistance of the Al-7075-T651 alloy. Pulsating bending fatigue tests (R = 0.05) were carried out on smooth samples exploring fatigue lives comprised between 10⁵ and 10⁸ cycles. Three peening treatments were considered to explore different initial residual stress profiles and surface microstructural conditions. An extensive analysis of the residual stress field was carried out by measuring with the X-ray diffraction (XRD) technique the residual stress profile before and at the end of the fatigue tests. Fatigue crack initiation sites were investigated through scanning electron microscopy (SEM) fractography. The surface morphology modifications induced by shot peening were evaluated using an optical profilometer. The influence of surface finishing on the fatigue resistance was quantified by eliminating the surface roughness in some peened specimens through a tribofinishing treatment. The capability of shot peening to hinder the initiation and to retard the subsequent propagation of surface cracks is discussed on the basis of a model combining a multiaxial fatigue criterion and a fracture mechanics approach.     

Effect of shot peening on fatigue performance of ductile iron castings

Abstract

Ductile iron is a commonly used structural material. However the unsatisfactory fatigue performance has limited its application for some dynamic loads. Shot peening is a mechanical surface modification process to extend the fatigue life of materials. Results of the influence of the shot peening treatment on ductile iron castings with as-cast surface and machined surface are presented. The results showed that shot peening ductile iron castings could double the fatigue life for an as-cast surface and quadruple the fatigue life for a machined surface. It is believed that shot peening affects fatigue life through the retardation of crack nucleation and growth as a result of the introduction of work hardening, the existence of compressive stresses on the surface layer, and the removal of the surface irregularities of the ductile iron castings.     

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.     

Improvement of fatigue properties by shot peening for Mg-10Gd-3Y alloys under different conditions

In the present study we investigated the influence of shot peening on the high cycle fatigue (HCF) performance of the Mg-10Gd-3Y magnesium alloys in four different conditions referred to as-cast, cast-T6, as-extruded and extruded-T5, respectively. The results show that shot peening can cause different degree of enhancement of fatigue performance for Mg-10Gd-3Y alloys depending on the Almen peening intensity applied; and that the Almen intensity could always be found that conferred the optimum improvement. The effect of shot peening was quantified, and for the as-extruded and extruded-T5 alloys it was found to be superior to that for the as-cast and cast-T6 alloys. The peened extruded-T5 Mg-10Gd-3Y alloy showed the highest fatigue strength at 10⁷ cycles of 240 MPa. The results of the analyses established a connection between the grain size, ductility and precipitates within the studied alloys. Microstructure affected the magnitude of the surface roughness induced by shot peening and also the maximum compressive residual stress and its relaxation during fatigue, and then determine the beneficial effect of shot peening.     

Hot corrosion of two nickel-base superalloys under alkali sulfate deposition conditions

Abstract

The single crystal MD2 (Ni – 8Cr – 5Al –5Co– 2Mo– 8W–6Ta – 1Ti) and the polycrystalline Inconel 792 (Ni –13Cr – 3Al –9Co– 2Mo– 4W–4Ta– 4Ti) were exposed at 850 and 900°C in an severely sulfidising environment comprising synthetic air with 8% water vapour and 2000 ppm SO₂, and a deposit of 20 mol% Na₂SO₄+80 mol% K₂SO₄ applied every 160 hours.

Results were evaluated in terms of mass change, which indicated the existence of an incubation time before the onset of extensive attack, and post-test metallography to evaluate metal loss. Metallographic studies are presented showing the complex external oxide scale formation and internal oxidation and sulfidation.     

EFFECT OF SHOT PEENING ON FATIGUE BEHAVIOR IN AL-ALLOYS

The individual contributions of residual compressive stresses, high dislocation densities, and surface roughness that are induced by shot peening to the improvement of fatigue life of Al 2024 are assessed. Stress amplitudes to number of fatigue cycles (S-N) curves and microcrack propagation (da/dN-ΔK curves) are determined for both underaged (T3) and peak-aged (T6) conditions. The fatigue behavior of the electropolished (which is also the reference condition), shot peened, shot peened and stress relieved, shot peened and polished, and shot peened, stress relieved, and polished condition is evaluated in fatigue tests.     

Einfluß der Oberflächenbeschaffenheit auf die Schwingfestigkeit von Aluminium-Druckguß

Effect of Surface Condition on Fatigue Strength of Die-Cast Aluminium Surface processing like milling or shot peening involves modifications of the surface and subsurface condition of a material that can be described by changes of the residual stresses, the hardness, and the surface roughness. Moreover, there is the possibility of introducing additional surface defects. In this paper the influence of these modifications on the fatigue behaviour of the aluminium die-casting alloy GD-AlSi8Cu3 is presented. S-N curves are determined for four surface conditions produced by milling, shot peening, and a combined treatment. The improvement of fatigue limit by shot peening is confirmed for this material. The additional effect of mean stresses is determined. Investigations of the fatigue fracture surfaces show that pores and pipes as well as surface defects induced by shot peening act as fatigue crack initiation sites.     

The high- and low-cycle fatigue behavior of Ni-contain steels and Ni-alloys in high pressure hydrogen

The effect hydrogen on short-term strength and plasticity, high- and low-cycle durability of 15Cr12Ni2MoNMoWNb martensitic steel, 10Cr15Ni27Ti3W2BMo austenitic dispersion-hardened steel, 04Kh16Ni56Nb5Mo5TiAl and 05Kh19Ni55Nb2Mo9Al Ni-base superalloys in range of pressures 0–30 MPa and temperatures 293–1073 K was investigated. In the case of 15Cr12Ni2MoNMoWNb steel and 04Kh16Ni56Nb5Mo5TiAl alloy the dependence of low-cycle durability (N) and characteristics of plasticity (δ and ψ) on the hydrogen pressure consists of two regions. In the first region (low pressures), the N, δ and ψ abruptly drops, and in the second, the negative action of hydrogen becomes stable or decrease negligibility. This means that there exists a pressure under which the degradation of this material with hydrogen reaches its limit. The additional effect of preliminary dissolved hydrogen on the properties of 15Cr12Ni2MoNMoWNb steel and 04Kh16Ni56Nb5Mo5TiAl alloy developed at hydrogen environment pressure least of 10 MPa. In the case of 10Cr15Ni27Ti3W2BMo steel and 05Kh19Ni55Nb2Mo9Al alloy the low-cycle durability N, characteristics plasticity δ and ψ decrease in whole hydrogen pressure range. Preliminary dissolved hydrogen leads to a considerable additional decrease in the properties of this alloy.     

Shot peening process: modelling,verification, and optimisation

Abstract

The paper describes the shot peening process and derives expressions for the indentation of surfaces by single shot impacts. These are supplemented by analysis of surface coverage and an assessment of the sources of residual stress. The high strain rate mechanical properties of 5052 aluminium alloy, 316 stainless steel and Ti–6Al–4V have been measured for use in a FEM/DEM simulation model. Specimens of these alloys have also been shot peened and examination of their surfaces has allowed an estimate of shot velocity to be made. Simulations of the process have been compared with diffraction scanning measurements of residual stress profiles and the correlation between the data is good. Procedures for optimising the shot peening process have been proposed.     

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.