火焰喷焊对碳钢疲劳寿命的影响

对三种不同基材状态的45~3钢经表面火焰喷焊Ni60后的疲劳性能及腐蚀疲劳性能变化的研究,表明强度高的调质态基材喷焊后的疲劳极限下降7%,而正火态和轧态基材喷焊后疲劳极限提高14%。当有3.5%NaCl腐蚀介质存在时,不管基材强度高或低,表面喷焊都使材料的腐蚀疲劳强度(10~7寿命)提高30%以上。文中通过断口金相分析阐明喷焊后基材表面组织结构变化及其对疲劳裂纹形成及扩展的影响,讨论了Ni60喷焊层在腐蚀疲劳过程的行为,为喷焊工艺在工业中的应用提供了依据。     

Corrosion fatigue behavior of a steel with sprayed coatings

This paper describes the corrosion fatigue behavior and fracture mechanisms of a steel with different sprayed coatings. Rotating bending fatigue tests were conducted in 3% NaCl solution using specimens of a medium carbon steel with sprayed coatings of a ceramic (Cr₂O₃), a cermet (WC-12%Co) and two metals (Ni-11 % P and Al-2% Zn). The corrosion fatigue process was basically the same for ceramic, cermet, and Ni-11 % P sprayed specimens. That is, the corrosive media could be supplied from the specimen surface to the substrate through cracks initiated during fatigue cycling and/or pores in the coatings, and thus corrosion pits were generated followed by subsequent crack initiation and growth in the substrate. The corrosion fatigue strength of ceramic sprayed specimens was slightly improved compared to that of the substrate steel because the under-coating (Ni-5%A1) could impede the penetration of the corrosive media although the ceramic coating had a poor resistance to cracking under cyclic loading. Cermet sprayed specimens also exhibited improved corrosion fatigue strength because of the high resistance to cracking and the low volume fraction of pores of the coating. In Ni-11 % Psprayed specimens, cracks were initiated in the coating even at low stress levels; thus the corrosion fatigue strength was the same as that of the substrate. Anodic dissolution took place in Al-2 % Zn coating because the coating was electrochemically poor, and thus the substrate was cathodically protected. Therefore, the corrosion fatigue strength of Al-2 % Zn sprayed specimens was enhanced to as high as the fatigue strength of the substrate in room air. Based on the experimental results, a dual-layer coating consisting of WC-12%Co and Al-2%Zn was fatigue tested. The coating was effective at low stress levels and exhibited long life under conditions where corrosion fatigue strength was critical.     

植入铸造不锈钢髋关节断裂失效事例分析

利用ＳＥＭ对实际使用时断裂的髋关节的断口和表面进行了分析，认为此关节的断裂为以弯曲应力为主的腐蚀疲劳断裂。疲劳裂纹首先在表面的腐蚀点孕育产生，应力和腐蚀的共同作用使得裂纹得以扩展断裂。     

The effects of gas nitriding on fatigue behavior in titanium and titanium alloys

Fatigue behavior has been studied on gas-nitrided smooth specimens of commercial pure titanium, an alpha/beta Ti-6Al-4V alloy, and a beta Ti-15Mo-5Zr-3Al alloy under rotating bending, and the obtained results were compared with the fatigue behavior of annealed or untreated specimens. It was found that the role of the nitrided layer on fatigue behavior depended on the strength of the materials. Fatigue strength was increased by nitriding in pure titanium, while it was decreased in the Ti-6Al-4V and Ti-15Mo-5Zr-3Al alloys. Based on detailed observations of fatigue crack initiation, growth, and fracture surfaces, the improvement and the reduction in fatigue strength by nitriding in pure titanium and both alloys were primarily attributed to enhanced crack initiation resistance and to premature crack initiation of the nitrided layer, respectively.     

Electrochemical Behavior of Novel Superelastic Biomedical Alloys in Simulated Physiological Media Under Cyclic Load

The aim of the present work was to study corrosion and electrochemical behavior of Ti-22Nb-6Ta and Ti-22Nb-6Zr (at.%) superelastic alloys under conditions which imitate the performance mode of target devices (bone implants), i.e., under cyclic load in simulated physiological solutions. Open circuit potential (OCP) measurements were carried out on wire specimens in Hank’s solution and artificial saliva at 37 °C with various strain values up to 1.5%. It is shown that at clinically relevant strain values (about 0.2%) the alloys exhibit OCP growth indicating their high stability and resistance to corrosion fatigue under these cycling conditions. At much higher strains (about 1%), fatigue crack initiation and propagation take place, however, the corresponding OCP variation indicates that the fracture process is significantly restrained by reversible martensitic transformation during cycling.     

S135钻杆钢预腐蚀后的弯曲疲劳性能

目的：考察有机盐钻井液对S135钻杆材料腐蚀及疲劳性能的影响。方法首先利用高温高压釜模拟有机盐钻井液井筒的工况环境,对疲劳试样进行预腐蚀,通过点蚀仪测定试样表面的腐蚀状况;然后利用旋转弯曲疲劳试验机在不同弯曲应力条件下对预腐蚀试样和未腐蚀试样的疲劳性能进行测试,算得不同存活率下的疲劳强度,并绘制不同存活率下的S-N曲线。用体视显微镜和扫描电镜观察预腐蚀试样和未腐蚀试样的疲劳断口形貌,进而得出S135钻杆材料表面腐蚀对其疲劳寿命的影响程度和影响机制。结果经过腐蚀的试样表面有较多腐蚀坑,腐蚀坑深度在0.4~0.7 mm之间。未腐蚀试样的疲劳强度为553 MPa,其疲劳断口只观察到单个疲劳裂纹源;腐蚀试样的疲劳强度为409 MPa,其疲劳断口观察到多个疲劳裂纹源。 S135钻杆材料腐蚀疲劳开裂敏感性指数为26%。结论经过高温高压有机盐钻井液环境腐蚀后,试样表面点蚀严重,腐蚀坑底部存在应力集中并导致裂纹源的形成,多个裂纹源的同时生长加快了裂纹的扩展,最终降低S135钻杆钢的疲劳强度。     

外加电位对奥氏体不锈钢应力腐蚀与腐蚀疲劳交互作用的影响SCIEI

本文研究了0Cr18Ni9Ti奥氏体不锈钢在42%沸腾MgCl_2中,在低频,高平均应力循环载荷下的环境敏感断裂行为,研究了应力腐蚀疲劳与应力腐蚀在裂纹扩展规律及断口形貌上的差别与联系。从断裂特征上分析了应力腐蚀与腐蚀疲劳的交互作用,并着重研究了外加极化电位对这种交互作用的影响。     

Untersuchungen zum SwRK-Verhalten des unlegierten Stahles Ck 45 in chloridionenhaltigen wäßrigen Medien

Corrosion fatigue behaviour of steel Ck 45 in aqueous solutions containing chloride ions The fatigue behaviour of carbon steel Ck 45 (comparable to AISI 1045x) is investigated for cyclic tension and rotating bending load with a frequency of 25 Hz. The fatigue limits under cyclic tension load in air are 410 N/mm² for smooth specimens and 290 N/mm² for notched specimens. For rotating bending load a value of 200 N/mm² is found for smooth specimen. The fatigue limits for N = 10⁷ in two different environments (0.3% and 3% NaCl-solution) reach only 37–57% of the according values in air. Cathodic protection of smooth specimens causes an improvement to 95% of the air fatigue limit. The evaluation of the free corrosion potential for all corrosion fatigue tests and the appearence of fracture show typical attributes of corrosion fatigue in the active state.     

EFFECT OF POTENTIAL ON INTERACTION BETWEEN STRESS CORROSION CRACKING AND CORROSION FATIGUE OF AUSTENITIC STAINLESS STEEL IN BOILING 42% MgCl_2 SOLUTION

The environment-sensitive fracture behaviour of 0Cr18Ni9Ti austenitic stainless steel inboiling 42% MgCl_2 under the specific load of low frequency and high mean stress was inves-tigated from the relations and differences of crack growth rates and fractographs betweenstress corrosion fatigue and stress corrosion cracking.The interaction between stress corro-sion cracking and corrosion fatigue was also studied from fracture characteristics with empha-sis on the effects of applied potential on the interaction.     

Verbesserung des Schwingungsrißkorrosionsverhaltens von Stahlproben durch Beschichtung

Improvement of the corrosion fatigue behavior of steels by paint-coating Paint-coatings have been used extensively to prevent corrosion of steel. In order to investigate the influence of an anticorrosive paint on the corrosion fatigue strength of steel, specimens of SAE 4135 in a quenched and tempered state, and in salt bath nitrocarburized state, on the one hand, and specimens of the steel SAE 5115 in a salt bath carburized state, on the other hand, were subjected to comparative rotating bending fatigue tests in inert media and in aqueous 5 pct NaCl. The results demonstrate that the 5 pct NaCl environment is reducing fatigue life drastically, but the painting treatment, however, was found to improve significantly the corrosion fatigue life. Regarding the beneficial effect of the painting treatment on the corrosion fatigue behavior, a superiority of the nitrocarburized variant in contrast to the other variants was ascertained.     

7B04铝合金及其螺接件的微观腐蚀机制及耐久性研究

目的 以飞机结构用7B04高强铝合金及其螺接件为实验对象,通过室内加速腐蚀试验模拟试样在南海海洋大气环境中的环境损伤,并深入分析其微观腐蚀机制与疲劳性能的内在联系。方法 通过数码相机、3D共聚焦显微镜、扫描电子显微镜等手段,研究模拟南海海洋大气环境下7B04铝合金及其螺接件的宏观/微观腐蚀特征,并借助疲劳测试分析经不同腐蚀周期后铝合金试样及螺接件的疲劳寿命。结果 铝合金及其螺接件经室内加速腐蚀试验后发生的腐蚀行为出现了明显差异,7B04铝合金试样表面发生的腐蚀行为以点蚀为主,而螺接件的腐蚀行为更加复杂。其中,远离螺接区域的暴露区的腐蚀情况与铝合金试样一致,在螺接区域发生了明显的缝隙腐蚀。此外,铝合金试样及螺接件随腐蚀周期变化的劣化规律也有所不同,腐蚀使得试样的疲劳性能均不同程度地下降。7B04铝合金疲劳寿命的递减趋势相对平缓,而螺接件在腐蚀进行到第2周期时其疲劳寿命就已降至原始寿命的一半,在腐蚀进行到第4周期时,螺接件的力学性能基本丧失。结论 经腐蚀后,铝合金试样出现了点蚀,且随着时间的延长出现了均匀腐蚀的趋势,疲劳寿命的递减趋势相对平缓。尽管螺接件的过渡区发生了严重腐蚀,但缝隙区诱发的局部腐蚀导致螺接件的受力面积减小,这是造成其疲劳寿命急剧衰减的首要因素。     

Study the Fatigue-Wear Behavior of a Plasma Electrolytic Nitrocarburized (PEN/C) 316L Stainless Steel

In the present study, a suitable machine was developed in the laboratory to investigate the fatigue-wear behavior of the untreated 316L austenitic stainless steel and samples treated by plasma electrolytic nitrocarburizing process under different combinations of cyclic loading and contact pressure. The fracture cycles as a function of bending stress were recorded while a constant contact pressure was applied simultaneously. As a result, the PEN/C treated specimens exhibited a higher resistance (about 40% for 15.6 N contact load and about 60% for 25 N contact load) under the application of simultaneous cyclic stress and contact pressure. Also it was shown that under a range of combined fatigue and wear stresses, the specimens exhibit a better life than the conditions of performing wear or fatigue tests separately and this effect was much more observable for PEN/C-treated samples. The gravimetrical weight loss values in the fatigue-wear test were also measured at intervals 5000 to 300,000 cycles (with the contact stress = 6.25 MPa and the bending stress = 87 MPa). The results showed a better wear resistance for the treated surface at the first stage of the process.     

Effect of Temper Condition on the Corrosion and Fatigue Performance of AA2219 Aluminum Alloy

The effect of temper condition and corrosion on the fatigue behavior of alloy AA2219 has been investigated in different temper conditions (T87 and T851). Corrosion testing was performed by exposing the tensile specimens to 3.5% NaCl solution for different time periods, and the corrosion damage was quantified using a 3D profilometer. The exposure-tested specimens were subjected for fatigue testing at different stress levels, and the reduction in fatigue life was measured along with detailed fracture morphology variations. The results indicated that the alloy in both tempers suffers localized corrosion damage and the measured corrosion depth was 120 and 1200 µm, respectively, for T87 and T851 conditions. The loss in fatigue strength was found to be high for T851 (67%) when compared to that of T87 temper condition (58%) for a pre-corrosion time of 15 days. In both cases, fatigue crack initiation is associated with corrosion pits, which act as stress raisers. However, the crack propagation was predominantly transgranular for T87 and a mixed transgranular and intergranular fracture in the case of T851 temper condition. This was shown to be due to the heterogeneous microstructure due to the thermomechanical working and the delay in quench time imposed on the alloy forging in T851 temper condition. The findings in this paper present useful information for the selection of appropriate heat treatment condition to facilitate control of the corrosion behavior which is of great significance for their fatigue performance.     

航空装备铝合金结构材料点蚀失效行为

对航空装备铝合金结构材料腐蚀疲劳行为中点蚀及点蚀萌生裂纹2个关键环节的研究进行综述。介绍了点蚀萌生机理、点蚀行为影响因素、点蚀萌生裂纹行为的研究方法，以及点蚀萌生裂纹行为机制等方面的研究结论。研究认为:航空装备铝合金点蚀的本质是受环境条件、结构微观因素、载体条件等多种因素影响的随机性电化学行为，点蚀损伤可通过其几何尺寸、点蚀率、失重率等多种指标进行描述；点蚀损伤在疲劳载荷作用下萌生裂纹，该行为可通过原位观测、断口分析等方式进行研究，并受点蚀形貌、载荷条件、材料微观结构等因素影响。在此基础上提出后续研究趋势:研究对象聚焦在新型航空铝合金材料上，点蚀试验方式注重模拟装备服役环境，研究内容则应深化点蚀萌生裂纹行为的量化分析。     

Corrosion and Fatigue Behavior of High-Strength Steel Treated with a Zn-Alloy Thermo-diffusion Coating

High and low cycle fatigue tests were conducted on high-strength steel using four-point bending. The materials tested were ASTM A723 steel in the as-machined condition, grit-blasted condition, MIL-DTL-16232 heavy manganese phosphate-coated condition, and ASTM A1059 Zn-alloy thermo-diffusion coated (Zn-TDC). The ASTM A723 steel base material exhibits a yield strength of ~1000 MPa. The effects of the surface treatments versus uncoated steel were examined. The fatigue life of the Zn-TDC specimens was generally reduced on as-coated specimens versus uncoated or phosphate-coated specimens. Several mechanisms are examined including the role of compressive residual stress relief with the Zn-TDC process as well as fatigue crack initiation from the hardened Zn-Fe alloy surface layer produced in the gas-metal reaction. Additionally, the effects of corrosion pitting on the fatigue life of coated specimens are explored as the Zn-TDC specimens exhibit significantly improved corrosion resistance over phosphate-coated and oiled specimens.     

Corrosion fatigue crack propagation behavior of A7N01P-T4 aluminum alloy welded joints from high-speed train underframe after 1.8 million km operation

Using the potentiodynamic polarization analysis, the fatigue crack propagation behavior of A7N01P-T4 aluminum alloy metal inert gas welded joints cut from a high-speed train underframe after 1.8 million km operation was studied in air and in a 3.5 wt% NaCl solution. The fracture surface and crack growth path were analyzed using optical microscopy, scanning electron microscopy, and electron backscattered diffraction. The results reveal that the corrosion fatigue crack growth rate of an A7N01P-T4 welded joint in a 3.5 wt% NaCl solution is higher than that in air. Furthermore, the corrosion fatigue crack growth rate is noted to be the fastest in the heat-affected zone, followed by the base metal, whereas it is the slowest in the weld metal, which is consistent with the corrosion resistance of the A7N01P-T4 joints. The second phase is observed to exhibit a significant influence on the corrosion fatigue crack propagation path. The cracks are noted to grow toward the soft orientation and have obvious plastic deformation during the propagation process, which indicates that the anodic dissolution is the main cause of the corrosion fatigue crack growth.     

Effect of stress ratio on long life fatigue behavior of Ti-Al alloy under flexural loading

A new ultrasonic three-point bending fatigue test device was introduced to investigate fatigue life ranging up to 10^10 cycles and associated fr＇dcture behavior of Ti-Al alloy. Tests were performed at a frequency of 20 kHz with stress ratio R=0.5 and R=0.7 at ambient temperature in air. Three groups of specimens with different surface roughness were applied to investigate the effect of surface roughness on fatigue life. Furthermore, optical microscopy（OM） and scanning electron microscopy（SEM） were used for microstructure characteristic and fracture surface analysis. The S-N curves obtained show that fatigue failure occurs in the range of 10^5-10^10 cycles, and the asymptote of S-N curve inclines slightly in very high cycle regime, but is not horizontal for R=0.5. Fatigue limit appears after 10s cycles for R=0.7. Surface roughness （the maximum roughness is no more than 3 μm） has no influence on the fatigue properties in the high cycle regime. A detailed investigation on fatigue fracture surface shows that the Ti-Al alloy studied here is a binary alloy in the microstructure composed of α2-Ti3Al and γ-Ti-Al with fully lamellar microstructure. Fractography shows that fatigue failures are mostly initiated on the surface of specimens, also, in very high cycle regime, subsurface fatigue crack initiation can be found. Interlamellar fatigue crack initiation is predominant in the Ti-Al alloy with fully lamellar structure. Fatigue crack growth is mainly in transgranular mode.     

Environment induced fatigue crack of type 40Cr steel in drilling muds

Drill pipes are subjected in service to aggressive environment (a wide range of drilling muds) and to a combination of high static and dynamic loads. Under such conditions, the high‐strength steel is susceptible to various forms of environmental cracking, particularly to corrosion fatigue. The fatigue life of type 40Cr steel in salt drilling muds was studied with a self‐made rotating bending corrosion fatigue testing apparatus. Environmental variables investigated included stress, frequency, temperature, and pressure of carbon dioxide. Experimental results show that carbon dioxide promotes the fatigue crack of 40Cr steel. These tests were supported by electrochemical corrosion measurements and hydrogen permeation.     

环氧涂层处理的Mg-3Al-1Zn镁合金在齿轮油中的腐蚀疲劳性能(英文)

研究环氧涂层处理后的Mg-3Al-1Zn合金在齿轮油环境下的腐蚀疲劳行为。采用扫描电子显微镜(SEM)观察疲劳试验后试样的腐蚀形貌及疲劳断口特征,并通过能谱仪(EDS)分析试样在齿轮油中的腐蚀产物成分。分析环氧涂层处理前、后2种试样的腐蚀疲劳性能和疲劳裂纹萌生机制。结果表明:经环氧涂层处理后,试样在齿轮油中的腐蚀疲劳极限高于未处理试样的。这是由于环氧涂层可以将镁合金与周围腐蚀环境良好地隔离。环氧涂层的力学性能比镁合金的差,这是疲劳裂纹优先从环氧涂层萌生的重要原因。另外,齿轮油的润滑作用可以使环氧涂层产生剥落现象。     

新型22Cr-15Ni奥氏体耐热钢高温低周疲劳行为

22Cr15Ni3.5CuNbN新型奥氏体耐热钢是为620 ~ 650 ℃的超(超)临界电站锅炉管道制造而研发的新型奥氏体耐热钢,其高温性能的优劣对机组的安全可靠运行具有重要意义. 文中通过22Cr15Ni3.5CuNbN钢在650 ℃下的低周疲劳试验,研究了其在不同应变幅条件下的应力?应变关系及疲劳寿命. 通过对断口形貌的分析研究了其断裂机理. 结果表明,22Cr15Ni3.5CuNbN钢在高温下表现出明显的循环硬化行为,且没有明显的应力饱和现象出现. 其硬化行为与材料内部位错密度的增加有关. 采用基于塑性应变能密度对其疲劳寿命进行了预测,取得了良好的预测效果. 疲劳断口可以分为3个区域:裂纹源区、裂纹扩展区以及瞬断区. 在较高的应变幅条件下,在断口处可观察到多个裂纹源. 多个裂纹源的形成和二次裂纹的产生是导致其疲劳寿命下降的重要原因.