离子注入对Ti合金疲劳行为的影响

研究了碳、硼离子注入对Ti-6Al-4V合金应力控制疲劳行为的影响。研究发现:注入C~+和B~+可分别使合金的疲劳极限提高28％和12％。高能C~+和B~+离子辐射,使合金的注入表面受到极度损伤并且在注入层中形成了许多细小的第二相沉淀粒子。使用透射电镜(TEM)和二次离子质谱(SIMS)研究了疲劳前后注入表面的结构变化。根据表面层微观分析的结果,分析疲劳寿命得到改善的原因。     

7449合金高周疲劳及裂纹萌生行为

研究7449-T7951合金的高周疲劳及裂纹萌生行为。在室温下,采用光滑及缺口试样进行疲劳寿命测试,应力比(R)分别为0.5和1.0。采用金相显微镜、扫描电镜及透射电镜对该合金的微观组织及疲劳试样断口进行分析,以揭示其疲劳裂纹萌生机理与合金微观组织之间的关系。结果表明:7449-T7951合金具有优异的疲劳性能;应力比为0.5和1.0时,光滑试样的疲劳寿命极限(σN)分别为349和134 MPa,而缺口试样的σN(缺口系数Kt=3.0)分别为138和70 MPa。其裂纹萌生行为受合金中粗大第二相、析出相、晶界和位错(滑移带)的共同影响。     

复合强化对渗铝K403合金组织和力学性能的影响

针对航空发动机涡轮叶片榫头渗铝污染后产生的尺寸偏大和力学性能下降的问题,采用水吹砂+振动光饰和水吹砂+喷丸强化+振动光饰两种复合方法对渗铝后的K403合金试样进行处理,研究复合方法对K403渗铝试样微观组织和力学性能的影响。对两种方法处理后试样的微观组织、渗铝层元素分布、物相组成、残余应力和疲劳寿命进行测试。结果表明:渗铝后,试样表面存在残余拉应力,渗铝层厚度约27.3μm,主要相为β-NiAl和α-Cr;水吹砂+振动光饰处理后,试样表面产生了360 MPa的残余压应力,试样的疲劳寿命提高了1.49倍;水吹砂+喷丸强化+振动光饰方法处理后,试样表层产生了较大的残余压应力,距离表面0.04 mm处残余压应力值最大,约为686 MPa,应力影响深度约0.2 mm,试样的疲劳寿命提高了3.44倍。     

硼离子注入对多晶Ni力学性能及微观结构的影响

用能量为50keV,剂量为3×10~(17)ions/cm_2的B~+注入多晶Ni,通过力学性能实验研究了多晶Ni注入前后表面硬度和疲劳性能的变化,以及多晶Ni表面层注入和疲劳前后化学成分、滑移特征、裂纹萌生、断裂方式和微观结构的变化。结果表明,B~+注入多晶Ni后,表面区域形成一个不同组织结构的由Ni-B非晶、Ni_3B和Ni_4B_3第二相以及辐照损伤组成的多层次的注入层,提高了多晶Ni的表面硬度,并使其疲劳极限提高16％。探讨了B~+注入影响多晶Ni疲劳极限的几种可能机制。     

高速微粒轰击对微弧氧化铝合金疲劳性能的影响

以获取高性能微弧氧化陶瓷膜,且不降低基体铝合金的抗疲劳性能为目标,采用高速微粒轰击处理工艺和微弧氧化处理工艺制备了未处理、高速微粒轰击处理、微弧氧化处理、高速微粒轰击+微弧氧化处理复合处理4种状态的试样,通过疲劳试验机对其疲劳寿命进行了测试;同时,采用TEM和XRD残余应力测试仪等分析方法对试样的表层微观组织结构和残余应力进行了观察与测试。结果表明:加载载荷较高时,4种试样疲劳寿命基本相同,寿命较短;加载载荷较低时,微弧氧化处理铝合金的疲劳寿命明显低于未处理试样,高速微粒轰击处理导致的微观组织结构细化和形成的残余压应力可以有效抑制疲劳裂纹的萌生和扩展,使未处理和微弧氧化铝合金的疲劳寿命均得到有效提高,这2种高速颗粒轰击处理过的试样的疲劳寿命均高于未处理试样,这表明高速颗粒轰击强化处理可有效提高低应力水平时微弧氧化铝合金的疲劳寿命。     

拉伸超载对超高强度钢A-100冲击疲劳性能的影响

研究了A-100钢单边缺口三点弯曲试样经拉伸超载处理后,冲击疲劳性能的变化。在室温下测得拉伸超载处理前后,冲击能量-冲击疲劳寿命曲线,并对冲击疲劳断口进行微观分析。结果表明:拉伸超载可延长A-100钢的冲击疲劳裂纹起始寿命而对裂纹扩展寿命无影响;试样超载后裂纹源区微观形貌发生变化,缺口根部残余压应力的存在是造成这些变化的主要原因。     

含1%混合稀土压铸镁合金的高周疲劳性能

研究含混合稀土1%(质量分数)的压铸镁合金AZ91D在应力比r=0.1的高周疲劳性能。组织分析表明,压铸镁合金试样的表面层和心部的显微组织存在差别。室温条件下抗拉强度为185 MPa,屈服强度为159 MPa,延伸率为1.5%。测试存活率p=50%的p-S-N曲线,结果显示在3.8×105循环周次时的疲劳强度为70 MPa,得出在循环周次103~106之间,p=50%时,S与Np的关系式为lgNp=17.85–6.83lgS。在较低的应力下,一些疲劳试样断口出现擦痕,当缺陷较小时,疲劳断口表现为韧窝、撕裂棱、疲劳条带等韧性断口和准解理的混合特征,属于具有较低韧性的材料。     

喷丸对H13钢单边带缺口试样疲劳裂纹扩展行为的影响

喷丸工艺通过改变试件的表面形貌、微观组织及残余应力等表面完整性可以影响裂纹的萌生和扩展;对于存在缺陷的试件,喷丸的作用机制和影响结果有所不同。采用白光干涉仪、SEM、XRD及显微硬度计等对单边带缺口的H13钢薄板试样喷丸前后的表面完整性进行了测定。并借助原位SEM开展了系列裂纹扩展试验,分析了喷丸对试样疲劳寿命、裂纹扩展速率以及疲劳断口特征的影响。研究结果表明,虽然残余压应力诱发裂纹闭合,但由于喷丸后表面粗糙度的大幅提高增强了缺口效应,表面加工硬化使得韧性有所降低,以及残余应力在加载过程中发生松弛等因素,喷丸后单边带缺口试样的裂纹萌生过程缩短,疲劳寿命降低,且裂纹扩展速率的变化较小。喷丸前后疲劳断口形貌均为准解理特征,喷丸后断口近表面处的撕裂棱特征消失。     

LSPwC对时效后GH3044合金疲劳性能的影响

目的 修复发生时效退化现象的GH3044合金,从而提高其使用寿命。方法 采用无保护层激光冲击强化（LSPwC）工艺处理GH3044合金时效试样,分析了该工艺处理前后试样表面的物相变化情况,研究了时效以及激光强化工艺对合金表层微观组织的影响,对比了激光强化前后合金试样高温应力松弛和疲劳寿命变化情况。结果 合金试样经过1200 ℃固溶处理后,其表面相为单相γ奥氏体以及WC,处理前后试样表面主要相组成不变,均为奥氏体和Cr23C6。经过时效处理100 h后,GH3044合金沿晶析出大量尺寸较大的碳化物,表面残余应力值约为-28.5 MPa,疲劳寿命约为1.013×106。通过LSPwC处理后,碳化物链式分布被打破,分布更加均匀弥散,表面残余应力值约为-479.3 MPa,其疲劳寿命提高至3.448×106,为时效试样的2.4倍;经过800 ℃保温120 min处理,试样表面残余应力为-324.2 MPa,下降约32%,说明该强化工艺处理后的试样具有较好的热稳定性。结论 LSPwC能够有效提高时效退化GH3044合金的疲劳性能。     

2A97铝锂合金的疲劳裂纹萌生及早期扩展行为(英文)

研究2A97铝锂合金的疲劳裂纹萌生及早期扩展行为。在室温条件下,采用光滑试样进行疲劳测试,其中最大应力为恒定值,应力比R为0.1,频率f为40 Hz。利用金相显微镜、透射电镜、扫描电镜及电子背散射衍射等手段对合金的微观组织进行分析,研究合金的疲劳裂纹萌生及早期扩展行为与其微观组织的关系。结果表明:2A97合金的疲劳裂纹主要萌生于试样表面的杂质相和粗大第二相处;其疲劳裂纹的早期扩展行为主要受晶粒结构与位错或滑移带共同作用的影响。当相邻晶粒的错配度接近于其晶内的最优滑移面的位向差时,大角度晶界强烈阻碍滑移带的运动,从而导致裂纹分叉和偏折。     

EFFECTS OF B~+ IMPLANTATION ON MECHANICAL PROPERTIES AND MICROSTRUCTURE OF POLYCRYSTALLINE Ni

50 keV B~+ ions was implanted to polycrvstalline with 50 keV B~+ to a dose o/ 3x10~17 ions/cm~2 at room temperature.The specimens with and without B~+implantation weretested in micro-hardness and load or unload tensile fatigue under stress-controlled eondition.The surface layer structure was observed with IMA,SEM and TEM before and afterimplantation and/or fatigue.The B~+ implanted surface region consists of amorphousNi-B phase,Ni_3B and Ni_4B_3 second phases,and damage structure.The correspondingmeasurements indicate that both surface micro-hardness and endurance limit of the specimenshave increased after implantation.Compared with unimplanted specimens under the same fa-tigue condition,all implanted specimens show the smallest overall fatigue danage.The cyclicloading at room temperature can lead to migration of implanted B~+ out surface layer andreerystallization of amorphous Ni-B phase,Possible strengthening mechanisms.for these ex-perimental results were discussed.     

IMPROVEMENT IN FATIGUE LIFETIME OF Ti-6Al-4V ALLOY BY CARBON IMPLANTATION

Carbon ions with a dose of 3×10~(17) ions/cm~2 was implanted into Ti-6Al-4V alloy at anenergy of 80 keV.A 28% increase in edurance limit was found with implantation understress-controlled fatigue tests(R=O).The surface microstructure changes induced by ionimplantation were identified using transmission electron microscopy(TEM).The feature ofthe fracture surface were observed on scanning electron microscope(SEM).The distributionprofile of the implanted ions was measured by secondary ion mass spectroscopy(SIMS).Theimplanted surface layers contain a high density of irradiation defects and fine TiCprecipitates.Subsurface crack origins were found in specimens either with or withoutimplantation.The implanted species diffuse into matrix metal under the action of cyclic load-ing.A possible reason and mechanism for improving fatigue lifetime are also discussed.     

贫铀表面碳氧离子注/渗及其抗蚀性能研究

利用离子注/渗方法,将CO2气体离解后,在不同能量、束流、温度下注入贫铀表面,利用SEM、XPS和X如等技术分析了改性层厚度、表面元素化学态以及表面改性层的相结构.用室温贮存实验和电化学方法对注入样品的腐蚀性能进行了考核.结果表明,在高能量、小束流下离子注入得到的改性层薄;在低能量、大束流下离子注入得到的改性层厚,注入样品表面是以大量UO2和少量石墨碳的形式存在.碳离子注入能量存在一极限值,当能量较小时,可导致碳无法注入样品内部.腐蚀实验考核表明,贫铀表面注入C、0离子后,在表面形成单一的UO2氧化膜,使其抗腐蚀性能增强.     

Thermal fatigue of hot working steel after hybrid surface treatment

Abstract

The application of surface treatment methods like ion nitriding, physical vapour deposition (PVD) coatings and their combination in duplex treatments effectively reduces the occurrence of oxidation, corrosion, erosion and wear processes. However, it is still uncertain whether nitriding and duplex treatment have any real effect on the decrease in the nucleation and growth of thermal fatigue cracks on the surface. This paper presents the results of thermal fatigue investigations of a nitrided layer and different composite layers ‘nitrided layer/PVD coating’ (TiN, CrN and TiAlN) obtained on the EN X40CrMoV5·1 hot working steel. The ion nitrided only and three different duplex treated substrates were compared, based on the intensity of the thermal fatigue cracks observed after testing. The nitrided layer and composite layers investigated were obtained with the use of the hybrid surface treatment technology consisting of ion nitriding followed by arc evaporation coating deposition. Apparatus based on high frequency induction heating and water spray cooling was used for thermal fatigue tests under the following conditions: maximum temperature 600°C, minimum temperature 80°C and two different rates of thermal cycling: 500 and 1000. The thermal fatigue intensities of the nitrided layer and the three different composite layers were measured according to the surface crack density and crack length (i.e. penetration into the testpiece) after different numbers of thermal cycles. Finally, based on the results obtained, the influence of different PVD coatings in the composite layer on the increase in thermal fatigue resistance of hot working steel was discussed.     

低温离子氮碳共渗温度对AerMet100钢摩擦学性能的影响

研究了不同温度对AerMet100钢渗氮层和氮碳共渗层的显微组织、表面硬度、渗层截面硬度梯度以及耐磨性的影响,并考察了渗层的磨损机理。结果表明,氮碳共渗层相较于渗氮层表面生成的化合物更加细小,表面更加平整光滑;离子渗氮、离子氮碳共渗处理都可显著提高AerMet100钢的表面硬度;随着温度的增加,共渗层厚度也明显增加;氮碳共渗层比渗氮层具有更低的摩擦因数,在共渗温度为480 ℃时氮碳共渗试样具有最低摩擦因数和磨损率,表现出最佳的耐磨性。渗氮层的磨损机理为氧化磨损和表面疲劳磨损,氮碳共渗层的磨损机理为氧化磨损、磨粒磨损以及表面疲劳磨损。     

Physical Simulation of the Random Failure of Implanted Braided NiTi Stents

A problem of random clinical failures of the braided esophageal NiTi stents has been addressed by performing physical simulation experiments on helical NiTi springs loaded in cyclic tension in air, water, and simulated biological fluid. Strains and stresses involved in spring deformation were analyzed through simulation by FEM implemented SMA model. It was found that the fatigue life of NiTi springs is significantly lower in fluids than in the air pointing toward the corrosion fatigue mechanism. There is, however, a fatigue limit roughly corresponding to the onset of martensitic transformation in the wire, which is not common for corrosion fatigue. It is proposed that surface TiO₂ oxide cracking plays major role in that. Once the oxide layer on the NiTi wire surface fractures, typically during the first mechanical cycle, cracks in the oxide layer periodically open and close during subsequent mechanical cycling. This leads to the localization of mechanical and corrosion attacks under the oxide cracked regions. Microcracks within the surface oxide layer crossing over into the NiTi matrix were indeed revealed by scanning electron microscopy of FIB sections of fatigued wires. A corrosion assisted mechanism for fatigue crack nucleation at the interface between the surface oxide and NiTi matrix is proposed based on the available evidence. The approach opens a space for a better assessment of the corrosion fatigue performance of superelastic NiTi and ultimately for estimation of the lifetime of implanted braided NiTi stents.     

The effect of surface modification on fretting fatigue in Ti Alloy turbine components

Severe fretting damage has been observed on the pressure surfaces of fan and compressor blade dovetails/disks in an aerospace gas turbine engine. A study has been carried out to evaluate the effect of an ion implantation technique in combination with the presently used surface treatments, such as shot peening and coating, on the fretting fatigue life of titanium alloy gas turbine engine components. The results from fretting fatigue tests, residual stress measurements, and nanoindentation tests were used to quantitatively evaluate the effect of various surface treatments on the fretting fatigue life of the fan blade and disk materials. Results from microstructural characterization and analyses of elemental and phase distributions within the implanted region are used to understand the effect of ion implantation on the surface properties of the alloys. Finally, an attempt has been made to evaluate the potential for improving the fretting fatigue life of the engine components using various surface modification techniques.     

高能离子注渗WC的实用效果及耐磨性分析

采用高能离子注渗技术向钢铁零部件表层注渗碳化钨(WC)，碳化钨含量高的富集层厚度0．35mm，碳化钨注渗层总厚度1．2mm。对3种工业产品进行实车对比试验，注渗碳化物的零件的相对耐磨性分别为3．6、3．9、6．25。对离子注渗碳化钨材料的耐磨机理进行分析。