复合细化超细晶工业纯钛高周疲劳性能

室温下,超细晶工业纯钛(UFG CP Ti)光滑试样在加载频率f=25 Hz、应力比R=–1的条件下进行高周应力疲劳测试,拟合超细晶工业纯钛应力幅σ_a与疲劳断裂循环周次Nf之间的关系曲线,并对疲劳断口形貌进行观察分析。结果表明:200℃退火60 min超细晶工业纯钛的疲劳极限值σ-1为376.5 MPa,比未退火超细晶工业纯钛的疲劳极限值提高56.5 MPa。疲劳裂纹源萌生于超细晶工业纯钛的表面,200℃退火60 min超细晶工业纯钛的疲劳辉纹间距较小,疲劳裂纹不易扩展,室温疲劳性能优良。     

复合细化超细晶工业纯钛高周疲劳性能研究

室温下,超细晶工业纯钛光滑试样在加载频率f=25 Hz、应力比R=-1的条件下进行高周应力疲劳测试,拟合超细晶工业纯钛应力幅σ_a与疲劳断裂循环周次N_f之间的关系曲线,并对疲劳断口形貌进行观察分析。结果表明：200 ℃退火60 min超细晶工业纯钛的疲劳极限值σ_-1为376.5 MP,比未退火超细晶工业纯钛的疲劳极限值提高56.5 MPa。疲劳裂纹源萌生于超细晶工业纯钛的表面, 200 ℃退火60 min超细晶工业纯钛的疲劳辉纹间距较小,疲劳裂纹不易扩展,室温疲劳性能优良。     

ECAP+旋锻变形制备超细晶纯锆的高周疲劳行为

室温采用等通道变形和旋锻复合工艺制备超细晶工业纯锆。对比研究了超细晶和粗晶工业纯锆拉伸和疲劳性能,并运用SEM对疲劳断口形貌进行观察和分析。结果表明：超细晶工业纯锆的室温抗拉强度明显大于粗晶工业纯锆,延伸率有一定程度地降低。超细晶工业纯锆疲劳性能优于粗晶工业纯锆,其应力幅(σa)与疲劳寿命(Nf)满足σa=750Nf-0.06,疲劳极限σ-1为285 MPa,较粗晶工业纯锆提高了70%。断口分析显示,疲劳裂纹萌生于超细晶工业纯锆的表面,疲劳裂纹扩展区辉纹间距较粗晶工业纯锆细小,疲劳裂纹扩展更为缓慢。     

循环载荷幅值对7075-T7451铝合金疲劳裂纹扩展行为的影响

在不同幅值循环载荷条件下对7075-T7451铝合金紧凑拉伸(CT)试样进行拉伸疲劳试验,对其疲劳裂纹扩展速率和应力强度因子幅值ΔK进行了研究,并用扫描电子显微镜观测试样的断口形貌。结果表明：随着循环载荷幅值的增大,试样的疲劳寿命缩短,裂纹的扩展速率增大;试样宏观断口形貌的裂纹稳态扩展区域减小,而瞬时断裂区域增大。稳态扩展区主要以疲劳条带扩展机制为主,且疲劳条带间距随循环载荷幅值的增大而增大;瞬断区的断口形貌以韧窝断裂为主,韧窝尺寸随循环载荷幅值的增大而减小。     

AZ31镁合金在高周疲劳过程中微观组织和孪晶演变特征

利用扫描电子显微镜（SEM）和电子背散射衍射（EBSD）技术研究了室温条件下AZ31镁合金在不同加载频率（3和30 Hz）和不同应力幅值（90,95,100,105,110 MPa）疲劳变形后的组织演变规律及断口形貌特征。结果表明：随着加载应力增加,基体内残余孪晶数量增加,残余孪晶主要以拉伸孪晶形式存在。随着应力幅值的增加晶粒逐渐细化,这是由于在循环过程中,拉伸孪晶演变诱导晶粒细化。随着应力幅值的增加,织构强度显著减弱,这与试样疲劳后的再结晶机制有关。通过对试样疲劳断口的分析,发现孪晶片层处容易引起裂纹萌生,随着应力的增加,试样中裂纹扩展区面积逐渐减小,在疲劳裂纹扩展区观察到明显的疲劳辉纹。最终断裂区表面粗糙,主要存在韧窝、撕裂脊以及二次裂纹等形貌。在最终断裂区可观察到韧窝,韧窝尺寸随着循环应力的增加,在较高加载频率下,韧窝的尺寸与数量均减小。     

CL60钢拉扭微动疲劳行为及断裂研究

在改进的微动试验装置上,实现了拉扭微动的复合.比较了不同应力幅值对CL60钢拉扭复合微动疲劳寿命的影响,利用扫描电镜分析了微动疲劳裂纹的萌生和扩展机制.结果表明:随着循环应力幅升高,拉扭微动疲劳寿命降低;在各个应力幅值下,试样总体上显示出循环软化的特征.疲劳裂纹萌生在微动区和未微动区的交界处,主裂纹聚合附近的一些微裂纹最后形成一条宏观裂纹扩展,导致试样断裂.     

316L奥氏体不锈钢非对称载荷下的疲劳与循环塑性行为

对316L奥氏体不锈钢非对称拉-拉疲劳载荷作用下的疲劳和循环塑性行为进行研究。通过疲劳寿命、循环应变幅、平均应变、平均应变率和失效应变的差异划分高、低应力区:在高应力区,平均应变、平均应变率和失效应变大,存在显著的循环塑性变形,疲劳寿命短;在低应力区,循环塑性变形累积有限,疲劳寿命显著增加。通过失效区域的显微组织观察和断口分析发现:在高应力区断口附近产生了大量的孔洞,断口以韧窝为主要特征;在低应力区存在疲劳裂纹,其扩展方向垂直于加载方向,断口由起裂点、疲劳裂纹扩展区、过渡区和快速断裂区组成。316L奥氏体不锈钢高应力区为循环塑性变形主导区,失效形式为循环塑性累积产生的韧性失效;低应力区为疲劳主导区,失效形式为疲劳裂纹扩展失效。     

钛合金自冲铆接头微动磨损机理及疲劳性能

对钛合金同种TA1-TA1（TT）及异种TA1-Al5052（TA）,TA1-H62（TH）自冲铆接头进行疲劳试验,用扫描电子显微镜对断口及微动区进行观测研究其微动磨损机理,并研究下板强度对接头疲劳寿命和失效形式的影响.结果表明,断口裂纹萌生区即为微动磨损区.微动磨损导致微动区亚表面产生微裂纹并逐步扩展为宏观疲劳裂纹导致接头最终失效;微动磨屑在微动磨损过程中主要起减轻磨损作用.总体上TT接头具有最优疲劳性能,疲劳载荷较高时TA接头疲劳性能优异,疲劳载荷较低时TH接头疲劳性能优异.两板强度相当且疲劳载荷较高时失效形式主要为铆钉断裂,疲劳载荷较低时失效形式主要为下板断裂;而下板强度与上板强度相差较大时,疲劳失效形式为下板断裂.     

工业纯钛的室温低周疲劳行为

采用应变控制研究了工业纯钛的室温低周疲劳行为,对循环应力-应变行为和低周疲劳寿命数据进行了分析,得到了低周疲劳的相关参数;并对疲劳组织和疲劳断口进行观察与分析。结果表明:当总应变幅为0. 5%和0. 6%时,工业纯钛在疲劳变形前期表现为循环硬化,后期发生轻微的循环软化;当总应变幅大于0. 6%时,工业纯钛在疲劳变形过程中均呈现循环硬化现象。由显微组织观察可知,在低应变幅下,位错滑移是工业纯钛主要的疲劳变形机理,孪生变形在局部高应力集中区被激活;在高应变幅下,微观变形机制以孪生为主导,伴随着滑移。疲劳断口表明工业纯钛发生多源疲劳失效,在裂纹扩展区还会呈现二次裂纹,疲劳断裂为混合型断裂。     

应力比对TC4-DT钛合金疲劳裂纹扩展速率的影响

对TC4-DT钛合金在不同应力比下的疲劳裂纹扩展行为进行了研究,绘制出疲劳裂纹扩展速率和应力强度因子幅值ΔK之间的关系曲线,用SEM对断口形貌进行了观测。实验结果表明,随着应力比增加,裂纹扩展速率增加;应力比降低,da/dN曲线向高ΔK方向移动。预裂区主要是以微区解理断裂机制为主,稳态扩展区主要是以疲劳条带扩展机制为主,同时也存在微区解理断裂机制,快速扩展区的断口形貌呈韧窝型静载断裂特征。     

Effect of nitrogen ion implantation dose on torsional fretting wear behavior of titanium and its alloy

Various doses of nitrogen ions were implanted into the surface of pure titanium, Ti6Al7Nb and Ti6Al4V, by plasma immersion ion implantation. Torsional fretting wear tests involving flat specimens of no-treated and treated titanium, as well as its alloys, against a ZrO₂ ball contact were performed on a torsional fretting wear test rig using a simulated physiological medium of serum solution. The treated surfaces were characterized, and the effect of implantation dose on torsional fretting behavior was discussed in detail. The results showed that the torsional fretting running and damage behavior of titanium and its alloys were strongly dependent on the dose of the implanted nitrogen ions and the angular displacement amplitude. The torsional fretting running boundary moved to smaller angular displacement amplitude, and the central light damage zone decreased, as the ion dose increased. The wear mechanisms of titanium and its alloys were oxidative wear, abrasive wear and delamination, with abrasive wear as the most common mechanism of the ion implantation layers.     

TC4合金在不同环境介质中微动磨损行为研究

采用SRV-IV微动磨损试验台,研究TC4钛合金在空气和纯水介质中不同位移幅值下的微动磨损行为及其在模拟海水中的微动腐蚀特性,利用扫描电子显微镜和激光共聚焦显微镜分别对磨痕表面形貌、磨损体积及磨痕轮廓进行表征,分析了钛合金在不同环境介质中的微动磨损机制。结果表明:摩擦系数随位移幅值的增大呈现出先增大后减小的趋势,磨损体积随位移幅值的增大而增大;干摩擦条件下,摩擦系数较高且波动剧烈,磨损体积较小,磨损机制主要为磨粒磨损、粘着磨损并伴有氧化磨损;与干摩擦相比,水介质中的摩擦系数较低,磨损体积显著增大,且模拟海水中的摩擦系数更低更稳定,磨损轮廓更深,说明腐蚀与磨损之间存在"正"交互作用;TC4合金在纯水介质中的微动磨损机制主要为疲劳磨损和磨粒磨损,而在模拟海水中的微动磨损机制主要为磨粒磨损和腐蚀磨损。     

Effects of temperature, slip amplitude, contact pressure on fretting fatigue behavior of Ti811 alloys at elevated temperatures

Effects of the temperature,slip amplitude,and contact pressure on fretting fatigue(FF) behavior of the Ti811 titanium alloy were investigated using a high frequency fatigue machine and a home-made high temperature apparatus.The fretting fatigue failure mechanism was studied by observing the fretting surface morphology features.The results show that the sensitivity to fretting fatigue is high at both 350 and 500 °C.The higher the temperature,the more sensitive to the fretting fatigue failure is.Creep is an i...     

TC4钛合金的微动疲劳行为研究

研究了TC4钛合金在柱面-平面接触条件下的微动疲劳行为.通过观察微动区的磨损特征和截面形貌,分析了微动疲劳损伤机制,探讨了磨屑的形成与演变过程及其对微动疲劳行为的影响,考察了摩擦系数随时间的变化.结果表明,TC4钛合金微动区的损伤机制以粘着磨损、磨粒磨损和接触疲劳为主,并伴有氧化磨损.磨屑是基体材料脱落、破碎、氧化形成的,磨屑中的硬质氧化物颗粒促进了合金表面的磨粒磨损,加速了疲劳失效.     

Fretting fatigue studies of titanium nitride-coated biomedical titanium alloys

Fretting fatigue is an adhesive wear mechanism caused by repetitive tangential micro-oscillation between two contacting materials pressed together under cyclic load. Bioimplants, such as hip joints and bone plates, are prone to undergo fretting fatigue failures during their service within the body. This article presents the fretting fatigue damage characterization of physical vapor deposition (PVD) TiN-coated biomedical titanium alloys (Ti-6Al-4V and Ti-6Al-7Nb) subjected to cyclic loads. The PVD TiN layer delayed the damage because of superior tribological properties compared with uncoated alloys. Delamination and abrasive wear damage of TiN at contact caused failure of the alloy. Friction coefficient curves of the PVD TiN-coated pair showed an irregular pattern caused by the influence of wear particulates and Ringer fluid at the contact.     

拉-拉载荷下2195-T8铝锂合金在N2O4中的预腐蚀疲劳研究

液体导弹在长期加注贮存的状态下,弹体与贮箱结构常因腐蚀损伤从而导致疲劳裂纹的产生乃至断裂等问题。采用疲劳寿命测试、扫描电镜以及能谱分析等方法,研究了2195-T8铝锂合金在N₂O₄中预腐蚀180d后的疲劳裂纹萌生、扩展和断裂机制,并与未腐蚀试样进行对比。结果表明：2种环境下试样的疲劳极限为145、118MPa,循环应力降低比值约为18.62%;试样在预腐蚀的过程中,由于形成“闭塞区”,同时与富铜相粒子形成原电池,进一步加速腐蚀历程,形成多源裂纹萌生的特征,且更易从非金属夹杂区域起裂;受到晶粒间的位错、堆积等因素的影响,发现了垂直于疲劳辉纹、穿越大晶粒及途经小角度晶界的二次裂纹;2种环境中的疲劳瞬断区的断口形貌呈现出典型的沿晶韧窝和韧性断裂的特征。     

纯钛和钛合金在人工唾液中的复合微动磨损行为(英文)

在改进后的液压伺服双向微动磨损试验机上实现双向微动。在人工唾液环境中,对TA2纯钛和Ti6Al7Nb合金在6 mm/min的加载速度下以不同接触倾角(45°和60°)和不同最大外加载荷(200~400 N)条件下进行复合微动磨损实验。详细研究循环垂向力和倾斜角的影响。结合动力学分析与微观检测结果显示:磨痕和塑性变形累积呈现强烈的非对称性。在人工唾液环境中和相同实验参数下,Ti6Al7Nb合金比TA2纯钛具有更好的抗磨损性能,并随着倾斜角度的增加和外加载荷的降低,磨损相应减轻。TA2纯钛和Ti6Al7Nb合金在人工唾液环境中的复合微动磨损机制是磨粒磨损、氧化磨损和剥层。     

柴油发电机主轴承螺栓断裂分析

分析柴油机发电机主轴承紧固螺栓断裂原因,对断裂件的化学成分、力学性能和断口宏、微观形貌等进行观察和检测。结果表明:该螺栓的化学成分除Cu元素外,其余均满足设计标准;抗拉强度高出设计要求值约为18%,硬度值超出设计要求范围上限约为5%,螺栓断裂与其材质无关,但螺栓高的强度和硬度容易使微动裂纹扩展,从而发生疲劳断裂;螺栓断面存在多处疲劳裂纹源,且裂纹扩展区较大,呈现微动疲劳断裂特征,微动疲劳是引起螺栓断裂的主要原因。     

Cyclic compression behavior of a Cu–Zr–Al–Ag bulk metallic glass

The cyclic compression behavior of a Cu₄₅Zr₄₅Al₅Ag₅BMG was investigated in order to elucidate the damage initiation and growth mechanisms. The present Cu₄₅Zr₄₅Al₅Ag₅ BMG was found to have a fatigue-endurance limit of 1418 MPa and fatigue ratio of 0.77. Fracture under cyclic compression occurred in a pure shear mode. The fracture surface forms an angle of 41° with respect to the loading axis. This angle was similar to the monotonic compressive fracture angle for the present BMG. The cyclic compression fracture surface displays a morphology nearly identical to the monotonic compression fracture surface. In addition to many shear bands and cracks, areas of “chipping” were commonly found on the outside surfaces of the fatigue specimens. An attempt was made to measure crack growth rates, and two types of crack growth behavior were found. With the first type, the growth rate decreased with cycles due to the decrease in the driving force for crack propagation. With the second type, the crack growth rate increased with cycles after chipped areas developed. The fatigue deformation process for BMGs under cyclic compression was carefully studied and rationalized.