共查询到19条相似文献,搜索用时 215 毫秒
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研究了通过热处理制度调整,在合金α片层之间形成细小的条状次生α相,形成一种新型的钛合金显微组织——双片层组织.通过对比等轴组织、双态组织、片层组织和双片层组织的性能,结果表明,在合金的强度和塑性不损失的条件下,双片层组织进一步提高了裂纹在合金中的扩展阻抗,使得合金的断裂韧性得到改善,疲劳裂纹扩展速率得到降低.双片层组织... 相似文献
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研究了ZTC4钛合金应变控制的室温低周疲劳行为,对循环应力-应变和应变疲劳寿命数据进行了分析,通过双对数线性回归处理,得出了Manson-Coffin处理模型的疲劳参数。结果表明:ZTC4钛合金总应变幅在0.6%~0.8%时,材料存在轻度循环软化的现象;总应变幅为0.4%~0.5%时,循环初期表现出循环硬化的现象,而后循环软化。合金的疲劳裂纹萌生于试样表面,裂纹扩展区存在明显的疲劳条带,合金疲劳断口呈现韧性断裂特征。 相似文献
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研究了Ti-6Al-4V钛合金细晶等轴组织的应变疲劳性能及其断裂行为.实验结果表明,Ti-6Al-4V铁合金的应变疲劳的过渡疲劳寿命Nt约为560个循环周次,其疲劳行为具有非常明显的循环软化特性.在不同应变幅测试条件下,均为多源疲劳萌生模式.Ti-6Al-4V合金应变疲劳断口表面大量的二次裂纹特征说明该合金具有优异的应变疲劳性能. 相似文献
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研究了Ti-6Al-4V ELI合金板材的显微组织对疲劳裂纹扩展速率的影响.用金相显微镜对不同热处理制度下该合金α和β转变组织的变化进行了观察分析.采用MTS-810低周疲劳试验机测试合金的裂纹扩展速率.通过Origin 6.0软件对数据进行处理并绘制裂纹扩展速率(△a/△N)与应力强度因子幅△K的关系曲线.结果表明:在Pairs区范围内,疲劳裂纹扩展速率对双态组织中初生α相含量的多少不敏感,而在近门槛区和快速扩展区,裂纹扩展速率对组织比较敏感;在本实验研究的条件下,细针编织状魏氏组织的da/dN<平直状片层组织的da/dN<双态组织的da/dN. 相似文献
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针对航空发动机压气机叶片在实际工况下的超高周疲劳断裂问题,研究了三种锻造温度下TC4钛合金三点弯曲–轴向拉伸复合加载的疲劳破坏行为。试验结果表明,S-N曲线呈直线下降型和双平台型,采用985℃近锻造时疲劳性能最好。随着应力幅值降低,裂纹由表面萌生向次表面萌生转变,断口形貌呈现准解理断裂特征。表面裂纹萌生于α晶界或α-β相界,由位错滑移堆积导致;而次表面裂纹萌生于刻面,由初生α相解理导致。疲劳寿命由裂纹萌生阶段主导,且所占比例随总寿命的增加而变大。双态组织中初生α含量和尺寸均小于等轴组织,且β转变组织含量更高,从而具备更好的疲劳性能。轴向拉伸改变了试件的轴向应力分布,有利于提高裂纹萌生于次表面的概率,使裂纹起源点向内部迁移。 相似文献
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研究了p锻TC17钛合金压气机盘件的应变控制低周疲劳性能及疲劳裂纹扩展途径.结果表明,当应变量△ε/2在0.5%~2.0%范围内,应变比R=-1和循环超过10次后,材料基本上表现为轻度的循环软化.疲劳裂纹萌生于试样表面.当疲劳裂纹与片状α或晶界α之间的夹角小于45°,裂纹沿片状α或晶界α的界面扩展;否则,疲劳裂纹将以穿过片状α或晶界α的方式增长. 相似文献
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Low-cycle fatigue behavior of TC21 alloy with equiaxed α phase embedded in the β transformed matrix (EM) and full lamellar α phase (LM) was investigated. The results show that the EM microstructure possesses higher strength, ductility and longer fatigue life than those of the LM one. Dislocation structures are straight dislocation lines in both EM and LM; however, more dislocation tangles and debris were observed in the α than in the β phase. The planar slip predominates cyclic deformation in the α phase, and promotes strain concentration and crack initiation at α phase boundaries. 相似文献
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On the titanium alloy Ti‐6Al‐4V a rugged transition from equiaxed to lamellar microstructure was produced by a specific thermomechanical treatment. Equiaxed microstructures of this alloy show plasticity induced crack closure over a wide range of ΔK whereas for lamellar microstructures roughness induced crack closure is observed up to relatively high loadings. Thus by the obtained microstructural transition the observation of a change of the crack closure mode becomes feasible at constant loading ΔK. For the crack propagation from equiaxed to lamellar microstructure, i. e. from plasticity to roughness induced crack closure, the closure load corresponds always to the particular microstructure at the crack tip. In the opposite direction significant closure effects in the crack path interfere leading to an increase of the crack closure load and consequently to a reduction of the crack velocity. Hereby for constant ΔK the crack velocity becomes dependent on the crack propagation direction. 相似文献
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H Wang 《Fatigue & Fracture of Engineering Materials & Structures》1998,21(9):1077-1087
The appearance of the fatigue fracture surface and crack growth curve have been examined for a Ti–2.5Cu alloy with different microstructures (two equiaxed and two lamellar microstructures), and for TIMETAL 1100 with a lamellar microstructure. With increasing Δ K , a slope change in the crack growth curve correlates with a transition in the fracture surface appearance (induced by a fracture mode transition); this being found in each microstructure. The microstructure size that controls the fatigue fracture is found to be the grain size for equiaxed microstructures and the lamella width for lamellar microstructures. The transitional behaviour can be interpreted in terms of a monotonic plastic zone size model in microstructures having a coarse microstructure size and in terms of a cyclic plastic zone size model for microstructures having a fine microstructure size. 相似文献
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Xu‐Teng Hu Lei Zhu Rong Jiang Ying‐Dong Song Shou‐Dao Qu 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(1):339-351
In this paper, the small fatigue crack behavior of titanium alloy TC4 at different stress ratios was investigated. Single‐edge‐notch tension specimens were fatigued axially under a nominal maximum stress of 370 MPa at room temperature. Results indicate that fatigue cracks in TC4 initiate from the interface between α and β phases or within α phase. More than 90% of the total fatigue life is consumed in the small crack initiation and growth stages. The crack growth process of TC4 can be divided into three typical stages, ie, microstructurally small crack stage, physically small crack stage, and long crack stage. Although the stress ratio has a significant effect on the total fatigue life and crack initiation life at constant σmax, its effect on crack growth rate is indistinguishable at R = ?0.1, 0.1, and 0.3 when crack growth rate is plotted as a function of ?K. 相似文献
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TC18钛合金热压参数对流动应力与显微组织的影响 总被引:1,自引:0,他引:1
通过在700~950℃和应变速率0.001~50s-1条件下的热模拟实验,系统研究了TC18钛合金应变速率、变形温度对变形抗力和显微组织的影响。结果表明:提高变形温度或降低应变速率,可显著降低TC18合金变形过程中的真应力,与单相区相比,两相区变形抗力对温度的变化更为敏感。在α+β区变形时,α相和β相都参与变形,球状初生α沿形变方向略有拉长,β相沿金属流动方向形成纤维组织;β相变点以上温度变形时,β相沿金属流动方向呈纤维状分布,在950℃可以观察到再结晶的等轴β晶粒。 相似文献
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M. BENEDETTI J. HEIDEMANN J. O. PETERS G. LÜTJERING 《Fatigue & Fracture of Engineering Materials & Structures》2005,28(10):909-922
The present study focuses on the effect of microstructural gradients on the fatigue crack growth resistance of Ti‐6Al‐4V and Ti‐6242 titanium alloys. Sharp microstructural gradients from fine‐grained bimodal to coarse‐grained lamellar microstructures were obtained by heat treating only a portion of fine‐grained plates in the β single‐phase field using a high‐frequency induction coil. For fatigue crack growth from a bimodal into a lamellar microstructure, it was found that the initial crack extension past the microstructural transition within the lamellar microstructure shows the same crack growth resistance as the reference bimodal microstructure. Similarly, for fatigue crack growth from a lamellar into a bimodal microstructure, the initial crack extension past the microstructural transition within the bimodal microstructure shows same crack growth resistance as the reference lamellar microstructure. Based on detailed crack front profile investigations using optical light and scanning electron microscopy as well as heat tinting procedures, these findings can be mainly attributed to the effect of the crack front geometry. 相似文献
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The fatigue crack growth behavior under constant amplitude and under single overload of 2024 aluminum alloy in sheet and plate product form has been investigated. Constant amplitude fatigue crack growth tests showed superior crack growth resistance of the plate attributed to a pronounced roughness induced crack closure as a result of the coarse and elongated grain structure. Crack growth tests with single overload showed that the retardation effect caused by the overload is not primarily influenced by roughness crack closure at the crack path. In this case, the sheet material with lower yield strength revealed a higher retardation effect than the plate material. The observed crack growth behavior has been simulated with the LTSM-F model, which accounts for retardation of crack growth after an overload due to material strain hardening at the crack front. Dissimilar strain hardening at the crack tip due to different yield strength for the sheet and plate has been considered by means of strength gradients inside the overload plastic zone. The analytical results confirmed the observed material crack growth trends. 相似文献
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本文对魏氏组织的TC11合金进行等轴化处理.研究了等轴化处理前后TC11合金组织和性能的变化。研究结果表明等轴处理后的TC11合金得到均匀分布的等轴组织,晶粒尺寸约为9μm;相比原始的TC11合金,等轴组织TC11合金,抗拉强度可以从830MPa增加到1190MPa,屈服强度从590MPa增加到1130MPa,延伸率从1.6%增加到13.7%,断口形貌由台阶状转变为韧窝状。 相似文献
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Z.M.Song L.M.Lei B.Zhang X.Huang and G.P.Zhang Shenyang National Laboratory for Materials Science 《材料科学技术学报》2012,28(7):614-621
Fatigue cracking behavior from a notch was investigated at room temperature for Ti-6.5Al-3.5Mo-1.5Zr-0.3Si(TC11) alloys with four different microstructures obtained at different cooling rates from the β transus temperature.It was found that the alloy with lamellar structures consisting of α/β lamellae or acicular α’ martensite laths had a higher fatigue crack initiation threshold from the notch,while the bimodal structure with coarse α grain had a lower fatigue cracking resistance.The alloy with α/β lamellar structure showed a higher fatigue crack growth resistance.The length scales of the microstructures were characterized to correlate with fatigue cracking behavior.Fatigue cracking mechanism related to microstructures was discussed. 相似文献