共查询到20条相似文献,搜索用时 187 毫秒
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TiC/Ti复合材料动态拉伸的裂纹形成及扩展机制 总被引:1,自引:0,他引:1
采用熔铸法制备的原位自生TiC/Ti复合材料,在SEM中静载动态拉伸,原位观察和研究了裂纹的萌生及扩展机制。结果表明,TiC颗粒表面及应力集中处最容易萌生微裂纹;在不同位置萌生的微裂纹中,处于有利位向的微裂纹不断扩展,并与周围的裂纹连接形成主裂纹;主裂纹扩展主要是通过自身扩展与周围的裂纹连接相结合的方式进行,当裂纹扩展受阻时,裂纹前方颗粒处形成新的裂纹或基体中形成塑性坑,并通过扩展相互连接;裂纹扩展到一定程度后,试样全面失稳而迅速断裂。根据试验观察与分析建立了裂纹萌生与扩展模型。 相似文献
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TWIP钢的低周疲劳断裂机制 总被引:1,自引:0,他引:1
通过采用扫描电镜及透射电镜等手段,观察并研究了TWIP钢在低周单轴循环对称拉压载荷下的疲劳断裂后的显微组织。结果表明:TWIP钢矩形试样的疲劳裂纹一般萌生于角部,从表面萌生时可能表现为多个疲劳源。在低周疲劳变形过程中,TWIP钢不但产生了形变孪晶,还产生了大量的微条带,其实质为细微孪晶片层和驻留滑移带。疲劳裂纹主要萌生于微条带对晶界和孪晶界的撞击引发的孔洞。孔洞串连接起来成为裂纹,夹杂物促进了裂纹扩展。随着裂纹的扩展,试样的承载面积不断减小,最终发生快速的韧性断裂。 相似文献
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在25 ℃下利用单轴微力疲劳试验机对96.5Sn-3Ag-0.5Cu无铅焊点进行不同驻留时间(1~20 s)和不同应变速率(0.01~0.08 mm/s)条件下的低周疲劳试验. 结果表明,在25 ℃下1~20 s的驻留时间对焊点的疲劳寿命影响不大;随着应变速率的加快,焊点的疲劳寿命逐渐降低,断裂机制逐渐由延性断裂向脆性断裂转变. 不同应变速率条件下的疲劳裂纹主要在焊点边缘钎料与金属间化合物(IMC)之间的界面处萌生,并在近IMC层的钎料内扩展. 焊点断口主要分为:裂纹扩展区和最终断裂区. 相似文献
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钢结硬质合金GJW50热疲劳开裂的探讨 总被引:1,自引:0,他引:1
对钢结硬质合金GJW50试样进行了冷热循环实验,观察了试样在热应力作用下热疲劳裂纹的萌生、扩展以及试样开裂的全过程。结果表明:热疲劳裂纹出现前,在试样的光滑缺口边缘上产生了明显的塑性变形,呈现出凹凸不平。在试样缺口顶端的凹坑内萌生首条裂纹,萌生地是小颗粒的WC粒子集聚区或大颗粒的WC"自裂纹"。萌生的首条裂纹沿着与热循环方向平行的方向扩展,最终成为主裂纹。其扩展途径主要为沿WC聚集区和钢基体相的界面扩展以及在大面积的WC粒子聚集区内扩展。主裂纹遇到钢基体相后受阻,裂纹尖端钝化、转向,寻找耗能少的区域扩展。主裂纹在扩展时形成二次裂纹,但未形成明显上的龟裂;最终,仍然是主裂纹导致试样断裂。 相似文献
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在工业电解槽上用不同的方式生产出电解Al-Si-Ti合金和电解低钛铝基合金,并以这两种合金分别制备ZL101A合金试样,在MTS810型材料试验机上测量疲劳裂纹扩展速率。采用拟合试验数据代表点的新方法处理数据,得到Paris公式中两个重要参数和疲劳裂纹扩展门槛值。对比分析表明,电解低钛铝基合金制备的ZL101A合金具有较好的抗疲劳裂纹扩展性能。微观分析说明,产生差异的原因在于电解Al-Si-Ti合金中含铁量较高。 相似文献
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通过采用不同应变幅控制,对不同变形量冷拉银铜合金进行室温低周疲劳试验.结果表明,随着应变幅的增大,滞后环面积也随之增大;随着循环周次的增加,循环应力逐渐降低,从而产生疲劳软化;加工率为38%的银铜合金循环周期大于加工率为19%的银铜合金循环周期;试样断裂后存在三个明显疲劳特征区:裂纹源、裂纹扩展区、瞬断区;银铜合金的裂纹扩展具有穿晶和沿晶两种方式. 相似文献
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TiB2/7050铝基复合材料在航空发动机等领域具有重要的应用前景。本文研究了TiB2颗粒质量分数为4%的原位自生7050铝基复合材料在T6热处理状态下的室温高周疲劳性能,利用扫描电子显微镜对复合材料的疲劳断裂机制进行分析。结果表明:在应力比R=?1、指定寿命为3×107周次时,TiB2/7050铝基复合材料的疲劳强度为211.9 MPa,高于7050铝合金的疲劳强度;疲劳裂纹萌生源主要分布在近样品表面的夹杂、大尺寸的TiB2颗粒及显微孔洞等区域;疲劳裂纹的扩展在遇到TiB2颗粒带时,疲劳条带的宽度会明显减小,即TiB2颗粒提高了复合材料的抗疲劳裂纹扩展能力,使得复合材料具有高的疲劳寿命。 相似文献
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In the present work,the effects of trace element Sr on the microstructure,tensile properties,fractography and morphology of the eutectic Si of ZL114A (Al-7Si) cast alloy were investigated.The cast ZL114A aluminum alloy was prepared using a metal mold,and then heat treated with the T6 technique.The test results of mechanical properties show that modification element Sr can improve significantly the ultimate tensile strength,elongation and hardness of the ZL114A-T6 aluminum alloy.By adding 0.04%Sr,the values of the tensile strength Rm,elongation A and hardness HB increase from 230 MPa,1% and 65 to the maximum of 305 MPa,8%,and 100,respectively.SEM analysis indicates that the near tensile fracture surface on longitudinal section of the ZL114A-T6 alloy reveals a transgranular fracture mode without Sr modification,while the tensile fracture is an intergranular fracture mode after Sr modification.The morphology of the eutectic Si phase is changed from acicular to fine fibrous. 相似文献
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Rheocast aluminum alloys, which consist of globular α-Al cells, refined grains and eutectic Si particle, were used to investigate
fatigue crack growth and wear characteristics. The Si particles were systematically varied from coarse and acicular shapes
to small and globular ones. At low ΔK fatigue crack growth rates decreased in samples consisting of acicular Si particles
of large grain size, which induced a large amount of crack closure. Large and acicular Si particles were easily cracked and
separated the particle/matrix interface, which promoted to fracture at smaller ΔK. On the other hand, small Si particles made
fatigue crack grow, even at a high ΔK region, and increased the fracture toughness of the alloy. However, in the wear test,
small eutectic Si particles were pulled out by friction force during sliding wear and the wear loss amount increased with
increase in sliding distance. 相似文献
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Zuo-Yan Ye Dao-Xin Liu Xiao-Hua Zhang Xiao-Ming Zhang Ming-Xia Lei Zhi Yang 《金属学报(英文版)》2015,28(8):1047
The S–N curves of 7A85-T7452 aluminum alloy in laboratory air and in neutral 3.5 wt% NaCl solution were obtained by axial fatigue tests. Results show that the detrimental effect of the aggressive solution was not noticeable at high-cyclic-stress regions, but the effect was significant at low-stress region. Corrosion fatigue mechanism was discussed by corrosion morphology analysis, fracture surface analysis and microstructure characterization. It was found that the corrosion fatigue crack commonly initialed at the localized intergranular corrosion site. TEM analysis showed that the microstructures of 7A85-T7452 aluminum alloy were characterized by fine and homogeneously distributed matrix precipitates, as well as continually distributed anodic grain boundary precipitates. The types of microstructures are the reason for its intergranular corrosion susceptibility. The corrosion fatigue process of 7A85 aluminum alloy in 3.5 wt% NaCl solution can be divided into four stages: the crack initiation stage, the stable growth stage with low and high growth rate and the final rupture stage. The sodium chloride solution mainly affected the crack initiation stage and the stable growth stage with low growth rate, and when the crack growth rate reached a threshold, the effect was reduced. 相似文献
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GH4169D合金电子束焊接接头显微组织和持久断裂特征 总被引:1,自引:0,他引:1
采用金相显微镜和扫描电镜分析了GH4169D合金电子束焊接接头的显微组织,利用显微硬度计测试了母材、热影响区和焊缝的显微硬度,采用体式显微镜和扫描电镜研究了焊接接头持久断裂特征.结果表明,GH4169D 母材中的主要析出相为1~20 μm 长的片层状晶界η相、30~80 nm 的颗粒状γ'相和少量的碳氮化物.热影响区中... 相似文献
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Kyu-Sik Kim Si-Young Sung Bum-Suck Han Chang-Yeol Jung Kee-Ahn Lee 《Metals and Materials International》2014,20(2):243-248
High cycle fatigue (HCF) behavior of a new heat-resistant aluminum alloy at elevated temperature was investigated. This alloy consists of an α-Al matrix, a small amount of precipitated Mg2Si, and distributed (Co, Ni)3Al4 strengthening particles. HCF tests were conducted with a stress ratio of (R)=0 and a frequency of (F)=30 Hz at 130 °C. The fatigue limit (maximum stress) of this alloy was 120 MPa at 107 cycles. This is a value superior to that of conventional heat-resistant aluminum alloys such as the A319 alloy. Furthermore, regardless of the stress conditions, the new heat-resistant Al alloy has an outstanding fatigue life at high temperatures. The results of fractography observation showed that second phases, especially (Co, Ni)3Al4 particles, were effective to the resistance of fatigue crack initiation and propagation. On the other hand, Mg2Si particles were more easily fractured by the fatigue crack. This study also clarifies the micromechanism of fatigue deformation behavior at elevated temperature related to its microstructure. 相似文献