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通过TEM、HAADF-STEM和室温拉伸实验开展Al-2.8%Cu-1.35%Li-0.3%Mn-0.11%Zr合金在人工时效和蠕变时效状态下的析出相演化规律和力学性能研究。结果表明,160 ℃时效条件下,人工时效和160 MPa应力时效过程中合金中析出相数量均随时效时间的延长而增多,相同时效时间条件下应力时效状态合金T1相数量较多,但其平均直径减小了约5~15 nm。这主要是因为外加应力增加了合金中的位错密度从而促进析出相析出。T1相在时效析出过程中并未受外加应力的影响而沿某个方向择优析出,无明显的应力位向效应,这可能与T1相具有更大的惯习平面变体上的形核与临界应力值有关。相比于人工时效,应力时效后合金的室温屈服强度和抗拉强度均增加,且在时效初期对屈服强度效果更为显著。 相似文献
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研究了固溶温度、时效温度、时效时间对Ti-6Cr-5V-5Mo-4Al-1Nb(Ti-65541)合金显微组织与力学性能的影响。结果表明,在β相变点以上固溶并时效后,合金中析出细小的次生α相,初生α相完全消失;在较低温度固溶并时效后,次生α相和初生α相同时存在。时效温度对合金强度和塑性的影响最为显著,固溶温度次之,时效时间的影响最弱。随着时效温度的升高,合金的抗拉强度和屈服强度降低,塑性提高。随着固溶温度的提高,合金的强度提高,塑性降低。随着时效时间的延长,合金强度和塑性总体呈降低趋势。在740~760℃范围内固溶处理,在540~580℃范围内时效且时效时间在4~6 h内,可获得综合性能优异的Ti-65541合金。 相似文献
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钢轨残余应力对其疲劳性能影响较大,文章采用回火试验和金相分析方法,研究了不同残余应力值对U75V热处理钢轨疲劳裂纹扩展速率的影响。通过回火试验,分析不同回火时长对钢轨残余应力的影响,得出随着回火时间的增加残余应力逐渐减小;通过对回火工艺处理后的钢轨进行金相组织检测,观察不同回火时长的钢轨金相组织,分析疲劳裂纹尖端处裂纹扩展路径,根据裂纹扩展的方式与长度来分析不同回火时长对疲劳裂纹扩展速率的影响;通过回火工艺控制,可有效降低钢轨残余应力,进而有效地降低钢轨裂纹扩展速率,提高钢轨抗疲劳性能。 相似文献
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本文研究了双相0.08C-1.45Mn-0.21Si钢在时效过程中,铁素体的时效反应及其对拉伸性能的影响。时效温度取室温至170℃,时效时间长短视时效温度高低而异。试验结果表明,时效导致铁素体中有大量细小碳化物析出。铁素体的时效反应有一定的不均匀性,碳化物多在铁素体区域内部析出,而在马氏体附近析出较少。在较高温度(70℃以上)时效时,可使不连续屈服重现,并且随着时效时间增加使小变形阶段应变硬化率降低,有利于塑性提高。钢的屈服强度因时效而增加,抗拉强度先增后减。文中针对铁素体的时效反应与拉仲性能的关系进行了相应的讨论。 相似文献
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对大规格盘条SWRH82B取样部位及各自然时效力学性能变化进行分析。对盘条进行力学性能和拉伸断口的分析研究,结果表明,随着时效时间的延长,盘条中的残余应力下降,抗拉强度、面缩率呈现上升趋势。 相似文献
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对大规格高碳钢盘条取样部位及自然时效后力学性能变化进行了分析。通过对盘条进行力学性能和拉伸断口的分析研究,结果表明随着时效时间的延长,盘条中的残余应力下降,抗拉强度、面缩率呈现上升趋势。 相似文献
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Larry A. Godlewski Xuming Su Tresa M. Pollock John E. Allison 《Metallurgical and Materials Transactions A》2013,44(10):4809-4818
Most cast aluminum-engineered components are water quenched after the solution-treatment cycle of the casting process. This rapid water quenching has the potential to induce high residual stresses in regions of the castings. Reducing the amount of residual stress can have a promising effect on the life of the component. This study was conducted to quantify how aging affects the amount of residual stress in an aluminum casting. An engineered high residual stress test sample and quenching technique has been developed, and a relaxation study has been completed. The study focused on four different temperatures: 463 K, 493 K, 513 K, and 533 K (190 °C, 220 °C, 240 °C, and 260 °C) and a range of aging times (0.3 to 336 hours). The aging data were used to verify a stress relaxation model. The results indicated that as the aging temperature increased, the amount of relaxation of the residual stress increased. 相似文献
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Laboratory Investigation on Reactivated Residual Strength 总被引:1,自引:0,他引:1
Recent research has outlined that mobilized in situ strength at the reactivation of displacements along a preexisting sliding surface may be slightly greater than laboratory residual strength. Although geotechnical literature explains this difference in various ways—for instance, strength gain due to soil aging—little work has been devoted to this topic. Bromhead ring shear tests were carried out on remolded samples of the Cormons flysch, a typical geological formation in northeastern Friuli-Venezia Giulia (Italy). The specimens came from the shallow weathered crust of the Cormons flysch, near the areas of Montona and Rosazzo. This experimental study aimed at highlighting the effect of a limited number of parameters on strength gain at the reactivation of displacements along aged sliding surfaces. The results of this research confirm that aging may cause a rising of reactivated shear strength above the residual value, depending on time of aging and vertical stress. The longest aging period—about a month—showed a 20% strength increase for the Rosazzo flysch, and a 30% increase for the Montona flysch. Reactivated strength increases according to a power law: Almost 50% develops over a short time, i.e., after 24?h of aging. In the long term, strength growth is characterized by a deviatoric creep rate gradually approaching zero. 相似文献
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本文通过对高强钢方管角部进行局部感应加热,提高其弯角区域的成形性能,降低其变形抗力,由此在不影响非变形区域组织性能的前提下,获得所需方管的截面尺寸和组织性能.在热辊压过程中,坯料在没有模具限制的方管角部外侧邻近区域发生堆积,且随着加热温度上升,角部外侧金属堆积更明显.同时,在方管内角表层出现显微裂纹恶化,裂纹以树枝状生长.热辊压成形后的残余温度会产生一个自回火过程,能够明显降低残余应力,且随着温度的升高,残余应力降低的幅度变大.当加热温度在650℃以上时,自回火对残余应力的影响大于宏观裂纹的扩展能力,起主导作用,且压扁过程中压下量超过方管对角线长度2/3时也不会产生裂纹. 相似文献
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采用全自动控制往复喷射成形工艺制备大规格7055铝合金锭坯。锭坯经热挤压和双级固溶处理后,在不同时效工艺条件下进行双时效处理,测定时效态合金的抗拉强度(σb)、屈服强度(σ0.2)、伸长率(δ)、硬度(HRB)和电导率(γ),并观察其微观组织,研究时效制度对合金组织和性能的影响,并与120℃/24 h单级时效的合金样品进行性能对比。结果表明,锭坯经120℃/24 h时效处理后获得最高强度,抗拉强度(σb)高达725 MPa,屈服强度(σ0.2)为685 MPa,伸长率(δ)10.0%,硬度为96 HRB,电导率为30%IACS;双级时效后获得较好的塑性和抗应力腐蚀能力,但强度较低,且随着二级时效温度升高和时效时间延长,合金强度下降,伸长率增加,电导率提高。通过对正交实验结果进行分析,确定最佳双级时效处理工艺为:120℃/8 h+170℃/8 h,其综合性能最佳,σb、σ0.2和δ分别达到659 MPa、630 MPa和11.7%,硬度和电导率分别为95 HRB和39%IACS。与单级时效处理相比,电导率提高30%,抗应力腐蚀性能显著改善。 相似文献
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Jingbo Yan Y Gu Hao Li Fang Yang Yong Yuan Peng Zhang Xinbao Zhao Yingying Dang Zhen Yang 《Metallurgical and Materials Transactions A》2018,49(5):1561-1570
In this study, the effects of aging temperature on the microstructure and properties of a nickel-iron (Ni-Fe)-based superalloy were investigated. On the one hand, owing to the increase in the size and particle spacing of Ni3Al (γ′) precipitate, long-term aging induced a significant drop in the alloy strength. Moreover, the increasing aging temperature from 700 °C to 750 °C further induced more than 75 MPa decline in the alloy yield strength. Furthermore, it led to a decrease in the critical stress because of dynamic recrystallization. On the other hand, the long-term aging increased the alloy’s ductility. The crack propagation along the grain boundary was inhibited, because of the decreasing grain boundary brittleness. Although the grain boundary precipitates changed from carbide to γ′ when the aging temperature increased, a distinct change in the alloy’s ductility was not observed. The transmission electron microscopy results showed that both precipitates were sheared by the grain boundary during the alloy deformation. These results confirm that aging temperature has less effect on alloy’s ductility. 相似文献