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The effect of long-term thermal exposure on the grain boundary carbides and the tensile behavior of two kinds of Ni–Mo–Cr superalloys with different silicon contents(0 and 0.46 wt%) was investigated. Experimental results showed granular M2C carbides formed at the grain boundaries after exposure for 100 h for the non-silicon alloy. Furthermore, these fine granular M2C carbides will transform into plate-like M6C carbides as exposure time increases. For the Si-containing alloys,only the granular M6C carbides formed at the grain boundaries during the whole exposure time. The coarsening of the grain boundary carbides occurred in both alloys with increasing exposure time. In addition, the coarsening kinetics of the grain boundary carbides for the non-silicon alloy is faster than that of the standard alloy. The tensile properties of both alloys are improved after exposure for 100 h due to the formation of nano-sized grain boundary carbides. The grain boundary carbides are coarsened more seriously for non-silicon alloys than that of Si-containing alloys, resulting in a more significant decrease in the tensile strength and elongation for the former case. Silicon additions can effectively inhibit the severe coarsening of the grain boundary carbides and thus avoid the obvious deterioration of the tensile properties after a long-term thermal exposure. 相似文献
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LIRong-de LIRun-xia YULi HUZhuang-qi 《材料热处理学报》2004,25(5):113-116
The present work has investigated the effect of trace elements Cd and Sn on the microstructure and mechanical properties of Al-Si-Cu-Mg cast alloy. With the increase of Cd addition the strength of alloy rises at first and then drops. The optimal amount of Cd and Sn addition for AI-Si-Cu-Mg alloy is about 0.27% and 0.1% respectively. Due to the formation of some coarse Cd-rich phases and pure Cd particles the mechanical properties of alloy decrease when Cd amount exceeds 0.27%. When more than 0.1% Sn added, some Sn atoms form low-melting eutectic compound at grain boundary, and then cause over-burning in alloy when solution treated, which may deteriorate properties of alloy, especially ductility of alloy.On the other hand, the addition of Cd and Sn remarkably increases the peak hardness and reduces the time to reach aging peak in Al-Si-Cu-Mg alloy. The action of Cd/Sn in quaternary Al-Si-Cu-Mg alloy is effectively the same as that occur in binary Al-Cu alloy that the enhanced hardening associated with Cd/Sn addition is due to the promotion of the θ‘phase. 相似文献
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Hua-Ping Tang Qu-Dong Wang Colin Luo Chuan Lei Tian-Wen Liu Zhong-Yang Li Kui Wang Hai-Yan Jiang Wen-Jiang Ding 《金属学报(英文版)》2021,34(1):98-110
This study investigates the eff ect of solution treatment(at 470 °C for 0–48 h) on the microstructural evolution,tensile properties,and impact properties of an Al–5.0Mg–3.0Zn–1.0Cu(wt%) alloy prepared by permanent gravity casting.The results show that the as-cast microstructure consists of α-Al dendrites and a network-like pattern of T-Mg_(32)(AlZnCu) 49 phases.Most of the T-phases were dissolved within 24 h at 470 ℃;and a further prolonging of solution time resulted in a rapid growth of α-Al grains.No transformation from the T-phase to the S-Al_2CuMg phase was discovered in this alloy.Both the tensile properties and impact toughness increased quickly,reached a maximum peak value,and decreased gradually as the solution treatment proceeded.The impact toughness is more closely related to the elongation,and the relationship between impact toughness and elongation appears to obey an equation:IT = 8.43 EL-3.46.After optimal solution treatment at 470 ℃ for 24 h,this alloy exhibits excellent mechanical properties with the ultimate tensile strength,yield strength,elongation and impact toughness being 431.6 MPa,270.1 MPa,19.4% and 154.7 kJ/m~2,which are comparable to that of a wrought Al–6.0 Mg–0.7 Mn alloy(5E06,a 5 xxx aluminum alloy).Due to its excellent comprehensive combination of mechanical properties,this cast alloy has high potential for use in components which require medium strength,high ductility and high toughness. 相似文献
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Yool Byun Sangwon Lee Seong-Moon Seo Jong-taek Yeom Seung Eon Kim Namhyun Kang Jaekeun Hong 《Metals and Materials International》2018,24(6):1213-1220
The effects of Cr and Fe addition on the mechanical properties of Ti–6Al–4V alloys prepared by direct energy deposition were investigated. As the Cr and Fe concentrations were increased from 0 to 2 mass%, the tensile strength increased because of the fine-grained equiaxed prior β phase and martensite. An excellent combination of strength and ductility was obtained in these alloys. When the Cr and Fe concentrations were increased to 4 mass%, extremely fine-grained martensitic structures with poor ductility were obtained. In addition, Fe-added Ti–6Al–4V resulted in a partially melted Ti–6Al–4V powder because of the large difference between the melting temperatures of the Fe eutectic phase (Ti–33Fe) and the Ti–6Al–4V powder, which induced the formation of a thick liquid layer surrounding Ti–6Al–4V. The ductility of Fe-added Ti–6Al–4V was thus poorer than that of Cr-added Ti–6Al–4V. 相似文献
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通过在830℃空气中保温1 h后水冷的热处理工艺,在Ti-10V-2Fe-3Al(Ti1023)钛合金表面形成厚度约为82μm的α富氧复合层。研究了α复合层内显微组织形貌、硬度及元素分布特点及复合α层后对Ti1023合金组织和性能影响。结果表明:α复合层从边缘到基体内部硬度值并非一直减小,而是呈现高-低-高-低-趋于稳定的变化规律。研究表明硬度变化规律与合金元素(尤其V、Fe)及组织形态分布相关。Ti1023合金试样复合α层后表面硬度增加了45%,而屈服强度和抗拉强度下降5%。在拉伸变形过程中,复合α层后试样首先会在垂直于拉伸应力方向的外表面产生裂纹,之后裂纹扩展穿过α层到基体内部直至试样断裂,试样拉伸断口呈现心部韧性断裂和边部脆性断裂特征。拉伸过程中试样内部存在应力诱发β相向α″相的组织转变。 相似文献
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Chenlin Li Ye Pan Tao Lu Lijun Jing Jinhong Pi 《Metals and Materials International》2018,24(5):1133-1142
The effects of Ti and La additions on the microstructures and mechanical properties of B-refined and Sr-modified Al–11Si alloys were investigated in the present work. The interactions among Ti, La, B and Sr elements were discussed employing microstructure observation, thermal analysis and tensile test, respectively. It was found that the addition of 0.05 wt% B induces a transformation of eutectic Si from finely fibrous to coarsely plate-like morphology in the Al–11Si alloy with 0.02 wt%Sr modification, owing to the poisoning of IIT mechanism, and the eutectic Si grows only with TPRE mechanism. Both titanium and lanthanum can neutralize the co-poisoning effect between Sr and B in the Al–11Si alloy, but the neutralizing effect of La is dependent on the addition sequence. The combinative addition of La and B elements promotes the effective refinement of α-Al grains, but an inhomogeneous modification of eutectic Si phases is also observed, leading to a slightly decrease in the elongation. 相似文献
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Guohua Wu Chunchang Shi Liang Zhang Wencai Liu Antao Chen Wenjiang Ding 《金属学报(英文版)》2020,33(9):1243-1251
The effect of different ageing processes on microstructure and mechanical properties of cast Al–3 Li–2 Cu–0.2 Zr alloy was investigated using transmission electron microscopy and tensile tests. The results showed that the mean size of δ′-Al_3 Li particles and the number density of Cu-rich precipitates both increased with increasing ageing temperature from 150 to 190 °C for 24 h, resulting in increasingly high strength. In contrast, the ductility deteriorated with the increase in ageing temperature as a result of the intensified planar slip. The duplex low-to-high ageing treatment(120 °C for 6 h followed by 160 °C for 24 h) was shown to be beneficial to the ductility compared with the corresponding single-stage ageing treatment(160 °C for 24 h). The reduced slip length induced by the precipitation of θ′-Al 2 Cu phases was found to be mainly responsible for this ductility improvement. 相似文献
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Kun Su Kun-kun Deng Fang-jun Xu Kai-bo Nie Li Zhang Xiao Zhang Wei-jian Li 《金属学报(英文版)》2015,28(8):1015
In this work, the Mg–5Al–2Ca alloy was extruded at 573, 623 and 673 K, with a ratio of 16:1 and a constant speed of 3 mm/s. Results demonstrate that the Al2Ca particle is formed in Mg–5Al–2Ca alloy. The size, amount and distribution of Al2Ca particles are influenced evidently by extrusion temperature. Unlike previous reports, the intensity of basal texture increases with increasing extrusion temperature, and the reasons are analyzed and given. Even though the average grain size increases as the extrusion temperature increased from 573 to 623 K, the YS, UTS and elongation of asextruded Mg–5Al–2Ca alloy are almost kept the same at 573 and 623 K. The reason is speculated as the balance of grain size, Al2Ca phase and texture at the two temperatures. The work hardening rate depends on extrusion temperature, and the largest θ value of Mg–5Al–2Ca alloy is obtained when the extrusion was performed at 623 K. 相似文献
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《Intermetallics》2000,8(8):869-875
The stability region of the B2 phase at 1000°C in the Ti-rich part of the Ti–Al–Cr and Ti–Al–Fe ternary systems are investigated by energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) using two-phase alloys and diffusion couples. It is established that the critical boundaries of the A2/B2 continuous ordering transition are functions of both the Al and Fe or Cr contents, and the phase equilibria between the α2 and the β and between the β and FeTi (B2) phases are strongly affected by the A2/B2 order–disorder transition. By extrapolating these ternary data to the Ti–Al binary and using the Bragg–Williams–Gorsky approximation a metastable A2/B2 ordering boundary is postulated to exist at 1000°C in the vicinity of 23.5 at%Al in the Ti–Al binary system. 相似文献
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1 INTRODUCTIONγTiAl/α2Ti3AltwophaseintermetallicsorTiAlalloyhasrecentlyreceivedincreasingattentionbecauseofitspotentialasastructuralmaterialforhightemperatureapplications,whicharisesfromitselevatedhightemperaturestrength,lowdensityandgoodoxidatio… 相似文献
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对合金Ti-44Al-4Nb-4Hf-1B在700℃大气气氛中开展了长达10 000 h的热暴露处理,系统地探索和分析含Nb-Hf的TiAl合金的高温热稳定性,采用透射电镜和扫描电镜观察合金的显微组织变化并测试相应的力学性能.研究发现:长期大气高温热暴露导致合金中α2+γ层片晶团内的a2层片发生了一定程度的α2→γ相变:部分α2层片转变成为细小的γ层片,到10 000 h时,α2层片的原始厚度减少了约一半.长期大气高温热暴露也导致合金中α2+γ层片条束上发生了α2+γ→B2(ω)相变:条束上部分α2+γ消失,代之以微米及亚微米尺度的B2(ω)块状相.在10 000 h时,其面积分数达到8.4%,随着高温热暴露的逐渐进行,合金的室温塑性伸长率逐渐降低.在10 000h时,合金的塑性约为热暴露前的2/3,表明在复合含Nb+Hf的TiAl合金中,热暴露所导致的“释氧脆化”和“B2+ω生成脆化”的影响有限.复合含Nb+Hf的TiAl合金具有优于单纯含Nb的TiAl合金的高温热稳定性.长期高温热暴露对合金的断裂强度和条件屈服强度没有明显的有害影响.在10 000 h时,其条件屈服强度总体上仍保持在600MPa级别,而合金的室温疲劳极限还有所提高. 相似文献
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真空感应熔炼Nb-16Si-22Ti-2Hf-2Cr-2Al合金的组织和性能 总被引:1,自引:0,他引:1
The melt with a nominal composition of Nb-16Si-22Ti-2Hf-2Cr-2Al was poured in a ceramic shell mould with a temperature gradient of about 4℃/mm, and the ingot with the dimension of 60 mm×170 mm was obtained. The relationship between the microstructure and mechanical properties was measured, and the effects of the silicide on fracture toughness at ambient temperature and compression strength at high temperature were analyzed. It is revealed that the microstructure of the alloy consists of Nb solid solution and silicides, and the cooling rate can obviously change primary phase and constituent phases. The volume fraction of Nb3Si formed at rapid cooling rate is significantly increased, and Nb5Si3 phase is formed with decreasing in cooling rate, whereas the volume fraction of the eutectic colonies and NbSS dendrites increase evidently, especially the second dendrite arm. Fine and uniform eutectic colonies are contributed to the ambient tensile strength, while the coarse primary Nb3Si decreases the tensile strength but improves the compression strength of the alloy. When the microstructure is mainly composed of fine (NbSS+Nb5Si3) eutectic colonies, the tensile strength and elongation of the alloy reach 449 MPa and 0.3%, respectively. When lath-like Nb3Si phase has 80 $\mu$m in width and 50% in volume fraction as well as its long axis is parallel to compression direction, the compression strength of the alloy at 1250℃ is about 650 MPa. 相似文献
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ZHANG Jinghua TANG Yajun YU Yang ZHANG Jishan HU Zhuangqi Institute of Metal Research Academia Sinica Shenyang China 《金属学报(英文版)》1989,2(1):35-41
The thermal fatigue behaviour and microstructure in a directionally solidified DZ38G alloyhas been investigated.It was found that DZ28G alloy has larger thermal fatigue resistancethan that of original M38G alloy because of the elimination of the transverse grain boundariesand the small elastic modulus.Detailed observation shows that microcrack is initiated at thegrain boundaries or the phase interfaces and propagates along interdendrites,grain boundariesand,sometimes,along the defined crystallographic direction and that the amount of carbidesat grain boundaries increases and the morphology of phase becomes irregular after thermal fa-tigue test. Both γ' denudation and recrystallization have been observed on both sides of thecrack. 相似文献