Subjects: Geosciences >> Geography submitted time 2024-04-29 Cooperative journals: 《干旱区研究》
Abstract： This study is based on the integrated valuation of ecosystem services and tradeoffs model, which quantifies the supply and demand of ecosystem services. This model uses root-mean-square deviation to quantify the intensity of tradeoffs in ecosystem services and analyze the driving factors of tradeoff intensity using a structural equation model. Results show that from 2000 to 2020, the tradeoff intensity of water yield (WY) and soil conservation (SC), as well as WY and carbon sequestration (CS) supply, increased. However, the demand coordination intensity of WY and SC services, as well as WY and CS services, decreased. Except for WY services, which had a supply–demand tradeoff intensity greater than 0 in 2020, the supply–demand tradeoff intensity for WY, SC, and CS services was less than zero from 2000 to 2020. The tradeoff and synergy of ecosystem services are primarily influenced by natural factors. Evapotranspiration has a positive effect on the tradeoff between water production and SC services, as well as on the tradeoff between supply and demand for water production and CS services. However, it has a restraining effect on the tradeoff between supply and demand for water production services. The proportion of grassland area has a restraining effect on the tradeoff between water production and CS services, as well as on the synergy between water production and SC service demands. In addition, it has a promoting effect on the supply–demand tradeoff of CS services. Precipitation has a restraining effect on the synergy between water production and CS service demands, as well as on the tradeoff between supply and demand for SC services. However, it has a promoting effect on the tradeoff between supply and demand for water production services. Socioeconomic factors have a secondary effect on the tradeoff and synergy of ecosystem services. Population density has a promoting effect on the synergy between water production and soil conservation service demands, whereas it has a restraining effect on the tradeoff between supply and demand for water production services and CS services. Therefore, when developing comprehensive management decisions for river basins, the spatial characteristics and driving factors that contribute to the tradeoff and synergy of ecosystem services must be considered.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The effect of Hf on the as- cast, heat- treated microstructures and stress rupture properties under 1100 ℃ and 140 MPa was investigated in four second generation Ni-based single crystal superalloys DD11 with various levels of Hf (0~0.80%, mass fraction) additions. The results indicate that increasing Hf addition resulted in decreasing the solidus and liquidus temperatures, while it enhanced the volume fraction of (g +g') eutectic and MC carbide as well as solidification segregation. The number of micropores reduced significantly and the volume fraction of residual (g +g') eutectic and MC carbide increased after heat treatment as Hf content increased. Compared to the Hf-free alloy, the stress rupture life was observed to increase in the alloys with 0.40%Hf, but dropped in the alloy containing 0.80%Hf. Hf addition increased the elemental partitioning ratio of Re, Mo, Cr, resulting in increasing g /g' misfit and decreasing the spacing of g /g' interfacial dislocation networks. The solution strengthing effect was also improved with the enhanced concentration of Re, Mo and Cr in g phase in Hf-modified alloys. However, when the Hf content was 0.80% in DD11 alloy, the stress rupture properties was decreased obviously due to high volume fraction of residual (g +g') eutectic and MC carbide in heat-treated microstructures.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The directionally solidificated (DS) Co-based superalloys are widely used in aircraft turbine vanes due to the good stress-rupture parameters and excellent hot corrosion resistance. The cyclic change of temperatures and complex stress state thermal fatigue (TF) cracks happen frequently in vanes during service. However, most of the work are conducted in Ni- based superalloys and there is rare report concerning the TF behavior of DS Cobased superalloys. Furthermore, due to the residual strain accumulated during processing, shot peening, grinding and recrystallization (RX) frequently occur when the DS components are exposed to high temperatures. It is believed that RX may change the microstructure, especially adding more grain boundaries to DS alloys, and result in the reduction of the mechanical properties of DS superalloys. Therefore, in this work, V-notch plate specimens with notch direction perpendicular and parallel to the DS orientation are machined from the DS plate. Local RX grains are prepared (local indented and then heat treated) in the notch areas of some samples. TF test is conducted between 1000 ℃ to room temperature. The effect of DS orientation and RX on TF properties of a DS Co-based superalloy is investigated. The results indicate that the cracks propagate along the interdendritic regions in the samples with notches parallel to the DS direction, which exhibites lower TF properties than samples with notches vertical to the DS direction. TF cracks initiate and propagate along RX boundaries in samples containing RX grains. Precipitation of M23C6 carbides is found along the RX boundaries during TF tests. Due to the oxidation at the tip of crack, M23C6 desquamates and leads to the formation of micro voids, which accelerates the crack propagation and decreases TF properties of tested alloy. In samples with notches parallel to the DS direction, cracks preferentially propagate along the RX grain boundaries.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Service safety of turbine blades in aircraft enγines are threatened by microstructural and property deγradation instantly caused by overheatinγ durinγ service. Systematic investiγations about microstructural deγradation durinγ overheatinγ exposures and its influence on mechanical properties of turbine blades durinγ service are limitedly reported. In this work, microstructure and mechanical properties of γH4033 alloy, which was sectioned from the shank of a serviced 2nd staγe turbine blade in an aircraft enγine, were studied after overheatinγ at 900~1100 ℃ for 3 min. Microstructural deγradation durinγ overheatinγ exposures as well as its influence on room temperature hardness and stress rupture life at 700 ℃, 430 MPa were analyzed. The results of microstructural characterization indicated that the coarseninγ and dissolution of γ' precipitates were introduced by overheatinγ exposures, and all of the γ' precipitates dissolved at 980 ℃ for 3 min. γradual dissolution of γrain boundary (γB) carbides was observed with the increase of overheatinγ temperature. Complete dissolution of γB carbides at 1100 ℃ resulted in γrain γrowth. The room temperature hardness after overheatinγ exposures decreased γrossly with the dissolution of γ' phase. Due to the dissolution and re-precipitation of γ' phase as well as the dissolution of γB carbides, the stress rupture life under 700 ℃, 430 MPa of γH4033 alloy was initially increased and then decreased siγnificantly.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Plasma arc cold hearth melting (PAM) is an effective technology to produce high purity titanium alloy ingots which are widely used in aeronautic and astronautic industries. To date, the development of PAM in our country is still at initial stage. It is necessary to investigate the melting parameters of PAM and the following thermal mechanical processing of the ingots fabricated by PAM. In this study, the TC1 alloy ingots casted by PAM were cogged at b transus temperature and then rolled by unidirectional rolling and cross rolling in the a+b phase field. The typical widmanstatten structure of cast- ingots turned to transformed b morphology after cogging at b transus temperature in which the a phases forms in smaller colonies of laths. After the unidirectinal rolling in the a+b phase field, the a colonies were distorted and the a laths re-arranged along the rolling direction, while they had weaker directivity after cross rolling. The sheets rolled by both unidirectional and cross rolling showed typical prismatic texture. After annealing treatment below the b transus temperature, the a phases turned to equiaxial morphology. The ambient yield strength of the sheet in transverse direction was significantly higher than in rolling direction, which could be attributed to the strong prismatic texture introduced by hot rolling process.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Ni- based single crystal superalloys have been widely used for blades and vanes in gas turbine. However, recrystallization (RX) induced by residual strain has been a serious problem for the application of single crystal superalloys. In previous work, effect of microstructure, such as g', g/g' eutectics and carbides, as well as heat treatment parameters, on the RX behavior have been studied. However, the effect of alloy elements on the RX behavior has rarely been reported. Therefore, in this work, the effect of the important solution strengthening elements, W and Re, on the deformation and RX of solution heat treated Ni-based single crystal superalloys was investigated. At first, two single crystal superalloys were prepared, and W and Re were added into one alloy among them. After solution heat treatment, these two single crystal superalloys were deformed by shot-peening or Brinell indentation. Then these deformed samples were heat treated to observe the microstructure of RX. It indicated that RX depth decreased with the addition of W and Re irrespective of deformation mode and heat treatment temperature. Short time heat treatment experiment of indented and shot-peened samples both indicated that incubation period of RX was prolonged and nucleation of RX was slowed with the addition of W and Re, which verified that RX was suppressed by W and Re. After shot-peening, micro-hardness of the alloy with W and Re increased, but the depth of deformation zone was obviously reduced. Higher density of dislocation was found in the single crystal superalloy with W and Re, and also lots of dislocation tangles were observed. So, in this alloy, dislocation annihilated slowly, that is, recovery was slowed down, which prolonged the incubation period of RX. During the process of RX grain growth, the maximum RX grain boundary migration velocity was reduced with the addition of W and Re. Moreover, the change of mean RX grain boundary migration velocity showed the same trend with the micro-hardness along the direction of RX depth.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Casting microporosity defect is one of the important issues for as- cast HK40 alloys preparation, which is of great importance to application performance of the alloy castings. A comprehensive understanding of the mechanism on formation of the casting microporosity defect is still unclear for the alloys. In this work, the casting microporosity defect and influences of boron micro-alloying on the as-cast microstructures and microporosities in HK40 alloys castings were investigated by means of SEM, OM and XRD, etc.. The microstructures in the HK40 alloys with and without boron micro-alloying after quenching at high temperatures were also examined to check the solidification characteristic change attribute to boron addition. The results show that there are two types of casting microporosities in the castings. Type A is mainly caused by the rapid growth of dendrites and thus dendritic bridge connecting which lead to feeding shortages between the bridge dendrites. Type B is, however, resulted by the growth of M7C3 carbides in coarsened dendritic morphology which induce to the feeding channel blockage in adjacent interdendritic regions. Boron micro-alloying decreases the tendency of columnar grain formation and refines the dendrites in HK40 alloys which therefore suppresses the casting microporosity defect of type A. Additionally, boron micro-alloying not only increases the volume fraction of eutectic phases, but also changes the M7C3 carbides in dendritic morphology into the M23C6 carbides in lamellar morphology, which prevents the feeding channal blockage in adjacent interdendritic regions, thus reduces the casting microporosity defect of type B.
Subjects: Biology >> Zoology submitted time 2017-10-10 Cooperative journals: 《动物营养学报》
Abstract：不同信号转导通路间的彼此协调保证了机体的正常运行。在众多的信号通路中，转化生长因子（TGF）β1/Smads信号传导通路越来越受到学者们的关注，已经成为分子生物学和细胞生物学研究的一大热点。已有研究证实，TGF-β1/Smads信号传导通路是调控卵泡发育的重要途径。本文就TGF-β1/Smads信号传导通路与哺乳动物卵巢卵泡的发育进行综述，分别从TGF-β受体、Smads蛋白、骨形态发生蛋白（BMP）、血小板反应蛋白1（THB-S1）、S期激酶相关蛋白1（SKP1）和其他调节机制阐述TGF-β1/Smads信号传导通路在哺乳动物卵巢发育中的调控作用及其机制，旨在引起人们对TGF-β1/Smads调控卵巢发育的关注，并为卵巢发育过程中某些疾病的治疗提供一些参考。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：利用SEM、OM和XRD等手段分析了HK40合金铸件铸造疏松形成原因，并研究了添加微量B对HK40合金的凝固组织及疏松形成的影响。结果表明：HK40合金铸件主要存在A、B 2种铸造疏松缺陷。A类疏松主要由于枝晶的快速生长并架桥联接导致架桥枝晶之间区域的补缩不足引起；B类疏松产生原因是相邻枝晶间区域生长的枝晶状M7C3型碳化物堵塞枝晶间补缩通道。B微合金化能降低HK40合金铸件较强的柱状晶生长趋势，细化枝晶，能抑制HK40合金A类铸造疏松缺陷的产生。同时，B微合金化增加了HK40合金枝晶间共晶相的体积分数，使枝晶间呈枝晶状M7C3型碳化物转变为层片状的M23C6型碳化物析出，避免碳化物堵塞相邻枝晶间的补缩通道，因而也减小了B类铸造疏松缺陷的形成倾向。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：本文以服役900 h的DZ125合金叶片为研究对象，通过对叶片服役前后的枝晶干、枝晶间、晶界及碳化物各类组织退化行为的研究，确定了枝晶干γ’相的体积分数作为反映服役温度的可量化表征参量。结合叶片用DZ125合金在900~1100 ℃下的显微组织的演变行为，研究了热暴露温度与枝晶干γ’相体积分数之间的量化对应关系。在此基础上，提出了一种基于显微组织的涡轮叶片服役温度的实验评估方法。同时，分别假设叶片服役温度恒定以及考虑叶片实际服役温度等两种情况，实现了对等效平均服役温度（Tave）及等效最高服役温度（Tmax）的定量评估。评估结果表明：叶片叶身中部服役温度最高，由叶身中部向叶尖和叶根服役温度逐渐降低；同一截面服役温度由高到低依次为：进气边＞叶盆＞排气边＞叶背；服役温度最高的区域为叶身中部截面的进气边，服役时经历的等效最高温度约为1050~1100 ℃。叶片等效平均服役温度及等效最高服役温度的的分布规律一致，但部分部位的等效最高服役温度高于等效平均服役温度，本研究认为叶片的等效最高服役温度的评估结果更为合理。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：等离子冷床炉由于其熔炼铸锭的高纯净度而广泛应用于航空航天钛合金的熔炼。我国工业化等离子冷床炉熔炼钛合金尚处于起步阶段，其熔炼参数及其熔炼铸锭的后续热加工工艺急待研究。本研究以工业化等离子冷床炉熔炼的TC1钛合金为研究对象，结合实际生产流程，并借助于中子衍射技术，研究不同轧制工艺对TC1轧制板材显微组织与性能演变的影响，揭示组织结构与力学性能之间的关系。研究结果表明，冷床炉熔炼的铸锭组织为魏氏组织。经过轧制后，α集束发生扭曲和破碎。单向轧制变形α相沿轧向排列较换向轧制更为明显。退火后，板材中变形α相发生等轴化。经过单向轧制和换向轧制后，轧制板材均表现为柱面织构类型，这是板材横向屈服强度均明显高于其轧向屈服强度的主要原因。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：本文采用"V"型缺口分别垂直和平行于凝固方向的板状热疲劳试样, 并在缺口位置预制再结晶组织, 研究了在最高温度为1000℃, 最低温度为室温的冷热循环下, 缺口取向和再结晶对定向凝固钴基高温合金热疲劳性能的影响. 结果表明: 缺口取向垂直于凝固方向时, 基体在应力作用下循环氧化开裂; 缺口平行于凝固方向时, 热疲劳性能下降, 裂纹沿枝晶间扩展. 再结晶降低定向凝固钴基高温合金的热疲劳性能, 再结晶晶界氧化开裂, 实验中晶界析出的M23C6型碳化物氧化脱落后形成的孔洞加速了裂纹扩展; 连接枝晶间碳化物的再结晶晶界成为缺口平行于凝固方向时热疲劳裂纹的优先扩展通道。
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