共查询到20条相似文献,搜索用时 15 毫秒
1.
The solute segregation at grain boundaries (GBs) of an ultrafine grained (UFG) Al-Zn-Mg-Cu alloy processed by equal-channel angular pressing (ECAP) at 200 °C was characterised using three-dimensional atom probe. Mg and Cu segregate strongly to the grain boundaries. In contrast, Zn does not always show clear segregation and may even show depletion near the grain boundaries. Trace element Si selectively segregates at some GBs. An increase in the number of ECAP passes leads to a decrease in the grain size but an increase in solute segregation at the boundaries. The significant segregation of alloying elements at the boundaries of ultrafine-grained alloys implies that less solutes will be available in the matrix for precipitation with a decrease in the average grain size. 相似文献
2.
Grain boundary engineering has been proposed to increase the lifetime performance of sensitized austenitic stainless steel in aggressive environments. Increased microstructure resistance is typically associated with higher fractions of twin (Σ3) grain boundaries, but there is uncertainty about the properties and role of other boundaries. To develop predictive models for stress corrosion crack nucleation, more information is required about how grain boundary crystallography and the orientations of the grain boundary plane and its surrounding grains affect crack development. Digital image correlation combined with electron backscatter diffraction has been used to characterize the microstructure and to observe, in situ , the nucleation and propagation of short stress corrosion cracks in thermo-mechanically processed type 304 stainless steel. The crack path and its growth rate have been determined and are found to be influenced by the microstructure. 相似文献
3.
本文通过裂纹密度,晶界开裂率,裂纹扩展速率和断口金相等的定量测定,讨论了晶界时效析出物对大气和真空中Ni-Cr奥氏体不锈钢高温低周疲劳裂纹的萌生和扩展的影响,并分析了该影响与晶粒大小的关系。时效材的高温低周疲劳裂纹的萌生周次,裂纹扩展速率和扩展方式取决于氧化程度,晶界和晶粒间的相对强度及晶界脆性等因素的综合作用。大气中,晶界时效析出物显著地提高了晶界和晶粒间的相对强度,故有时效析出物的晶界是强的,而真空中有时效析出物的晶界是弱的,因为,晶界时效析出物此起的晶界脆性已成为主要的影响因素。 相似文献
4.
The random sampling provided by classical atom probe sample preparation methods is one of the major factors limiting the types of problems that can be addressed using this powerful technique. A focused ion beam enables not only site-specific preparation, but can also be used to give the specimen, which acts as the lens in an atom probe experiment, a specific shape. In this paper we present a technique that uses low accelerating voltages (10 and 5 kV) in the focused ion beam (FIB) to reproducibly produce specimens with selected grain boundaries <100 nm from the tip at any desired orientation. These tips have a high rate of successfully running in the atom probe and no Ga contamination within the region of interest.This technique is applied to the analysis of grain boundaries in a high purity iron wire and a strip-cast steel. Lattice resolution is achieved around the boundary in certain areas. Reconstruction of these datasets reveals the distribution of light and heavy elements around the boundary. Issues surrounding the uneven distribution of certain solute elements as a result of field-induced diffusion are discussed. 相似文献
5.
Edward A. Kenik 《Microscopy research and technique》1991,18(2):167-171
It is shown that material segregated to grain boundaries can be lost during ion milling. This specimen preparation artifact has been studied in the case of bismuth in copper and has also been observed for phosphorus in stainless steel. The loss is associated with specimen heating during ion milling and can be alleviated by good clamping and cooling of the specimen during milling. Specimen heating permits grain boundary diffusion of the segregating element to the specimen surfaces with subsequent loss of segregant from the specimen by evaporation or sputtering during ion milling. Loss of bismuth during in situ heating to 200–300°C is demonstrated. Therefore, care must be taken in specimen preparation for analytical electron microscopy measurement of such segregation. Similar effects may occur during ion milling of other materials, especially those where low thermal conductivity will result in high beam heating. In these cases, care must be taken to avoid loss of segregant during specimen preparation. Additional tests showed that no significant loss of segregant was observed during X-ray microanalysis, even at nominal room temperature and probe currents five-fold higher than that normally used for microanalysis. 相似文献
6.
7.
Studies on wears of ultrafine-grained ceramic tool and common ceramic tool during hard turning using Archard wear model 总被引:1,自引:1,他引:0
Hardened steels are difficult to be machined due to their high tensile strength and work-hardening rate, low thermal conductivity, and abrasive behavior. In this paper, finite element modeling (FEM) approaches with lagrangian increment method for 3D metal turning of hardened steel H13 by common ceramic tool and ultrafine-grained tool respectively have been investigated by simulation of DEFORM-3D software and turning test. Conditions of initial and boundary and turning process parameters have been chosen. Material properties of H13 and ceramic have been described in details. Johnson–Cook model of H13 model has been applied to the hard turning modeling. Archard wear model has been built, and the correlation coefficients were decided by reciprocating friction experiments. The simulation results showed that predicted primary turning force and maximum temperature in common ceramic are bigger than which was caused by ultrafine-grained ceramic tool for the ultrafine-grained ceramic tools have better thermal stability and bigger hardness. The wear depths of common ceramic tool are about many times than that of ultrafine-grained ceramic tool according to the simulation and experimental results. And their wear patterns are very different. The FEM simulation results have entirely explicated experimental results. The obtained results would provide the fundamental and practical guidelines of tool material choice for hard turning. 相似文献
8.
The structures of boundaries in a deformed and dynamically recovered and recrystallized quartz polycrystal (mylonite) were characterized by transmission electron microscopy, after the misorientation angles across the same grain boundaries had been analysed using electron backscatter diffraction in a scanning electron microscope. In this new approach, a specific sample area is mapped with electron backscatter diffraction, and the mapped area is then attached to a foil, and by the ion beam thinned for transmission electron microscopy analysis. Dislocations in grain boundaries were recognized as periodic and parallel fringes. The fringes associated with dislocations are observed in boundaries with misorientations less than 9°, whereas such fringes cannot be seen in the boundaries with misorientations larger than 17°. Some boundaries with misorientations between 9° and 17° generally have no structures associated with dislocation. One segment of a boundary with a misorientation of 13.5° has structures associated with dislocations. It is likely that the transition from low‐angle to high‐angle boundaries occurs at misorientations ranging from approximately 9° to 14°. Change in the grain boundary structure presumably influences the mobility of the boundaries. In the studied deformed quartz vein, a relative dearth of boundaries between misorientation angles of θ = 2° and θ = 15° has previously been reported, and high‐angle boundaries form cusps where they intersect low‐angle boundaries, suggesting substantial mobility of high‐angle boundaries. 相似文献
9.
Hono K Ohkubo T Chen YM Kodzuka M Oh-ishi K Sepehri-Amin H Li F Kinno T Tomiya S Kanitani Y 《Ultramicroscopy》2011,111(6):576-583
Laser assisted field evaporation using ultraviolet (UV) wavelength gives rise to better mass resolution and signal-to-noise ratio in atom probe mass spectra of metals, semiconductors and insulators compared to infrared and green lasers. Combined with the site specific specimen preparation techniques using the lift-out and annular Ga ion milling in a focused ion beam machine, a wide variety of materials including insulating oxides can be quantitatively analyzed by the three-dimensional atom probe using UV laser assisted field evaporation. After discussing laser irradiation conditions for optimized atom probe analyses, recent atom probe tomography results on oxides, semiconductor devices and grain boundaries of sintered magnets are presented. 相似文献
10.
11.
铸造高速钢刀具的生产工艺及组织、性能的改善 总被引:1,自引:0,他引:1
概述了铸造高速钢的生产工艺、发展过程以及铸造刀具的性能和应用情况。铸造高速钢存在的主要问题是组织中粗大的晶界网状并晶碳化物使铸造高速钢晶界脆化严重,韧性降低;改善的途径有孕育处理、变质及合金化、共晶碳化物的高温顶球化及电渣重熔等。 相似文献
12.
Grain boundary engineering of austenitic stainless steel, through the introduction of plastic strain and thermal annealing, can be used to develop microstructures with improved resistance to inter‐granular degradation. The influence of low‐strain thermo‐mechanical processing on grain boundary network development, with systematic variations of annealing treatments, has been investigated. Three stages of the microstructure development during grain boundary engineering in low‐strain processing conditions are identified, and correlated with changes in grain boundary character and deviation distributions. Low‐energy connected length segments at triple junctions, which have been proposed to be responsible for crack bridging during inter‐granular stress corrosion cracking, can be influenced by the choice of the annealing treatment parameters. The development of individual grain boundary length segments of different character showed consistent trends with increasing grain size. Crack length predictions are consistent with the beneficial effect of designing microstructures with high fractions of twin grain boundaries and smaller grain size. 相似文献
13.
The next generations of advanced energy systems will require materials that can withstand high doses of irradiation at elevated temperatures. Therefore, a methodology has been developed for the fabrication of high-dose ion-irradiated atom probe tomography specimens at a specific dose with the use of a focused ion beam milling system. The method also enables the precise ion dose of the atom probe tomography specimen to be estimated from the local concentration of the implanted ions. The method has been successfully applied to the characterization of the distribution of nanoclusters in a radiation-tolerant 14YWT nanostructured ferritic steel under ion irradiation to doses up to 400 displacements per atom. 相似文献
14.
M.E. De Morton 《Wear》1977,41(2):223-231
Examination of the nozzle assemblies of solid propellant rocket motors has shown that erosion of molybdenum inserts occurs by three distinct processes. Wear was initiated by the physical erosion of the steel nozzle body due to particles in the gas stream. Material removed in this manner wetted and alloyed with the surface of the molybdenum inserts in the high temperature reducing gas flame to form a low melting point Fe-Mo-C eutectic alloy. Subsequent liquid metal erosion occurred by blasting of the continuously forming liquid eutectic from the surface of the nozzle by the high velocity gas stream. Finally, additional erosion at the insert throat occurred by the rapid ingress of oxygen to grain boundaries; this weakened the cohesion between the grains and allowed whole grains to be eroded from the surface by the gas stream. 相似文献
15.
为提高2.25Cr-1Mo-0.25V耐热钢埋弧焊接头的韧性,采用冲击试验和三点弯曲试验找到接头韧性的薄弱环节,并通过进一步的微观分析,试图揭示接头韧性的弱化机理。冲击试验显示,焊缝的韧性低于母材和热影响区,因此利用三点弯曲试验,对裂纹在焊缝中的扩展过程进行更深入的研究。在三点弯曲试验时观察到焊缝中出现阶梯形断口。通过扫描电镜观察到断口表面呈现出韧窝和准解理共存的混合形貌。金相观察发现,阶梯形断口出现在焊缝的柱晶区,其方向与柱晶生长方向平行或垂直。利用苦味酸腐蚀试样,观察到阶梯形断口与结晶方向平行的部分是沿原奥氏体晶界开裂,电子背散射衍射(Electron backscattered diffraction, EBSD)试验结果也证明了这一点,而垂直于结晶方向的部分是沿层状线开裂。因此,原奥氏体晶界和层状线是焊缝中需要特别关注的部位。通过调整焊丝成分和工艺参数,减少了焊缝中的层状线,焊缝韧性明显提高。 相似文献
16.
A technique was developed to study in situ the early stages of the reaction between iron and air. Using a high‐temperature microscope, we observed at temperatures between 1000°C and 1050°C and within the first 30 s of reaction, the formation of iron‐oxide layers on the surface of low‐carbon steel. We observed the nucleation and growth of a first layer of iron oxide and the consecutive formation in sequence, of higher iron oxides sweeping over the surface of the former oxide. The grain boundaries of the steel substrate remain visible for quite some time following exposure to an oxidizing atmosphere indicating that diffusion through steel grain boundaries may have a determining influence on the formation of oxides. These findings emphasize the importance of conducting further studies to better understand the kinetics and mechanisms by which iron‐oxide layers form in the early stages of oxidation. 相似文献
17.
18.
19.
20.