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1.
The structure of Al3Zr precipitates in Al‐1.0Mg‐0.6Si‐0.5Zr (in wt.%) alloy was investigated using conventional transmission electron microscopy (TEM) and high‐resolution TEM (HREM). After annealing of the alloy in the temperature range 450–540 °C, spherical precipitates of metastable L12‐Al3Zr phase appeared nearly homogeneously within the matrix, and elongated particles were found at grain boundaries. L12‐structured Al3Zr were about 20–30 nm in diameter and coherent with the matrix. Inside some of them, planar faults parallel to {100} planes were revealed by use of HREM. Most probably, these faults are an indication of the transition stage of transformation to the stable D023‐type Al3Zr phase. The elongated precipitates (about 100 nm) were identified as D022‐type Al3Zr. Energy‐dispersive X‐ray analysis showed that they contain, apart from Al, mainly Zr with small amounts of Si. The substitution of Al by Si increased the stability of the D022‐Al3Zr as compared with D023‐Al3Zr. 相似文献
2.
Crack/particle interactions in alumina/silicon carbide nanocomposites have been investigated by scanning electron microscopy and transmission electron microscopy, with cracks induced by Vickers microindentation. Intergranular cracks are frequently deflected into grains by SiC particles on grain boundaries inclined to the average direction of crack propagation. This mechanism is proposed to explain the change in the fracture mode from intergranular fracture for monolithic alumina to predominantly transgranular fracture for the nanocomposites. Neither stress-induced microcracking around SiC particles nor significant crack deflection by intragranular particles was found to occur in the nanocomposites. It is argued that an addition of nanoparticles may not be a promising approach for increasing the toughness of alumina. 相似文献
3.
The microstructures of diffusion‐bonded Cu/(0001)Al2O3 bicrystals annealed at 1000 °C at oxygen partial pressures of 0.02 or 32 Pa have been studied with various microscopy techniques ranging from optical microscopy to high‐resolution transmission electron microscopy. The studies revealed that for both oxygen partial pressures a 20–35 nm thick interfacial CuAlO2 layer formed, which crystallises in the rhombohedral structure. However, the CuAlO2 layer is not continuous, but interrupted by many pores. In the samples annealed in the higher oxygen partial pressure an additional reaction phase with a needle‐like structure was observed. The needles are several millimetres long, ~10 µm wide and ~1 µm thick. They consist of CuAlO2 with alternating rhombohedral and hexagonal structures. Solid‐state contact angle measurements were performed to derive values for the work of adhesion. The results show that the adhesion is twice as good for the annealed specimen compared to the as‐bonded sample. 相似文献
4.
K. Barmak S. W. Banovic C. M. Petronis D. F. Susan & A. R. Marder 《Journal of microscopy》1997,185(2):265-274
The structure of electrodeposited composite coatings of Ni–Al–Al2 O3 , with Ni as the matrix and Al and Al2 O3 as second-phase particles, was investigated using light microscopy and scanning electron microscopy. Ni coatings with no particles, which were used as reference samples, had progressively coarser structures with increasing current density. Co-deposition with Al resulted in refinement of the Ni matrix structure at high (>10 A dm−2 ) current densities. For single-particle baths, the co-deposition of Al2 O3 was more strongly affected by current density and bath particle content than was the co-deposition of Al. However, for baths containing both Al and Al2 O3 the amount of incorporated Al2 O3 no longer depended on current density. With the choice of appropriate conditions, coatings of Ni with up to 39 vol.% Al2 O3 were made. Similar experiments with Al yielded a maximum of 17.5 vol.% only. Uniform and graded mixed-particle coatings were also produced. When coatings containing Al were annealed, the reaction of the two elements resulted in the formation of either single-phase γ or two-phase γ–γ' alloys, in agreement with the equilibrium phase diagram. 相似文献
5.
The Al2O3?10 wt% ZrO2 composites were subjected to hardness tests using a Vickers diamond indenter up to 98.1 N. The microstructure observation using a transmission electron microscopy technique helped to identify up to four zones differing in defect level and character. The densest dislocation tangles, twins accumulation and frequent presence of three slip systems were found in regions that were in contact with the sides of the diamond pyramid. The second zone, characterized by two, or at least one, active slip systems, started at the bottom of the indentation mark and extended up to a distance comparable with the depth of indentation. In the third zone, with a thickness comparable to that above, only some α‐Al2O3 crystallites showed the presence of dislocations, whereas other crystallites were defect free. In the last zone the alumina crystals were left unaffected but the ZrO2 crystallites showed twinning characteristic of strain‐induced transformation. 相似文献
6.
This paper considers the microstructures of an Al(Mg)–Al2 O3 interpenetrating composite produced by a pressureless infiltration technique. It is well known that the governing principle in pressureless infiltration in Al–Al2 O3 system is the wettability between the molten metal and the ceramic phase; however, the infiltration mechanism is still not well understood. The objective of this research was to observe the metal–ceramic interface to understand the infiltration mechanism better. The composite was produced using an Al-8 wt% Mg alloy and 15% dense alumina foams at 915°C in a flowing N2 atmosphere. After infiltration, the composite was characterized by a series of techniques. Thin-film samples, specifically produced across the Al(Mg)–Al2 O3 interface, were prepared using a dual-beam focussed ion beam and subsequently observed using transmission electron microscopy. XRD scan analysis shows that Mg3 N2 formed in the foam at the molten alloy–ceramic infiltration front, whereas transmission electron microscopy analysis revealed that fine AlN grains formed at the metal–ceramic interface and MgAl2 O4 and MgSi2 grains formed at specific points. It is concluded that it is the reactions between Al, Mg and the N2 atmosphere that improve the wettability between molten Al and Al2 O3 and induce spontaneous infiltration. 相似文献
7.
Three‐dimensional (3D) data represent the basis for reliable quantification of complex microstructures. Therefore, the development of high‐resolution tomography techniques is of major importance for many materials science disciplines. In this paper, we present a novel serial sectioning procedure for 3D analysis using a dual‐beam FIB (focused ion beam). A very narrow and reproducible spacing between the individual imaging planes is achieved by using drift correction algorithms in the automated slicing procedure. The spacing between the planes is nearly of the same magnitude as the pixel resolution on scanning electron microscopy images. Consequently, the acquired stack of images can be transformed directly into a 3D data volume with a voxel resolution of 6 × 7 × 17 nm. To demonstrate the capabilities of FIB nanotomography, a BaTiO3 ceramic with a high volume fraction of fine porosity was investigated using the method as a basis for computational microstructure analysis and the results compared with conventional physical measurements. Significant differences between the particle size distributions as measured by nanotomography and laser granulometry indicate that the latter analysis is skewed by particle agglomeration/aggregation in the raw powder and by uncertainties related to calculation assumptions. Significant differences are also observed between the results from mercury intrusion porosimetry (MIP) and 3D pore space analysis. There is strong evidence that the ink‐bottle effect leads to an overestimation of the frequency of small pores in MIP. FIB nanotomography thus reveals quantitative information of structural features smaller than 100 nm in size which cannot be acquired easily by other methods. 相似文献
8.
Hayrettin Ahlatci Tolga Koer Ercan Candan Huseyin imenolu 《Tribology International》2006,39(3):213-220
In this study, dry sliding metal–metal and metal–abrasive wear behaviours of the aluminium matrix hybrid composites produced by pressure infiltration technique were investigated. These composites were reinforced with 37 vol% Al2O3 and 25 vol% SiC particles and contained up to 8 wt% Mg in their matrixes. While matrix hardness and compression strength increased, amount of porosity and impact toughness decreased with increasing Mg content of the matrix. Metal–metal and metal–abrasive wear tests revealed that wear resistance of the composites increased with increasing Mg addition. On the other hand, abrasive resistance decreased with increasing test temperature, especially above 200 °C. 相似文献
9.
Yong Luo Shirong GeDekun Zhang Qingliang WangHongtao Liu 《Tribology International》2011,44(11):1471-1475
Fretting wear of carburized titanium alloys was investigated on the universal multifunctional tester (UMT) with the ball-on-flat fretting style under bovine serum lubrication. The tangential load and friction coefficient during the fretting process were analyzed, and the evolution of fretting log during the fretting process was investigated to understand the wear mechanism of the titanium alloy and carburized titanium alloy. Furthermore, the wear scar was examined using a SEM and three-dimension surface profiler. It was found that the friction coefficient of the titanium alloy increased faster than that of carburized titanium alloy in the first stage under serum lubrication, and then remained steady with a similar value in the second stage. The Ft-D curve indicated that there was wear mechanism transition from gross slip to mixed stick and slip. Finally, it was observed that there was a slight damage of the titanium alloy and carburized titanium alloy showed excellent performance during the fretting wear process under serum lubrication. All of the results suggested that carburized titanium alloy was a potential candidate for the stem material in artificial joints. 相似文献
10.
S. Casey E. Hill J. Miles P. Sivasamy K. Birtwistle B. Middleton & D. Joyce 《Journal of microscopy》1997,185(2):117-121
Pt x Co(1− x ) thin films where x =0.24 have been deposited onto Si3 N4 windows and studied using transmission electron microscopy. The films are used in ultrahigh-density recording studies and it was found that the surface of the substrate had a strong influence on the microstructure, crystallography and magnetic properties of the film. An investigation of the early growth of the film was made by studying films of different thickness between 100 and 300 Å. It was found that the grains were hexagonal in structure with a strong c -axis orientation perpendicular to the surface. 相似文献
11.
The decreasing process of oxygen in YBa2 Cu3 O y is investigated through high resolution electron microscopy (HREM) and convergent beam electron diffraction (CBED). Measurements of the axial length in HREM images show that oxygen content y decreases faster near a twin boundary than at the inner part of a twin lamella. The transformation from an orthorhombic to a tetragonal phase starts at a twin boundary and the transformed region propagates to an inner region of lamella. Lattice strains are observed near boundaries between transformed and non-transformed regions. The transformation is almost complete within 30 s during observation of HREM images at 400 kV and at room temperature. A value of y was quantitatively measured by analysing observed intensities of energy-filtered CBED patterns with the dynamical theory. The value of y decreases from 6.9 to 6.5 when 200 kV electrons are irradiated for 160 s in a microscope at 108 K. More precise analysis of the intensities provides information on charge distribution along the c -axis as well as local oxygen content at a spatial resolution of several nanometres. 相似文献
12.
J. CAZAUX 《Journal of microscopy》2004,214(3):341-347
The relative weight, δΒ, of the yield of secondary electrons, SE2, induced by the backscattered electrons, BSE, with respect to that, δP, of secondary electrons, SE1, induced by the primary electrons, PE, is deduced from simple theoretical considerations. At primary energies E0 larger than EM (where the total SE yield δ = δP + δB is maximum), the dominant role of the backscattering events is established. It is illustrated in SEM by a direct comparison of the contrast between SE images and BSE images obtained at E0 ~ 5 keV and E0 ~ 15 keV on a stratified specimen. At energies E0 less than EM, the dominant role of SE1 electrons with respect to SE2 (and SE3) is established. It is illustrated by the better practical resolution of diamond images obtained with an in‐lens detection in low voltage SEM E0 ~ 0.2–1 keV range compared with that obtained with a lateral detector. The present contribution illustrates the improved performance of LVSEM in terms of contrast and of practical resolution as well as the importance of variable voltage methods for subsurface imaging. The common opinion that the practical lateral resolution is given by the incident spot diameter is also reconsidered in LVSEM. 相似文献
13.
J. Campa-Molina† O. Blanco† A. Correa-Gomez M. Czank‡ & A. G. Castellanos-Guzman 《Journal of microscopy》2002,208(3):201-211
The domain structures of Zn3B7O13Cl, Zn3B7O13Br and Zn3B7O13I boracite single crystals were studied by means of polarized light in conjunction with electron microscopy. Single crystals of the three compositions were grown by chemical transport reactions in closed quartz ampoules, at a temperature of 900 °C and were examined by polarizing optical microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For both PLM and SEM, the same as‐grown samples were used without having to resort to metallization of the crystal faces. For TEM the single crystals were crushed and mounted on holey carbon films. Comparative electron microscope images were useful for revealing the domain structure of these ferroelectric/ferroelastic materials previously observed between the crossed polars of an optical microscope. X‐ray diffraction analysis of the pulverized crystals was performed for this triad of halogen boracites containing zinc as a common metal. 相似文献
14.
Solid state interface reactions in highly dispersed Lu2O3– SiO2 binary oxide system were studied at 600–1100 °C with X‐ray powder diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM) and Fourier Transform Infrared spectroscopy (FTIR). The results show that at 600–900 °C an amorphous, nanometer thick Lu‐O‐Si layer covering SiO2 particles exists in the system. At higher temperatures the breakage of the layer into amorphous islands occurs and crystalline silicates with various structures are formed. In particular, Lu4[Si3O10][SiO4] silicate, analogue of B‐type Dy – Tm disilicates, forms at 1000 °C. 相似文献
15.
Electron backscattered diffraction is used to investigate the preferred CSL (coincidence site lattice) distribution of polycrystalline SrTiO3 as a function of annealing times (1 h and 16 h). Comparison of the CSL misorientations suggests that the CSL boundary energy plays a role in the preferred grain growth. 相似文献
16.
A dispersion of TiB2 particulates in an Al alloy matrix was formed via the in-situ reaction between mixtures of K2 TiF6 (K2 ZrF6 ), KBF4 and molten aluminium. The dispersion of the ceramic phase in the aluminium matrix was also achieved in some experiments by adding exogenous TiB2 particles to the fluoride melt in contact with molten aluminium.
In this work, we have examined the microstructure of the as-cast metal matrix composites using analytical electron microscopy and X-ray diffraction techniques. The phases formed as a result of the reaction between the molten fluoride flux and liquid aluminium have been identified. These were (Ti, Zr, Al)B2 , Al3 Ti and possibly AlB12 in the Al-matrix, and KAlF4 and KMgF3 in the solidified flux. The mechanism of formation of TiB2 and Al3 Ti is explained. The role of alloying elements is also explained in the context of interfacial chemistry and dispersion. 相似文献
In this work, we have examined the microstructure of the as-cast metal matrix composites using analytical electron microscopy and X-ray diffraction techniques. The phases formed as a result of the reaction between the molten fluoride flux and liquid aluminium have been identified. These were (Ti, Zr, Al)B
17.
Sliding wear characteristics of plasma-sprayed Al2O3 and Cr2O3 coatings against copper alloy under severe conditions 总被引:2,自引:0,他引:2
Al2O3 and Cr2O3 coatings were deposited by atmospheric plasma spraying and their tribological properties dry sliding against copper alloy were evaluated using a block-on-ring configuration at room temperature. It was found that the wear resistance of Al2O3 coating was superior to that of the Cr2O3 coating under the conditions used in the present study. This mainly attributed to its better thermal conductivity of Al2O3 coating, which was considered to effectively facilitate the dissipation of tribological heat and alleviate the reduction of hardness due to the accumulated tribological heat. As for the Al2O3 coating, the wear mechanism was plastic deformation along with some micro-abrasion and fatigue-induced brittle fracture, while the failure of Cr2O3 coating was predominantly the crack propagation-induced detachment of transferred films and splats spallation. 相似文献
18.
L. Aeschimann† T. Akiyama U. Staufer N. F. De Rooij L. Thiery‡ R. Eckert† & H. Heinzelmann† 《Journal of microscopy》2003,209(3):182-187
The fabrication of silicon cantilever‐based scanning near‐field optical microscope probes with fully aluminium‐coated quartz tips was optimized to increase production yield. Different cantilever designs for dynamic‐ and contact‐mode force feedback were implemented. Light transmission through the tips was investigated experimentally in terms of the metal coating and the tip cone‐angle. We found that transmittance varies with the skin depth of the metal coating and is inverse to the cone angle, meaning that slender tips showed higher transmission. Near‐field optical images of individual fluorescing molecules showed a resolution < 100 nm. Scanning electron microscopy images of tips before and after scanning near‐field optical microscope imaging, and transmission electron microscopy analysis of tips before and after illumination, together with measurements performed with a miniaturized thermocouple showed no evidence of mechanical defect or orifice formation by thermal effects. 相似文献
19.
The 3D morphology and distribution of lenticular Ni4 Ti3 precipitates in the austenitic B2 matrix of a binary Ni51 Ti49 alloy has been investigated by a slice-and-view procedure in a dual-beam focused ion beam/scanning electron microscope system. Due to the weak contrast of the precipitates, proper imaging conditions need to be selected first to allow for semi-automated image treatment. Knowledgeable imaging is further needed to ensure that all variants of the precipitates are observed with equal probability, regardless of sample orientation. Finally, a volume ratio of 10.2% for the Ni4 Ti3 precipitates could be calculated, summed over all variants, which yields a net composition of Ni50.27 Ti49.73 for the matrix, leading to an increase of 125 degrees for the martensitic start temperature. Also, the expected relative orientation of the different variants of the precipitates could be confirmed. 相似文献