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排序方式: 共有258条查询结果,搜索用时 15 毫秒
81.
82.
Laser treatment of Inconel 718 alloy surface is carried out. The alloy surface is coated with a carbon layer containing 7% TiC particles prior to the laser treatment. The carbon coating provides increased absorption of the incident laser beam and holds TiC particles. The microstrutural and morphological changes in the laser treated region are examined using optical and scanning electron microscopes, energy dispersive spectroscopy, and X-ray diffraction. The microhardness of the surface is measured and the residual stress formed at the surface vicinity is determined from the XRD technique. It is found that partial dissolution of carbide particles takes place at the surface. The composition of fine grains at the surface vicinity, nitride compounds formed, and dissolution of Laves phase at the surface region enhances the hardness at the treated surface. In addition, laser treated surface is free from the micro-crack network and cavities. 相似文献
83.
C.-Y. YenS.-R. Jian G.-J. ChenC.-M. Lin H.-Y. LeeW.-C. Ke Y.-Y. LiaoP.-F. Yang C.-T. WangY.-S. Lai Jason S.-C. JangJ.-Y. Juang 《Applied Surface Science》2011,257(17):7900-7905
ZnO thin films grown on Si(1 1 1) substrates by using atomic layer deposition (ALD) were annealed at the temperatures ranging from 300 to 500 °C. The X-ray diffraction (XRD) results show that the annealed ZnO thin films are highly (0 0 2)-oriented, indicating a well ordered microstructure. The film surface examined by the atomic force microscopy (AFM), however, indicated that the roughness increases with increasing annealing temperature. The photoluminescence (PL) spectrum showed that the intensity of UV emission was strongest for films annealed at 500 °C. The mechanical properties of the resultant ZnO thin films investigated by nanoindentation reveal that the hardness decreases from 9.2 GPa to 7.2 GPa for films annealed at 300 °C and 500 °C, respectively. On the other hand, the Young's modulus for the former is 168.6 GPa as compared to a value of 139.5 GPa for the latter. Moreover, the relationship between the hardness and film grain size appear to follow closely with the Hall-Petch equation. 相似文献
84.
Guangwei Guo Guangze Tang Yajun WangXinxin Ma Mingren SunLiqin Wang Ken Yukimura 《Applied Surface Science》2011,257(10):4738-4742
a-C:H films were prepared by middle frequency plasma chemical vapor deposition (MF-PCVD) on silicon substrates from two hydrocarbon source gases, CH4 and a mixture of C2H2 + H2, at varying bias voltage amplitudes. Raman spectroscopy shows that the structure of the a-C:H films deposited from these two precursors is different. For the films deposited from CH4, the G peak position around 1520 cm−1 and the small intensity ratio of D peak to G peak (I(D)/I(G)) indicate that the C-C sp3 fraction in this film is about 20 at.%. These films are diamond-like a-C:H films. For the films deposited from C2H2 + H2, the Raman results indicate that their structure is close to graphite-like amorphous carbon. The hardness and elastic modulus of the films deposited from CH4 increase with increasing bias voltage, while a decrease of hardness and elastic modulus of the films deposited from a mixture of C2H2 + H2 with increasing bias voltage is observed. 相似文献
85.
The microstructure and properties of AlCrMnMoNiZrB0.1 nitride films prepared by reactive direct current sputtering at various N2-to-Ar flow ratios (RN) were investigated. The films had an amorphous structure at low RN and a face-centered cubic structure at a high RN. As the RN increased, the decrease in clusters and defects resulted in a dense columnar structure and low surface roughness. The peak hardness and modulus of the nitride films were 10.3 and 180 GPa, respectively. The enhanced hardness is ascribed to the increased metal-nitrogen bonding, solid solution strengthening of several metallic nitrides, and lattice strain. The nitride films deposited at RN = 0.2, 0.5, and 0.8 had friction coefficients of 0.16, 0.12 and 0.15, respectively. Wear-out failure occurred within 400 s when RN = 0 and 1.0. Adhesive wear was the dominant wear mechanism. 相似文献
86.
The effects of laser processing parameters on the microstructure and mechanical properties of selective laser-melted magnesium were investigated. The results show that the microstructure characteristics of the laser-melted samples are dependent on the grain size of SLM magnesium. The grains in the molten zone coarsen as the laser energy density increases. In addition, the average hardness values of the molten zone decreases significantly with an increase of the laser energy densities and then decreased slowly at a relatively high laser energy density irrespective of mode of irradiation. The hardness value was obtained from 0.59 to 0.95 GPa and corresponding elastic modulus ranging from 27 to 33 GPa. The present selective laser-melted magnesium parts are promising for biomedical applications since the mechanical properties are more closely matched with human bone than other metallic biomaterials. 相似文献
87.
Effect of laser surface hardening on the microstructure, hardness and residual stresses of austempered ductile iron grades 总被引:1,自引:0,他引:1
C. Soriano J. LeundaJ. Lambarri V. García NavasC. Sanz 《Applied Surface Science》2011,257(16):7101-7106
A study of the laser surface hardening process of two austempered ductile iron grades, with different austempering treatments has been carried out. Hardening was performed with an infrared continuous wave Nd:YAG laser in cylindrical specimens. The microstructure of the laser hardened samples was investigated using an optical microscope, microhardness profiles were measured and surface and radial residual stresses were studied by an X-ray diffractometer. Similar results were achieved for both materials. A coarse martensite with retained austenite structure was found in the treated area, resulting in a wear resistant effective layer of 0.6 mm to 1 mm with a microhardness between 650 HV and 800 HV. Compressive residual stresses have been found at the hardened area being in agreement with the microhardness and microstructural variations observed. The achieved results point out that the laser surface hardening is a suitable method for improving the mechanical properties of austempered ductile irons. 相似文献
88.
杜小旺 《四川师范大学学报(自然科学版)》2006,29(5):595-598
提出了确定稀土氧化物中元素硬度均衡值町ηcq的计算公式,用该式计算了252种稀土氧化物超导体的硬度均衡值ηcq。研究了稀土氧化物的超导性与稀土氧化物硬度均衡值之间的关系.结果表明,稀土氧化物超导体的硬度均衡值ηcq多数集中在4.511-5.343之间,而硬度均衡值在此范围之外的稀土氧化物一般不具有超导性.显然硬度均衡值ηcq。可作为稀土氧化物超导性的新的经验判据,这对进一步探讨稀土氧化物的超导机制有一定意义. 相似文献
89.
Novel high performance aluminum nitride (AlN)/poly(ether-ether-ketone) (PEEK) composites containing 0-50 wt.% fractions of AlN were prepared by solution blending method followed by hot pressing to evaluate their density, melting temperature, crystallization, thermal stability, morphological behavior and Vickers hardness by using different characterization techniques. Differential scanning calorimetry results indicated that the AlN particles are very effective nucleating agent, which results in increase in melting point, hot crystallization temperature and crystallinity of composites as the AlN content increases. Thermogravimetric analysis showed enhanced thermal stability of the composites with respect to PEEK. Density and X-ray diffraction techniques showed that crystallinity of the composites increases as the wt.% of AlN content increases in polymer matrix. Scanning electron microscopy revealed that AlN particles were well dispersed with no porosity in composites. Vickers hardness of the samples increased from 24 kg/mm2 for the pure PEEK to 35 kg/mm2 for AlN/PEEK composites. 相似文献
90.
Three of the five structures obtained from the evolutionary algorithm based structure search of Ruthenium Carbide systems in the stoichiometries RuC, Ru2C and Ru3C are relaxed at different pressures in the range 0–200 GPa and the pressure-induced variation of their structural, elastic, dynamical, electronic and thermodynamic properties as well as hardness is investigated in detail. No structural transition is present for these systems in this pressure range. RuC–Zinc blende is mechanically and dynamically unstable close to 100 GPa. RuC-Rhombohedral and Ru3C-Hexagonal retain mechanical and dynamical stability up to 200 GPa. For all three systems the electronic bands and density of states spread out with pressure and the band gap increases with pressure for the semiconducting RuC–Zinc blende. From the computed IR spectrum of RuC–Zinc blende at 50 GPa it is noted that the IR frequency increases with pressure. Using a semi-empirical model for hardness it is estimated that hardness of all three systems consistently increases with pressure. The hardness of RuC–Zinc blende increases towards the superhard regime up to the limiting pressure of its mechanical stability while that of RuC-Rhombohedral becomes 30 GPa at the pressure of 150 GPa. 相似文献