Y.S. Li
University of Saskatchewan
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Publication
Featured researches published by Y.S. Li.
ACS Applied Materials & Interfaces | 2010
Y.S. Li; Y. Tang; Q. Yang; J. Maley; Ramaswami Sammynaiken; T. Regier; C. Xiao; A. Hirose
The adherence of diamond coated on steel is commonly low and needs to be strengthened with thick intermediate layers. In this paper, a nanoscale W-Al dual metal interlayer has been applied on SS304 substrates to facilitate deposition of continuous, adherent and smooth diamond thin films. During the microwave plasma-enhanced chemical vapor deposition process, the Al inner layer 30 nm thick diffuses into steel surface inhibiting carbon diffusion and graphitization. The W outer layer 20 nm thick is transformed into W carbides, both preventing carbon diffusion and enhancing diamond nucleation. The diamond films synthesized are of high purity and have smooth surfaces and dense structures. Indentation and shear deformation tests indicate high delaminating tolerance of the diamond films.
ACS Applied Materials & Interfaces | 2013
Xiulan Li; Lifan He; Y.S. Li; Qiuhua Yang; A. Hirose
Direct CVD deposition of dense, continuous, and adherent diamond films on conventional Fe-based alloys has long been considered impossible. The current study demonstrates that such a deposition can be realized on Al, Cr-modified Fe-based alloy substrate (FeAl or FeCrAl). To clarify the fundamental mechanism of Al, Cr in promoting diamond growth and enhancing interfacial adhesion, fine structure and chemical analysis around the diamond film-substrate interface have been comprehensively characterized by transmission electron microscopy. An intermediate graphite layer forms on those Al-free substrates such as pure Fe and FeCr, which significantly deteriorates the interfacial adhesion of diamond. In contrast, such a graphite layer is absent on the FeAl and FeCrAl substrates, whereas a very thin Al-rich amorphous oxide sublayer is always identified between the diamond film and substrate interface. These comparative results indicate that the Al-rich interfacial oxide layer acts as an effective barrier to prevent the formation of graphite phase and consequently enhance diamond growth and adhesion. The adhesion of diamond film formed on FeCrAl is especially superior to that formed on FeAl substrate. This can be further attributed to a synergetic effect including the reduced fraction of Al and the decreased substrate thermal-expansion coefficient on FeCrAl in comparison with FeAl, and a mechanical interlocking effect due to the formation of interfacial chromium carbides. Accordingly, a mechanism model is proposed to account for the different interfacial adhesion of diamond grown on the various Fe-based substrates.
Materials Research Innovations | 2007
Y.S. Li; S. A. Gerasimov; U. A. Puckov; Hongwei Ma; Wang J
Abstract Fe3Al intermetallic and 18–8 stainless steel were welded by means of tungsten inert gas (TIG) arc welding. The microstructure performance of the welding zone was analysed using a metalloscope and a scanning electron microscope. The test results indicated that microstructure of the welded metals consists of austenite, proeutectoid ferrite, acicular ferrite, carbide free bainite and lath martensite distributed on the austenitic boundaries as well as grains inside. The microhardness of the fusion zone was lower than that of Fe3Al base metal. The NiAl in the fusion zone was favourable to improve toughness and avoid the welding cracks.
Journal of Physics D | 2010
Y. Tang; Y.S. Li; Q. Yang; A. Hirose
Well-aligned diamond nanotips are fabricated by etching as-grown diamond thin films using a Kaufman type broad ion beam source. The nanotips have nanometre-size heads, micrometre-size roots and the same apex angle. All of the nanotips consistently point in the direction against the incident ion beam. The orientation of diamond nanotips can be controlled by adjusting the incident direction of the ion beam. The Raman spectrum does not show a significant increase in graphitic peak intensity after etching, indicating that the quality of diamond is barely degraded by ion beam etching. Near-edge x-ray absorption fine structure spectra show that the diamond sp3 structure is dominant in the spectra of both as-grown and ion etched diamond. The sp2 fraction is found to increase by about 12% at the surface layer of the diamond nanotips as compared with as-grown diamond. The formation of diamond nanotips is explained by Sigmunds sputtering theory and the angle-dependent sputtering mechanism. This method to produce diamond nanotips has the advantage of excellent orientation control and the capability to produce nanotip arrays on a large area.
Materials Research Innovations | 2007
Y.S. Li; P. Liu; Wang J; Hongwei Ma
Abstract The microstructure and phase constitution near the interface of diffusion bonding in Mg/Al dissimilar materials were researched by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The test results indicated that an obvious diffusion zone was formed near the Mg/Al interface during the vacuum diffusion bonding. The diffusion transition zone near the interface consists of MgAl, Mg3Al2 and Mg2Al3 phases. The transition region on the Mg side mainly consists of Mg crystals, and the new phase formed was Mg3Al2 with a face-centered cubic lattice. This is favorable for improving the combination strength of the Mg substrate and the diffusion transition zone.
Acta Metallurgica Sinica (english Letters) | 2009
Y.S. Li; Y. Tang; W. Chen; Q. Yang; C. Xiao; A. Hirose
Diamond growth on Fe-Cr-Al-Si steel and Si substrates was comparatively investigated in microwave plasma enhanced chemical vapor deposition (MPCVD) reactor with different deposition parameters. Adherent nanocrystalline diamond films were directly deposited on this steel substrate under a typical deposition condition, whereas microcrystalline diamond films were produced on Si wafer. With increasing CH 4 concentration, reaction pressure, or the total gas flow rate, the quality of nanocrystalline diamond films formed on Fe-Cr-Al-Si substrates is gradually deteriorated in terms of density and adhesion. This impaired diamond quality on steels is primarily associated with a combined effect by the substrate composition and the specific process conditions that favor excessive nucleation of diamond.
Materials Research Innovations | 2014
Y.S. Li; L. Yang; Hongwei Ma; Renfei Feng; Q. Yang; A. Hirose
Abstract During chemical vapour deposition of diamond coatings on transition metal (Fe, Co, Ni) substrates, porous graphitic carbon preferentially forms on the substrate surfaces and it induces a spontaneous spallation of the diamond films. In this study, an Al surface barrier film of 80nm thick has been used on a Kovar alloy substrate to enhance the interfacial adhesion of diamond films. Characterisation of the top deposit, interlayer and the underlying substrate was performed by Raman spectroscopy, energy dispersive X-ray analysis, scanning electron microscopy, synchrotron NEXAFS, and X-ray diffraction. The Al interlayer has effectively inhibited the formation of intermediate graphitic carbon and markedly enhanced the adhesion of diamond films. Continuous and adherent diamond films were achieved on the alloy substrate. This investigation also indicates the importance of the continuity of the Al interlayer in maintaining an integrity of the adherent diamond films.
Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena | 2010
Y.S. Li; Y. Tang; Q. Yang; A. Hirose
Diamond nucleation experiments on Si wafers, precoated with Ni, Al, and Ni–Al duplex intermediate layers, have been conducted in a microwave plasma enhanced chemical vapor deposition reactor. The diamond nucleation density is dependent on the thickness of the single Ni interlayer and also the ratio of Ni/Al. The diamond nucleation density increases with the Ni thickness up to approximately 100 nm. Above 100 nm, decrease in the nucleation density is observed. The nondiamond carbon concentration increases when the Ni thickness increases from 40 to 200 nm, along with a simultaneous increase of nondiamond carbon accumulation on the Si substrate surface. The diamond grown on Si with an Al interlayer is of high purity but of low nucleation density. For the Ni–Al duplex interlayer, increase of Al fraction enhances both the purity and nucleation density of diamond, and markedly reduces the formation of nondiamond carbon on the Si substrate surfaces.
International Journal of Refractory Metals & Hard Materials | 2008
Y.S. Li; Y. Tang; Q. Yang; Shiro Shimada; R. Wei; K.Y. Lee; A. Hirose
Diamond and Related Materials | 2010
Y. Tang; Y.S. Li; Q. Yang; A. Hirose