| 1. |
- Melaibari, Ammar A., et al.
(författare)
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Ultrahard boron nitride material through a hybrid laser/waterjet based surface treatment
- 2016
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Ingår i: Acta Materialia. - : Elsevier BV. - 1873-2453 .- 1359-6454. ; 102, s. 315-322
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Tidskriftsartikel (refereegranskat)abstract
- We report a dual phase boron nitride (BN) material composed of 50% cubic and 50% wurtzite phases that has the same level of hardness as polycrystalline diamond. The dual phase BN material was initially synthesized from high pressure and high temperature consolidation of powder materials and subsequently, a laser/waterjet heat treatment (LWH) was applied to the material surface. The LWH process consisted of heating the sample surface using a continuous wave CO2 laser beam followed by tandem waterjet quenching of the laser irradiated material. The indentation hardness of the as-synthesized material was measured to be nominally 37 GPa. After the heat treatment the indentation hardness increased to nominal values of 75 GPa reaching the hardness of polycrystalline diamond 65-80 GPa. Dispersive Raman spectroscopy, high-resolution scanning electron microscope (HRSEM) and surface grazing XRD were used to characterize the BN phase signatures, grain size changes and phase transitions in both as-synthesized and heat treated material. Comparison of the as-synthesized and heat treated material microstructure revealed that heat treatment resulted in microstructure that consists of large grains; surrounded with regions of nano-grains between larger grains and; formation of solid interlayer along the grain boundaries. The increase in hardness was observed for LWH processing at laser fluence below 35 J/mm(2), and LWH processing above this value resulted in spallation of BN material from the surface. Raman spectrums of the material processed below the laser fluence of 35 J/mm(2) indicated that there are minimal phase transitions in the material; however, above that fluence, BN transformed into hexagonal phase resulting in surface damage through spallation. A combination of amorphous phase formation at the grain boundaries and grain size refinement are suggested as the mechanisms responsible for the LWH processing induced hardness increase. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 2. |
- Melaibari, Ammar, et al.
(författare)
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Extreme Hardness Achievements in Binderless Cubic Boron Nitride Tools
- 2013
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Ingår i: Transactions of the North American Manufacturing Research Institution of SME Volume 41, 2013. - 9781627486972 ; , s. 449-457
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Konferensbidrag (refereegranskat)abstract
- Binderless cubic boron nitride tools are available in two forms: single phase cBN and dual phase wBN/cBN (w is wurtzite phase). In this work, a novel heat treatment process involving surface heating using a continuous wave CO2 laser followed by tandem waterjet quenching of the laser beam path was applied to increase the hardness of both forms of boron nitride. Stress-induced phase transitions and nanometric grain sizes accompanying the rapid quench heat treatment enabled a hardness increase of 20% in single phase cBN (nominal 60 GPa) and 100% in dual phase wBN/cBN (nominal 75 GPa) that attest the ability of cBN to reach the hardness of polycrystalline diamond (65-80 GPa). The effects of laser heat treatment are identified by an examination of the changes in phase and microstructure by Raman spectroscopy, high resolution scanning electron microscopy and X-ray diffraction.
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| 3. |
- Tu, Juei-feng, 1959-, et al.
(författare)
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Laser synthesis of a copper-single-walled carbon nanotube nanocomposite via molecular-level mixing and non-equilibrium solidification
- 2016
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 49:49
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Tidskriftsartikel (refereegranskat)abstract
- A copper-single-walled carbon nanotube (Cu-SWCNT) metal nanocomposite could be an ideal material if it can substantially improve the strength of copper while preserving the metal’s excellent thermal and electrical properties. However, synthesis of such a nanocomposite is highly challenging, because copper and SWCNTs do not form intermetallic compounds and are insoluble; as a result, there are serious issues regarding wettability and fine dispersion of SWCNTs within the copper matrix. In this paper we present a novel wet process, called the laser surface implantation process (LSI), to synthesize Cu-SWCNT nanocomposites by mixing SWCNTs into molten copper. The LSI process includes drilling several microholes on a copper substrate, filling the microholes with SWCNTs suspended in solution, and melting the copper substrate to create a micro-well of molten copper. The molten copper advances radially outward to engulf the microholes with pre-deposited SWCNTs to form the Cu-SWCNT implant upon solidification. Rapid and non-equilibrium solidification is achieved due to copper’s excellent heat conductivity, so that SWCNTs are locked in position within the copper matrix without agglomerating into large clusters. This wet process is very different from the typical dry processes used in powder metallurgy. Very high hardness improvement, up to 527% over pure copper, was achieved, confirmed by micro-indentation tests, with only a 0.23% SWCNT volume fraction. The nanostructure of the nanocomposite was characterized by TEM imaging, energy-dispersive x-ray spectroscopy mapping and spectroscopy measurements. The SWCNTs were found to be finely dispersed within the copper matrix with cluster sizes in the range of nanometers, achieving the goal of molecular-level mixing.
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