| 1. |
- Melk, Latifa, et al.
(författare)
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Coefficient of friction and wear resistance of zirconia-MWCNTs composites
- 2015
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 41:1 Part A, s. 459-468
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Tidskriftsartikel (refereegranskat)abstract
- Composites of 3 mol.% yttria-doped tetragonal zirconia (3Y-TZP) reinforced with multiwalled carbon nanotubes (MWCNT) up to 2 wt. % content have been produced using spark plasma sintering (SPS). The theoretical densities of the studied composites were found to be between 99.4 and 97.4%. The addition of MWCNT content resulted in reduction of 3Y-TZP grain size from 174 to 148 nm. The effect of MWCNT on the friction coefficient (COF) was studied by performing nano- and macro-scratches using diamond Berkovich and Rockwell indenters, respectively. Moreover, the COF and the wear rate were also investigated in reciprocating sliding against a zirconia ball under a load of 5 N. The results showed that the COF decreased upon the increase in MWCNT content. However, in macro-scratch testing, there was a critical load over which brittle fracture sets in and its value decreases as the MWCNT content increases. The wear resistance was found to be decreasing very slightly for less than 1 wt. % MWCNT, while it increases strongly for the addition of 2 wt. % MWCNT under the conditions studied. The results were discussed in terms of material properties, scanning electron microscopy observations of the wear track and nanoindentation tests.
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| 2. |
- Melk, Latifa, et al.
(författare)
-
Nanoindentation and fracture toughness of nanostructured zirconia/multi-walled carbon nanotube composites
- 2015
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 41:2, s. 2453-2461
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Tidskriftsartikel (refereegranskat)abstract
- Multi-walled carbon nanotubes (MWCNTs)/3 mol% yttria-doped tetragonal zirconia (3Y-TZP) composites were produced using spark plasma sintering (SPS) with MWCNT content ranging within 0-2 wt%. In the present paper, it was shown that the addition of MWCNTs results in a refinement of the composites microstructure. Moreover, nanoindentation tests were performed in order to monitor the change in elastic modulus and hardness with MWCNT content and it was found that both properties decrease with the addition of MWCNT content. A novel method was used to measure the true fracture toughness of the composites by producing a shallow surface sharp notch machined by ultra-short pulsed laser ablation on the surface of beam specimens. The true fracture toughness obtained on this laser machined single edge V-notch beam (SEVNB) specimens tested in four point bending was compared to the indentation fracture toughness measured using a Vickers indenter. It was found that the indentation fracture toughness increases with increasing MWCNT content, while the true fracture toughness determined with SEVNB was practically independent of the composition. Finally, it was concluded that the increase in the resistance to indentation cracking of the composites with respect to 3Y-TZP matrix cannot be associated to higher true fracture toughness. The results were discussed in terms of transformation toughening, damage induced in front of the notch tip, microstructure of the composites, and fracture toughness of 3Y-TZP.
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| 3. |
- Sefer, Birhan, et al.
(författare)
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Evaluation of the bulk and alpha-case properties in Ti-6Al-4V at micro- and nano-metric length scale
- 2016
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Ingår i: 13th World Conference on Titanium. - : John Wiley and Sons. ; , s. 1619-1624
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Konferensbidrag (refereegranskat)abstract
- In the present study the hardness of individual alpha (α)-Ti grains in Ti-6Al-4V was measured by nanoindentation using Berkovich tip indenter. Additionally, alpha-case layer was induced by performing isothermal heat treatment at 700°C in air for 500 hours. The average hardness of the α-Ti grains found in the bulk material and in the alpha-case layer were 6.7 ± 0.7 GPa and 9.4 ± 1.4 GPa, respectively. The high hardness of the α-Ti grains in the alpha-case layer is due to solid solution strengthening caused by interstitial oxygen diffusion. The thickness of the developed alpha-case layer was estimated metallographically and compared with that measured from a hardness profile performed along the layer. Moreover, electron back-scattered diffraction was used to determine the local crystallographic orientation, the texture of the alloy microstructure, as well as phase fraction changes, where the nanoindentation measurements were performed.
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