This paper reports the results of a systematic investigation which has confirmed that the contiguity of the carbide phase in WC–Co alloys is only a function of cobalt content. The investigation, ...which was based on a wide range of WC–Co alloys varying in cobalt content as well as grain size, has also shown that the contiguity of the carbide phase has an approximately constant value (≈0.25) at cobalt volume fractions
V
Co
>
≅0.20 (but ≠1). This result is consistent with the observed tendency of WC grains to coalesce into groups of two or more at high cobalt contents, with the formation of WC/WC boundaries of energy lower than twice the energy of WC/Co interfaces.
A quantitative relationship between WC grain size, Co content and coercivity has been derived using data from a wide range of WC–Co alloys. The relationship has been found to agree with data from ...independent investigations.
Freeze-drying and gamma irradiation are commonly used for preservation and sterilization in bone banking. The cumulative effects of preparation and sterilization of cancellous graft material have not ...been adequately studied, despite the clinical importance of graft material in orthopaedic surgery. Taking benefit from the symmetry of the left and right femoral heads, the influence of lipid extraction followed by freeze-drying of a femoral head and a final 25-kGy gamma irradiation was determined, with the nonirradiated, nonprocessed counterpart as the control. Five hundred and fifty-six compression tests were performed (137 pairs for the first treatment and 141 pairs for the second). Mechanical tests were performed after 30 minutes of rehydration in saline solution. Freeze-dried femoral heads that had undergone lipid extraction experienced reductions of 18.9 and 20.2% in ultimate strength and stiffness, respectively. Unexpectedly, the work to failure did not decrease after this treatment. The addition of gamma irradiation resulted in a mean drop of 42.5% in ultimate strength. Stiffness of the processed bone was not modified by the final irradiation, with an insignificant drop of 24%, whereas work to failure was reduced by a mean of 71.8%. Freeze-dried bone was a bit less strong and stiff than its frozen control. Its work to failure was not reduced, due to more deformation in the nonlinear domain, and it was not brittle after 30 minutes of rehydration. Final irradiation of the freeze-dried bone weakened its mechanical resistance, namely by the loss of its capacity to absorb the energy (in a plastic way) and a subsequent greater brittleness.
Slip in tungsten monocarbide I. Some experimental observations NABRRO, F. R. N; BARTOLUCCI LUYCKX, S; WAGHMARE, U. V
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
06/2008, Letnik:
483-84
Conference Proceeding, Journal Article
Recenzirano
Tungsten carbide crystal is trigonal rather than hexagonal as is often assumed. The dependence of the room temperature hardness on the geometry of indentation is discussed in terms of its orientation ...in the crystal systems, and the temperature dependence of hardness is discussed on the assumption that slip in the basal plane has a very high Peierls stress. Unexpected dominance of a + c dislocations in the deformation process is discussed.
Towards a centralized Grid Speedometer Dzhunov, I; Andreeva, J; Fajardo, E ...
Journal of physics. Conference series,
01/2014, Letnik:
513, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Given the distributed nature of the Worldwide LHC Computing Grid and the way CPU resources are pledged and shared around the globe, Virtual Organizations (VOs) face the challenge of monitoring the ...use of these resources. For CMS and the operation of centralized workflows, the monitoring of how many production jobs are running and pending in the Glidein WMS production pools is very important. The Dashboard Site Status Board (SSB) provides a very flexible framework to collect, aggregate and visualize data. The CMS production monitoring team uses the SSB to define the metrics that have to be monitored and the alarms that have to be raised. During the integration of CMS production monitoring into the SSB, several enhancements to the core functionality of the SSB were required; They were implemented in a generic way, so that other VOs using the SSB can exploit them. Alongside these enhancements, there were a number of changes to the core of the SSB framework. This paper presents the details of the implementation and the advantages for current and future usage of the new features in SSB.
The size effect in microindentation Nabarro, F. R. N.; Shrivastava, Sanjiv; Luyckx, S. B.
Philosophical magazine (Abingdon, England),
09/2006, Letnik:
86, Številka:
25-26
Journal Article
Recenzirano
The theory by Stelmashenko et al., De Guzman et al. and Nix and Gao of the size effect in microindentation is outlined and some implicit assumptions are discussed. By an algebraic rearrangement, the ...slope of the straight-line plot of the square of hardness against the reciprocal of the diameter or depth of an indentation acquires a value which is predictable and in order of magnitude in agreement with experiment. The corresponding scale length, of order 1 micron in copper, is thus a real physical property of the material, although it is not visible in the undeformed material. In the recent experiments of Motz et al. it is observed directly. The two-phase 'hard metal' WC-Co has a microscopic intrinsic scale length, accordingly, the plot is no longer linear.
Thermal spray coatings based on tungsten carbide are widely used in wear applications. This paper presents results obtained from commercial WC–12
wt.%Co and WC–17
wt.%Co as well as experimental WC–10
...wt.%VC–12
wt.%Co and WC–10
wt.%VC–17
wt.%Co coatings. The coatings have been deposited on stainless steel substrates using a high pressure high velocity oxy-fuel (HP/HVOF) Tafa
® JP 5000™ thermal spraying system. They have all been tested under identical conditions in order to compare their resistance to abrasion and slurry erosion. Similar tests have been carried out previously in our laboratory H.L. de Villiers-Lovelock, S. Luyckx, Preliminary investigation on the potential of VC-WC-Co HP/HVOF powders and coatings, in: C.C. Berndt (Ed.), Proceedings of the First International Thermal Spray Conference, Montreal, Canada, 8–11 May 2000, pp. 647–656 1 but gave inconclusive results which were found due to the VC-containing powders (WC–VC–Co) not being optimal. The tests have now been repeated with optimized WC–VC–Co powders. The present results show that the WC–VC–Co coatings produced with the optimized powders exhibit higher abrasion resistance then commercial WC–Co coatings. In slurry erosion, the best performance of the VC-containing coatings is as good as that of the commercial WC–Co coatings. The role of VC and cobalt in the wear process of the coatings is discussed.
The results presented in this paper show that the abrasion resistance of WC–Co alloys can be increased by increasing the WC grain size while keeping the hardness constant, within a wide range of ...compositions and grain sizes. The cobalt content must be decreased in order to keep the hardness constant when increasing grain size, but the results show that the mean free path in cobalt (
λ) increases with increasing grain size (
d) at constant hardness, although the ratio
λ/
d decreases. The increase in mean free path can explain the increase in toughness at constant hardness and larger grain size observed in a wide range of alloys, while the decrease in
λ/
d ratio can explain the increase in abrasion resistance.
The Vickers hardness of WC–Co alloys has been measured at temperatures ranging from −196 to 900°C. The cobalt content of the alloys ranged from 10 to 24 vol% and the grain size from 0.5 to 2.3 μm. It ...was found that, at all cobalt contents and all temperatures, the decrease in hardness with increasing grain size can be approximated by a Hall–Petch type relationship. Up to about 600°C the decrease in hardness with increasing temperature appears to be due mostly to the decrease in the intrinsic hardness of the individual phases. Above 600°C the decrease in hardness appears to be due mostly to easier slip transfer across grain boundaries. Finer grained alloys have been found to preserve their hardness at high temperature better than coarser grained alloys, at all cobalt contents.
The composition and microstructure of agglomerated and sintered WC–VC–Co thermal spray powders and of the high pressure/high velocity oxy-fuel (HP/HVOF) coatings produced from the powders were ...analysed and compared to those of agglomerated and sintered commercial WC–Co thermal spray powders of equal Co mass fraction and of the commercial WC–Co coatings that were deposited under the same conditions as the WC–VC–Co coatings. The results of the analyses helped to explain the abrasion resistance of WC–VC–Co coatings being superior to that of WC–Co coatings.
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