Plasticity and Size Effects in High Purity Cobalt: An Experimental Study

2016 ◽  
Vol 879 ◽  
pp. 560-565
Author(s):  
Gwendoline Fleurier ◽  
Mayerling Martinez ◽  
Pierre Antoine Dubos ◽  
Eric Hug
Keyword(s):  
Size Effects ◽  
Threshold Value ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
Tem Analysis ◽  
Cubic Metals ◽  
Hexagonal Close Packed ◽  
A Value ◽  
Face Centered ◽  
Two Phases

The occurrence of size effects in cobalt was examined by the analysis of mechanical properties of samples with thickness t, in a large range of grain size d giving a number of grains across the thickness t/d. On Hall-Petch plots, from the very beginning of plastic strain, two linear behaviors are notable: the polycrystalline one for higher t/d and the multicrystalline one for lower t/d in which the flow stress is strongly reduced. (t/d)c is the threshold value between the two behaviors taking a value of around 14. This high value is directly linked to the low stacking fault energy of cobalt. The microstructure of the polycrystalline samples exhibits a strong basal texture and a small proportion of a secondary face-centered cubic phase in a hexagonal close-packed main phase was evidenced. TEM analysis enables to characterize the dislocations and the stacking faults present in the two phases. To complete the analysis, two plasticity stages can be distinguished: stage A corresponding to dislocations gliding and stage B driven by twinning. Size effects in cobalt are found to occur during gliding process and could be related to surface effects as previously shown in face-centered cubic metals.

Preparation of Co3Ni Film Composed of Nanosheets and their Catalytic Activity in Hydrogen Generation from Sodium Borohydride Solution

2013 ◽  
Vol 860-863 ◽  
pp. 822-825
Author(s):  
Jin Yun Liao ◽  
Hao Li ◽  
Xi Bin Zhang
Keyword(s):  
Catalytic Activity ◽  
High Performance ◽  
Hydrogen Generation ◽  
Deposition Process ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
X Ray Diffraction ◽  
Original Activity ◽  
Hexagonal Close Packed ◽  
Face Centered

In this study, aiming to obtain high performance nanocatalysts for NaBH4 hydrolysis, Co3Ni film composed of nanosheets with a mean thickness of 10 nm was fabricated by a magnetic field induced deposition process. X-ray diffraction analysis indicated that the as-prepared Co3Ni film is presented in both face-centered cubic phase and hexagonal close-packed phase. The nanostructured Co3Ni film catalyst showed good catalytic activity in the hydrolysis of NaBH4 and the rate constant was 5.77 mL·min-1. It was revealed that Co3Ni film catalysts didnt lose their catalytic original activity essentially after 10 cycles, which exhibited much improved reusability and stability compared with with recently reported nanocatalysts.

Size Effects in Thin Face-Centered Cubic Metals for Different Complex Forming Loadings

2013 ◽  
Vol 44 (12) ◽  
pp. 5478-5487 ◽  
Author(s):  
Pierre-Antoine Dubos ◽  
Eric Hug ◽  
Simon Thibault ◽  
Mohamed Ben Bettaieb ◽  
Clément Keller
Keyword(s):  
Size Effects ◽  
Face Centered Cubic ◽  
Cubic Metals ◽  
Face Centered

scholarly journals Effect of Different Post-Sintering Temperatures on the Microstructures and Mechanical Properties of a Pre-Sintered Co–Cr Alloy

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 1036 ◽  
Author(s):  
Seong-Ho Jang ◽  
Bong Min ◽  
Min-Ho Hong ◽  
Tae-Yub Kwon
Keyword(s):  
Mechanical Properties ◽  
Cubic Phase ◽  
Carbide Formation ◽  
Face Centered Cubic ◽  
Cobalt Chromium ◽  
Hexagonal Close Packed ◽  
Soft Metal ◽  
Face Centered ◽  
Few Data ◽  
Sintered State

Although a cobalt–chromium (Co–Cr) blank in a pre-sintered state has been developed, there are few data on the optimal temperature for the alloy in terms of the desired mechanical properties. A metal block (Soft Metal, LHK, Chilgok, Korea) was milled to produce either disc-shaped or dumbbell-shaped specimens. All the milled specimens were post-sintered in a furnace at 1250, 1350 or 1450 °C. The microstructures, shrinkage and density of the three different alloys were investigated using the disc-shaped specimens. The mechanical properties were investigated with a tensile test according to ISO 22674 (n = 6). The number and size of the pores in the alloys decreased with increased temperature. The shrinkage and density of the alloys increased with temperature. In the 1250 °C alloy, the formation of the ε (hexagonal close-packed) phase was more predominant than that of the γ (face-centered cubic) phase. The 1350 °C and 1450 °C alloys showed γ phase formation more predominantly. Carbide formation was increased along with temperature. The 1450 °C group showed the largest grain size among the three groups. In general, the 1350 °C group exhibited mechanical properties superior to the 1250 °C and 1450 °C groups. These findings suggest that 1350 °C was the most optimal post-sintering temperature for the pre-sintered blank.

Evolution of the Transrotational Structure During Crystallization of Amorphous Ge2Sb2Te5 Thin Films

2009 ◽  
Vol 1160 ◽  
Author(s):  
Emanuele Rimini ◽  
Riccardo De Bastiani ◽  
Egidio Carria ◽  
Maria Grazia Grimaldi ◽  
Giuseppe Nicotra ◽  
...  
Keyword(s):  
Thin Films ◽  
Film Surface ◽  
Xrd Analysis ◽  
Lattice Parameter ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
Tem Analysis ◽  
The Face ◽  
Face Centered ◽  
Average Lattice

AbstractThe crystallization of amorphous Ge2Sb2Te5 thin films has been studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The analysis has been performed on partially crystallized films, with a surface crystalline fraction (fS) ranging from 20% to 100%. XRD analysis indicates the presence, in the partially transformed layer, of grains with average lattice parameters higher than that of the equilibrium metastable cubic phase (from 6.06 Å at fS=20% to 6.01 Å at fS=100%). The amorphous to crystal transition, as shown by TEM analysis, occurs through the nucleation of face-centered-cubic crystal domains at the film surface. Local dimples appear in the crystallized areas, due to the higher atomic density of the crystal phase compared to the amorphous one. At the initial stage of the transformation, a fast bi-dimensional growth of such crystalline nucleus occurs by the generation of transrotational grains in which the lattice bending gives rise to an average lattice parameter significantly larger than that of the face-centered-cubic phase in good agreement with the XRD data. As the crystallized fraction increases above 80%, dimples and transrotational structures start to disappear and the lattice parameter approaches the bulk value.

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