Hardness and deformation microstructures of nano-polycrystalline diamonds synthesized from various carbons under high pressure and high temperature

2007 ◽  
Vol 22 (8) ◽  
pp. 2345-2351 ◽  
Author(s):  
H. Sumiya ◽  
T. Irifune
Keyword(s):  
High Pressures ◽  
Polycrystalline Diamond ◽  
Direct Conversion ◽  
Knoop Hardness ◽  
Indentation Hardness ◽  
Hardness Tests ◽  
Layered Crystals ◽  
Microindentation Testing ◽  
Nano Grains ◽  
Knoop Indenter

Mechanical properties of high-purity nano-polycrystalline diamonds synthesized by direct conversion from graphite and various non-graphitic carbons under static high pressures and high temperatures were investigated by microindentation testing with a Knoop indenter and observation of microstructures around the indentations. Results of indentation hardness tests using a superhard synthetic diamond Knoop indenter showed that the polycrystalline diamond synthesized from graphite at ⩾15 GPa and 2300–2500 °C (consisting of fine grains 10–30 nm in size and layered crystals) has very high Knoop hardness (Hk ⩾ 110 GPa), whereas the hardness of polycrystalline diamonds synthesized from non-graphitic carbons at ⩾15 GPa and below 2000 °C (consisting only of single-nano grains 5–10 nm in size) are significantly lower (Hk = 70 to 90 GPa). Microstructure observations beneath the indentations of these nano-polycrystalline diamonds suggest that the existence of a lamellar structure and the bonding strength of the grain boundary play important roles in controlling the hardness of the polycrystalline diamond.

Microstructure and Mechanical Behaviors of Nano-polycrystalline Diamonds Synthesized by Direct Conversion Sintering under HPHT

2006 ◽  
Vol 987 ◽  
Author(s):  
Hitoshi Sumiya ◽  
Tetsuo Irifune
Keyword(s):  
Particle Size ◽  
Diffusion Process ◽  
Lamellar Structure ◽  
High Pressures ◽  
Polycrystalline Diamond ◽  
Direct Conversion ◽  
Knoop Hardness ◽  
Mechanical Behaviors ◽  
Hardness Values ◽  
Very High

AbstractHigh-purity nano-polycrystalline diamonds have been synthesized by direct conversion from graphite and various non-graphitic carbons under static high pressures and high temperatures. The polycrystalline diamond synthesized from graphite at ≥15 GPa and 2300-2600 °C has a mixed texture comprising a homogeneous fine structure (particle size: 10-30 nm, formed in a diffusion process) and a lamellar structure (formed in a martensitic process), and has a very high Knoop hardness of 120-145 GPa. In contrast, the polycrystalline diamonds made from the non-graphitic carbons at ≥15 GPa and 1600-2000 °C have a single texture consisting of a very fine homogeneous structure (5-10 nm, formed in a diffusion process) without a lamellar structure. The hardness values of the nano-polycrystalline diamonds made from non-graphitic carbons (70-90 GPa) are significantly lower than that of polycrystalline diamond made from graphite. The investigation of the microstructure beneath the indentation of these nano-polycrystalline diamonds revealed that the existence of the lamellar structure and the bonding strength of the grain boundary have a decisive effect on the hardness.

Further analysis of the size effect in indentation hardness tests of some metals

1995 ◽  
Vol 10 (11) ◽  
pp. 2908-2915 ◽  
Author(s):  
M. Atkinson
Keyword(s):  
Size Effect ◽  
Strain Hardening ◽  
Indentation Size Effect ◽  
Plastic Hinge ◽  
Small Scale ◽  
Indentation Hardness ◽  
Vickers Indentation ◽  
Indentation Size ◽  
Hardness Tests ◽  
Indentation Tests

The variation of apparent hardness observed in previously reported Vickers indentation tests of metals is reexamined. Common deseriptions of the effect are shown to be inaccurate: the variation of apparent hardness is monotonic but not simple. The effect is consistent with varying size of a previously postulated “plastic hinge” at the perimeter of the indent. This complexity confers uncertainty on the estimation of characteristic macrohardness from small scale tests. Association of the indentation size effect with friction and with strain hardening is confirmed.

scholarly journals ELECTRICALLY CONDUCTIVE POLYCRYSTALLINE SUPER HARD MATERIAL BASED ON DIAMOND AND n-LAYER GRAPHENES

2018 ◽  
Vol 59 (8) ◽  
pp. 69
Author(s):  
Alexandr A. Shul’zhenko ◽  
Lucyna Jaworska ◽  
Alexandr N. Sokolov ◽  
Vladislav G. Gargin ◽  
Ludmila A. Romanko
Keyword(s):  
Physical Properties ◽  
High Pressures ◽  
Polycrystalline Diamond ◽  
Sharp Decrease ◽  
Hard Material ◽  
Electrically Conductive ◽  
High Pressures And Temperatures ◽  
Polycrystalline Diamond Compact

The electrical and physical properties of the electrically conductive super hard material on the basis of polycrystalline diamond and n-layered graphenes obtained at high pressures and temperatures were studied. It was established that the increase in graphene in a polycrystalline diamond compact leads to a sharp decrease in resistance. Wherein the hardness of the samples is slightly inferior to the hardness of diamond poly crystals obtained without the use of graphene.

scholarly journals Effect of repeated cycles of chemical disinfection in microhardness of acrylic resins of complete denture base

2017 ◽  
Vol 65 (3) ◽  
pp. 196-201
Author(s):  
Elisa das Graças MARTINS ◽  
Rafael Tobias MORETTI NETO
Keyword(s):  
Sodium Hypochlorite ◽  
Knoop Hardness ◽  
Sodium Hypochlorite Solution ◽  
Chlorhexidine Digluconate ◽  
Water Control ◽  
Denture Base ◽  
Acrylic Resins ◽  
Hardness Tests ◽  
Before And After ◽  
Edentulous Patients

ABSTRACT Objective: To evaluate the microhardness of specimens of acrylic resins VipiCril® (thermally polymerized resin) and Bosworth New Truliner® (self-polymerized resin), before and after immersion in solutions of 0.12% chlorhexidine digluconate, 1% sodium hypochlorite, Corega Tabs® and water (control), testing the null hypothesis that the mouthwashes and chemicals used to disinfect complete dentures do not interfere with the superficial microhardness, and can therefore be used as adjuncts to oral hygiene of edentulous patients. Methods: Sixty specimens of resin VipiCril®(thermally polymerized resin) and 60 specimens of resin Bosworth New Truliner® (self-polymerized resin) measuring 16 mm of diameter and 6 mm of height were prepared, which were randomly divided into four groups of 15 specimens each, undergoing Knoop hardness tests (KHN) both before and after cycles of immersion in solutions of 0.12% chlorhexidine digluconate, 1% sodium hypochlorite, Corega Tabs® and water (control). Results: The specimens of resins VipiCril and Bosworth immersed in solutions of 0.12% chlorhexidine, Corega Tabs® and water showed decreased microhardness. Conclusion: The 1% sodium hypochlorite solution caused least damage to the denture structure, not leading to decrease of the superficial microhardness.

Rapid Synthesis of Nanostructural Intermetallics and their Bulk Properties

1996 ◽  
Vol 457 ◽  
Author(s):  
S. M. Pickard ◽  
A. K. Ghosh
Keyword(s):  
Grain Size ◽  
Physical Vapor Deposition ◽  
High Speed ◽  
Single Phase ◽  
Deposition Process ◽  
Indentation Hardness ◽  
Rotational Rate ◽  
Fine Grain ◽  
Compositional Variability ◽  
Nano Grains

ABSTRACTA rapid physical vapor deposition process (PVD) utilizing a high speed rotating substrate and small substrate-to-source spacing has been used to produce bulk sheet of Ti-Al alloys in the compositional range Ti-12% Al to Ti-75% Al1 at a rate of 1–3 μm/minute. Microstructural architectures produced by the method comprise of either fully homogenous phase mixtures of nano-grains, or nanolaminated material, depending on the substrate rotational rate, with lower rotational rate producing a layered microstructure. Defect populations within the as-deposited material are characterized by TEM and SEM, and hot pressing consolidation of the as-deposited material, which retains a grain size < 1000 nm, has been investigated. While indentation hardness of α2+γ(2 phase) alloys exceeded 7 GPa, brittle failure occurred in the elastic regime at nominally lower tensile stress than that for conventionally produced alloys containing Nb and Cr as solute elements. α2+γ alloys can exhibit tensile elongations of more than 100% at 850°C with retention of fine grain size. Elevated temperature failure occurs by the formation of voids in regions of compositional variability in the composite where single phase α2-Ti3Al structure was present.

scholarly journals Ion Beam Mixing of Ceramic Alloys - Preparation Andmechanical Properties

1981 ◽  
Vol 7 ◽  
Author(s):  
M. B. Lewis ◽  
C. J. McHargue
Keyword(s):  
Noble Gas ◽  
Ion Beam ◽  
Ceramic Materials ◽  
Knoop Hardness ◽  
Ion Beams ◽  
Crystal Surfaces ◽  
Ion Beam Mixing ◽  
Hardness Tests ◽  
Thin Chromium ◽  
Pure Metals

ABSTRACTTechniques used to produce unique states of pure metals mixed into ceramic materials are presented. The samples were prepared by irradiating a 1-MeV Fe+ beam on A12O3 crystal surfaces over which a thin chromium or zirconium film had been evaporated. The limitations of using noble gas ion beams are noted. Micro Knoop hardness tests performed near the surfaces of the samples indicated a significant increase in the hardness of most samples prepared by ion beam mixing.

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