Mechanical Properties of Superhard Nanocomposites with High Thermal Stability

2003 ◽  
Vol 791 ◽  
Author(s):  
Stan Veprek ◽  
Ali S. Argon
Keyword(s):  
Elastic Recovery ◽  
High Hardness ◽  
Phase Segregation ◽  
Grain Boundary Sliding ◽  
Structural Flexibility ◽  
Ideal Strength ◽  
Crystallite Sizes ◽  
Boundary Sliding ◽  
Plastic Transformation ◽  
The Ideal

Abstract Superhard nanocomposites, nc-MnN/a-XxNy (M = Ti, W, V, Zr, (Al1-xTix)N; X = Si, B) with hardness of 40–100 GPa are prepared by plasma CVD or PVD under a sufficiently high nitrogen activity and deposition temperature that allow the formation of a stable nanostructure by self-organization upon strong thermodynamically driven, spinodal phase segregation. These nanocomposites display an extraordinary combination of a high hardness, high elastic recovery, high resistance against brittle fracture and tensile strength of 5 to 40 GPa approaching the ideal strength of flaw-free materials. These properties can be understood in terms of conventional fracture physics scaled appropriately down to crystallite sizes of few nm. The interfacial monolayer of Si3N4 or BN with strong bonding to the nanocrystallites and high structural flexibility avoids grain boundary sliding. With increasing thickness of this interface the hardness decreases, possibly due to an increase of this “liquid-like” component in which plastic transformation can be triggered.

First-Principles Calculations of Grain Boundary-Surface for Various Grain Boundaries with Different Energies in Aluminum

2007 ◽  
Vol 551-552 ◽  
pp. 331-336 ◽  
Author(s):  
Tokuteru Uesugi ◽  
Y. Inoue ◽  
Yorinobu Takigawa ◽  
Kenji Higashi
Keyword(s):  
Shear Strength ◽  
Grain Boundary ◽  
First Principles ◽  
Boundary Surface ◽  
Grain Boundary Sliding ◽  
Excess Energy ◽  
First Principles Calculations ◽  
Perfect Single Crystal ◽  
Boundary Sliding ◽  
The Ideal

The grain boundary surface is the excess energy of the grain boundary as the lattice on one side of the grain is translated relative to the lattice on the other side of the grain. The maximum in the slope of the grain boundary surface determines the ideal shear strength for the grain boundary sliding. We presented the ideal shear strength for the grain boundary sliding in aluminum Σ3(11 2)[110] tilt grain boundary from the first-principles calculations. The ideal shear strength for the grain boundary sliding was much smaller than the ideal shear strength of a perfect single crystal.

Damping Mechanisms in Oxide Materials and Their Potential Applications

2006 ◽  
Vol 319 ◽  
pp. 167-172 ◽  
Author(s):  
Qian Feng Fang ◽  
T. Liu ◽  
Chun Li ◽  
X.P. Wang ◽  
G.G. Zhang
Keyword(s):  
Short Range ◽  
Oxygen Vacancies ◽  
Domain Walls ◽  
High Hardness ◽  
Grain Boundary Sliding ◽  
Damping Capacity ◽  
Oxide Materials ◽  
Potential Applications ◽  
Boundary Sliding ◽  
Damping Materials

In this paper, we review the damping mechanisms in oxide materials, such as the short-range jump of oxygen vacancies and cation vacancies, movement of domain walls, and grain boundary sliding. Some examples in doped ZrO2, La2CuO4+δ, La2Mo2O9 and other oxide materials are briefly discussed, in which the damping capacity can reach as high as 30%. These oxides could be possibly applied as high damping materials either in the form of bulk components, or as additives in composites, or as hard damping coatings. In the last two potential applications, the high hardness and strength as well as high damping capacity of the oxides are simultaneously exploited, which cannot be realized by the usual high-damping metals and alloys.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

INTERNAL FRICTION PEAKS CONNECTED WITH GRAIN BOUNDARY SLIDING IN Al

1983 ◽  
Vol 44 (C9) ◽  
pp. C9-759-C9-764
Author(s):  
E. Bonetti ◽  
A. Cavallini ◽  
E. Evangelista ◽  
P. Gondi
Keyword(s):  
Internal Friction ◽  
Grain Boundary ◽  
Grain Boundary Sliding ◽  
Boundary Sliding

scholarly journals Friction of Metals: A Review of Microstructural Evolution and Nanoscale Phenomena in Shearing Contacts

2021 ◽  
Vol 69 (4) ◽  
Author(s):  
Michael Chandross ◽  
Nicolas Argibay
Keyword(s):  
Shear Strength ◽  
Grain Boundary Sliding ◽  
Deformation Mechanisms ◽  
Low Friction ◽  
Friction Behavior ◽  
Important Conclusion ◽  
Fundamental Properties ◽  
Wide Range ◽  
Boundary Sliding ◽  
Metal Interfaces

AbstractThe friction behavior of metals is directly linked to the mechanisms that accommodate deformation. We examine the links between mechanisms of strengthening, deformation, and the wide range of friction behaviors that are exhibited by shearing metal interfaces. Specifically, the focus is on understanding the shear strength of nanocrystalline and nanostructured metals, and conditions that lead to low friction coefficients. Grain boundary sliding and the breakdown of Hall–Petch strengthening at the shearing interface are found to generally and predictably explain the low friction of these materials. While the following is meant to serve as a general discussion of the strength of metals in the context of tribological applications, one important conclusion is that tribological research methods also provide opportunities for probing the fundamental properties and deformation mechanisms of metals.

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