Superhard Nanocomposites

The following chronological sequence showing the contributions to the research and development of superhard nanocomposites is based on the original published papers.

1951 Sylwestrowitz and Hall [859] as well as Hall [328, 860] independently published a set of three papers where the yield stress behavior of mild steel in tensile tests was first presented in the form of a well-known relationship such as a0 — a' ~ 1/d1/2. Explanation of the relationship was given in terms of a grain boundary theory [328].

1953 Petch, using polycrystals of mild steel, ingot iron, and spectrographic iron, found [329] that the cleavage strength (a) depends on the grain size (d) as ac = a0 + k—1/2. Later, this relationship became known as the Hall-Petch relationship.

1970 Koehler showed that it was possible [395] to design superhard composite coatings using thin alternate layers of high and low elastic materials. Such combinations do not allow Frank-Read dislocation sources to operate within the thin-layered composites. Some combinations such as Ni/Cu, MgO/LiF, and W/Ta were considered for the design.

1978 Lehoczky, building on Koehler's proposal [395] and using combinations of Al/Cu [396, 410] and Al/Ag [410], demonstrated that the yield strength of the layered composites, when the thickness of the single layers was within the nanoscale range, is a few times larger than the values given by the rule of mixture for the metal components if the thickness of the layers was reduced from 1000 to 70 nm.

1985 Demyashev determined [682] that the novel super-hard tungsten carbide (35-40 GPa) previously deposited [45] represents a nanocomposite of nc-W3C/nc-carbynes where carbynes are chainlike arrangements of carbon atoms.

1987 Helmersson et al. were the first to obtain a nanolay-ered composite of TiN/VN [377], which reached a micro-hardness of approximately 56 GPa at a bilayer repeat period of 5.2 nm.

1988 Birringer and Gleiter summarized the current (at the time) knowledge related to nanocrystalline materials for the first edition of the "Encyclopedia of Materials Science and Engineering" [180].

1990 Palumbo et al. showed [303] that the effect of grain size between 2 and 100 nm on the volumetric portion of intercrystalline regions, grain boundaries, and triple junctions is significant.

1992 Suryanarayana et al. obtained results [198] similar to [303]. There are critical grain sizes [198] at which nanocrystalline materials reach maximum hardness.

Scattergood and Koch modernized the Hall-Petch relationship as applied to nanocrystalline materials [360].

Shinn et al. synthesized a nanolayered composite of TiN/NbN, which had a hardness of 49 GPa at a bilayer repeat period of 4.6 nm [397].

1994 Gissler [639] obtained superhard nanocomposite coatings of titanium boron nitride (55 GPa).

1996 Setoyama et al. synthesized a superhard nanolayered composite of TiN/AlN (~40 GPa) with NaCl-type AlN for a bilayer repeat period of approximately 3 nm [552].

Veprek et al. reported nanocrystalline-amorphous composites of nc-TiN/a-Si3N4 and nc-W2N/a-Si3N4 [597], which reached a microhardness of approximately 50 GPa when the average nanograin sizes of nc-TiN and nc-W2N were between 30 and 40 nm.

1997 Wu et al. obtained a superhard nanocomposite of CNx/ZrN with a microhardness exceeding 40 GPa [539].

1998 Inspector et al. reported that a superhard nanolayered composite of TiN/BN (~40 GPa) had been obtained [568].

Selinder et al. obtained a nanolayered composite of TiN/TaN [433], which had a hardness of 39 GPa at hTiN = 7 nm and hTaN = 4 nm.

He et al. synthesized a hybrid ceramic-metal nanolayered composite of TiC/Fe [272], which reached a microhardness of approximately 42 GPa when hTiC ~ 8 nm and hFe ~ 5 nm.

1999 Diserens et al. reported on a superhard nanocomposite of TiN/SiNx (38 GPa), which was deposited by reactive unbalanced magnetron sputtering [606].

Niederhofer et al. reported [612] that a microhardness of 105 ± 20 GPa had been obtained for nanocomposites of nc-TiN/TiSix.

Musil and Hruby reported [618] that a superhard nanocrystalline-amorphous composite of nc-TiAlN/a-AlN with a microhardness of up to 47 GPa had been synthesized.

Benda and Musil synthesized a superhard nano-crystalline-amorphous composite of nc-Mo2C/(a-C + a-Mo2N) with a hardness of about 53 GPa [620].

2000 Xu et al. deposited a nanolayered composite of TiN/TaWN having a microhardness of 50 GPa at a bilayer repeat period of 5.6 nm [345].

Hovsepian et al. synthesized superhard nanolayered composites of TiAlN/CrN (42-78 GPa), TiAl-YN/VN (4256 GPa), and CrN/NbN (42-56 GPa) [471].

Yoon et al. deposited a superhard nanolayered composite of ß-WC1-x/TiN [570], which was as hard as 40 GPa at a bilayer repeat period of 7 nm.

2001 Yoon et al. synthesized a nanolayered composite of ß-WC1-x/Ti0 43Al0 57N with a microhardness of approximately 50 GPa [571].

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