Surface amorphous and crystalline microstructure by alloying zirconium using Nd : YAG pulsed laser

A novel composite coating was synthesized by laser alloying of zirconium nanoparticles on an austenite stainless steel surface using a pulsed Nd:YAG laser. The coating contained duplex microstructures comprising an amorphous phase and an austenitic matrix. A discontinuous zirconium-containing region formed at a depth of 16 mum below the surface. The amorphous phase was present in the zirconium-rich region, with the composition of zirconium ranging from 7.8 to 14.5 at. pet. The formation of the amorphous phase was attributed to the zirconium addition. The hardness, corrosion, and wear-corrosion resistance of the irradiated coating were evidently enhanced compared to those of the stainless steel.

Metallographic Analysis of Cu-Zr-Al Bulk Amorphous Alloys with Yttrium Addition

Minor yttrium addition can improve the glass-forming ability of Cu-Zr-Al ternary alloys via suppression of the growth of eutectic clusters. Yttrium addition also makes the room temperature ductility of the alloys decrease, and both the compressive strength and elastic strain limits increase slightly.

Amorphous Coatings Deposited on Aluminum Alloy by Plasma Electrolytic Oxidation

Amorphous [Al-Si-O] coatings were deposited on aluminum alloy by plasma electrolytic oxidation (PEO). The process parameters, composition, micrograph, and mechanical property of PEO amorphous coatings were investigated. It is found that the growth rate of PEO coatings reaches 4.44 mu m/min if the current density is 0.9 mA/mm(2). XRD results show that the PEO coatings are amorphous in the current density range of 0.3-0.9 mA/mm(2). EDS results show that the coatings are composed of O, Si and At elements. SEM results show that the coatings are porous. Nano indentation results show that the hardness of the coatings is about 3 - 4 times of that of the substrate, while the elastic modulus is about the same with the substrate. Furthermore, a formation mechanism of amorphous PEO coatings was proposed.

Influence of ion energy and substrate temperature on the optical and electronic properties of tetrahedral amorphous carbon (ta-C) films

The properties of amorphous carbon (a-C) deposited using a filtered cathodic vacuum arc as a function of the ion energy and substrate temperature are reported. The sp3 fraction was found to strongly depend on the ion energy, giving a highly sp3 bonded a-C denoted as tetrahedral amorphous carbon (ta-C) at ion energies around 100 eV. The optical band gap was found to follow similar trends to other diamondlike carbon films, varying almost linearly with sp2 fraction. The dependence of the electronic properties are discussed in terms of models of the electronic structure of a-C. The structure of ta-C was also strongly dependent on the deposition temperature, changing sharply to sp2 above a transition temperature, T1, of ≈200°C. Furthermore, T1 was found to decrease with increasing ion energy. Most film properties, such as compressive stress and plasmon energy, were correlated to the sp3 fraction. However, the optical and electrical properties were found to undergo a more gradual transition with the deposition temperature which we attribute to the medium range order of sp2 sites. We attribute the variation in film properties with the deposition temperature to diffusion of interstitials to the surface above T1 due to thermal activation, leading to the relaxation of density in context of a growth model. © 1997 American Institute of Physics.

Nature of disorder and localization in amorphous carbon

The electronic structure of amorphous diamond-like carbon is studied. Analysis of the participation ratio shows that π states within the σ-σ* gap are localized. The localization arises from dihedral angle disorder. The localization of π states causes the mobility gap to exceed the optical gap, which accounts for the low carrier mobility and the flat photoluminesence excitation spectrum. © 1998 Elsevier Science B.V. All rights reserved.

Doping mechanism in tetrahedral amorphous carbon

Doping in hydrogenated amorphous silicon occurs by a process of an ionised donor atom partially compensated by a charged dangling bond. The total energies of various dopant and dopant/bonding combinations are calculated for tetrahedral amorphous carbon. It is found that charged dangling bonds are less favoured because of the stronger Coulombic repulsion in ta-C. Instead the dopants can be compensated by weak bond states in the lower gap associated with odd-membered π-rings or odd-numbered π-chains. The effect is that the doping efficiency is low but there are not charged midgap recombination centres, to reduce photoconductivity or photoluminescence with doping, as occurs in a-Si:H.

Properties of tetrahedral amorphous carbon deposited by a filtered cathodic vacuum arc

The properties of a highly sp3 bonded form of amorphous carbon denoted ta-C deposited from a filtered cathodic vacuum arc (FCVA) are described as a function of ion energy and deposition temperature. The sp3 fraction depends strongly on ion energy and reaches 85% at an ion energy of 100 eV. Other properties such as density and band gap vary in a similar fashion, with the optical gap reaching a maximum of 2.3 eV. These films are very smooth with area roughness of order 1 nm. The sp3 fraction falls suddenly to almost zero for deposition above about 200 °C.

Doping mechanism in tetrahedral amorphous carbon

Doping in hydrogenated amorphous silicon occurs by a process of an ionized donor atom partially compensated by a charged dangling bond. The total energies of various dopant and dopant/bonding combinations are calculated for tetrahedral amorphous carbon. It is found that charged dangling bonds are less favored because of the stronger Coulombic repulsion in ta-C. Instead the dopants can be compensated by weak bond states in the lower gap associated with odd-membered π-rings or odd-numbered π-chains. The effect is that the doping efficiency is low but there are not charged midgap recombination centres, to reduce photoconductivity or photoluminescence with doping, as occurs in a-Si:H.

Surface atomic properties of tetrahedral amorphous carbon

The surface energy and surface atomic structure of tetrahedral amorphous carbon has been calculated by an ab-initio method. The surface atoms are found to reconstruct into sp2 sites often bonded in graphitic rings. Placing the dangling bonds on adjacent surface atoms lower their energy by π-bonding and this is the source of the low surface energy. The even lower surface energy of hydrogenated amorphous carbon (a-C:H) is due to the hydrogenation of all broken surface bonds. © 2005 Elsevier B.V. All rights reserved.