1. |
- Joelsson, Torbjörn, 1972-, et al.
(författare)
-
Phase stability tuning in the NbxZr1-xN thin-film system for large stacking fault density and enhanced mechanical strength
- 2005
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:13
-
Tidskriftsartikel (refereegranskat)abstract
- The phase stability of hexagonal WC-structure and cubic NaCl-structure 4d transition metal nitrides was calculated using first-principles density functional theory. It is predicted that there is a multiphase or polytypic region for the 4d transition metal nitrides with a valence electron concentration around 9.5 to 9.7 per formula unit. For verification, epitaxial NbxZr1-xN (0 <= x <= 1) was grown by reactive magnetron sputter deposition on MgO(001) substrates and analyzed with transmission electron microscopy (TEM) and x-ray diffraction. The defects observed in the films were threading dislocations due to nucleation and growth on the lattice-mismatched substrate and planar defects (stacking faults) parallel to the substrate surface. The highest defect density was found at the x=0.5 composition. The nanoindentation hardness of the films varied between 21 GPa for the binary nitrides, and 26 GPa for Nb0.5Zr0.5N. Unlike the cubic binary nitrides, no slip on the preferred [1 (1) over bar0]{110} slip system was observed. The increase in hardness is attributed to the increase in defect density at x=0.5, as the defects act as obstacles for dislocation glide during deformation. The findings present routes for the design of wear-resistant nitride coatings by phase stability tuning.
|
|
2. |
- Lu, J, et al.
(författare)
-
Chemical vapour deposition of molybdenum carbides: aspects of phase stability
- 2000
-
Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 370:1-2, s. 203-212
-
Tidskriftsartikel (refereegranskat)abstract
- Thin films of different molybdenum carbides (δ-MoC1−x, γ′-MoC1−x and Mo2C) have been deposited from a gas mixture of MoCl5/H2/C2H4 at 800°C by CVD. The H2 content in the vapour has a strong influence on the phase composition and microstructure. Typically, high H2 contents lead to the formation of nanocrystalline δ-MoC1−x films while coarse-grained γ′-MoC1−x is formed with an H2-free gas mixture. This phase has previously only been synthesized by carburization of Mo in a CO atmosphere and it has therefore been considered as an oxycarbide phase stabilized by the presence of oxygen in the lattice. Our results, however, show that γ′-MoC1−x films containing only trace amounts of oxygen can be deposited by CVD. Stability calculations using a FP-LMTO method confirmed that the γ′-MoC1−x phase is stabilized by oxygen but that the difference in energy between e.g. δ-MoC0.75 and oxygen-free γ′-MoC0.75 is small enough to allow the synthesis of the latter phase in the absence of kinetic constraints. Annealing experiments of metastable δ-MoC1−x and γ′-MoC1−x films showed two different reaction products suggesting that kinetic effects play an important role in the decomposition of these phases.
|
|