Structural properties, internal stress and thermal stability of nc-TiN/a-Si3N4, nc-TiN/TiSix and nc-(Ti1−yAlySix)N superhard nanocomposite coatings reaching the hardness of diamond

Niederhofer, A.; Nesládek, Pavel; Männling, H.-D.; Moto, Keba; Vepřek, S.; Jílek, Mojmír

doi:10.1016/s0257-8972(99)00451-x

Cited by 208 publications

(40 citation statements)

References 26 publications

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“…Moreover, the comparison with the literature results, particularly with the interpretation suggested above [4][5][6], will be discussed.…”

Section: Introductionmentioning

confidence: 81%

“…As referred to for nanocrystalline TiaSiaN system [6], the grain size was determined applying the Scherrer formula with the integral width of the main diffraction peak.…”

Section: Methodsmentioning

confidence: 99%

“…The softening observed was attributed to the high volume fraction of interfacial regions that leads to high deformation by different mechanisms of grain boundary sliding. Recently, other authors found that Hall-Petch relationship can be verified either for very low period multilayers [3] or in thin coatings of the system MaSiaN (M=W, Ti, V) [4][5][6]. These last films were described as a nanocomposite consisting of nanocrystalline nitride phases ( down to 3 nm) in an amorphous silicon nitride matrix (nc-MN x /a-SiN x ) or in a crystalline phase matrix (nc-MN x /c-MSi x ) which had sufficient structural flexibility to form a strong interface.…”

Section: Introductionmentioning

confidence: 99%

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Nanocrystalline structure and hardness of thin films

Cavaleiro

Louro

2002

Vacuum

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WaSiaN films were deposited by reactive sputtering in a N 2 +Ar atmosphere from a W target incrusted with different number of Si pieces. The coatings present different crystallographic structures from the crystalline a-W and W 2 N to amorphous phase. Crystalline films have very low grain sizes from 15 down to 3 nm.For WaSi films there is a good correlation between the increase of the hardness and both the increase of lattice parameter and decrease of grain size. However, for N containing films these tendencies are not systematically observed. The homogeneity in the lattice distortion seems to be more adequate to interpret the hardness variation.Generally, crystalline films have higher hardness (35-41 GPa) than amorphous coatings (21-31 GPa). r

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“…Moreover, the comparison with the literature results, particularly with the interpretation suggested above [4][5][6], will be discussed.…”

Section: Introductionmentioning

confidence: 81%

“…As referred to for nanocrystalline TiaSiaN system [6], the grain size was determined applying the Scherrer formula with the integral width of the main diffraction peak.…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nanocrystalline structure and hardness of thin films

Cavaleiro

Louro

2002

Vacuum

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“…Superhard nanocomposites consisting of 3-4 nm size, randomly oriented [1] nanocrystals of stable, hard transition metal nitride (TmN) ''glued'' together by about one monolayer (1 ML) of a covalent nitride (e.g., Si 3 N 4 ), with hardness between 45 [2] to !100 GPa [3] have attracted wide attention of the scientific community, and have already found large-scale industrial applications [4]. Hardness maxima of 33 to 35 GPa have recently been reported also for fcc-TmN=SiN=TmN heterostructures when the pseudomorphic fcc-SiN, between roughly 4 nm thick TiN [5][6][7][8][9][10] or ZrN [11] slabs, was about 1 to 2 ML thick.…”

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confidence: 99%

Friedel Oscillations are Limiting the Strength of Superhard Nanocomposites and Heterostructures

2009

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To obtain a deeper understanding of the mechanism of plastic deformation and failure in superhard nanocomposites and heterostructures we studied, by means of the ab initio density functional theory, the stress-strain response and the change of the electronic structure during tensile and shear deformation of a prototype interfacial systems consisting of 1 monolayer SiN sandwiched between a few nm thick TiN layers. This shows that peak Friedel oscillations of valence charge density weaken the Ti-N interplanar bonds next to that interface, where decohesion in tension and slip in shear occurs. These results provide ways to design new, stronger and harder materials. ZrN [11] slabs, was about 1 to 2 ML thick. Because the TiN-SiN x system is regarded as a ''prototype'' of all nitride-based superhard nanocomposites, we focus on it in this Letter.Hao et al. studied the stoichiometric TiN-Si 3 N 4 system by means of ab initio density functional theory (DFT). They found that the strongest configuration is a TiN= Si 3 N 4 =TiN sandwich containing 1 ML of -or -Si 3 N 4 -derived interfaces possessing decohesion strength larger than that of bulk Si 3 N 4 [12]. They also confirmed [13] the experimental finding [14] that oxygen impurities strongly degrade the strength of the Si 3 N 4 interface. Liu et al. studied several configurations of Si-atoms incorporated into TiN and found that the highest cohesive energy of 426.86 eV (bulk Ti-N 430.19 eV) have Si atoms tetrahedrally coordinated to 4N and 4Ti atoms with Si-N bonds being significantly shorter than the Si-Ti distance [15].We have shown that 1 ML of the interfacial, substoichiometric, pseudomorphic SiN is strengthened by a factor of 4 to 10 [16] as compared with bulk SiN [17]. Using the shear strength of the TiN=1 ML-SiN=TiN interfaces, calculated by ab initio DFT, Sachs averaging of these to obtain a tensile yield strength of the nanocrystalline assembly of grains, together with appropriately accounting for pressure enhancement of the shear resistances of the interfaces and using the Tabor relationship between hardness and the yield strength, the measured superhardness in excess of 100 GPa of nanocomposites has been fully explained [16]. However, in the papers quoted here, the electronic structure of the interface and its effect on the mechanism of decohesion and ideal shear under applied stress had not been studied. This is the subject of the present Letter which reveals for the first time that, although SiN is the weakest of all covalent materials under consideration, and unstable in bulk, the weakest link in the TiN=1 ML-SiN=TiN sandwich is the bond between Ti and N atoms within the interlayer next to the SiN x interface. This is a consequence of the ubiquitous Friedel oscillations that are found in electronically perturbed solids adjacent to their surfaces and interfaces [18].The ab initio DFT calculations were done using the ''Vienna ab initio simulation package'' (VASP) [19] with the projector augmented wave method employed to describe the electron-ion interaction [2...

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“…Thus, the hardening mechanism for coatings by high-energetic bombardment during growth is not suitable to obtain high hot hardness due to decreasing onset-temperature for recovery [14,17]. Other hardening mechanism like internal boundaries, second phase particles and solutes as mentioned above seem to be much more promising to obtain high hardness which sustains also higher temperatures [17][18][19]. These mechanisms can be effective due to self-arranging nanostructures either during coating growth an annealing treatment afterwards e.g., during coating operation.…”

Section: Introductionmentioning

confidence: 99%

Thermal Stability and Self-Arrangement of Nanocrystalline Hard Coatings

Mayrhofer

Nanostructured Thin Films and Nanodispersion Strengthened Coatings

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Nanocrystalline hard coatings have attracted increasing interest in modern development of hard coatings. Their increased volume fraction of interfaces is often responsible for superior properties, but they stimulate also microstructural processes. Whereas for single-phase coatings a remarkable reduction in hardness occurs around 500°C, nanocomposites maybe stable up to 1000°C. In physical vapor deposited (PVD) hard coatings nanostructures can arise during growth or during a post annealing treatment. In non-reactively sputtered overstoichiometric TiB 2 coatings the excess of boron forms a tissue phase surrounding TiB 2 crystals. Thus, a nanocolumnar structure with a diameter of about 5 nm is formed during the deposition process. Another example for segregation driven formation of a nanostructure is TiN-TiB 2 , where the coating consists mainly of TiN and TiB 2 nanocrystals of about 3 nm due to their extremely limited solubility. Nanostructures can also arise during annealing of supersaturated coatings. Thermal treatment of Ti 1-x Al x N coatings causes the metastable phase to decompose into its stable constituents TiN and AlN. Initially Ti 1-x Al x N coatings undergo spinodal decomposition generating an increase in hardness at elevated temperatures. The results presented show that next generation's coatings with increased ability for self-arrangement can effectively be prepared by PVD.

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Structural properties, internal stress and thermal stability of nc-TiN/a-Si3N4, nc-TiN/TiSix and nc-(Ti1−yAlySix)N superhard nanocomposite coatings reaching the hardness of diamond

Cited by 208 publications

References 26 publications

Nanocrystalline structure and hardness of thin films

Nanocrystalline structure and hardness of thin films

Friedel Oscillations are Limiting the Strength of Superhard Nanocomposites and Heterostructures

Thermal Stability and Self-Arrangement of Nanocrystalline Hard Coatings

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