Structure and mechanical properties of MoSi<sup>2</sup>-Sic nanolayer composites

Kung, H.; Jervis, T. R.; Hirvonen, J.; Embury, J.D.; Mitchell, T. E.; Nastasi, M.

doi:10.1080/01418619508236219

Cited by 22 publications

(15 citation statements)

References 27 publications

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“…1(a)-1(d) transmission electron images are shown for an as-deposited sample and samples annealed at 500 and 800 ± C. The microstructure of as-deposited coatings was amorphous; Fig. 18 In this work the temperature range of oxidation measurements includes the regime where the nanolayered structure was maintained, i.e., 450-800 ± C. This temperature range includes a pest disintegration temperature for MoSi 2 . Annealing at 500 ± C for 1 h resulted in the crystallization of the amorphous MoSi 2 phase; Fig.…”

Section: Resultsmentioning

confidence: 81%

“…18 On the other hand, the transformation of the metastable MoSi 2 with the C40 structure into the stable C11 b seems to be retarded in the nanolayered MoSi 2 ͞SiC composite. It seems that the nanolayered structure enhances the recrystallization of amorphous SiC by enhancing nucleation as explained elsewhere.…”

Section: Discussionmentioning

confidence: 99%

“…18 In brief, the microstructure of both MoSi 2 and SiC is amorphous following the deposition. The mechanical properties and temperature stability of this system have been reported elsewhere.…”

Section: Introductionmentioning

confidence: 99%

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Oxidation of MoSi₂/SiC nanolayered composite

et al. 1998

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The oxidation behavior of a nanolayered MoSi 2 ͞SiC composite material was determined at the temperature range of 400-900 ± C in wet oxidation conditions. The samples were produced in the form of thin films using a sputtering technique from two different sources, and a rotating substrate holder, onto silicon single crystals and low carbon steel. For comparison, the oxidations of both constituents, MoSi 2 and SiC, produced with the same sputtering technique, were measured separately. The microstructure of the MoSi 2 ͞SiC samples was determined with high resolution transmission electron microscopy (HRTEM), and the composition of the sputtered samples was measured using backscattering (BS) of protons. For quantitative determination of oxidation, the nuclear reaction 16 O͑d, p͒ 17 O was utilized. Oxide layers were also analyzed using a secondary ion mass spectrometry (SIMS) and the appearance of the oxidized surface with a scanning electron microscopy (SEM). As expected, the SiC films had both the lowest initial oxidation and steady state oxidation rate. The results show that the oxidation behavior of the MoSi 2 ͞SiC nanolayered composite material differs from that of both its constituents and involves a degradation mechanism of its own, resulting in the highest oxidation during the initial phase of the oxidation. A steady-state oxidation rate was observed after the initial transient phase to be the highest for the metastable C40 structure of the single MoSi 2 layer. The oxidation rate of the nanolayered structure was retarded by the SiC layers. No signs of pest disintegration were observed on either of the MoSi 2 containing coatings during the steady-state phase of the oxidation at 500 ± C up to 40 h. Our results show that the oxidation of nanolayered structures can be only in part explained by the oxidation behavior of the constituents and that during the steady-state oxidation of the nanolayered structure the oxidation rate is largely determined by the constituent with the lowest oxidation rate and by the layered structure.

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Section: Resultsmentioning

confidence: 81%

Section: Discussionmentioning

confidence: 99%

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Oxidation of MoSi₂/SiC nanolayered composite

et al. 1998

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“…5 At higher temperatures MoO 3 is volatile and a protective SiO 2 layer is formed on the surface. [19][20][21] Nanolayered (multilayers with the sublayer thickness on the nanometric scale) and nanocrystalline materials may possess many unique properties, which are fundamentally different and often superior compared to those of materials with coarser microstructure. While accelerated oxidation is generic to all forms of MoSi 2 , pesting has been concluded to result from accelerated oxidation within the preexisting microcracks.…”

Section: Introductionmentioning

confidence: 99%

Oxidation of nanocrystalline Mo–Si–N and nanolayered Mo–Si–N/SiC coatings

Torri

1999

J. Mater. Res.

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Oxidation of sputter-deposited nanocrystalline Mo-Si-N (MoSi 2.2 N 2.5 ) coatings in oxygen-water vapor atmosphere has been studied in the temperature range 400-850°C. In addition, the oxidation properties of nanolayered Mo-Si-N/SiC coatings at 700°C were studied and compared to those of single-layer coatings of both components. No pest disintegration was observed in Mo-Si-N up to 200 h of oxidation. A preexponential rate constant of (3.7 ± 0.5) × 10 9 (10 15 atoms/cm 2 ) 2 /h and activation energy 1.03 ± 0.02 eV were determined from an Arrhenius plot for parabolic oxygen buildup on Mo-Si-N. Up to 20% less oxygen was detected in the oxidized nanolayered coatings compared to either of the components as a single layer, indicating an improvement in oxidation resistance.

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“…Experimental and theoretical results indicate a significant influence in the size of nanoparticles on the elastic properties of the consolidated nsM (e.g., [2,4,[9][10][11][12][13]). In turn, the elastic properties are expected to reflect the predicted transition from the amorphous to the nsS.…”

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Evidence of an Elastic Instability between the Amorphous and the Microcrystalline State of Ca-modified Lead Titanate as revealed by Brillouin Spectroscopy

et al. 1997

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Brillouin spectroscopy was used to probe the hypersonic properties of Ca-modified lead titanate between the pure amorphous and the coarse grained state. The samples were thin films rf sputtered onto (100)-silicon wafer at ambient temperature, followed by an annealing process in the range from 673 to 873 K. An elastic instability of the longitudinally polarized sound mode suggests the existence of a discontinuous structural transformation from the amorphous to the nanostructured state. [S0031-9007(97)02610-0] PACS numbers: 81.05. Ys, 68.35.Rh, 68.60.Bs, 78.35. + c Against the background of an increasing interest in nanostructured materials (nsM) the physical properties of the intermediate metastable structures between the pure amorphous and the microcrystalline states require special attention. One possible way to realize such intermediate states is to produce sputtered amorphous (dielectric) films and to anneal these films successively in an appropriate way. It is likely that the annealing-induced transformation from the initial amorphous state to the final coarse grained state may pass through one or more so-called metastable nanocrystallized states (e.g. [1][2][3][4][5]). It is a matter of current physical interest (i) whether these intermediate nanostructured states (nsS) can be fixed, (ii) how the transformation from the amorphous to the microcrystalline states takes place, and (iii) what are the properties of these intermediate states. Although the amorphous state as well as the nsS are metastable, the possibility of a structural phase transformation between the crystalline and the amorphous states has been proposed in the literature [1,5]. Based on free-energy simulations, Wang et al. [6], only recently, have predicted a phase transition from the nanocrystalline to the glassy state. A hint for the existence of such a transition may be drawn from the work of Rehn et al. [1]. These authors have reported an elastic shear instability for ion damaged Zr 3 Al.It is well established now that the evolution of the nsS is accompanied by an anomalous behavior in the elastic properties when compared to the amorphous and the microcrystalline reference states [2,4,7,8]. Experimental and theoretical results indicate a significant influence in the size of nanoparticles on the elastic properties of the consolidated nsM (e.g., [2,4,[9][10][11][12][13]). In turn, the elastic properties are expected to reflect the predicted transition from the amorphous to the nsS. The aim of the current paper is to show evidences for such a transformation in rf-sputtered films of Ca-modified lead-titanate ͑Pb 0.76 Ca 0.24 ͒TiO 3 (PTC) at a critical annealing temperature ͑T ca ഠ 823 K͒. As a sensitive probe we used the lon-gitudinally polarized acoustic phonon mode as detected by high resolution Brillouin spectroscopy (BS).PTC is -in the single or coarse grained polycrystalline state-a ferroelectric perovskite with a phase transition from the paraelectric to the ferroelectric state at T c ഠ 530 K [14]. At room temperature, the material is t...

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Structure and mechanical properties of MoSi²-Sic nanolayer composites

Cited by 22 publications

References 27 publications

Oxidation of MoSi₂/SiC nanolayered composite

Oxidation of MoSi₂/SiC nanolayered composite

Oxidation of nanocrystalline Mo–Si–N and nanolayered Mo–Si–N/SiC coatings

Evidence of an Elastic Instability between the Amorphous and the Microcrystalline State of Ca-modified Lead Titanate as revealed by Brillouin Spectroscopy

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Structure and mechanical properties of MoSi2-Sic nanolayer composites

Cited by 22 publications

References 27 publications

Oxidation of MoSi2/SiC nanolayered composite

Oxidation of MoSi2/SiC nanolayered composite

Oxidation of nanocrystalline Mo–Si–N and nanolayered Mo–Si–N/SiC coatings

Evidence of an Elastic Instability between the Amorphous and the Microcrystalline State of Ca-modified Lead Titanate as revealed by Brillouin Spectroscopy

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Structure and mechanical properties of MoSi²-Sic nanolayer composites

Oxidation of MoSi₂/SiC nanolayered composite

Oxidation of MoSi₂/SiC nanolayered composite