Evolution kinetics and microstructure of MoSi2 and Mo5Si3 surface layers on two-phase Mo-9Si-18B alloy during pack-cementation and high-temperature oxidation

Ito, Kazuhiro; Hayashi, Teruaki; Yokobayashi, Masato; Numakura, Hiroshi

doi:10.1016/j.intermet.2003.12.009

Cited by 36 publications

(24 citation statements)

References 13 publications

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“…Figure 5 shows (a) an EBSP orientation image of a vertical cross section of a specimen pack cemented for 48 hours then oxidized at 1500 °C in air for 50 hours. [15] Grain orientations normal to the coating surface, i.e., in the diffusion direction, were determined by EBSP and are differentiated by colors as indicated in the inset [001]-[100]-[110] stereographic triangle. The columnar grains in the T 1 layer exhibit a [001] texture in the growth direction parallel to the diffusion direction.…”

Section: Figures 4(b) and (C)mentioning

confidence: 99%

“…The growth rate constant of T 1 is found to be about 0.43, 1.4, and 2.9 ϫ 10 Ϫ14 m 2 /s at 1300 °C, 1400 °C, and 1500 °C, respectively. [15] Figure 6 shows their Arrhenius plots, together with the results of earlier studies in the binary Mo-Si system [17][18][19][20][21][22] for comparison. The values of the present study fall at the lower bound of the data for the binary Mo-Si system reported by Tortorici.…”

Section: Reaction Diffusion Of Mosi 2 /(Mo 5 Sib 2 ϩ Mo Ss )mentioning

confidence: 99%

“…Figure 7(a) shows a sample current image of a vertical cross section of a specimen pack cemented for 48 hours and oxidized at 1500 °C in air for 12 hours and (b) EPMA concentration profiles in the diffusion direction. [15] Since the oxidation rate of the pack-cemented specimens is as low as that of MoSi 2 , [10] the consumption of Si during isothermal oxidation is negligible. The traces of the electron beam in the step-by-step measurements are visible in Figure 7(a), along which the layer interfaces are marked correspondingly to those in the concentration profiles in Figure 7(b).…”

Section: Reaction Diffusion Of Mosi 2 /(Mo 5 Sib 2 ϩ Mo Ss )mentioning

confidence: 99%

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Oxidation protective silicide coating on Mo-Si-B alloys

Ito

Numakura

Hayashi

et al. 2005

Metall Mater Trans A

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A MoSi 2 coating was successfully formed on a Mo-9Si-18B alloy, consisting of Mo 5 SiB 2 (T 2 ) and Mo solid solution (Mo ss ) phases, using pack cementation with Si. Isothermal and cyclic oxidation tests of pack-cemented Mo-9Si-18B alloys were performed at 1300 °C and 1500 °C. Steady-state oxidation rates at both temperatures are almost equal to those of pure MoSi 2 . The MoSi 2 layer is completely transformed into Mo 5 Si 3 (T 1 ) containing B after oxidation at 1500 °C for 24 hours. Thermal expansion of the T 1 phase is anisotropic, but a [001] texture in the growth direction for the columnar grains in the T 1 layer reduces thermal stresses generated around the phases. Evolution of T 1 layers during oxidation between 1300 °C and 1500 °C was investigated; their growth rate constants and the interdiffusion coefficient of Mo and Si in the Mo-Si-B system have been evaluated and compared with those in the binary Mo-Si system. Furthermore, we have studied phase transformations in a simpler system MoSi 2 vs T 2 using MoSi 2 /T 2 diffusion couples. Layers of T 1 and MoB ϩ T 1 were formed in the diffusion zone during oxidation at temperatures between 1400 °C and 1600 °C. This behavior is different from that of the pack-cemented Mo-9Si-18B alloy. Pack-cemented T 2 single crystals show a diffusion structure similar to that of MoSi 2 /T 2 diffusion couples, but the ratio of layer thickness is different. Based on these diffusion results, a method for extending the lifetime of the MoSi 2 layer is proposed.

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Section: Figures 4(b) and (C)mentioning

confidence: 99%

Section: Reaction Diffusion Of Mosi 2 /(Mo 5 Sib 2 ϩ Mo Ss )mentioning

confidence: 99%

Section: Reaction Diffusion Of Mosi 2 /(Mo 5 Sib 2 ϩ Mo Ss )mentioning

confidence: 99%

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Oxidation protective silicide coating on Mo-Si-B alloys

Ito

Numakura

Hayashi

et al. 2005

Metall Mater Trans A

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“…The peaks observed in 36.4 (in overlap with a peak of the T 2 phase), 40.9 and 63 (pointed out by stars in the Fig. 1) were indexed as Ta 3 Ge phase published elsewhere [12] (space group 86 and Ni3P prototype structure). A sample with this composition was prepared in other to investigate if this phase could give rise to the superconductivity observed and regarding the low temperature properties this compound is found to be a Pauliparamagnetic (data not shown).…”

Section: Resultsmentioning

confidence: 99%

“…Recent reports propose the existence of stoichiometric phases in the binary system Ta e Ge such as Ta 3 Ge, Ta 5 Ge 3 , [12e15]. Ta 3 Ge, for instance, can assume two different prototype structures, a-Ta 3 Ge and b-Ta 3 Ge.…”

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confidence: 99%