Effects of microstructure on the oxidation behavior of multiphase Mo–Si–B alloys

Supatarawanich, V; Johnson, David R.; Liu, Chang

doi:10.1016/s0921-5093(02)00446-x

Cited by 109 publications

(75 citation statements)

References 14 publications

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“…For example, bubbles were observed in the MoÀ11SiÀ11B alloy scale at 800 8C, indicating that oxidation of molybdenum was occurring and that the MoO 3 bubbles were moving through the scale. [12] This behavior illustrates the ease with which material may be transported across the protective scale if the coating chemistry is not optimized. In addition, there is an issue with the high volatility of B 2 O 3 at temperatures above 1200 8C, which consequently impacts the metal recession rate even though a continuous borosilicate glass can be retained.…”

Section: Moàsiàb Alloy Systemmentioning

confidence: 99%

“…[11] Three phase alloys comprised of the Mo [solid solution (s.s.)], T 2 (Mo 5 SiB 2 ) and Mo 3 Si phases offer favorable combinations of high temperature mechanical properties and oxidation resistance due to the formation of an adherent borosilicate layer during high temperature oxidation. [12][13][14][15] Similarly, a combination of mostly the Mo 5 Si 3 (T 1 ) phase with T 2 and MoB phases shows an excellent oxidation resistance comparable to that of MoSi 2 . [16,17] While there are several factors influencing the oxidation resistance that have been identified, it is clear that the B to Si ratio of the alloy is the dominant factor that controls the constitution, the viscosity, and oxygen diffusivity as well [18] of the in situ SiO 2 ÀB 2 O 3 passive layer upon oxidation.…”

Section: Moàsiàb Alloy Systemmentioning

confidence: 99%

“…In addition, there is an issue with the high volatility of B 2 O 3 at temperatures above 1200 8C, which consequently impacts the metal recession rate even though a continuous borosilicate glass can be retained. [12][13][14][15] Thus, coating designs are necessary to provide enhanced oxidation protection to the MoÀSiÀB alloys.…”

Section: Moàsiàb Alloy Systemmentioning

confidence: 99%

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Oxidation Resistant Coatings for Ultrahigh Temperature Refractory Mo‐Base Alloys

Perepezko¹,

Sakidja²

2009

Adv Eng Mater

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The use of Mo base alloys is limited by severe oxidation above about 650 8C. While MoSi 2 coatings offer protection at high temperature, they are ineffective at low temperature. An integrated coating design has been developed based upon (B þ Si) co-deposition and an in-situ diffusion barrier that offers robust, long term oxidation protection and self-healing for Mo alloys over a wide temperature range to over 1600 8C.In recognition of the need for increased operating temperatures in order to satisfy the demands for increased gas turbine engine performance and improved energy efficiency that cannot be satisfied by Ni-base superalloys, new ultrahigh temperature structural materials in refractory metal systems and ceramic materials are under study. [1] Within these efforts, alloys in the MoÀSiÀB system have been identified with a number of attractive features based upon strength and creep resistance. [2][3][4][5] The base system does develop a protective borosilica oxidation scale, but the alloy recession rate that is too high for desired lifetimes. [6] For structural applications, the requirements for high strength at high temperature along with environmental attack resistance are not usually satisfied concurrently for most materials. One effective strategy to address an enhanced resistance to environmental attack in high strength materials is the application of oxidation resistant coatings. While this strategy is attractive, the successful implementation of protective coatings over the entire operating temperature range requires the satisfaction of other requirements involving thermodynamic and mechanical compatibility between the coating and the alloy substrate and the robust stability of the coating in order to maintain the integrity of the environmental protection.For the development of a coating design, the first step is to identify the key compositional and kinetic factors controlling the oxidation response. In the current work, this has been accomplished by analyzing the oxidation products and the reaction pathway as a basis for applying a novel kinetic biasing strategy to control the coating phase structure and sequencing and enhance the oxidation resistance. The approach for refractory metals is illustrated first for MoÀSiÀB ÀB alloys where the key components of the coating design are identified and then extended to other Mo-base systems.

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Section: Moàsiàb Alloy Systemmentioning

confidence: 99%

Section: Moàsiàb Alloy Systemmentioning

confidence: 99%

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Oxidation Resistant Coatings for Ultrahigh Temperature Refractory Mo‐Base Alloys

Perepezko¹,

Sakidja²

2009

Adv Eng Mater

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“…Balancing the B/Si ratio was found to be one important factor in adjusting the quality of the silica layer. Lowering the B/Si ratio yields a decrease of the high temperature oxidation resistance because silica formed at a very slow rate at low temperatures (750°C) [7]. This enhances the so-called pesting phenomenon, the simultaneous formation of silica and MoO 3 , at temperatures of 600-800°C [8].…”

Section: Introductionmentioning

confidence: 99%

Effect of Zr Addition on the High-Temperature Oxidation Behaviour of Mo–Si–B Alloys

et al. 2009

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Mo-Si-B alloys are promising candidates for structural high-temperature applications due to their excellent high-temperature mechanical properties along with high melting temperatures and oxidation resistance. After an initial period with high weight loss rates as a consequence of the volatilization of Mo-oxide, a protective borosilica (glass) layer develops on the alloy surface and steady-state oxidation is achieved. Aiming at improved mechanical properties of Mo-Si-B alloys which exhibit a continuous Mo solid solution matrix as a consequence of a powder metallurgical production route, small amounts of Zr were added. The presence of oxygen in the alloy leads to the formation of thermodynamically very stable Zr-oxide precipitates in the bulk alloy causing an enhancement of its mechanical properties. It was observed that the addition of Zr (distributed in the alloy matrix) also has significant influence on the oxidation behaviour of Mo-Si-B alloys by reducing the period for the formation of the protective and stable silica scale. Furthermore, the weight loss due to vaporization of Mo-oxides is consequently reduced. Besides this beneficial effect, Zr is harmful for the oxidation resistance at temperatures beyond 1,200°C. This is mainly due to the increased oxygen transport through defects in the silica scale.

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“…[13] Protection against environmental degradation is provided in the case of B-doped Mo 5 Si 3 and Mo-Si-B alloys by the formation of a borosilicate (B 2 O 3 -SiO 2 ) scale. [14][15][16][17] Because the B 2 O 3 has a low melting temperature of 450°C, [18] the oxidation resistance of B-doped Mo 5 Si 3 is improved due to sintering of the viscous oxide scale, leading to the closure of its pores. [13] Isothermal oxidation studies [17] of the selected Mo-Si-B and Mo-Si-B-Al alloys have shown pestlike accelerated degradation in the temperature range of 700°C to 900°C, whereas a continuous and stable scale of either B 2 O 3 -SiO 2 or B-doped silica could be formed during isothermal exposure at 1150°C for 24 hours.…”

Section: Introductionmentioning

confidence: 99%

Nonisothermal and Cyclic Oxidation Behavior of Mo-Si-B and Mo-Si-B-Al Alloys

Paswan

Mitra

Roy

2009

Metall Mater Trans A

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A study on nonisothermal and cyclic oxidation behavior of the reaction-hot-pressed 76Mo-14Si-10B, 77Mo-12Si- alloys has been carried out in dry air, and the results have been compared with those of isothermal tests. Nonisothermal studies by thermogravimetric (TG) analysis up to 1300°C have shown a transient mass gain between 700°C and 860°C, followed by a sharp mass loss with increased temperature, with the amount of mass change dependent on the heating rate (5°C/min to 35°C/min). The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies of oxide scales formed on the alloys held at 790°C and 820°C for 10 or 20 minutes suggest that the oxidation of a-Mo and Mo 3 Si precedes that of Mo 5 SiB 2 . Thermal cyclic tests involving exposure at 1150°C for 1 hour, followed by either air cooling to room temperature (RT) or furnace cooling to 700°C, 800°C, or 900°C, and the subsequent examination of oxidation products, have confirmed that the formation of B 2 O 3 -SiO 2 scale provides complete and partial protection for the Mo-Si-B and Mo-Si-B-Al alloys, respectively. The results of this study show that oxidation resistance is deteriorated upon Al addition. Residual stress measured by XRD is found to be largely compressive in Mo and in mullite phases of oxide scales. Thermal shock and the mismatch in the coefficients of thermal expansion (CTEs) between the constituent phases of the oxide scale appear to be the main causes of damage.

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Effects of microstructure on the oxidation behavior of multiphase Mo–Si–B alloys

Cited by 109 publications

References 14 publications

Oxidation Resistant Coatings for Ultrahigh Temperature Refractory Mo‐Base Alloys

Oxidation Resistant Coatings for Ultrahigh Temperature Refractory Mo‐Base Alloys

Effect of Zr Addition on the High-Temperature Oxidation Behaviour of Mo–Si–B Alloys

Nonisothermal and Cyclic Oxidation Behavior of Mo-Si-B and Mo-Si-B-Al Alloys

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