Oxidation mechanisms in Mo-reinforced Mo5SiB2(T2)–Mo3Si alloys

Parthasarathy, Triplicane A.; Mendiratta, M. G.; Dimiduk, Dennis M.

doi:10.1016/s1359-6454(02)00039-3

Cited by 227 publications

(125 citation statements)

References 13 publications

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“…These results are generally in good agreement with those of Mendiratta et al [9,10], who reported on the cyclic oxidation behavior of the same three-phase Mo-12Si-12B alloy as in the present study at 750°C, 800°C, 1200°C and 1300°C. In agreement with their findings [9], the present results on the cyclic oxidation kinetics and oxide scale microstructures indicate that there are two temperature regimes of behavior, the first from 900-800°C and lower and the second at 1000°C and higher.…”

Section: Discussionsupporting

confidence: 94%

Microstructure Effects on Creep Behavior of Next Generation of Refractory Alloys for Very High Temperature Applications

Vasudevan¹,

Leonard²

2002

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The primary objective of the present project was to gain a basic understanding of the effects of microstructure on the creep behavior of a new class of Mo-Si-B alloys that are being considered for very high temperature structural applications. A second objective was to obtain insight into the oxidation behavior of these materials. During this one-year project, thermal effects on microstructure evolution in a Mo-7.44Si-8.51B (at.%) alloy were studied. The results indicate that it is possible to exert some control over microstructure and properties by very high temperature heat treatments. Significant changes in volume fraction of oc-Mo, Mo 3 Si and T2 phases occur at temperatures al700°C. The cyclic oxidation behavior in air at temperatures between 800-1100°C were also studied in a three-phase Mo-12Si-12B (at.%) and near-single T2 phase Mo-12.5Si-25B alloy: The results indicate that catastrophic oxidation occurs in both alloys at/below 800-900°C; performance and oxidation protection is better at 2lOOO°C. A porous, non-protective borosilicate/B-Si0 2 layer forms at low temperatures, which permits easy oxygen diffusion and increased weight loss through volatilization of Mo as Mo0 3 gas. A stable, dense silica scale forms at/above 1000°C, which provides protection from oxidation and reduced weight loss.

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Section: Discussionsupporting

confidence: 94%

Microstructure Effects on Creep Behavior of Next Generation of Refractory Alloys for Very High Temperature Applications

Vasudevan¹,

Leonard²

2002

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“…2 b) during cooling. The faster turnover from mass loss to mass gain at 1200 °C in contrast to 1100 °C is caused by the lower viscosity of the borosilicate glass at higher temperatures [13,26].…”

Section: Oxidation Behaviormentioning

confidence: 99%

“…Unfortunately, such alloys exhibit a relatively high density of 9.6 g/cm³ compared to densities below 9 g/cm³ for common Ni-base superalloys [8] and fail in a brittle manner at lower temperatures [9 -12]. Furthermore, at temperatures at around 600 -900 °C the oxidation resistance of Mo-Si-B alloys is dominated by MoO 3 vaporization and results in a catastrophic oxidation behavior [13].…”

Section: Introductionmentioning

confidence: 99%

Enhanced Oxidation Resistance of Mo–Si–B–Ti Alloys by Pack Cementation

et al. 2017

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Abstract.As new high temperature structural materials, Mo-Si-B alloys satisfy several requirements such as oxidation and creep resistance. Recently, novel Ti-rich Mo-Si-B alloys have shown an increased creep resistance compared to Ti-free alloys. However, due to the formation of a duplex SiO 2 -TiO 2 oxide layer, which allows for fast ingress of oxygen, the oxidation resistance is poor. To improve the oxidation resistance a borosilicate based coating was applied to a Mo-12.5Si-8.5B-27.5Ti (in at.%) alloy. After co-deposition of Si and B by pack cementation at 1000 °C in Ar, a conditioning anneal at 1400 °C is used to develop an outer borosilicate layer followed by an inner MoSi 2 and Mo 5 Si 3 layer. During both isothermal and cyclic oxidation after an initial mass loss during the first hours of exposure, a steady state is reached for times up to 1000 h at temperatures ranging from 800 to 1200 °C demonstrating a significantly enhanced oxidation resistance.

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“…These dislocations are visible when imaged with g = 0-11 (Figure 30(a,b)) and g = 101 ( Figure 30(c)), but are invisible when imaged with g = -101 (Figure 30(d)) and g = 110 (Figure 30(e)). Based on these visibilities and invisibilities, the Burgers vector of these dislocations could be established as being b = ½ [1][2][3][4][5][6][7][8][9][10][11]. Compared with the α-Mo regions, the Mo3Si and T2 particles were found to contain very few dislocations (Figure 30(f)), indicating that the bulk of the deformation strain occurs in the α-Mo.…”

Section: Microstructure Of Deformed Samplesmentioning

confidence: 99%

“…Indeed, studies of phase relations and microstructure have shown that the alloy compositions having the best potential for balanced properties through microstructure manipulation lie in the three-phase region ( Figure 1) composed of the intermetallic phases T2-Mo5SiB2 and Mo3Si in an α-Mo solid solution matrix [6][7][8]. The oxidation resistance of candidate alloys is excellent at temperatures above 1000°C, which is achieved through the formation of an adherent and protective SiO2 scale [2][3][4]9,10].…”

Section: Introductionmentioning

confidence: 99%

Processing, Microstructure and Creep Behavior of Mo-Si-B-Based Intermetallic Alloys for Very High Temperature Structural Applications

Vasudevan¹

2008

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This research project is concerned with developing a fundamental understanding of the effects of processing and microstructure on the creep behavior of refractory intermetallic alloys based on the Mo-Si-B system. In the first part of this project, the compression creep behavior of a Mo-8.9Si-7.71B (in at.%) alloy, at 1100 and 1200°C was studied, whereas in the second part of the project, the constant strain rate compression behavior at 1200, 1300 and 1400°C of a nominally Mo-20Si-10B (in at.%) alloy, processed such as to yield five different α-Mo volume fractions ranging from 5 to 46%, was studied. In order to determine the deformation and damage mechanisms and rationalize the creep/high temperature deformation data and parameters, the microstructure of both undeformed and deformed samples was characterized in detail using x-ray diffraction, scanning electron microscopy (SEM) with back scattered electron imaging (BSE) and energy dispersive x-ray spectroscopy (EDS), electron back scattered diffraction (EBSD)/orientation electron microscopy in the SEM and transmission electron microscopy (TEM). The microstructure of both alloys was three-phase, being composed of α-Mo, Mo3Si and T2-Mo5SiB2 phases. The values of stress exponents and activation energies, and their dependence on microstructure were determined. The data suggested the operation of both dislocation as well as diffusional mechanisms, depending on alloy, test temperature, stress level and microstructure. Microstructural observations of post-crept/deformed samples indicated the presence of many voids in the α-Mo grains and few cracks in the intermetallic particles and along their interfaces with the α-Mo matrix. TEM observations revealed the presence of recrystallized α-Mo grains and sub-grain boundaries composed of dislocation arrays within the grains (in Mo-8.9Si-7.71B) or fine sub-grains with a high density of b = ½<111> dislocations (in Mo-20Si-10B), which are consistent with the values of the respective stress exponents and activation energies that were obtained and provide confirmatory evidence for the operation of diffusional (former alloy) or dislocation (latter alloy) creep mechanisms. In contrast, the intermetallic phases contained very few dislocations, but many cracks. The relative contributions of the α-Mo and the intermetallic particles to the overall deformation process, including their individual and collective dependence on temperature and strain rate are discussed in light of the present results and those from previous reports.iii

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Oxidation mechanisms in Mo-reinforced Mo5SiB2(T2)–Mo3Si alloys

Cited by 227 publications

References 13 publications

Microstructure Effects on Creep Behavior of Next Generation of Refractory Alloys for Very High Temperature Applications

Microstructure Effects on Creep Behavior of Next Generation of Refractory Alloys for Very High Temperature Applications

Enhanced Oxidation Resistance of Mo–Si–B–Ti Alloys by Pack Cementation

Processing, Microstructure and Creep Behavior of Mo-Si-B-Based Intermetallic Alloys for Very High Temperature Structural Applications

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