Deformation behavior of a two-phase Mo–Si–B alloy

On the fracture toughness of fine-grained Mo-3Si-1B (wt.%) alloys at ambient to elevated (1300 °C) temperatures

“…Finally, it is of note that the ULTMAT and Middlemas alloys achieve nominally identical microstructures via very different 12 The strain-energy release rate, G, is another measure of toughness, which describes the amount of strain-energy dissipated by an advancing crack. G is related to the linear-elastic fracture toughness, K, by G ¼ K I 2 /E 0 þ K II 2 /E 0 þ K III 2 /2m, where E' is E (plane stress) or E/(1Àn) 2 (plane strain, n is Poisson's ratio) and m is the shear modulus.…”

“…It is unclear at this time how the contribution to toughening by uncracked ductile ligaments will differ between the finegrained and coarser-grained materials. The additional toughness afforded by uncracked ductile ligaments can be understood by an examination of the strain-energy release rate, G. 12 Sigl, et al [59] described the toughening contribution of uncracked ligaments, in terms of the strain-energy release rate G ¼ K 2 /E, by:…”

Mo‐Si‐B Alloys for Ultrahigh‐Temperature Structural Applications

“…Powders rapidly solidified from the melt11, 18, 19, 32, 93–101 can avoid the formation of deleterious boride phases. Small, spherical particles consisting of either an intermetallic matrix phase surround primarily solidified α‐Mo93, 94 or an α‐Mo matrix phase95–97 can be produced, depending on the atomizing gas (and thus the cooling rate).…”

“…Centrifugal forces eject the molten melt, which solidify into spheres in flight. The PREP process has proven effective at forming α‐Mo matrix powders containing Mo 5 SiB 2 dispersions 18, 19, 32, 98–101. Consolidation of these powders by hot pressing and sintering can lead to the formation of dense, well bonded three‐phase microstructures.…”

“…Hot pressing of blended powders provides a relatively simple means of creating a two‐ or three‐phase microstructure without the pitfalls of direct solidification; for this reason it is now widely used in processing of Mo‐Si‐B alloys. The technique has been used to successfully compact and sinter mixtures of molybdenum silicides, Mo and B,81, 113 precast Mo‐Si‐B powders,82–87 elemental Mo, Si and B114 as well as rapidly‐solidified,18, 19, 32, 95–101 surface‐modified,115–118 reaction synthesized15, 119–123 or mechanically alloyed4, 10, 11, 14, 123–137 Mo‐Si‐B powders. Heat treatment is required after hot pressing to further homogenize the material.…”