Mo–Si–B Alloys for Ultrahigh Temperature Applications

Oxidation behaviour of Mo–Si–B–(Al, Ce) ultrafine-eutectic dendrite composites in the temperature range of 500–700 °C

“…However, it has been reported that in the cases of MoeSieB, NbeSieB, VeSieB, and WeSieB systems [23], there exists a stable two phase field between the a-bcc solid solution phase and the ternary B rich "5-1-2" type of phases. Therefore, in case of the MoeSieB ternary system after the formation of the proeutectic Mo ss, the residual melt undergoes partitioning between Si and B in order to form an eutectic comprising Mo 3 Si and Mo 5 SiB 2 phases.…”

“…Even with limited successes achieved through application of coatings, the possibility of catastrophic failure by oxidation still exists [3,21,22]. The main reason for poor oxidation resistance is attributed to the non-protective character of the oxide scale due to the formation of MoO 3 , which vaporizes at 704 C, and accelerates the process of degradation [23,24]. Although the oxidation resistance of the MoeSieB alloy has been found to be impressive above 1000 C due to the formation of a glassy borosilicate layer [25], yet unabated mass loss with vaporization of MoO 3 has been observed at lower temperatures of around 700 C. It has been reported that Al can enhance the oxidation resistance and arrest the pest disintegration of MoSi 2 [26,27] and Mo 3 Si based [28] silicides.…”

Viscosity control of borosilica by Fe doping in Mo–Si–B environmentally resistant alloys

“…The Mo-rich Mo-Si-B alloys are attractive for high-temperature structural applications due to high strength levels well above that for pure Mo, while offering some oxidation protection by the formation of a protective borosilica glass layer [1][2][3][4][5][6][7]. The alloys derive their ductility and fracture toughness from the presence of a continuous Mo(ss) matrix, which in cast alloys may require a Mo(ss) volume fraction greater than 40% [8,9].…”

Surface Engineering of Mo-Base Alloys for Elevated-Temperature Environmental Resistance

“…In terms of the available phase combinations in the Mo-Si-B system that are indicated in the phase diagram in Figure 1 (57)(58)(59)(60)(61)(62), a number of studies have been reported on the microstructures and properties . However, as noted in the recent comprehensive review by Lemberg & Ritchie (87), the most attractive option involves multiphase microstructures based upon (Mo + Mo 3 Si + T 2 ) three-phase alloys that can offer an effective balance of high-temperature performance (2,59,69,71,83,87) with superior high-temperature mechanical properties and some oxidation resistance due to the formation of an adherent borosilica layer Isothermal section of Mo-Si-B phase diagram at 1,600 • C. The crystal structures are illustrated for several Mo silicides. The micrograph is a SEM back-scattered image of an as-cast Mo-14.2at%Si-9.6at%B alloy.…”