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

Abstract

A continuing quest in science is the development of materials capable of operating structurally at ever-increasing temperatures. Indeed, the development of gas-turbine engines for aircraft/aerospace, which has had a seminal impact on our ability to travel, has been controlled by the availability of materials capable of withstanding the higher-temperature hostile environments encountered in these engines. Nickel-base superalloys, particularly as single crystals, represent a crowning achievement here as they can operate in the combustors at ~1100 °C, with hot spots of ~1200 °C. As this represents ~90% of their melting temperature, if higher-temperature engines are ever to be a reality, alternative materials must be utilized. One such class of materials is Mo-Si-B alloys; they have higher density but could operate several hundred degrees hotter. Here we describe the processing and structure versus mechanical properties of Mo-Si-B alloys and further document ways to optimize their nano/microstructures to achieve an appropriate balance of properties to realistically compete with Ni-alloys for elevated-temperature structural applications.

Alloy design for intrinsically ductile refractory high-entropy alloys

“…Today's engines expose nickel-based superalloys to temperatures approaching 1150 C, close to 90% of their melting points. 1 Although the use of complex cooling systems and thermal barrier coatings can enable them to exist in the hottest region of a turbine engine with temperatures approaching 1500 C, the efficiency gained from operating at higher temperatures is greatly reduced. New ultrahigh temperature materials, therefore, must be developed that can operate at higher temperatures (>1300 C) without the need for cooling.…”

“…New ultrahigh temperature materials, therefore, must be developed that can operate at higher temperatures (>1300 C) without the need for cooling. 1,2 Conventional alloys, including nickel-based superalloys, are based on one or sometimes two principal elements, for example, Fe in steels and Ti and Al in TiAl based intermetallics. The recently emerging high-entropy alloys (HEAs), however, provide a novel alloying strategy that significantly expands the scope of the conventional alloy design.…”

Environmentally Resistant Mo-Si-B-Based Coatings

“…Previous work on the oxidation of silica by steam in a flowing gas stream has been successfully modeled as paralinear behavior that results in rapid recession of the surface ( Ref 6,[17][18][19][20]. With the addition of boron to the silica, additional hydroxide phases become relevant, some of which are stable, including BO(OH), [BO(OH)] 3 and B(OH) 3 (Ref 17,21,22). Boron exposed to wet oxidation has been observed to form volatile boron hydroxides in significant amounts at relatively modest temperatures (Ref 17).…”

“…Next the samples were preheated to 204°C in preparation of the thermal spray process. The source of the Mo to be deposited was as-received H. C. Starck Amperit 105 powder: 99.5% agglomerated and sintered, a particle size range of 18-57 lm and a measured density of 2.25 g/cm 3 . A Thermach SG-100 gun was used in the single-pass plasma spraying method, and a Fanuc M-16ib robot was employed for controlled and repeatable application.…”

Effect of Boron on Microstructure and Microhardness Properties of Mo-Si-B Based Coatings Produced Via TIG Process

“…[7][8]. There is no study on the production of Mo-Si-B coatings by tungsten inert gas (TIG) surfacing process.…”