Japanese scientists develop molybdenum-base high-temperature high-strength alloy

October 1, 2018
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Tohoku University, Japan, reports that its researchers have developed a titanium carbide-reinforced, molybdenum-silicon-boron (Mo-Si-B)-based alloy, or MoSiBTiC, whose high-temperature strength was identified under constant forces in the temperature ranges of 2550 to  2900°F.

The study was published in Nature's open access journal Scientific Reports in July 2018. "Our experiments show that the MoSiBTiC alloy is extremely strong compared with cutting-edge nickel-base single crystal superalloys, which are commonly used in hot sections of heat engines such as jet engines and gas turbines for electric power generation," says lead author Prof. Kyosuke Yoshimi of Tohoku University's Graduate School of Engineering.

"This work suggests that the MoSiBTiC, as ultrahigh temperature materials beyond nickel-based superalloys, is one promising candidate for those applications," added Yoshimi.

Yoshimi and colleagues report several parameters that highlight the alloy's favorable ability to withstand disruptive forces under ultrahigh temperatures without deforming. They also observed the alloy's behavior when exposed to increasing forces and when cavities within MoSiBTiC formed and grew, resulting in to microcracks and final rupturing.

The researchers assessed the alloy's creep in a stress range of 100 to 300 MPa for 400 hours. All experiments were performed in a computer-controlled test rig under vacuum in order to prevent the material from oxidizing, or reacting with the any potential air moisture, which could ultimately result in rust formation.

Furthermore, the study reports that, contrary to previous studies, the alloy experiences larger elongation with decreasing forces. This behavior, they write, has so far only been observed with superplastic materials that are capable of withstanding against unexpected premature failure.

These findings are an important indicator for MoSiBTiC's applicability in systems that function at extremely high temperatures, such as energy conversion systems in automotive applications, power plants, and propulsion systems in aircraft engines and rockets. The researchers say that several additional microstructural analyses are needed in order to fully understand the alloy's mechanics and its ability to recover from exposure of high stresses such as large forces under high temperatures.

Mipar software enables precise and repeatable quantification of nickel alloy precipitates

September 26, 2018
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Mipar Software, Worthington, Ohio, announces that it has developed a software package called Mipar that enables engineers to quantify the size distribution and volume fraction of gamma-prime Ni₃Al precipitates in nickel-base superalloys. Nickel-base superalloys are extensively used in high-temperature, high-stress applications. The presence of coherent γ′-Ni₃Al precipitates provides the requisite elevated temperature strength and creep resistance in these alloys.

Therefore, quantification of the precipitate size distribution and volume fraction is essential for accurate model predictions and future alloy design. Current γ′ volume fraction characterization techniques lack precision and repeatability. Without a reproducible procedure, unacceptable variations and errors have plagued the past six decades of superalloys research and have inhibited the implementation of accurate precipitation models for these alloys.

Through the use of high resolution, low kV, scanning electron microscopy pioneered at NASA, and state-of-the-art image post-processing, a new, accurate γ′ characterization technique has been developed, and will be demonstrated at MS&T 2018 (booth 407). Using the new technique, secondary γ′ volume fractions in superalloy ME3 were calculated, and confirmed through phase extraction, thus opening the possibility for validation of presently used superalloy precipitation databases.

Using Mipar, along with a new imaging technique, NASA overcame barriers to accurate image analysis that had frustrated the aerospace materials community for decades. This led to published methods which NASA has proposed as a new standard for nickel superalloy analysis.

Link to Paper: https://www.sciencedirect.com/science/article/pii/S1044580318304716

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