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

Abstract

The synthesis of robust coatings that provide protection against environmental attack at ultrahigh temperatures is a difficult challenge. To achieve this goal for Mo-base alloys, the fundamental concepts of reactive diffusion pathway analysis and kinetic biasing are used to design a multilayer Mo-Si-B-base coating with a phase sequencing that allows for structural and thermodynamic compatibility and an underlying diffusion barrier to maintain coating integrity. The coating design concepts have a general applicability. The coating structure evolution during high-temperature exposure facilitates a prolonged lifetime as well as self-healing capability. The borosilicide coatings that can be synthesized by a pack cementation process yield superior environmental resistance for Mo-base systems at temperatures up to at least 1,700 • C and can be adapted to apply to other refractory metal and ceramic systems. 9.1

Quantitative analysis of Mo–Si–B alloy phases with wavelength dispersive spectroscopy (WDS–SEM)

“…To manage this challenge, the higher energy set point (5) is determined experimentally by the use of Mo 5 SiB 2 phase FIGURE 2 Wavelength dispersive spectroscopy spectrum for Mo ss (blue) with a simulated overlaid small B-K peak (green) on the Mo-M tail. Marker (1) and (2) illustrate the low energy and high energy background set points for calculation the net boron intensity FIGURE 3 Wavelength dispersive spectroscopy spectrum over the B-K (1) and Mo-M (2) peaks and determination of the correct background set points (3,5) for calculation the net boron intensity (4) as a standard sample. The set point is determined by extrapolating a line starting from the left point (3) with the slope of the pure Mo-M ζ low energy tail onto the right shoulder of the Mo-M ζ peak in the first case.…”

“…The line from (3) to (5) represents the valid background. The intersection of the B-K α peak with the line (3) to (5) results in point (4), which is used to calculate the right boron content. For quantification, the acquisition process is the same such as explained above.…”

“…Refractory metals and their alloys show potential for high temperature applications due to the increased melting point and creep resistance. [1][2][3][4][5] The investigated Mo-9Si-8B (stated in at.%) ternary alloys consisting of the phases Mo ss (molybdenum-based solid solution), Mo 3 Si (A15), and Mo 5 SiB 2 (T2). [6,7] With melting points over 2,000°C, these alloys are particularly favorable for new high-temperature materials.…”

Elastic Properties of Novel Co- and CoNi-Based Superalloys Determined through Bayesian Inference and Resonant Ultrasound Spectroscopy

“…Inherent limits exist for future development, as the melting temperature (or more accurately the liquidus and solidus temperatures) is intrinsic to the material and cannot be appreciably increased. This reality has spurred research and development of ordered intermetallic alloys such as NiAl-, [2] Nb-, and Mo-based refractory alloys, [3][4][5][6] and ceramic composites of alumina [7] and silicon carbide, [8] all with the goal of supplanting Ni-based superalloys for the most demanding high-temperature applications. However, these alternatives often suffer from poor fracture toughness and processing constraints that make their current use costly and limited, [3][4][5]9] especially considering the safety requirements for use in aerospace.…”

Influence of Ingot and Powder Metallurgy Production Route on the Tensile Creep Behavior of Mo–9Si–8B Alloys with Additions of Al and Ge

“…However, below 900 C, this alloy suffers from catastrophic oxidation because the borosilicate scale is porous allowing evaporation of gaseous MoO 3 . Perepezko [11] showed recently that additions of Al are beneficial for the oxidation resistance.…”