Abstract
The cyclic oxidation response of Mo-14Hf-23B and Mo-14.8Zr-26B (compositions in at. %) was investigated in air at 800 °C, which is a critical temperature for Mo-based alloys because of the pesting phenomenon. Rapid oxidation was observed for the unprotected samples, and an oxidation protection coating was developed based on a preceramic polymer with silicon and boron as particulate fillers. Cyclic oxidation tests of the coated samples showed excellent oxidation protection: no Mo, Hf or Zr oxides were found after testing and a small mass gain in the initial stage of oxidation indicated the formation of a glassy protection layer on the alloys surfaces after exposure to air at 800 °C.
Highlights
One of the challenging tasks in materials science is the development of novel high-temperature materials; characteristics of high temperature structural materials, besides high melting temperatures, are a high creep resistance, an appropriate tolerance for crack initiation and crack growth, resistance against oxidative, corrosive and erosive attacks, and thermal shocks [1,2]
The oxidation behaviour of the Mo-14Hf-23B and Mo-14.8Zr-26B alloys was cyclically proven at 800 ◦ C. This temperature was chosen since it is the harshest temperature for Mo alloys because of the occurrence of the pesting phenomenon, which means the formation of a volatile MoO3 phase [16]
A further oxygen penetration into the samples and evaporation of MoO3 led to a rapid oxidation of the entire bulk of the alloys
Summary
One of the challenging tasks in materials science is the development of novel high-temperature materials; characteristics of high temperature structural materials, besides high melting temperatures, are a high creep resistance, an appropriate tolerance for crack initiation and crack growth, resistance against oxidative, corrosive and erosive attacks, and thermal shocks [1,2]. The properties of known high-temperature structural materials can limit the advance of machine design in airplane engines or power plants [3,4]. The most common materials in high-pressure turbines of aero-engines and gas turbines—nickel-based super alloys—have reached their technological limit, and are not capable of having structural components at temperatures above 1150 ◦ C [5]. The reinforcement of the refractory metals with a stronger phase, which may preferably be oxidation resistant, might solve this problem [4]. In this context, refractory metal borides, carbides and silicides are the most appropriate candidates
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