High-Performance Materials for Extreme Conditions: Effects of Interstitials and the Science of Processing

events hall

Dr. Ravit Silverstein

27.03.2022

David Wang Auditorium, 3rd floor Dalia Meidan Bldg.

14:30

Refractory multi-principal elements alloys (RMPEs) and SiC-based ceramic matrix composites (SiC-CMCs) are examples of advanced materials for high-temperature structural applications. However, some limiting factors prevent them from reaching their ultimate performance. Examples include effects of interstitials along with processing design issues. This presentation will provide insights into the role of interstitials in RMPEs, the implications for structural design, and discuss a novel processing approach to elevate the temperatures of SiC matrices for CMCs.

The first part of this presentation will discuss the key challenges of fabricating robust SiC matrices caused by the hindrance to wetting of C surfaces by the Si melt. This work explores a preconditioning approach, using Si vapor of C surfaces, to mitigate reactive wetting with a controlled infiltration rate, hinder reaction chocking, and to ultimately achieve robust SiC matrices. A variant of the fabrication approach involves using Si-rich alloys as they can capture residual Si in the form of a high-temperature silicide. This section will focus on in-situ heating TEM investigations to study the phase constitutions and elucidate the drive for polymorphism of yttrium silicides.

The second part of this presentation will focus on effects of dilute concentrations of interstitials (<1at%) in refractory equimolar Ti-Nb alloys, which is intended to provide insight into the potential underlying mechanisms of interstitials-induced phase transformation in higher-order RMPEs. This work will look into the transformation pathways between the parent BCC phase and the reaction products and provide insights into the preferred interstitials environments. To conclude, I will discuss how these phase transformation paths can be applied to peruse further developments in advancing engineering materials.

Host: Asst. Prof. Joshua M. Grolman