Refractory Metals: Alloy Development, Silicides, and Hardmetals
Sponsored by: TMS Structural Materials Division, TMS: Refractory Metals Committee
Program Organizers: Eric Taleff, University of Texas at Austin; Lauren Garrison, Commonwealth Fusion Systems; Alexander Knowles, University of Birmingham

Tuesday 8:00 AM
March 1, 2022
Room: 252B
Location: Anaheim Convention Center

Session Chair: Eric Taleff, The University of Texas at Austin

8:00 AM  Invited
Development of Heat-treatable Crss-Cr3Si-based Alloys: Microstructure, Oxidation, and Creep: Anke Ulrich¹; Petra Pfizenmaier²; Uwe Glatzel²; Mathias Galetz¹; ¹Dechema-Forschungsinstitut; ²University Bayreuth
    Crss-Cr3Si-based alloys are promising candidates in the field of refractory metals for high temperature applications. In comparison to the commonly used Ni-base superalloys, these materials offer possible higher working temperatures and lower densities. In addition, Cr is the only refractory metal which intrinsically builds an oxide scale suitable for protecting the alloy from detrimental oxidation. Si improves the oxide scale formation even further as well as high temperature strength by Cr3Si formation. In this study it was found, that the addition of further alloying elements such as Mo, Ge, and Pt lead to an improvement in creep properties (Mo), oxidation resistance (Ge), and nitridation resistance (Pt) by simultaneously maintaining the two-phase microstructure. Tests were conducted at temperatures up from 980 °C. The microstructures, scales, and reaction products were investigated using XRD, SEM, EPMA, and Image Analysis.

8:20 AM
Effect of Heating Rate and Substrate on the Oxidation Behavior of Hafnium Aluminum Diboride Thin Films: Samyukta Shrivastav¹; Dana Yun¹; Carly Romnes¹; Kinsey Canova¹; John Abelson¹; Jessica Krogstad¹; ¹University of Illinois at Urbana Champaign
    The oxidation resistance of hafnium diboride in high temperature applications is attributed to a liquid boria phase, which can be volatile depending on temperature and pressure. This volatility poses a problem for thin films, as it may lead to spallation and consumption of the film. Here, aluminum is alloyed with hafnium diboride via a low-temperature CVD process to enable the formation of a protective aluminum oxide and suppress boria volatilization. We show that the oxidation behavior of HfAlB_x thin films is strongly dependent on heating rate and substrate interaction. The thickness, phase, and composition of the oxide formed were determined using HRTEM and SEM. In cases that did not develop a continuous passivating oxide, complete oxidation of films was observed. Films on sapphire gave rise to the formation of nano-whiskers of Al₄B₂O₉ with traces of alumina, while films deposited on silicon resulted in the formation of an amorphous silica layer

8:40 AM
Oxidation Behavior of Mo-Si-B-Al Alloys at Elevated Temperature: Longfei Liu¹; Ranran Su¹; John Perepezko¹; ¹University of Wisconsin-Madison
    Both isothermal and cyclic oxidation behavior of Mo-6Si-12B-(1, 2, 4, 8)Al samples have been studied. With an increase of Al content, isothermal oxidation resistance is enhanced while cyclic oxidation resistance is degraded. The Mo-6Si-12B-4Al sample oxide layer consists of both Al-doped borosilicate glass phase and mullite phase and has the best overall oxidation performance. A model was developed to analyze the transient oxidation stage and provides a good agreement with the experimental data. The Al diffusion rate is two orders of magnitude bigger than Si in mullite, it accounts for the high Al sample exhibiting the best isothermal resistance. The low viscosity of the Al-doped borosilicate glass provide a self-healing effect which is related to the good cyclic oxidation performance of low Al content samples.

9:00 AM  Cancelled
Hydrogen Reduction of Cobalt(II,III) Oxide to Make Sub-micron and Micron Size Cobalt Metal Powder for WC-Co Synthesis: Raj Singh Gaur¹; Thomas Jewett²; Scott Braymiller²; ¹SH Chemicals; ²Global Tungsten and Powders
    This paper pertains to the hydrogen reduction of mixed valence cobalt oxide. The reduction of Co3O4 in hydrogen was studied via a design-of-experiment approach. The effect of three parameters i.e. temperature gradient (°C/min), time of reduction (h) and temperature of reduction (°C) was studied on the reduction of Co3O4 to cobalt metal powders. BET particle surface areas of cobalt powders were measured and used as a response for developing experimental conditions for making different. sizes of cobalt metal powders such as sub-micron, micron and extra-fine. Both temperature gradient (°C/min) and reduction temperature (°C) were found as significant factors. The proposed mechanism of the reduction of Co3O4 under various experimental conditions as well as the application of cobalt metal powders containing different particle sizes (FSSS) in WC-Co powders synthesis will be presented in this paper.