Oxidation behavior of Hf1-xAlxB2 and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2 coatings synthesized by high power pulsed magnetron sputtering (HPPMS) using massive subplantation of Al

• Applicant: Professor Jochen M. Schneider, Ph.D.
• Subject Area: Coating and Surface Technology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 506336880

Resistance against oxidation is one of the critical design criteria for ultra-high temperature ceramics utilized in harsh environment. While the oxidation behavior of HfB2 has been investigated, neither the Al solubility nor the Al concentration-dependent oxidation behavior of Hf1-xAlxB2 or (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2 with x and y varying from 0 to 1.0 has been studied.We have previously demonstrated the synthesis for single-phase V1-xAlxN coatings with unprecedented Al concentrations of up to x = 0.74 by massive subplantation of Al. This supersaturation was obtained by separating the film-forming species in time and energy domains through synchronization of the pulsed substrate bias with intense periodic fluxes of energetic Al ions during reactive hybrid high power pulsed magnetron sputtering. Here, we will utilize massive Al ion fluxes for the first time during synthesis of single-phase Hf1-xAlxB2 and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2 coatings with maximized Al concentrations (xmax , ymax) following the subplantation approach conceived by G. Greczynski and the applicant. In addition to the two films with maximized Al concentration, also films with a 5 and 10 at.% lower Al concentration than the respective maximum concentration, as well as samples without Al (as a reference), will be grown and evaluated for both material systems. The oxidation behavior of all six compositions will be evaluated at temperatures of up to 1200 °C and exposure times of up to 60 min in a furnace. The complete data set will allow for straightforward comparisons of the temperature-dependent oxidation behavior, time-dependent oxidation behavior, Al concentration-dependent oxidation behavior of metastable Hf1-xAlxB2 and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2 solid solutions.Specifically, the project is aimed at answering the research questions motivated at the end of section 1, namely:1. What is the critical solubility (xmax, ymax) of Al in single-phase Hf1-xAlxB2 and in (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2? 2. How does the oxidation behavior of single-phase Hf1-xAlxmaxB2 and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-ymaxAlymaxB2 compare to that of the corresponding phases without Al?3. What are the consequences of Al incorporation for the oxidation kinetics of single-phase Hf1-xAlxB2 and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2?Based on spectroscopy, diffraction, microscopy, and tomography data obtained from the as-grown compared to the oxidized coatings, we seek to advance our understanding concerning the Al concentration dependence of the oxidation behavior. We expect that this will enable future design of ultra-high temperature diboride coatings with superior oxidation resistance.

• DFG Programme: Research Grants