Md Shafkat Bin Hoque1,Milena Milich1,Mingde Qin2,Md Sabbir Akhanda1,Kathleen F. Quiambao-Tomko1,Sashank Shivakumar2,Eric Hoglund1,John Tomko1,Jeffrey L. Braun1,Joshua Gild2,David Olson3,Kiumars Aryana1,Yee Rui Koh1,Roisul Galib1,John Gaskins3,Mona Zebarjadi1,Jian Luo2,Patrick Hopkins1
University of Virginia1,University of California, San Diego2,Laser thermal analysis3
Md Shafkat Bin Hoque1,Milena Milich1,Mingde Qin2,Md Sabbir Akhanda1,Kathleen F. Quiambao-Tomko1,Sashank Shivakumar2,Eric Hoglund1,John Tomko1,Jeffrey L. Braun1,Joshua Gild2,David Olson3,Kiumars Aryana1,Yee Rui Koh1,Roisul Galib1,John Gaskins3,Mona Zebarjadi1,Jian Luo2,Patrick Hopkins1
University of Virginia1,University of California, San Diego2,Laser thermal analysis3
High-entropy metal diborides have emerged as promising candidates for extreme structural applications such as next generation gas turbines, nuclear reactors, and rocket nozzles. However, detailed thermal characterizations of these materials are still missing from literature. To remedy this, we have performed extensive thermal characterizations of a high-entropy diboride (HEB): (Hf<sub>0.2</sub>Zr<sub>0.2</sub>Ti<sub>0.2</sub>Ta<sub>0.2</sub>Nb<sub>0.2</sub>)B<sub>2 </sub>in this study. The thermal conductivity of the HEB is only ~1/3 to 1/4 of the constituent metal diborides. This stems from the significant electron and phonon scattering caused by the five different metal cations in the crystal lattice. The volumetric heat capacity of the HEB, on the other hand, is nearly the same as that of the monolithic diborides. To determine the thermal conductivity distribution across different grain orientations, spatial mapping is performed on the polycrystalline HEB specimen and a prototypical ZrB<sub>2</sub> system. Our measurements reveal that the thermal conductivity remains nearly isotropic among different grain orientations despite HEB and ZrB<sub>2 </sub>possessing a highly anisotropic layered crystal structure. Additionally, we compare the ablation resistance of the HEB and ZrB<sub>2 </sub>and find that the two are within experimental error of each other. Thus, the measurements performed in this study establish the suitability of HEB for high thermal load applications in extreme environments.