Stress control of heterogeneous nanocrystalline diamond sphere through pressure-temperature tuning

The hollow nanocrystalline diamond (NCD) sphere, a promising ablator material for inertial confinement fusion capsule, is generally fabricated by the chemical vapor deposition method. Herein, we report on a method to transform hydrogenated tetrahedral amorphous carbon coatings on spherical molybdenum (Mo) substrates into nanocrystalline diamond films via a designed high pressure high temperature (HPHT) treatment that balances the mismatch in the thermal expansion coefficient between a diamond coating and the Mo substrate through the difference in the bulk modulus. The results show that the density and strength of the diamond shell increase significantly and the residual stress is eliminated as well. The methodology of the designed HPHT treatment can not only provide an alternative way to fabricate NCD spheres but also can apply to other heterogeneous material stress control applications.