Internal friction and torsional creep behavior of chemically vapor deposited boron nitride

Dense hexagonal BN processed via chemical vapor deposition (CVD) was tested with respect to damping, shear modulus, and torsional creep rate up to tem peratures as high as approximate to 2300 degrees C, The microstructural cha racteristics of the material both before and after creep testing were studi ed by high-resolution electron microscopy (HREM). The CVD process yields a homogeneous nanosized microstructure with no other secondary phase detectab le. Damping experiments revealed no plastic relaxation during testing up to approximate to 2000 degrees C, which is consistent with the fact that also no creep deformation could be detected below such a high temperature. Smal l porosity and an increased amorphization process were noted by HREM inspec tion after stress exposure at approximate to 2300 degrees C, These phenomen a may be responsible for both the enhanced damping capacity and the creep r ate of the material which, in the range of the present testing conditions, seems to follow the simple viscoelastic behavior of a Maxwell solid.