The thermal boundary conductance (TBC) between thin films of Cr, Mo, Nb and W and diamond substrates has been measured using time domain thermoreflectance before and after a high-vacuum heat treatment at 800 degrees C for 2 h. While no signs of carbide formation could be detected in as-deposited layers by scanning transmission electron microscopy energy dispersive X-ray spectroscopy elemental analysis, the heat treatment led to partial (W,Mo) or full conversion (Cr,Nb) of the film into carbide. The measured TBC values on as-deposited samples of 315, 220, 220 and 205 MW m (-2) K (-1) measured for, respectively, the Cr, Mo, Nb and W samples, were found to not be significantly altered by the heat treatment. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.