Citation:
R.G. Wellman, H. Tourmente, S. Impey, J.R. Nicholls, Nano and microhardness testing of aged EB PVD TBCs, Surface and Coatings Technology, Volumes 188-189, Proceedings of the 31st International Conference on Metallurgical Coatings and Thin Films, November-December 2004, Pages 79-84
Abstract:
Previous studies on the erosion of electron beam physical vapour deposited
thermal barrier coatings (EB PVD TBCs) has shown that aging the coatings at
between 1100 and 1500 à °C before erosion increases the erosion rate. These
changes in the erosion rate were attributed to a number of factors including
changes to the nanoporosity within the coatings as well as phase changes within
the coatings. Such changes in the morphology of the coatings should be
measurable as changes in their hardness. Thus, it was decided to ascertain the
effect that the aging had on the hardness of the coatings. Since, during
erosion, the size of the interaction zone between the impacting particle and the
coating is in the same range as the size of the individual columns of the
coating, it was decided to measure the change in the hardness of the columns as
well as the coating as a whole. It was found that the aging increased the
hardness of both the coating as a whole and the individual columns of the
coatings. The microhardness of the coating was found to increase from 2.5â  3.5
GPa in the as-received condition to 4.5â  6 GPa after 100 h at 1100 à °C and to
7.5â  8 GPa after 24 h at 1500 à °C. The nanohardness of the individual columns
on the other hand was found to increase from 18 GPa in the as-received condition
to 35 GPa after aging. This paper discusses the increases in hardness due to
aging in terms of the sintering and morphological changes that occur in the
coating. The difference in the nano- and microhardness results are discussed in
terms of the relative size of the indents and column size and the associated
interactions that occur under the different indenter heads a