CRITICAL REVIEW ON THE ELASTIC PROPERTIES OF TRANSITION METAL CARBIDES, NITRIDES AND CARBONITRIDES
C. Kral1, K.
Fatrdla1, W. Lengauer1,
D. Rafaja2 and M. Manghnani3
1Institute for Chemical
Technology of Inorganic Materials, Vienna University of
Technology, Getreidemarkt
9/161, A-1060 Vienna, Austria; http://info.tuwien.ac.at/physmet/
2Dept. of
Semiconductor Physics, Charles University, Ke Karlovu 5, CZ-121 16 Prague
2, Czech Republic; http://krystal.karlov.mff.cuni.cz/
3Hawaii Institute of
Geophysics and Planetology, University of Hawaii at Manoa, 2525 Correa Road, Honolulu,
Hawaii 96822; http://www.pgd.hawaii.edu/
Keywords: Young's modulus, Poisson ratio, thin films, bulk samples, porosity
Transition metal carbides, nitrides and carbonitrides are used in a variety of industrial applications due to their outstanding physical properties [1-4]. The mechanical characteristics of these hard constituents will critically influence the performance of composites and therefore, Young's modulus, Poisson ratio, shear and bulk modulus are of much interest.
The information available on the elastic properties are rather inconsistent and contradictory such as for the Ti-N system (see Fig.1), probably because of different and sometimes insufficient chemical and microstructural characterization (chemical analysis of carbon, nitrogen and oxygen, porosity and pore shape, phase analysis, grain size and orientation). If materials cannot be prepared in "zero-porosity" state, accurate measurement of the porosity is important. A quite new method is the investigation of porosity by acoustic microscopy. The advantage of this method is that not the surface, but the interior of the sample is scanned by sound and therefore artifacts from the metallographic polishing are absent. The depth of the investigation is dependent on the applied frequency. Fig.2 shows an acoustic microscope image of a HfCN sample. The pores are dark and the evaluation of porosity with image processing tools (10.4%) gave good agreement with density measurements (9.91%).
The equations proposed in literature have been compared using the data measured by Speck et al. [5] for NbC0.96 and the data received by Wolf [6] for d-TiN and d-ZrN. The free parameters of the respective model were obtained from the non-linear least-square calculation performed with the use of Matlab®. In Fig.3 the representative output is presented for NbC0.96. It can be seen that the experimental data form a Gaussian curve where the equations proposed by Wang [7], Phani [8] and Kupkova [9] fit best in contrast to the evaluation formulas proposed by Hasselman [10] and Ondracek [11] and the one used by Frantsevich [12]. However, the parameters introduced by Kupkova [9] correlate strongly. The results obtained for show that the parameters necessary for the calculation of the Young's modulus for the non-porous state change significantly from system to system. This means that for the statement of a Young's modulus at zero-porosity a set of samples with uniformly distributed porosity is necessary to calculate the accurate parameters in order to obtain appropriate results.
Acknowledgments
The authors would like to thank Mr. Klaus
Krämer, KSI, Herborn, Germany for supplying an acoustic
microscope investigation on a HfCN sample. This work was
supported by the Austrian National Science Foundation (FWF) under
project No.11892-PHY.
Fig.1 Young's modulus of d-TiN1-x as a
function of the nitrogen content. Different behavior of the
Young's modulus vs. [N]/[Ti] depending on the preparation method
can be observed.
 Fig.2 Acoustic microscope image of an HfCN sample (size: 200mm x 100mm; 1GHz; depth: -10mm; KSI SAM 2000, Krämer Scientific Instruments, Germany). |
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| Fig.3 Comparison of the porosity correction methods. |
References