Thermal expansion of chromium-rich iron-based or iron /nickel-based alloys reinforced by tantalum carbides
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THERMAL EXPANSION OF CHROMIUM-RICH IRON-BASED OR IRON /NICKEL-BASED ALLOYS REINFORCED BY TANTALUM CARBIDES P. Berthod,1,2 L. Aranda,1 and Y. Hamini1 Six alloys reinforced by TaC carbides based on iron (ferritic) or both iron and nickel (austenitic) were studied in thermal expansion between 100 and 1200°C for two microstructural orientations. The heating, isothermal, and cooling parts of the dilatometry curves were characterized. The thermal expansion of the ferritic alloys is less important than the thermal expansion of the austenitic alloys. A compressive deformation of the matrix subjected to stresses applied by the carbides network was observed. The importance of this phenomenon seems to depend more on the matrix nature than on the microstructural orientation. Keywords: thermal expansion, chromium-rich iron-based alloys, tantalum carbides.
An increase in temperature induces a geometric expansion for most materials, especially for the metallic alloys, with (as a consequence) possible development of internal stresses observed when the materials are not free to deform or when the entire considered piece is not homogeneous in temperature. This is particularly true for refractory alloys and superalloys the temperature of which may vary between the room temperature and more than 1000°C [1] in service. To minimize the stresses appearing when the variations of temperature are significant, one usually looks for lowering the Young’s modulus or the average thermal expansion coefficient of materials. Several parameters can influence the thermal expansion of an alloy: its chemical composition, the natures and volume fractions of the phases present in the microstructure (if their thermal expansion behaviors are different from each other), and possibly the local microstructural orientation in the case of foundry alloys. The aim of the present work is to study the possible effects of these three parameters on the thermal expansion of selected metallic alloys, which are especially refractory and, hence, can be candidates for uses at high temperatures in corrosive environments.
Materials and Methods Three iron-based alloys and three {iron+nickel}-based alloys, all containing about 30 wt.% Cr but various amounts of Ta and C were produced by high-frequency induction foundry (about 100 g for each ingot) from pure elements. Their obtained chemical compositions are given in Table 1 (the obtained contents are measured by the energy dispersion spectrometry), while their microstructures are illustrated by several micrographs and X-Ray diffraction patterns in Figs. 1 and 2 (Philips-XL30 scanning electron microscope; back-scattered electrons mode, an accelerating voltage of 20 kV; Bruker XPERT-Pro diffractometer). 1 2
Jean Lamour Institute, Nancy, France. Corresponding author; e-mail: [email protected].
Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 47, No. 3, pp. 46–52, May–June, 2011. Original article submitted December 7, 2009. 1068-820X/11/4703–0319
© 2011
Springer Science+Business Media, Inc.
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