Some of the wear-resistant pieces or coatings, constituted of a metallic matrix and of carbides present in high fractions, are a mix, in similar quantities, of two materials displaying greatly different levels of hardness but also of thermal expansion coefficient. When temperature increases, the second difference of property may lead to particular geometrical behaviours. To study these differences, nine nickel-based, cobalt-based, and iron-based alloys containing very high quantities of carbides were elaborated by foundry. In their as-cast conditions, the microstructures of these alloys were characterized; their hardness and thermal expansion until 1200°C were measured and analysed, with regard to the evolution of the structures predicted by thermodynamic calculations. The hardness of the alloys is high (nickel alloys) or very high (cobalt and iron alloys, 600？Hv and more) while the thermal expansion is greatly influenced by carbides, notably when temperature has become very high. Some of the variations of thickness at the end of heating or during an isothermal stage at 1200°C, essentially contraction, directly result from the mechanical interaction between matrix and carbides which was accumulated during the heating. 1. Introduction Refractory metallic alloys containing significant quantities of carbides are of a great importance for high temperature applications [1, 2], even if they are less common than the -type superalloys, solid-solution strengthened cobalt-based superalloys, or heat-resistant steels. Many of the carbides-strengthened alloys are based on nickel, cobalt, or iron and elaborated by foundry. They generally contain great quantities (several tens percents in weight) of chromium, which is a carbide-former element promoting, in presence of carbon, the formation of Cr7C3 or Cr23C6 carbides. The chromium-rich cast nickel-based alloys are used for numerous applications, notably for turbine blades in aeronautics, for which chromium brings to the alloys a good resistance against high temperature oxidation [3, 4]. Carbon can be added to the (Ni, Cr-) based alloys in order to obtain high levels of mechanical resistance and an example of hardness [5–8]. Cobalt-based alloys rich in chromium are also considered for hot parts in aeronautic turbines and power generation machines, as well as for other applications like some of the fiberizing tools used in the glass industry [9]. Generally several tens of weight percents of chromium are added to cobalt to allow the alloy sufficiently resisting hot corrosion by various molten substances (salts, glasses,
References
[1]
E. F. Bradley, Superalloys: A Technical Guide, ASM International, Materials Park, Ohio, USA, 1988.
[2]
C. T. Sims and W. C. Hagel, The Superalloys, John Wiley & Sons, New York, NY, USA, 1972.
[3]
P. Kofstad, High Temperature Corrosion, Elsevier Applied Science, London, UK, 1988.
[4]
D. Young, High Temperature Oxidation and Corrosion of Metals, Elsevier, Amsterdam, The Netherlands, 2008.
[5]
A. Klimpel, L. A. Dobrzański, A. Lisiecki, and D. Janicki, “The study of properties of Ni-W2C and Co-W2C powders thermal sprayed deposits,” Journal of Materials Processing Technology, vol. 164-165, pp. 1068–1073, 2005.
[6]
Z.-T. Wang and H.-H. Chen, “Microstructure and friction and wear behavior of induction clad Ni-based composite coating reinforced with micro- and nano-WC particulates,” Mocaxue Xuebao/Tribology, vol. 25, no. 3, pp. 203–206, 2005.
[7]
H. Han, S. Baba, H. Kitagawa et al., “Plasma-carburization of nickel-based self-fluxing alloy,” Vacuum, vol. 78, no. 1, pp. 27–32, 2005.
[8]
D. Zhang and X. Zhang, “Laser cladding of stainless steel with Ni-Cr3C2 and Ni-WC for improving erosive-corrosive wear performance,” Surface and Coatings Technology, vol. 190, no. 2-3, pp. 212–217, 2005.
[9]
P. Berthod, J. L. Bernard, and C. Liébaut, Cobalt Alloy and Fabrication of Articles from the Alloy, Patent WO99/16919.
[10]
B. Roebuck and E. A. Almond, “Deformation and fracture processes and the physical metallurgy of WC-Co hardmetals,” International Materials Reviews, vol. 33, no. 2, pp. 90–110, 1988.
[11]
H. E. N. Stone, “Hardness, oxidation and constitution in chromium-iron alloys,” Journal of Materials Science, vol. 14, no. 12, pp. 2787–2790, 1979.
[12]
B. V. Cockeram, “Some observations of the influence of δ-ferrite content on the hardness, galling resistance, and fracture toughness of selected commercially available iron-based hardfacing alloys,” Metallurgical and Materials Transactions A, vol. 33, no. 11, pp. 3403–3419, 2002.
[13]
T. B. Shafffer, Handbooks of High-Temperature Materials No.1. Materials Index, Plenum Press, New York, NY, USA, 1964.
[14]
Thermo-Calc version N: “Foundation for Computational Thermodynamics” Stockholm, Sweden, Copyright (1993, 2000).
[15]
J. O. Andersson, “Thermodynamic properties of Cr-C,” Calphad, vol. 11, no. 3, pp. 271–276, 1987.
[16]
A. Gabriel, C. Chatillon, and I. Ansara, “Thermochemical and phase diagram analysis of the Ni-C, Co-C, and Co-Ni-C systems,” High Temperature Science, vol. 25, no. 1, pp. 17–54, 1988.
[17]
A. Fernández Guillermet, “Critical evaluation of the thermodynamic properties of cobalt,” International Journal of Thermophysics, vol. 8, no. 4, pp. 481–510, 1987.
[18]
A. F. Guillermet, “Thermodynamic analysis of the Co-Al-C and Ni-Al-C systems,” Zeitschrift für Metallkunde, vol. 78, no. 10, pp. 700–709, 1987.
[19]
A. F. Guillermet, “Thermodynamic properties of the iron-cobalt-carbon system,” Zeitschrift für Metallkunde, vol. 79, no. 5, pp. 317–329, 1988.
[20]
A. Fernandez Guillermet and P. Gustafson, “Assessment of the thermodynamic properties and the (p,T) phase diagram of iron,” High Temperatures—High Pressures, vol. 16, no. 6, pp. 591–610, 1984.
[21]
J. O. Andersson and B. Sundman, “Thermodynamic properties of the CrFe system,” Calphad, vol. 11, no. 1, pp. 83–92, 1987.
[22]
P. Gustafson, “A thermodynamic evaluation of the C-Fe system,” Scandinavian Journal of Metallurgy, vol. 14, no. 5, pp. 259–267, 1985.
[23]
J.-O. Andersson, “A thermodynamic evaluation of the Fe-Cr-C system,” Metallurgical Transactions A, vol. 19, no. 3, pp. 627–636, 1988.
[24]
G. V. Samsonov, Handbooks of High-Temperature Materials No. 2. Properties Index, Plenum Press, New York, NY, USA, 1964.
[25]
P. Berthod, “Influence of carbides and of the dendritic orientation on the thermal expansion of Ni-base, Co-base and Fe-base simple cast alloys,” International Journal of Materials Research, vol. 99, no. 3, pp. 265–272, 2008.
[26]
P. Berthod, C. Heil, and L. Aranda, “Influence of the morphologic evolution of the eutectic carbides at high temperature on the thermal expansion behavior of refractory cast alloys,” Journal of Alloys and Compounds, vol. 504, no. 1, pp. 243–250, 2010.
