Structure and Properties of ZrC/C Heteromodulus High-Temperature Composites
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Russian Physics Journal, Vol. 63, No. 5, September, 2020 (Russian Original No. 5, May, 2020)
STRUCTURE AND PROPERTIES OF ZrC/C HETEROMODULUS HIGH-TEMPERATURE COMPOSITES Yu. А. Mirovoy, A. G. Burlachenko, and S. P. Buyakova
UDC 539.37;539.42
The influence of free carbon on densification and mechanical properties of ZrC/C heteromodulus composites is studied. It is shown that free carbon in the amount of up to 3 vol % decreases residual porosity in the heteromodulus composites, while the content of free carbon of more than 3 vol % increases it. Furthermore, increased carbon content in ZrC/C composites improves the sintered material toughness. In particular, for pure ZrC KIc = 4.3 MPa·m1/2, and for the composite with 3 vol.% carbon KIc = 7 MPa·m1/2. The lowest fracture toughness is demonstrated by the composite with 15 vol.% carbon KIc = 5.3 MPa·m1/2. Keywords: ceramic composites, carbides, toughness, hardness, elasticity, heterostructures.
INTRODUCTION High melting temperature, oxidation stability, high chemical stability and satisfactory heat capacity make zirconium carbide a promising material for numerous industrial applications – rocket engineering, power engineering, metal working, etc. [1–3]. On the other hand, excessive brittleness of ZrC (KIc ≈ 3–4 MPam1/2) [4–6] and hence uncontrollable damage development are an essential obstacle to its wider use. A higher fracture toughness of brittle ceramic materials is achieved by creating dissipative structures in them, which arrest cracks or stop their formation and development [7, 8]. One of the mechanisms of effective improvement of fracture toughness is the mechanism of crack arrest at comparatively weak internal interfaces between the matrix and the reinforcing components in multiphase ceramics. This mechanism was described by James Gordon and John Cook [9], its specific feature consists in branching of the crack at the matrix–inclusion interface if the inequality of the ratio of the energy of adhesive rupture of the matrix–inclusion interface to the matrix fracture energy is fulfilled. The main precondition for implementation of the Gordon–Cook mechanism is heterogeneity of the matrix and inclusion materials. These materials have been recently classified as heteromodulus composite materials (HCMs), in which the matrix and the inclusions have essentially differing elastic modulus values [10–17]. The purpose of this work is to identify the influence of low-modulus inclusions in a ZrC high-modulus matrix on mechanical properties of ZrC/C heteromodulus composites.
MATERIALS AND EXPERIMENTAL PROCEDURE The initial components of the experimental ZrC/C ceramic composites were commercial powders of stoichiometric zirconium carbide, ZrC (average particle size = 1.4 µm), and technical-grade carbon powder, C (average particle size = 1.2 µm). The ZrC and C powders were mixed in a mixing drum in an ethanol solution; the content of carbon in the ZrC–C powder mixtures was from 1 to 15 vol.%. The samples of ZrC ceramics and ZrC/C
Institute of Strength Physics and Materials
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