PSI - Issue 36

Ihor Koval et al. / Procedia Structural Integrity 36 (2022) 51–58 Ihor Koval et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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1. Introduction Titanium carbide alloys are used for manufacturing of cutting tools, dies, wear-resistant parts, surfacing of the part working surfaces, being widely used to replace tungsten-cobalt alloys in machining operations (Norgren et al. (2015), Lengauer (2000), Shihab et al. (2020), Ivanov et al. (2020)). Significant advantages of such materials are high hardness, wear resistance, resistance to build up edge, but they possess low strength and crack resistance (Garcia et al. (2019), Rajabi et al. (2015)). For improving mechanical properties, the following methods are used: technological ones – the preliminary synthesis of carbides, heat compression treatment, etc. (Marynenko et al. (2008)); alloying of the carbide base with other carbides of metals 4-6 transition groups (Wang et al. (2009), Peng et al. (2013)); nano sized powders as components (Chao et al. (2005), Xiaobo and Ning (2009) , Pötschke et al. (2018)), in particular nano Ni (Kramar et al. (2018)). The use of fine and nano powder results in increasing of the surface energy, speed and shrinkage value of the samples during sintering, especially at the initial stage. It is known that the alloying of titanium carbide/carbonitride in small amounts (5-10% wt.) by carbides of metals 4-6 transition groups positively affects the mechanical properties of alloys, tungsten carbide being the most effective (Xiong et al. (2007), Syzonenko et al. (2020)). Vanadium and niobium carbides are used as the growth inhibitors of carbide grains, tungsten carbide – to increase the strength of alloys. While alloying TiC-VC/NbC carbide base by tungsten carbide, both high hardness and crack resistance HV 30 = 17. 2 … 17 .45 GPa, K 1c = 7. 9 … 8 .3 MPa · m 1/2 were achieved ( Pötschke et al. (2018), Bodrova et al. (2014))]. Since the mechanical properties of alloys are structurally sensitive, it is important to study the correlation of structure dispersion, properties and factors influencing them (Brieseck et al. (2010)). In recent years, a number of publications have appeared on the effect of carbide grain size (from ultrafine to coarse-grained) on the microstructure and properties of alloys based on both tungsten carbide and titanium carbide / carbonitride with various, alternative, metallic binders, in particular Co, Ni, Fe-Ni-Co, Ni-Cr, etc., as demonstrated by Garcia et al. (2019) , Koval’ et al. (2016), Bondarenko et al. (2017)). Reducing of the carbide phase size to submicron or nano levels increases the hardness, wear resistance, tensile strength, but to ensure sufficient plasticity it is necessary to improve the strength and ductility of the binder. A polycarbide base and nano sized binder are used in alloys to obtain the optimal combination of competing properties. Thus, it is interesting to investigate the influence of the carbides and nano sized metals of binder on the alloys’ microstructure formation. 2. Problem statement One of the ways to form a microstructure of the required size is to stimulate the diffusion of alloy components in the process of structure formation. The diffusion of alloy components can be intensified by increasing the specific surface area of structural components with the introduction of alloying nano sized additives. The objective of the paper is to establish the regularities of the binder chemical composition and the size of the starting nickel powder influence on the nature of components interaction and the morphology of the alloys after sintering. 3. Methods and materials In the paper the alloys TiC-5% (wt.) NbC-5% (wt.) WC-x (wt.) (NiCr), where x is 10, 18, 24% (wt.) at the ratio Ni:Cr = 3:1 have been investigated. In the alloys the starting nano sized nickel powder was used, their content being 7.5, 13.5 and 18% (wt.), respectively. For comparison, an alloy of 18% (wt.) binder was prepared, which contained 13.5% (wt.) of fine nickel. The alloys were assigned by numbers 1, 2, 3, 4 respectively. The chemical composition and size of the starting powders of alloys are presented in Table 1. The alloys were obtained by the powder metallurgy technology, which included homogenization of carbides powders and binder metals in a ball mill at ethyl alcohol for 72 h, the adding of a plasticizer (synthetic rubber in gasoline), pressing at the specific pressure 100 MPa, sintering in the high temperature furnace SNV 1.3.1./20I1 at temperature 1350 º C during 40 minutes.