PSI - Issue 59

Lyudmyla Bodrova et al. / Procedia Structural Integrity 59 (2024) 731–738 L. Bodrova et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Tool materials must have high heat resistance and thermal shock resistance (capable of withstanding at least 10 cycles of heating and cooling at the temperature gradient of 600°C), have high resistance to thermal and mechanical fatigue under significant loading while heating, possessing high thermal conductivity and low coefficient of thermal linear expansion (Kříž and Bricín (2017), Teppernegg et al. (2016)). TiC based hard alloys being alloyed by other carbides (VC, NbC, ZrC, TaC, WC) with different metallic binder (Ni-Mo, Ni-Cr, Ni-Fe-Co) have replaced conventional cemented carbides in finishing and semi-finishing high-speed metal machining operations for manufacturing components of technological equipment for metal pressure processing and for structural high-temperature materials (Rajabi et al. (2015), Huo et al. (2021), Chen et al. (2019), Zou et al. (2018)). As compared with cemented carbides, TiC based hard alloys have some advantages – higher hardness, heat resistance and wear resistance, in particular, possessing sufficient strength and fracture toughness. They have high thermal shock resistance and a slight tendency to adhesive interaction with the processed material, which reduces tool wear on the tool face and provides lower roughness of the processed surface. Thermal shock resistance can be improved by increasing thermal conductivity and material strength, reducing the thermal expansion coefficient and the level of internal stresses. The problem of the thermal shock resistance of both cemented carbides and TiC/TiCN-based alloys has been the subject of research in various papers (Wang et al. (2019), Zhang et al. (2008), Liu and Liu (2013)). It is known that the thermal shock resistance of cemented carbides decreases with an increase in the amount of metallic binder due to the increase in the thermal expansion coefficient. Comparing the thermal shock resistance of cemented carbides with those having a high content of metallic binders, such as WC-43 vol.% Co and WC-40.7 vol.% CoNiCr, testified the strength loss caused by water quenching, and microcrack growth at the carbide-binder boundaries in the first alloy appears at 700°C, while in the second alloy, it appears at 400°C (Ezquerra et al. (2018)). Under similar conditions, the thermal shock resistance of WC-6 wt.% Co and TiMoCN-26 wt.% Ni alloys was investigated. It testified that cemented carbide had significantly higher thermal shock resistance (Ezquerra et al. (2016)). It was concluded that a low thermal expansion coefficient combined with high strength and toughness are critical parameters to provide maximum thermal shock resistance. The authors (Ishihara et al. (1991)) investigated the behavior and changes in the mechanical properties of cermet and polycarbide-based cemented carbide. WC-TiC-TaC-NbC-Co and TiCN-TaC WC-Ni-Co-Mo, during the cooling of specimens in water from heating temperatures 495 K and 613 K. It was found that with an increase in the temperature difference in the cemented carbide, the transverse rupture strength decreases, while hardness and fracture toughness remain unchanged. In cermet, hardness increases, fracture toughness decreases, and transverse rupture strength remains unchanged. The authors consider it to be caused by the fact that crack initiation is rare in cermets under thermal shock conditions than in cemented carbides. Most scientists have investigated the behavior of cemented carbides and cermet with fine grained original powders. However, it is known that the use of nano powders is advantageous for the physical and mechanical properties, thermal conductivity and fracture toughness in particular, which is caused by the ability of durable operation of products at elevated temperatures (Wang et al. (2009), Chao (2005), Pötschke et al. (2018)). In the paper ( Kříž and Bricín (2017)), it is noted that the increase of hardness, fracture toughness and thermal shock resistance can be obtained using special fine grained and nano powders in combination with a polycarbide base. Research of cemented carbides' thermal shock resistance with the same chemical composition WC-10 wt.%Co but with different carbide grain sizes - 0.39 and 2.39 μm, testified that fine grain possess a higher resistance to crack initiation than coarse grained ones, but are more sensitive to the crack propagation (Tarragó et al. (2015)). It is known that the additives of 5-15% (wt.) nano WC contribute to the reduction of the average size of carbide grains from 1…1.2 μm to 0.76…0.8 μm ( Bukhta et al. (2020)). The additives of 13.5-18% (wt.) nano Ni reduce carbide grains to 0.59…0.77 μm ( Koval et al. (2022)) and are advantageous for fracture toughness and strength. Therefore, such alloys are expected to contribute to thermal shock resistance. 2. Problem Statement To expand the temperature range of operations and enhance their durability, it is important to determine the influence of the chemical composition and sizes of the original components on the operating temperature range