Formation and Properties of the Ta-Y2O3, Ta-ZrO2, and Ta-TaC Nanocomposites

Hindawi Advances in Materials Science and Engineering Volume 2018, Article ID 2085368, 12 pages https://doi.org/10.1155/2018/2085368 Research Article Formation and Properties of the Ta-Y2O3, Ta-ZrO2, and Ta-TaC Nanocomposites J. Jakubowicz ,1 M. Sopata,1 G. Adamek,1 P. Siwak,2 and T. Kachlicki1 1 2 Institute of Materials Science and Engineering, Poznan University of Technology, Jana Pawla II 24, 61-138 Poznan, Poland Institute of Mechanical Technology, Poznan University of Technology, Piotrowo 3, 60-965 Poznan, Poland Correspondence should be addressed to J. Jakubowicz; Received 19 February 2018; Accepted 9 May 2018; Published 3 June 2018 Academic Editor: Akihiko Kimura Copyright © 2018 J. Jakubowicz et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The nanocrystalline tantalum-ceramic composites were made using mechanical alloying followed by pulse plasma sintering (PPS). The tantalum acts as a matrix, to which the ceramic reinforced phase in the concentration of 5, 10, 20, and 40 wt.% was introduced. Oxides (Y2O3 and ZrO2) and carbides (TaC) were used as the ceramic phase. The mechanical alloying results in the formation of nanocrystalline grains. The subsequent hot pressing in the mode of PPS results in the consolidation of powders and formation of bulk nanocomposites. All the bulk composites have the average grain size from 40 nm to 100 nm, whereas, for comparison, the bulk nanocrystalline pure tantalum has the average grain size of approximately 170 nm. The ceramic phase refines the grain size in the Ta nanocomposites. The mechanical properties were studied using the nanoindentation tests. The nanocomposites exhibit uniform load-displacement curves indicating good integrity and homogeneity of the samples. Out of the investigated components, the Ta-10 wt.% TaC one has the highest hardness and a very high Young’s modulus (1398 HV and 336 GPa, resp.). For the Ta-oxide composites, Ta-20 wt.% Y2O3 has the highest mechanical properties (1165 HV hardness and 231 GPa Young’s modulus). 1. Introduction Refractory materials of the melting point higher than 3000°C are the most desired in design and manufacturing of heavy load-bearing components where resistance to high temperature and wear plays a crucial role. Additionally, these materials usually have high corrosion resistance in very aggressive environments as well as high mechanical properties [1]. The examples of refractory materials are pure metals such as Ta, W, or Mo and theirs alloys [2]. Other most commonly used refractory materials are ceramics such as oxides (ZrO2 and Y2O3), carbides (TaC, ZrC, and WC), or nitrides (TiN and Si3N4) [3–5]. Both types of refractory materials, that is, metals and ceramics have found applications in the design of bulk parts or coatings. Due to their high hardness, refractory materials (particularly ceramics) are brittle. Both materials can be joined together in the form of composites, which usually constitutes a combination of the best properties of both the metals and the ceramics [6–8]. Particularly, the high brittleness of ceramics can be limited by the addition of a metallic phase and vice versa, and the addition of ceramic phase into the metallic matrix leads to the improvement of the hardness and wear resistance of refractory metals. Refractory materials require high temperature processes for the formation of materials and products. For example, powder metallurgy requires the sintering temperature of at least 1500°C (usually above 2000°C) for proper microcrystalline powder consolidation [9]. Conventional high temperature and longtime sintering processes can be applicable for coarse-grained materials of micrometer size grains. Nanomaterials, compared to microcrystalline ones, can be consolidated for a shorter time and at significantly lower temperatures to achieve optimum properties. The consolidation processes used for nanocrystalline powders are usually different than conventional powder metallurgy used for microcrystalline powders. For 2 example, for the consolidation of nanomaterials, the hot pressing working in the heating mode of the spark plasma sintering (SPS) or pulse plasma sintering (PPS) gives the best results [10, 11]. In these processes of consolidation, both the pressure and the temperature increase simultaneously, which results in a shortening of the time for which the material is kept at a given high sintering temperature, and this process can be done at a significantly lower consolidation temperature compared to conventional pressureless sintering [12]. Both factors (temperature and time) are crucial for the reduction of the grain growth and the maintenance of the nanostructure or ultrafine structure [13]. Differences in the absence of wetting and the densities of the melted metal and ceramic components result in their segregation, which requires special casting techniques [14]. Therefore, powder metallurgy is very useful for the formation of homogeneous composites [15]. In the process of preparation of the refractory composites, the powders of metallic and ceramic components of the designed chemical composition are mixed together and then consolidated using hot pressing, SPS, PPS, or other relevant techniques [16–18]. For the formation of nanocomposite powders, the mechanical alloying process can be applied, in which the reduction of microcrystalline into nanocrystalline grains is provided by high-energy impacts of the balls in the milling vial [19]. In the mechanical alloying process, the final powders’ mixture comes in the form of agglomerates of the micrometer or submicrometer size composed of nanometer size grains of metallic as well as ceramic phases uniformly distributed in the entire volume of the material [20]. New prospects for refractory nanomaterials are related to their outstanding mechanical properties [21], whereas high-temperature applications are limited due to excess grain growth at elevated temperatures [22]. At high temperatures, the nanostructure is unstable and grows up, which leads to deterioration of the mechanical properties. In this work, the authors focus on the preparation and properties of tantalum-based nanocomposites, reinforced by ceramic Y2O3, ZrO2, and TaC. Ta has the melting point of 3017°C and the density of 16.4 g/cm3. The ceramics have the melting point of 2690, 2715, and 3985°C for Y2O3, ZrO2, and TaC, respectively. The density of ceramics is 5.03, 5.68, and 14.5 g/cm3 for Y2O3, ZrO2, and TaC, respectively. The nanocomposites having 5, 10, 20, and 40 wt.% of the ceramic phase were formed using mechanical alloying and PPS. The paper studies the formation of nanocomposites and their structure, microstructure, and mechanical properties. 2. Materials and Methods In this work, nanocrystalline Ta-xY2O3, Ta-xZrO2, and TaxTaC composites (x � 5, 10, 20, and 40 w (...truncated)