Investigations on microstructure and mechanical properties of HfC particle-reinforced WMo composites
Introduction
Tungsten (W) and W-based composites are utilized widely in high-strength and high-temperature applications (e.g., turbines [1], target materials in spallation neutron source and fusion reactors [[2], [3], [4]]) owing to their high melting points, high moduli of elasticity, low tritium retention, good thermal shock resistances, and superior strengths at high temperatures [[5], [6], [7]]. However, some serious drawbacks, such as low temperature brittleness, recrystallization embrittlement and poor oxidation resistance [[8], [9], [10]], have severely limited their extensive application. For instance, the strength of W can be reduced by 60% near 1000 °C due to the high temperature oxidation. Meanwhile, some deleterious elements including O, N and P, are always prone to aggregate on the grain boundary (GB), which will significantly weaken the cohesion of GB. It is considered to be one of the main reasons causing the intergranular fracture and the deterioration of mechanical properties [11]. Therefore, to maintain the excellent mechanical properties or delay the degradation of comprehensive performance on high and low temperature service conditions, the microstructural optimization and stability of W-based composites, as well as the purification or elimination of impurity elements in GBs [12,13], will need to be solved urgently.
In recent decades, an effective improving solution is the addition of some additives into W matrix as solid solution strengthening and dispersion strengthening. As another important refractory metal, molybdenum (Mo) has also a relatively higher melting point and can form the solid solution in any proportion with W element, which is ascribed to the similarity between Mo and W. Affiliated to the same family, they have a similar atomic radius in element attributes, as well as exhibit the identical body centered cubic (BCC) structure and lattice constant in terms of elemental structure. Relevant literatures manifest that the formed WMo solid solution can improve effectively the hardness, strength, toughness and other high temperature mechanical properties with the aid of solid solution strengthening [[14], [15], [16]]. Besides, an addition of high-temperature ceramics as a second phase particle reinforcement in W matrix has produced composites with better thermal and mechanical properties. With the highest melting point (3900 °C) and a low thermal conductivity (20 W/m·K) [17,18], hafnium carbide (HfC) ceramic particles have been added to the alloy to enhance its mechanical properties. Lee [19] probed into the effects of the HfC-content on the mechanical properties of the W-HfC composites. It was found that the flexural strength of the composites was increased to 1578 MPa when 10 vol% HfC is added. Meanwhile, it is reported that HfC particles can react with oxygen impurity to produce HfO2, which contributes to purify GBs and refine the grain size of W matrix [20]. As HfC-content reaches 2.0 wt%, the compressive strength and strain were raised to 1.9 GPa and 34.7%, respectively. The dispersion strengthening impact of HfC particles on the properties and microstructure stability of W-Mo-based composites are few investigated and reported.
Therefore, it is of great significance to study the effect of HfC addition on the mechanical properties and microstructure of WMo alloy. In this study, W-Mo-HfC composites are fabricated by using the conventional powder metallurgy with different sintering temperature and same forging technology with 50% deformation. The mechanical properties and microstructures of W-Mo-HfC composites are comparatively investigated. The tensile tests, Vickers hardness and microstructure analysis are used to determine effects of dispersed HfC particles on the mechanical properties.
Section snippets
Experimental procedures
The W-Mo-HfC composites were prepared by ball milling and powder metallurgy technology. The starting materials were commercially available tungsten, molybdenum and HfC powders, which are purchased from Naiou Nano technology Co. Ltd., Shanghai, China and have a purity of 99.9% and particle size of 3.0, 3.5 and 1.0 μm, respectively. The chemical composition and process parameters of W-Mo-HfC composites are indicated in Table 1, where two categories of W-Mo-HfC composites are abbreviated as WMo1
Results and discussion
Fig. 1 presents the XRD patterns of two kinds of W-Mo-HfC composites. At first sight, both samples show the similar XRD results, where only a single phase with a high diffraction peak intensity and integrity peak shape is easily discerned. These diffraction peaks can be assigned to the commercial pure tungsten (JCPDS No.04–0806) but with a ~ 0.16° shift to higher 2θ angles. A close inspection reveals that these reflections with the higher intensities (2θ = 40.4°, 58.4°, 73.4° and 87.3°) are
Conclusions
In this work, the two categories of W-Mo-HfC composites were fabricated by the conventional powder metallurgy with the different sintering temperature (2100 °C and 2150 °C) and the identical amount (50%) of forging deformation. The microstructure and mechanical properties of both were investigated comparatively. The main results are as follows:
- 1)
It is confirmed that WMo infinite solid solution acts as the matrix of W-Mo-HfC composites. The W-Mo-HfC composites are composed mainly of WMo matrix,
Author statement
We are sending a revised manuscript to International Journal of Refractory Metals and Hard Materials. The title is “Investigations on microstructure and mechanical properties of HfC particle-reinforced W-Mo composites”. The authors are Xueshan Liu, Meng Liu, Ximeng Zhao, Rong Li, Benzhe Sun, Yang Qi, Jiupeng Song in sequence. We state that all authors have read and approve this version of the article, and due care has been taken to ensure the integrity of the work. No part of this paper has
Declaration of Competing Interest
We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “Investigations on microstructure and mechanical properties of HfC particle-reinforced W-Mo composites”.
Acknowledgements
This research is supported by funds from National Natural Science Foundation of China (No. 61971116).
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