| Preparation of mullite-HfN composites through spark plasma sintering: investigation of the microstructure and mechanical properties |
Hamidreza Moslemi-firoozabadi1, Sahebali Manafi1
, Davoud Ghahremani2 |
1Department of Engineering, Shahrood Branch, Islamic Azad University, Shahrood, Iran
2Department of Engineering, Maybod Branch, Islamic Azad University, Maybod, Iran |
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Received: August 2, 2022; Revised: September 16, 2022 Accepted: September 24, 2022. Published online: October 12, 2022. |
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| ABSTRACT |
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This study focused on the production of mullite ceramic and composites containing HfN reinforcements through spark plasma sintering. Accordingly, 5, 10 and 15wt% HfN powders with calcined Aluminum nitrate nonahydrate (ANN) and colloidal silica mixture were blended through a high-energy mixer mill in ethanol media. Spark plasma sintering of mullite ceramic and composite was performed under almost the same condition consisting of the initial and final applied pressure of 10 and 50 MPa, respectively, vacuum of 15–25 Pa, and the maximum sintering temperature of 1350 °C. The measured relative densities showed the nearly full densification of all prepared samples. The XRD patterns also depicted perfect mullitization for the mullite sample, while in the sintered composites, mullite, HfN and HfO2 peaks were obtained as the crystalline phases. The uniform distribution of HfN and HfO2 as the reaction products of ANN water desorption was recognized in the microstructure of mullite composites with 5 and 10 wt% HfN samples. Meanwhile, the mullite-15wt% HfN composite displayed some agglomerates and porosities. The attained mechanical properties also showed that Vickers hardness was increased by raising HfN contents. However, the maximum bending strength of 424 ± 25 and fracture toughness of 3.74 ± 0.22 MPa m1/2 were achieved for the composite containing 10 wt% HfN. |
| Key words:
Mullite · HfN · Ceramic matrix composite · Spark Plasma Sintering |
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