Ultrahigh-Temperature HfB2-Based Ceramics: Structure, High-Temperature Strength, and Oxidation Resistance

• Published in: Powder metallurgy and metal ceramics 2022-03, Vol.60 (11-12), p.685-697
• Main Authors: Vedel, D.V., Grigoriev, O.N., Mazur, P.V., Kozak, I.V.
• Format: Article
• Language: English
• Subjects: Bend strength; Boron oxides; Borosilicate glass; Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Composites; Corrosion resistance; Diffusion rate; Glass; Hafnium compounds; Hafnium oxide; High temperature; Hot pressing; Inclusions; Interlayers; Materials Science; Maximum bending; Metallic Materials; Molybdenum disilicides; Natural Materials; Oxidation; Oxidation rate; Oxidation resistance; Oxide coatings; Refractory materials; Room temperature; Silicon carbide; Silicon dioxide; Structural members; Thickness; Zirconium compounds; Zirconium dioxide
• ISSN: 1068-1302; 1573-9066
• DOI: 10.1007/s11106-022-00280-2

Ultrahigh-temperature hafnium diboride ceramics with additions of 15 vol.% MoSi 2 or 15 vol.% SiC or a combined addition of 15 vol.% SiC and 5 vol.% WC were produced by hot pressing in the range 1800–2000°C. The density of the produced composite ceramics was >98%. The components interacted in the hot pressing process to form new high-temperature phases (WB, MoB). The graine size of all structural elements did not exceed 5 μm. The maximum bending strength was reached by the HfB 2 –15 vol.% SiC–5 vol.% WC samples: 587 ± 25 MPa at room temperature and 535 ± 18 MPa at a test temperature of 1800°C, being associated with transcrystalline fracture of the ceramics. A three-layer oxide film formed: the upper layer was borosilicate glass with a HfSiO 4 interlayer, the middle layer was HfO 2 with B 2 O 3 –SiO 2 inclusions, and the lower layer consisted of hafnium oxide and inclusions of other oxides. The total thickness of the oxide film was ~50 μm for the material oxidized at 1600°C for 5 h and ~150 μm at 1500°C for 50 h. The highest oxidation resistance was acquired by the HfB 2 –15 vol.% MoSi 2 composite, where the oxidation rate did not exceed ~1 mg/cm 2 ∙ h because a dense and homogeneous HfSiO 4 layer developed on the surface. However, the most corrosion-resistant zirconium diboride composite, ZrB 2 –15 vol.% MoSi 2 , showed an oxidation rate of ~2 mg/cm 2 ∙ h. This high oxidation resistance of the hafnium diboride ceramics is explained by slower oxygen diffusion in HfO 2 and HfSiO 4 than in ZrO 2 and ZrSiO 4 , which is confirmed by mathematical modeling of the oxidation process.