Strength, Fracture Mode, and Thermal Stress Resistance of HfB₂and ZrB₂

Abstract

Zirconium diboride and hafnium diboride were fabricated by hot-pressing at 180OoC and 120,000 psi. Bend strengths were measured on the fully dense materials from 25' to 140OoC in an argon atmosphere. These diboride compounds do not exhibit any gross plastic flow in the temperature range studied. The bend strengths go through a maximum between 700' and 1000°C and vary from 39,000 to 68,000 psi for HfB2 and 30,000 to 56,000 psi for ZrBz. The maxima in strength correspond to maxima in the fraction of transgranular fracture. The bend strength and room-temperature elastic modulus measurements Were combined with available thermal conductivity and expansion data to calculate thermal stress resistance parameters. Under steady-state heat flow conditions, the calculated thermal stress resistance parameters of the borides are higher than those calculated for other refractory compounds.

Vibrational Properties of Zr(Hf)B2–SiC UHTC Composites by Micro-Raman Spectroscopy

“…The high melting point of ZrB 2 and HfB 2 coupled with their high hardness, low density, and ability to form refractory oxide layers make them potential candidates for operation in the ultra high temperature range of 2,000-3,000 o C. Both ZrB 2 and HfB 2 are reported to have excellent resistance to thermal shock and oxidation [13][14][15][16] [17]) that very few materials exhibit. Also they exhibit high elastic modulus (E = 489 GPa for ZrB 2 [18] and 480 GPa for HfB 2 [19]), high hardness (H v = 23 GPa for ZrB 2 [18,20] and 28 GPa for HfB 2 [21][22][23][24]) along with very high thermal conductivity (k = 60 W/mK for ZrB 2 2 toughness of ZrB 2 and HfB 2 is not very high, which is a major drawback for their most promising aerospace applications [11].…”

Effect of SiC content, additives and process parameters on densification and structure–property relations of pressureless sintered ZrB2–SiC composites

“…The possibilities of reactions ((12)- (14)) explain why the peaks of WC have not been found in the XRD patterns representing the sintered ZrB 2 -SiC composites (Fig. 5).…”

“…The values of E p calculated using Eq. (14) for the investigated composites are also shown in Fig. 15(a).…”

“…9), where W appears to be contributed by reaction (14). Based on this assumption, it may be further proposed that the C-rich areas adjacent to the W-enriched locations at the ZrB 2 -SiC interfaces, as shown in Fig.…”

“…Therefore, densification of pure ZrB 2 powder generally requires very high temperatures [9] (Z2100 1C) with moderate pressure (E20-30 MPa), [10][11][12] or lower temperatures ($ 1800 1C) with extremely high pressures (4800 MPa) [13][14]. In recent years, significant attention has been devoted to pressureless sintering of the ZrB 2 and ZrB 2 -based composites, as this process is relatively inexpensive compared to hot pressing and offers the flexibility of near-net shaping of the finished products [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”