Zirconium diboride (ZrB) ceramics have high melting point, high hardness, high electrical conductivity, excellent corrosion resistance against molten iron and non-basic slags and superb thermal shock resistance. They constitute a class of promising materials for high temperature applications in several industrial sectors, like foundry or refractory industries. Parts of electrical devices such as heaters and igniters are currently in use. Likewise TiB2, ZrB2 is wetted by molten metals but is not attacked by them, making it a useful material for molten metal crucibles or thermowell tubes for steel refining. The poor sinterability of ZrB2 powders represents one of the technological barriers to obtain highly dense ceramics. The successful densification of ZrB2 powders requires conditions of high temperature approaching 2200°C in pressure-assisted sintering technologies like hot-pressing. The addition of sintering aids enables the activation of densification mechanisms at lower processing temperatures. However, microstructure and properties are known being strongly dependent on the characteristics and composition of the starting powders, and on processing parameters adopted to obtain dense bodies. In this study several examples regarding role and effects of various sintering aids (Ni, Si3N4, AlN, ZrN, HfN, MoSi2) on the microstructure development and properties of ZrB2-based materials are shown. Densification techniques like pressureless sintering, hot-pressing, gas pressure sintering, and spark plasma sintering and their influence on microstructure and properties are investigated. In addition, the influence on sinterability and properties (i.e micro-hardness, fracture toughness, Young's modulus, flexural strength up to 1500°C, oxidation resistance) of second phases like SiC, HfB2 or MoSi2 incorporated into ZrB2 matrices is evaluated and discussed. Forming techniques like cold isostatic pressing and machining, or slip casting on plaster moulds (followed by hot-consolidation) are suitable to have complex shaped components. Another possibility is offered by the electrical discharge machining that allows the realization of complex final shapes from simple ZrB2 based pieces.
Ultra-refractory ZrB2-based ceramics
Monteverde F
2006
Abstract
Zirconium diboride (ZrB) ceramics have high melting point, high hardness, high electrical conductivity, excellent corrosion resistance against molten iron and non-basic slags and superb thermal shock resistance. They constitute a class of promising materials for high temperature applications in several industrial sectors, like foundry or refractory industries. Parts of electrical devices such as heaters and igniters are currently in use. Likewise TiB2, ZrB2 is wetted by molten metals but is not attacked by them, making it a useful material for molten metal crucibles or thermowell tubes for steel refining. The poor sinterability of ZrB2 powders represents one of the technological barriers to obtain highly dense ceramics. The successful densification of ZrB2 powders requires conditions of high temperature approaching 2200°C in pressure-assisted sintering technologies like hot-pressing. The addition of sintering aids enables the activation of densification mechanisms at lower processing temperatures. However, microstructure and properties are known being strongly dependent on the characteristics and composition of the starting powders, and on processing parameters adopted to obtain dense bodies. In this study several examples regarding role and effects of various sintering aids (Ni, Si3N4, AlN, ZrN, HfN, MoSi2) on the microstructure development and properties of ZrB2-based materials are shown. Densification techniques like pressureless sintering, hot-pressing, gas pressure sintering, and spark plasma sintering and their influence on microstructure and properties are investigated. In addition, the influence on sinterability and properties (i.e micro-hardness, fracture toughness, Young's modulus, flexural strength up to 1500°C, oxidation resistance) of second phases like SiC, HfB2 or MoSi2 incorporated into ZrB2 matrices is evaluated and discussed. Forming techniques like cold isostatic pressing and machining, or slip casting on plaster moulds (followed by hot-consolidation) are suitable to have complex shaped components. Another possibility is offered by the electrical discharge machining that allows the realization of complex final shapes from simple ZrB2 based pieces.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
