Preparation And Properties Of High Temperature Resistant Ceramic-Metal Composites

The rapid development of the energy and power industry has placed higher requirements on the high-temperature performance of materials.The maximum operating temperature of traditional high-temperature metals and alloys is only about 1000?,and even the temperature of long-term uses silicon carbide ceramics with excellent high-temperature performance is only 1650?,in view of this,new ultra-high temperature materials have very important significance for the development of the power industry.In this dissertation,two series of ultra-high temperature refractory metal-ceramic composites,xZrB₂-NbMo(x=0,15,30,45,60vol.%)and x(70vol.%ZrB₂-30vol.%SiC)-NbMo(x=15,30,45,60vol.%)were prepared using a new hot-press sintering process(2400?-2600?/50MPa/10min).The composites'microstructure,phase composition,mechanical properties at room and high temperature,and the oxidation resistance at high temperature were tested using an electron microscope,X-ray diffraction machine and other property testing equipment,respectively.Its deformation behavior at room temperature and high temperature,the mechanism of strengthening and toughening and fracture mechanism have been studied in detail.The microstructure analysis shows that the type of niobium boride phase formed in the xZrB₂-NbMo composites is decided by the initial ratio of Nb and B.The 30vol.%ZrB₂-NbMo has the most uniform phase and fine microstructure.In the composites with 45 vol.%and 60 vol.%ZrB₂ added,unreacted ZrB₂ remains and their sizes are larger.The type of phases in x(70vol.%ZrB₂-30vol.%SiC)-NbMo depends on the amount of ceramic phase added.The eutectic structure was found only in the composite with 15vol.%ceramic phase added,and there is unreacted large size ZrB₂ remains in the composite with 60vol.%(70vol.%ZrB₂-30vol.%SiC)added.The density of xZrB₂-NbMo reaches more than 94%,the highest density belongs to 30vol.%ZrB₂-NbMo,reaching 99.63%,and the highest density of x(70vol.%ZrB₂-30vol.%SiC)-NbMo belongs to composite with 30vol.%ceramic added,and the value is 98.69%.The fracture toughness values of both the two series of composites are inversely related to the amount of ZrB₂ added.The addition of SiC can further increase the microhardness of NbMo solid solution in the composite material on the basis of ZrB₂.The highest room temperature compressive strength of xZrB₂-NbMo series composites belongs to 60vol.%ZrB₂-NbMo samples,which is 1635.91MPa,and the highest room temperature compressive strength of x(70vol.%ZrB₂-30vol.%SiC)-NbMo composites belongs to the sample with 15 vol.%addition of ceramic phase,which was 1053.30 MPa.At room temperature,the optimum ZrB₂ content in NbMo solid solution was determined to be 30 vol.%for excellent comprehensive mechanical property,and the highest ZrB₂ concentration that react with NbMo solid solution is at the range of 30 to 45 vol.%,the ZrB₂ residue in samples with high ZrB₂ content changed the phase composition and reduced the mechanical properties.At high temperatures,the addition of ZrB₂ can significantly increase the compressive strength of xZrB₂-NbMo composites.Below 1100?,the composite material containing 30vol.%ZrB₂ has the best comprehensive high-temperature mechanical properties,including strength and toughness,which is related to its fine grains.The compressive strength of 30vol.%ZrB₂-NbMo was about 6 times higher than pure NbMo alloy at 800? in air,and 14 times higher than pure NbMo alloy at 1000? in air.High-temperature compression experiments show that the ductile-brittle transition temperature of xZrB₂-NbMo series composites at high temperature is positively correlated with the ZrB₂ content.The main influencing factors are the content of solute elements,pores and interstitial solute atoms in the NbMo solid solution.As far as the macro-fracture mechanism is concerned,the final failure mode of high-temperature compression for samples without ZrB₂ or low ZrB₂ content is dominated by shear failure at an angle of 45° to the compression direction.However,for composites with high ZrB₂ content,the fracture mode of most samples is dominated by splitting in the direction parallel to the compression direction.High temperature oxidation experiments show that xZrB₂-NbMo and x(70vol.%ZrB₂-30vol.%SiC)-NbMo composites all have "pulverization" phenomenon when oxidized at 700?,and the addition of ceramic phase could improve the oxidation resistance of the NbMo matrix to a certain extent at this temperature.When xZrB₂-NbMo composites are oxidized at 900? and 1100?,the addition of ZrB₂ can effectively improve the oxidation resistance of pure NbMo-based composites,because the generated ZrO₂ and complete and dense outer B₂O3 protective film increase.At 1200?,the evaporation of B₂O₃ does harm to its protection effects,while the addition of SiC can further improve the oxidation resistance of the niobium-molybdenum-based composite material on the basis of ZrB₂ because of the production of SiO₂.