| In this paper,nano-Ti C/Al cermet was prepared by reactive hot pressing based on Al-Ti-MWCNTs system.The thermokinetic mechanism of nano-Ti C/Al cermet synthesis was studied.The effects of MWCNTs/Ti molar ratio and alloying elements(Mo/Ta/Cr/Nb/Zr)doping on the microstructure,mechanical properties and thermophysical properties of cermet were analyzed.The strengthening mechanism of nano-Ti C/Al cermet was revealed.The results of thermodynamic calculation and thermal analysis of the potential reaction in Al-Ti-MWCNTs system show that,the reaction process is as follows: Al and MWCNTs react first to form Al4C3,then Ti and MWCNTs react to form Ti C,Al and Ti react to form Al3 Ti,at the same time,Al4C3 and Ti react to form Ti C,and finally Al3 Ti reacts with MWCNTs to form Ti C.With the decrease of MWCNTs/Ti ratio,it can promote the reaction Ti + MWCNTs ? Ti C and the reaction 3Al + Ti ? Al3Ti;it can inhibit the reaction 4Al +3MWCNTs ? Al4C3 and the reaction Al4C3 + 3Ti ? 4Al + 3Ti C.When MWCNTs/Ti ratio is equal to 1,only Ti C and Al are in the final product.When MWCNTs or Ti are redundant,there will be Al4C3 or Al3 Ti.The microstructure analysis shows that with the decrease of MWCNTs/Ti ratio,the particle size of Ti C increases from 0.49 ?m to 1.39 ?m,and the morphology changes from lamellar hexahedron to near spherical and then to angular octahedron.The addition of Mo/Ta/Cr/Zr can refine Ti C particles.However,the addition of Nb increases the size of Ti C particles.At the same time,the addition of alloy elements changes the morphology of Ti C from nearly spherical to octahedral with cut angle.Nano-Ti C/Al cermets with MWCNTs/Ti ratio of 1:1.1 have the best compression properties at high temperature.At room temperature,the yield strength(?0.2),the maximum compressive strength(?UCS)and the fracture strain(?f)are 658.50 Mpa,977.21 Mpa and7.65%,respectively.At 300?,its ?0.2,?UCS and ?f are 344.70 Mpa,593.47 Mpa and 8.95%,respectively.The strengthening mechanism of MWCNTs/Ti ratio on nano-Ti C/Al cermet is revealed:(1)the existence of a small amount of small size Al3 Ti improves the interface bonding between metal and ceramic;(2)the closer the morphology of Ti C ceramic particles is to the sphere,the lower the stress concentration and the lower the crack source.At room temperature and high temperature,the compression properties of nano-Ti C/Alcermet strengthened by Mo are the most significant.At room temperature,the ?0.2,?UCS and?f are 757.43 Mpa,1101.47 Mpa and 7.96% respectively,which are 13.06%,11.28% and3.89% higher than that of nano-Ti C/Al cermet without Mo.At 300?,its ?0.2,?UCS and ?f are448.76 Mpa,781.15 Mpa and 15.1%,respectively,which are 23.19%,24.03% and 40.73%higher than that of nano-Ti C/Al cermet without Mo.The strengthening mechanism of nano-Ti C/Al cermets by Mo doping is revealed:(1)alloy element solution in Al causes lattice distortion and solid solution strengthens Al binding phase;(2)improve the wettability between Ti C particles and Al,improve the bonding strength of Ti C/Al interface;(3)decrease the size of Ti C particles,increase the number of Ti C/Al interface per unit area,and hinder crack growth.The minimum thermal expansion coefficient of cermet with MWCNTs/Ti of 1:1.3 is9.48×10-6/?,and the best thermal conductivity of cermet with MWCNTs/Ti of 1:1.2 is95.89W·m-1·K-1.The addition of alloy elements reduced the thermal conductivity of nano-Ti C/Al,and increased the thermal expansion coefficient of nano-Ti C/Al except Cr. |
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