Study On The Preparation And Properties Of Nano-TiC_p Reinforced?Mo,W??Si,Al?₂ Composite Ceramics

With the continuous development of high-tech industries such as aviation,aerospace and advanced energy,increasingly requirements are placed on the performance of materials,especially high-temperature structural materials requiring high temperature,high strength,small specific gravity and good stability.MoSi2 is considered to be a very promising new generation of high temperature structural materials due to its high melting point,low density,excellent high temperature oxidation resistance,corrosion resistance and thermodynamic stability,and good high-temperature toughness and electrical thermal conductivity.However,the low room temperature toughness(2.5?3.0 MPa.m1/2)of MoSi2 limits its application as structural materials to some extent.In this paper,nano-TiCp/(Mo,W)(Si,Al)2 composite ceramics were prepared by W,Al alloyed MoSi2 and nano-TiC particles composite to further improve the performance of MoSi2 matrix composite.MoSi2 and(Mo0.99W0.1)(Si1-xAlx)2(0,0.03,0.06,0.09,0.12)samples were prepared by self-propagating high-temperature synthesis technology using Mo,W,Si and Al powders as raw materials.The combustion mode of self-propagating high-temperature synthesis,the phase composition and microstructure of the product were analyzed.The image analysis of the reaction process shows that the combustion mode of the self-propagating high-temperature synthetic samples of W and Al alloyed MoSi2 is the non-steady-state combustion mode.The phase analysis of the synthesized product shows that the phases of the(Mo0.9W0.1)(Si1-xAlx)2 samples are mainly Cllb phase,the C40 type Mo(Si,Al)2 phase begins to form when x=0.06,and as the amount of A1 continues to increase,the intensity of the diffraction peak of the C40 phase gradually increases.Micromorphology analysis shows that the structures of the self-propagating high-temperature synthesis products are porous and loose.Using the(Mo0.9W0.1)(Si1-xAlx)2 sample powders prepared by self-propagating high-temperature synthesis reaction as raw materials,(Mo0.9W0.1)(Si1-xAlx)2 ceramic samples with relative density of about 95%were prepared by vacuum hot pressing.The results of phase analysis show that the phase compositions of ceramic samples are basically the same as that before hot press sintering,but the diffraction peak intensity of C40 Mo(Si,Al)2 phase is lower than that before hot press sintering.By testing the mechanical properties of MoSi2 and(Mo0.9W0.1)(Si1-xAlx)2 ceramic samples,it can be concluded that the hardness and flexural strength of ceramic samples increase and the fracture toughness decreases with the addition of a small amount of W alloying elements.On the basis of W alloying,the addition of A alloying elements can effectively improve the fracture toughness of ceramic samples,but the hardness and bending strength of ceramic samples are reduced.Comparing the mechanical properties of MoSi2 and(Mo0.9W0.1)(Si1-xAlx)2 ceramic samples,the comprehensive performance of(Mo0.9W0.1)(Si0.94Al0.06)2 ceramic sample is better.The flexural strength,hardness and fracture toughness of(Mo0.9W0.1)(Si0.94A10.06)2 ceramic sample are better than those of pure MoSi2 ceramics.The fracture toughness of(Mo0.9W0.1(Si0.94Al0.06)2 ceramic reaches 6.38 MPa·m1/2,which is 42.41%higher than that of pure MoSi2 ceramic.The nano-TiC particles are mixed with the(MO0.9W0.1)(Si0.94A10.06)2 sample powder prepared by the self-propagating high-temperature synthesis reaction to form mixed powders,and then the nano-TiCp/(M00.9W0.1)(Si0.94Al0.06)2 high-density composite ceramics were prepared by vacuum hot pressing using the mixed powders as raw materials.The results of phase analysis show that the phase compositions of composite ceramics are Cllb phase and TiC phase,and no reaction occurs between(M00.9W0.1)(S10.94Al0.06)2 and TiC to form other new phases.Through the test of the mechanical properties of composite ceramics,it is concluded that the addition of nano-TiC is beneficial to improve the relative density,flexural strength,hardness and fracture toughness of composite ceramics.As the amount of nano-TiC added increases,the mechanical properties of the composite ceramic increase first and then decrease.When the amount of nano-TiC added is 20 vol%,the performance of the composite ceramic is the best,its hardness,flexural strength and fracture toughness reach 14.71 GPa,433 MPa and 9.73 MPa,m1/2,respectively,which are 65.84%,68.48%and 117.19%higher than pure MoSi2.