Preparation And Characterization Of Textured Ti₂AlC And Ti₃AlC₂ Composites

The development of national economy and defense industry drive the development of new high tech ceramic materials.Ti2AlC and Ti3AlC2 are two potential ceramics which belong to the family of nanolayered ternary carbides or nitrides(MAX phases).These compounds are constituted by covalent ionic M-X bonds and metallic M-A bonds,which endow them with a combination of metallic and ceramic properties.The extraordinary properties of Ti2AlC and Ti3AlC2 make them very promising for nuclear,aerospace,armory,transportation,maritime engineering and other applications.However,compared with conventional structural ceramics,Ti2AlC and Ti3AlC2 have relatively low compressive strength,lower flexural strength and hardness.Compared with metallic material,the lack of fracture toughness also limits the application of Ti2AlC and Ti3AlC2 ceramics.In this work,textured Ti2AlC and Ti3AlC2 composites were fabricated and the strengthening and toughening effects were studied.Ti2AlC and Ti3AlC2 nano flakes were prepared by reactive ball milling method.The hot pressing method was used for fabricating ultra-fined Ti2AlC and Ti3AlC2 bulks which have grain refining effect for strengthening.The oxygen introduced to Ti2AlC and Ti3AIC2 nano flakes was converted into in-situ synthesized nano dispersive Al2O3 phase which would further improve the strength of the materials.The Ti2AlC and Ti3AlC2 composites are highly textured and have high fracture toughness along certain directions due to crack deflection effect.In this work the influence of Al addition in the sintering process of Ti2AlC and Ti3AlC2 composites was studied.The microstructure,physical properties,mechanical properties,and oxidation behavior of as fabricated materials were studied and characterized by several methods.The main results are as follows:In Ti2AlC composites,the Ti2AlC,Ti3AlC2 and Al2O3,phase fraction was around 60 wt%,30 wt%and 9.3 wt%,respectively.In Ti3AlC2 composites,the Ti3AlC2,TiC and Al2O3 phase fraction was around 75 wt%,15 wt%and 9.5wt%respectively.The grain size of Ti2AlC composites is 1.09 ?m in length and 0.37 ?m in thickness.The grain size of Ti3AlC2 composites is 1.53?m in length and 0.42?m in thickness.The hardness of textured composite samples increased to 6?8 GPa,compared with?4 GPa of untextured coarse grain samples.The compressive strength of textured Ti2AlC and Ti3AlC2 samples was around 2 and 1.8 GPa,which is almost 3 times that of the coarse grain samples.The average fracture toughness of textured Ti2AlC and Ti3AlC2 samples stretched along the c-axis is 8.5 and 16.1 MPa.m1/2,respectively.The average flexural strength of textured Ti2AlC and Ti3AlC2 samples parallel to c-axis is 735 and 853 MPa,respectively.The high temperature oxidation resistance of Ti2AlC and Ti3AlC2 composites became poor due to Al element converting to Al2O3 phase and lack of protective Al2O3 film.So,this work studied the method of adding Al element to improve the oxidation resistance of Ti2AlC and Ti3AlC2 composites.The result shows that,by addition of 2 wt%Al,the oxidation resistance of Ti2AlC and Ti3AlC2 composites could be improved and comparable to normal coarse grain samples.Besides,the decline of mechanical property in Ti2AlC and Ti3AlC2 composites was acceptable.By studying the microstructure of Al added samples,we proposed several mechanisms of Al element addition promotes diffusion in the sintering process.