Flushing Behavior And High-Temperature Oxidation And Ablation Of Layered Ternary M₂AlC Ceramics

Layered ternary ceramics Mn+iAXn?abbreviated as MAX phase,where M is transition metal element,A is mainly stand for III A and IV A elements,X is C or N,and n is mainly 1,2,3?are new types of machinable structural ceramic materials.They possess a unique combination of the properties of both metals and ceramics.such as high temperature resistance,oxidation resistance,corrosion resistance,good electrical conductivity,thermal conductivity,with high strength,high elastic modulus,as well as good plasticity and easy mechanical processability.Ta₂ AlC,Cr₂AlC and Ti₂ AlC belong to the 211 phase of the layered ternary ceramics,they are typical representative of the excellent properties of the layered ternary ceramics,with potential application value.In this paper,layered ternary ceramics,Ta₂ AlC,Cr₂AlC and Ti₂ AlC were prepared by hot pressing sintering process.The phase composition and microstructure of layered ternary ceramics were characterized by XRD and SEM.The mechanical properties of the layered ternary ceramics were investigated by flushing test.Isothermal oxidation,cyclic oxidation and high-temperature ablation tests were carried out to investigate the anti-erosion properties of Ta₂ AlC,Cr₂AlC and Ti₂ AlC ceramics under high temperature conditions and ablation conditions.Oxidation resistance and ablation resistance of the layered ternary ceramics were assessed by the phase composition,oxidation surface and cross-section microstructure,oxidation kinetic curves and ablation rates.The erosion resistance of layered ternary ceramics is related to the structure of the materials.The less of cracks,the better of the erosion resistance of the materials have.When the erosion angle is 90°,the materials were subjected to both stress impact and micro-cutting.The loss of the materials were caused by the microcrack growth due to axial and radial microcracks,and the furrow produced by the micro-cutting effect.The materials have the erosion properties of plastic materials and brittle materials at the same time.The wearing rate of Ta₂ AlC,Cr₂AIC and Ti₂ AlC is11.34%,14.38% and 20.06%,respectively,Ta₂ AlC has the best anti-erosion wear performance.The surface of layered ternary ceramics Ta₂ AlC,Cr₂AlC,Ti₂ AlC was covered with oxide layer by isothermal oxidation and cyclic oxidation experiments at 800?,900? and 1000?.With the increase of oxidation time and oxidation temperature,the thickness of oxide layer also increased.The main oxidation products of Ta₂ AlC is Ta₂O₅ and the main oxidation products of Cr₂ AlC is Al2O3,TiO₂ is the main oxidation products of Ti₂ AlC.In the processes of isothermal oxidation and cyclic oxidation,the surface oxide layer of Ta₂ AlC peeled off,the oxidation resistance was poor,Ta₂O₅ was not dense enough to form protective films,and the oxidation kinetics curve followed the straight line rule.In the process of isothermal oxidation and cyclic oxidation,Ti₂ AlC formed a thick oxide layer,but no oxidation layer peeling occurred,the oxidation kinetics curve met the parabolic law.In the process of oxidation,Cr₂ AlC rapidly formed a thin layer of dense oxide on the surface.The kinetic curve of isothermal oxidation conformed to the parabolic law.With the increase of oxidation time,the oxidation weighting tended to be gentle.In the process of isothermal oxidation at 900? and cyclic oxidation,The oxidation kinetics curve showed weight loss,generally,Cr₂ AlC showed good oxidation resistance.The layered ternary ceramic Ta₂ AlC,Cr₂AlC and Ti₂ AlC have good thermal shock resistance during the process of oxyacetylene ablation.After thermal shock,there is no macroscopic thermal shock damage.At the same time,N₂ in the air was involved in the reaction,and combined nitrides.The linear ablation rates of Ta₂ AlC,Cr₂AlC and Ti₂ AlC were 2.08 ×10^-4 mm/s,0.25×1 0-4 mm/s and 6.08×10^-4mm/s,respectively.The mass ablation rates of Ta₂ AlC,Cr₂AIC and Ti₂ AlC were 1.58×10^-5g/s,0.27×10^-5g/s and 4.9×10^-5g/s,respectively.Cr₂ AlC has good ablation resistance.