Research On Microstructure And Properties Of In-situ Synthesized TiC And TiC+TiB Reinforced TB8 Titanium Matrix Composites

Titanium Matrix Composites?TMCs?combine the ductility and toughness of matrix with the high modulus and strength of the ceramic reinforcements,improving the modulus,strength,thermal stability and corrosion resistance of the material,which makes it widely used in aerospace and become candidate materials for advanced aero engine components.In this paper,Spark Plasma Sintering?SPS?technology was used to prepare TMCs with four different contents of TiC and TiC+TiB through in-situ reaction between CNT/CNT+B₄C and TB8:TMC1 containing 2.5 vol.%TiC,TMC2 containing 3.75vol.%TiC,TMC3 containing 5vol.%TiC and TMC4 containing 7 vol.%?TiC+TiB??1:1?.The effects of TiC content and different reinforcement mixture on the microstructure and properties of the materials were studied.The main researches and results are as follows:?1?The as-sintered microstructure?microhardness and apparent porosity of Matrix and TMCs prepared by the SPS process were studied.The results show that the mixed powder was refined obviously after the mechanical milling.After SPS,TiC reinforced TMCs is mainly composed of?-Ti,?-Ti and TiC.There is obvious TiB phases in TiC+TiB reinforced TMC4.The apparent porosity of TMCs is generally larger than that of Matrix,and the apparent porosity of TMC2 is the largest.The microhardness of TMCs increases with the increase of TiC content.TMC3 has the highest microhardness,929.24 HV,which is slightly higher than 912.87 HV of TMC4.?2?The effects of solid solution temperature and aging process on the microstructure and properties of Matrix and TMCs were studied.The actual phase transition temperature of TMC2 is between 860?-890?and closer to the latter.The solid solution temperature has a significant effect on the microhardness of TMC2,and the increase in microhardness decreases as the solution temperature increases.The microhardness of TMC2 after solid solution treatment at 890?/3h/AC is the highest,reaching 1105.6 HV,which 28.91%higher than the sintered state.The ability of890?/3h/AC+550?/8h/AC heat treatment to improve the microhardness of TMCs is much greater than that of the matrix.After heat treatment,TMC3 has the the largest microhardness increase,25.05%higher than the sintered state,which is higher than the5.72%increase of Matrix.The compressive strength of TMCs increases significantly with the increase of the reinforcements.The compressive strength of TMC4 is the largest,reaching 1298.5 MPa,which is 20.30%higher than that of Matrix.The compressive strength of TMC3 is second,which is 1242.7 MPa,but its strength and plasticity are well matched.?3?The high-temperature oxidation resistance of Matrix and TMCs was studied.The results show that the sequence of the high-temperature oxidation resistance of the four materials after cyclic oxidation at 800?for 100h is:TMC4,TMC1,TMC3 and Matrix.The oxidation law of Matrix is a mixture of linear and parabolic law,while the oxidation of TMCs mainly follows the parabolic law.The oxidation products of TMCs are similar,all containing the phases in Matrix,TiO₂,Al₂O₃ and SiO₂.In addition,there are traces of Nb₂O₅ and MoO₃ in TMC1,and C is detected in TMC3.Compared with TMC1,TMC4 has a small amount of B₂O₃ phase on the surface.The oxide layer of Matrix is mainly composed of TiO₂+Al₂O₃/TiO₂,which is the thickest and has obvious structural defects.The oxide layers of TMCs are mainly composed of Al₂O₃+TiO₂/TiO₂/Al₂O₃+TiO₂+SiO₂,without any obvious defects.Among them,the oxide layer of TMC4 has a higher Si content,and the content of Si element is positively correlated with the content of Al element,but negatively correlated with the content of Ti element,which improves the activity of Al ions,effectively inhibits the formation of TiO₂ and promotes the formation of a continuous dense and Al₂O₃ oxide film,thereby improving the oxidation resistance of TMC4.?4?The hot corrosion resistance of Matrix and TMCs was studied.The results show that after hot corrosion in mixed salt of 75 wt.%Na2SO4+25 wt.%NaCl at 800?for 30h,Matrix and TMCs basically followed the liner law,and the corrosion mechanism is mainly a mixture of alkaline fusion corrosion and sulfurized corrosion.The products of Matrix and TMCs after corrosion are basically similar,mainly TiO₂?Al₂O₃?SiO₂?Nb₂O₅?TiCl₂?NaTiO₂ and NaAlO₂,the main difference is the diffraction peak intensity of some phases.After corrosion for 30h,a large area on the surface of TMC2 was corroded and dissolved,and part of layer was obviously cracked and peeled off.The apparent porosity and the agglomeration of C element have a great influence on the thermal corrosion resistance of TMC2.However,the corrosion layer of TMC4after corrosion is dense and has no obvious defects.Many Si elements in the cross section effectively hinder the infiltration of the corrosion element,making the corrosion layer the thinnest and exhibiting the most excellent hot corrosion resistance.In summary,the TiC and TiC+TiB reinforced TMCs have been successfully prepared through the in-situ reaction between CNT/CNT+B4C and TB8 by using SPS technology.Studies have shown that the TiC reinforcement can effectively increase the hardness and compressive strength of the matrix,and the strengthening effect becomes more and more obvious with the increase of content.TiC+TiB reinforced TB8 titanium matrix composites are superior to the other three composites in terms of compressive strength,high-temperature oxidation and hot corrosion resistance.At present,there are few studies on the TMCs based on TB8 and this article can provide a reference for subsequent research.