Microstructure And Properties Of TiB₂-MoSi₂-SiC Composites Fabricated By Silicon Infiltration

Titanium diboride(TiB2)has excellent properties such as high melting point,high hardness,abrasion resistance,corrosion resistance,oxidation resistance,good conductivity and thermal conductivity.It has wide application prospects in metallurgy,chemical industry,machinery,and so on.At present,the main fabrication methods of TiB2 ceramics are pressureless sintering(PS),hot pressing sintering(HPS)and spark plasma sintering(SPS).However,these methods have disadvantages such as high sintering temperature,limited product size and shape.Therefore,in this study,based on the principle of reactive sintering,TiB2-MoSi2-SiC composites were fabricated by silicon infiltration under vacuum.This novel method has a series of advantages,such as simplicity in processing,lower sintering temperature and lower cost than the pressureless sintering and hot pressing methods,near net shape sintering and in favor of preparing large,complex products,etc.Specifically,this work aim to study the influence of Mo content and infiltration temperature on the phase composition,microstructure,density and mechanical properties of TiB2-MoSi2-SiC composites.The electrical conductivity,oxidation resistance and corrosion resistance in the process of aluminum electrolysis of TiB2 composites will also be studied.The main results are shown as follows:TiB2-MoSi2-SiC composites were fabricated successfully by infiltrating silicon into titanium diboride preforms with molybdenum and phenolic resin under vacuum at infiltration temperature of 1450? for a dwell time of 0.5 h.Phase composition of the composite are:TiB2,MoSi2,SiC,Si and Ti0.4Mo0.6Si2.The free Si fills in the continuous gaps between other phases.With the increase of Mo contents,the volume content of MoSi2 and SiC increased,while that of free Si decreased;the size of MoSi2 particles increased.The volume density of the composits increased,an inverse trend was observed for the open porosity.The mechanical properties of TiB2-MoSi2-SiC composites increased with the increase of Mo contents.The optimum volume density,open porosity,flexural strength,fracture toughness and Vickers-hardness of the obtained composites fabricated with 15 wt%Mo content were 3.89 g·cm-3,0.40%,361 MPa,5.9 MPa·m1/2,21 GPa and 6.31×10-7 ?·m,respectively.The effect of infiltration temperature on microstructure and properties of TiB2-MoSi2-SiC composites was further investigated on the basis of the optimum addition of 15 wt.%Mo content.The results showed that the composites fabricated at different infiltration temperatures(1450-1650?)all are composed of TiB2,MoSi2,SiC,Si and Ti0.4Mo0.6Si2.With the increase of infiltration temperatures,the volume content of SiC in the composites increased;while that of MoSi2 and free Si decreased;the size of MoSi2 particles increased.The volume density,flexural strength,fracture toughness and Vickers-hardness decreased with the increase of infiltration temperatures.During the Si infiltration,the Mo diffused to molten Si,which resulted in the decrease of MoSi2 content in the composites.The oxidation behavior of TiB2-MoSi2-SiC,TiB2-SiC and TiB2-MoSi2 composites were studied also.The results showed that these composites exhibit excellent oxidation resistance at different oxidation temperatures ranging from 400 to 1350?.The size of the oxidation layer increased initially and then decreased with the increase of oxidation temperatures.With the increase of oxidation temperatures,the TiB2 phase was oxidized firstly,then the MoSi2 phase was oxidized,and the SiC phase was oxidized finally.When the oxidation temperature is 1350?,the TiB2-MoSi2-SiC composite exhibited the best oxidation resistance in the three composites.And the TiB2-SiC composites exhibited the best corrosion resistance in the three composites,after electrolysis test at 950? for 8 h.