Research On Thermodynamics And Microstructure And Properties Of In-situ Synthesized (TiC+TiB)/Ti Matrix Composites

In this paper,pure titanium particles and B₄C powder were used as raw materials to make different volume fractions of TiB whisker and TiC particles reinforced?TiC+TiB?/Ti compositessuccessfully through high-energy ball milling and vacuum hot pressing sintering technologyin different temperature 1200?,1300?and 1400?.The volume fraction of the reinforcements in the composites respectivelywas5 vol.%,10 vol.% and 15 vol.%.The effects of sintering temperature and the volume fraction of the reinforcement on the influence of the microstructure and properties of?TiC+TiB?/Ti composite was also studied.The optimum sintering temperature was determined.Chemical reactions involved in the Ti-B₄C system in the thermodynamic calculation,the calculation results show that the 1155K¹800K test temperature range,the Ti-B₄C system 3Ti+ B₄C = TiC + 2TiB₂ reaction and reaction 5Ti + B₄C = TiC + 4TiB,the reaction in 1155K¹800K are exothermic,from thermodynamics.Considering the reactions are also feasible.And the reaction 5Ti + B₄C = TiC + 4TiB Gibbs free energy and enthalpy of formation is lower,so in the 1155K¹800K temperature range,the reaction of TiB is more preferential.At the same time in the 1155K¹800K test temperature range,the presence of large amounts of Ti in the reactant,TiB₂ is unstable,the excess titanium powder by reaction of Ti + TiB₂ = 2TiB and the generation of TiB₂ further reaction,the final product of TiB.Therefore,it is feasible to prepare titanium matrix composites by Ti-B₄C reaction in1155K¹800K.The exploratory study of raw material mixing process shows that the best ball milling parameters are ball to material ratio,5:1,rotational speed 300 rpm,time 12 h,adding control agent is alcohol 6ml.The results of hot pressing sintering show that the increase of sintering temperature is beneficial to the diffusion and mixing between phases,and the densification of composites is improved.At the same sintering temperature,the density of composites decreases with the increase of the content of the reinforcing phases.In the composite,in-situ TiB and TiC can significantly improve the hardness of the composites.At1400 ?,the hardness of the sintered composites with the increase of the volume fraction of the reinforcing phase increases to HRC30.37,39.46 and 44.82 respectivelyThe compressive strength of the composites is obviously improved by hot pressing.when sintering at 1400?with the increase of volume fraction of the reinforcements,theyield strength of the composites were 775 MPa,870MPa,820 MPa,compression ratio were10.3%,7.6%,8.2% respectively;the 10%volume fraction of the reinforcement of the composites,with the increase of sintering temperature the compression yield strength of the composites reached 800 MPa,830MPa,870 MPa,and the compression ratiowere 10%,8.6%,7.6% respectively..