Study On High Pressure And High Temperature Sintering Of Ti-B Composites

The development and application of advanced ceramics have been presented inthis work. Moreover the properties and application of the structural ceramics has alsobeen presented.Being high temperature structural ceramics, TiB possesses light weight,splendiferous heat conductivity, good electric conductivity, superior chemicalstability, high hardness and high Young's modulus. It can be used as light-weighthigh temperature structural ceramics in many fields, such as military armor,mechanical bearing and gear used in aerospace field. Moreover, TiB possess goodthermal stability, low residual stress and comparatively high stiffening effect in theTi-based matrices. TiB has been identified as a splendid reinforcement fortitanium-based matrices.The TiB ceramics has absorbed extensive attention in material research field forthe recent decade. There is many literatures reported on the synthesis method ofTiB such as self-propagating high temperature combustion synthesis, reactiomsintering technique, hot pressing reaction, powder metallurgy technique, sparkplasma sintering reaction, and so on. There is no literature reported on the synthesisof TiB by the high pressure high temperature method. The high temperature highpressure sintering of Ti-B composite materials is investigated in this work.The reasons to choose the high temperature high pressure method to synthesizethe Ti -B composite materials are as below:(1) As widely known, the materials synthesized under high pressure arewith higher compactibility; and the high pressure cavity as a closedsystem, can reduced the impurity introduced.(2) The high temperature high pressure condition may optimize theperformance;(3) There may be new phase of Ti-B system formed under high temperature high pressure condition;(4) The reaction of Ti with TiB₂ or B may be prefered under hightemperature high pressure condition.The raw materials used in this work are Ti powder, TiB₂ powder and B powder.According to the result of thermodynamics analysis, Ti and TiB₂ or B can react toform TiB for the negativity of the free energy of these two reactions.The experiment materials are mixed by different mixture method with differentcomponents of the hereinbefore materials. This paper mainly introduces the phaseanalysis and hardness testing for the samples obtained from the hereinbeforematerials under different high temperature high pressure process. The experimentalresults show:(1) There are some unknown X-ray diffraction peaks appear in the XRD ofthe sample obtained under high pressure and lower temperature, and disappearwhen the temperature step up.(2) Compared with the XRD of the samples sintered in the vacuum firingfurnace, the TiB peaks in the XRD of the samples obtained under high pressureprocess are apparently more wide, The TiB crystal grains are with nanometerstructure.(3) With the temperature increase, more TiB phase formed from the Ti+TiB₂ starting materials under high pressure, and the samples have a more uniformmicrostructure.(4) As compared to the Ti+TiB₂ starting materials, it has a higher yield ofTiB when Ti+B powder mixture is used as the raw materials.(5) Extra content of Ti can increase the yield of TiB for the Ti+TiB₂system treated at high pressure and high temperature.(6) The ball milling process of the Ti+TiB₂ raw material can debase thetemperature need by the reaction of Ti+TB₂→TiB, and make it easier, moreoverit can lead to a more uniform microstructure for the sintered products.(7) A stabler cell assembly and longer reaction time at high pressure andhigh temperature are also helpful for the formation of TiB phase.The experimental results also show that the well-sintered Ti-B composite withhigh hardness and high content of TiB (≥50% in weight ratio) can be obtained athigh pressure and high temperature.