Hardness Properties Of Titanium Monoboride Prepared At High Temperature & High Pressure

Transition Metal?TM?Light Element?LE?Compound?TMLE?has excellent properties such as high hardness,friction resistance,catalytic properties,magnetic properties,superconductivity,etc.It is widely used in many fields of industry and has become a popular candidate for designing hard multifunctional materials.So TMLE has become a hot spot in materials science research.In TMLE,high boron content transition metal borides?TMBs?have high covalent bond density and do not show ideal high hardness,while low boron content low boron phase reflects comparable to high boron.Hardness results.This contradicts the traditional high covalent bond density leading to high hardness theory.How to recognize the hardness characteristics of TMLE and improve the hardness of TMLE has been a hot and difficult point in this field.In this paper,the low boron phase titanium monoboride?TiB?,containing no covalent bond,was selected as the research object.And the hardness enhancement mechanism without covalent bond materials was explored.TiB is widely used in composite materials such as TiB and TiC,TiB and silicide due to its excellent properties.However,the preparation of single phase is difficult,and the intrinsic physical properties of single phase TiB are reported less.The reason is that TiB two-phase orthogonal phase?o-TiB?and cubic phase?c-TiB?have relatively close formation enthalpy,resulting in overlapping synthesis temperature intervals of TiB two phases;And TiB₂ is easily generated at high temperature,so The TiB currently prepared is a mixed phase?c-TiB+o-TiB or c-TiB+TiB₂?.Therefore,the lack of experimental data on physical properties of TiB,such as intrinsic hardness,hinders its potential functional applications.In this paper,we are using the advantages of high-temperature and high-pressure synthesis of materials.The preparation of single-phase TiB is carried out by selecting the conditions of raw material particle size and accurately controlling the formation conditions of TiB.The growth of grains during synthesis is inhibited by high temperature and high pressure.In the process,the small grain size is obtained,the grain boundary density is increased.Therefore,the Hall-Petch effect is induced inside the material,and the hardness of the low boron phase is enhanced,and the obtained research results are as follows:1.Micron-sized Ti powder and B powder are used,at the pressure is 3 GPa,and at the temperature range is 1100 K-1600 K.The single phase TiB is not synthesized due to the close formation of two phases.Therefore,the hot sulphuric acid was used to remove Ti from the o-TiB and Ti mixed phase samples to obtain relatively pure o-TiB,and the single phase intrinsic hardness was measured to be 17.6 GPa.It provides the basis for studying the intrinsic properties of o-TiB.2.We used nano-scale Ti?50-100nm?powder and B?100-200nm?powder to synthesize the sample at a pressure of 3 GPa and at a temperature of 1000 K,and removing the titanium by hot sulfuric acid to obtain a nano-c-TiB pure phase.The nano-polycrystalline c-TiB bulk material was obtained by secondary sintering at 2-20GPa and 1000 K.The high pressure environment effectively inhibits grain growth,and the particle size decreases with the sintering pressure,the grain boundary increases.So the Hall-Petch effect was induced,which in turn increases the hardness of c-TiB.The particle size of the sample was calculated to be 16 nm by the Scherrer formula at a pressure of 5 GPa,and the hardness value is 19 GPa.At a pressure of 20GPa,the sample particle size is 10 nm and the hardness is 25 GPa.The hardness of TiB is enhanced about 31%,which is not only beneficial to the application of the functional material,but also the method of strengthening the hardness in this study is also instructive for the improvement of the hardness of other materials.3.The Vanderbilt method was used to test the resistivity of the samples sintered at high temperature and high pressure.The results show that the resistivity of the sample is on the order of 10^-5?.m.And as the synthesis pressure increases,the grain boundary density increases,causing the scattering of electrons at the grain boundaries enhanced,so the resistivity has increased.Therefore,access to functional materials requires an overall balance of performance.