Solid Boronizing Of Titanium Surface And The Study Properties Of Boronizing Layers

From the standpoint of industrial value, resource lifetime and development prospect, titanium will become the third metal following iron and aluminum as new technologic and industrial revolution develop, thus,21st century will become the century of titanium. From the standpoint of application significance of titanium, how much titanium one country has used has symbolized one country’s technology level, military power and economical power. Therefore, promoting applications of titanium is a direction of modern technology development. However, the low hardness, poor wear resistance limit their applications in the friction and wear and other related industries. In order to overcome the deficiencies in mechanical properties, surface modification to improve the wear resistance of titanium alloy has become a new research focus.In this paper, the solid powder boronizing preparing boron-titanium compounds layer was studied to improve the surface properties of titanium. The morphology, structure and performance of boride layers were analyzed by Scanning Electron Microscopy (SEM), Optical Microscopy, X-ray Diffraction, Micro-Hardness Tester, Friction and Wear Testing Machines and other instruments.The microstructure observed by SEM revealed that the diffusion layer was composed of the outer surface TiB2and the inner surface TiB whisker, and the TiB interlocked closely with the titanium substrate. It was also found that the thickness of diffusion layer varied from13μm to98um when boronizing at1000°C,1050°C and1100℃for5～20h. The hardness was increased from2400HV0.05for TiB2to8OOHV0.05for TiB, which were eight more times higher than the matrix. However, brittleness of TiB2and TiB is higher than that of the matrix.The results obtained by friction and wear experiments showed that the friction coefficient of TiB2and TiB varied from0.2to0.3, and the friction coefficient of the outer surface of the TiB2was the lowest, compared with0.4-0.45of the matrix, The wear resistance was significantly enhanced.RE (rare earth)-boronizing experiments were carried out on pure-titanium surface. The thickness of layer was varied by changing the amount of added rare earth, thus, the optimum content of rare earth was determined. The existing form and distribution of rare earth were analyzed, and the effect of rare earth on morphology and elemental distribution of the diffusion layer was investigated. The hardness, wear resistance and corrosion properties of boronizinng and re-boronizing diffusion layer in various mediums were systematically studied. The results showed that the optimum content of rare-earth was8%, and the depth of TiB2and TiB layer was increased and nano-scale tiny holes was formed in TiB2layer after adding rare earth. When comparing boronizinng with RE-boronizing, It was found that the microhardness of TiB2and TiB obtained by adding rare earth element varied from33OOHV0.05to HOOHV0.05, which was increased by about30%compared with that of boronizinng. And the brittleness of RE-boronizing samples was lower than that of boronizinng samples.The boronizing mechanism and the effect of added rare earth oxide on the boride layer were analyzed and the growth kinetics curves of boronizinng and RE-boronizing were also established. The results showed that TiB could be formed in the interface between the Ti matrix and B4C powders at temperature varing from1000°C to1100°C with the effects of trace oxygen remaining in the system, and then TiB2was generated when TiB reacted with active boron atoms. Results also showed that the diffusion coefficient of boron in titanium is increased adding rare earth, and rare earth oxide had an acceleration effect on the growth of boron-titanium compounds.