It is understood that titanium foam and its alloys have important application value in some special fields, especially in the biomedical industry, due to the porous titanium both high biocompatibility and excellent mechanical properties, so the advantages are very obvious. Compared with the whole porous titanium material, only in the surface of the porous titanium material with higher mechanical strength, can withstand greater physiological loads, and therefore in the field of medicine to show a broader application prospects.
Recently, the China Academy of Armaments Science (CAAS) has demonstrated that the perfect combination of cold spraying technology and vacuum distillation can be used to prepare pure titanium coatings with a through-pore structure.
The method is to prepare a Ti-Mg composite coating by cold spraying technology and realize the preparation of porous titanium coating by vacuum distillation of Mg in this coating. They used homemade Ti powder and Mg powder, physically mixed at a mass ratio of 80:20, as the spraying powder for this coating. The selected substrate for spraying was TC4 grade titanium alloy (0.002% H, 0.07% O, 0.02% N, 0.02% C, 0.04% Fe, 6.2% Al, 4.1% V, TiBal). The Ti-Mg composite coatings were prepared using a high-speed and high-pressure cold spraying equipment, with the working gas of N2, the working pressure of 3.0 MPa, the gas heating temperature of 300 ℃, and the spraying distance of 25 mm.Then, a vacuum sintering furnace was used to vacuum distill the Ti-Mg composite coatings in the sprayed state, with the chamber pressure of 2.0-2.3 MPa, the distillation temperature of 1100 ℃, and the distillation time of 2 h. The vacuum sintering furnace was also used to distill the Ti-Mg composite coatings in the sprayed state, and the distillation time of 2 h was used.
The detection showed that the bonding interface between the obtained coating and the substrate was relatively tight, the densification of the coating was high, the average thickness was about 250 μm, and the distribution of the two compositions in the coating was relatively uniform. The bonding strength between the coating and the substrate was determined to be 60 MPa, and the porosity of the coating was less than 1%. Compositional analysis of the surface using an energy spectrum analyzer showed that the titanium particles in the coating had no obvious oxygen content, indicating that the cold spraying technology well avoids the excessive oxidation of the titanium powder, which is conducive to the retention of the original chemical composition of the sprayed powder; however, the magnesium particles in the coating were found to have a high number of impurities, which is mainly due to the excessive activity of magnesium metal and the occurrence of natural oxidation in the atmosphere. In order to make the coating porous, it is necessary to remove the magnesium component from the coating in the sprayed state, so vacuum distillation was carried out on the coating in the sprayed state. The microstructure of the coating after vacuum distillation showed obvious through-pore structure, and the porosity of the coating reached 50%, with a pore size distribution of 30-100 μm. The results of energy spectrum analysis on the surface of the coating showed that only titanium elemental components existed in the coating after vacuum distillation treatment, and magnesium elemental components had been completely distilled.
