At present, the preparation methods for porous titanium materials include space occupation method, metal powder injection molding and resin impregnated
titanium replacement technology. It focuses on the application of ammonium bicarbonate and urea as pore-forming agents in the space-occupying method, and compares the advantages and disadvantages of different pore-forming agents in this method. In addition, further analysis clarifies the restrictive factors of the application of porous titanium materials in biomedicine due to the problem of surface inertness.
1. Preparation of porous titanium materials by pore-forming agent method
This method uses powder metallurgy to mix the pore-forming agent with metal powder, remove the pore-forming agent, and then sinter in vacuum or under a protective atmosphere to obtain a porous material. The method can prepare porous metal with higher porosity, and its pore shape, pore size distribution and porosity can be controlled by controlling the shape, size and addition amount of pore-forming agent materials. Common pore-forming agents include ammonium bicarbonate, urea, and sodium chloride.
1.1 Preparation of porous titanium materials by space occupation method using ammonium bicarbonate as pore forming agent
Because ammonium bicarbonate decomposes when heated at a lower temperature, it is used as a pore-forming agent to prepare porous materials. The decomposition of the pore-forming agent at a lower temperature can avoid the reaction between the decomposition products of the pore-forming agent and the porous material, thereby causing foreign impurities to contaminate the matrix. Therefore, this pore-forming agent can prepare a relatively pure porous material.
1.2 Preparation of porous titanium materials by pore-forming agent method using urea as pore-forming agent
In addition, urea can be decomposed at a higher temperature and is also used as a pore-forming agent to prepare porous materials. Some scholars have concluded that urea can be completely removed when heated to 460°C through thermogravimetric analysis, but the holding time can be increased to reduce the removal of urea. temperature.
1.3 Preparation of porous titanium materials by pore-forming agent method using other materials as pore-forming agents
Water-soluble materials (such as sugar spheres and soluble salts, etc.) can also be used as pore-forming agents.
2. Other common methods for preparing porous titanium materials
2.1 Preparation of porous titanium materials by 3D printing
In addition to the above pore-forming agent method used to prepare porous materials, 3D printing is a popular method. Selective laser melting (SLM) as a method of 3D printing is to design the model of the required test piece through 3D modeling software, and then use Selective laser sintering.
2.2 Preparation of porous titanium materials by organic sponge impregnation and sintering technology
Organic sponge impregnation and sintering uses organic sponge as a carrier, immerses the organic sponge in the slurry made of metal, makes the organic sponge fully absorb the slurry, takes it out to dry, and then sinters at high temperature. The material prepared by this method has high porosity, but the process is relatively complicated.
2.3 Preparation of porous titanium materials by metal injection molding
Metal powder injection molding is to mix the metal powder with an organic binder first, then heat to keep the molten state, inject it into the prepared mold for solidification and molding, and then degrease to remove the binder in the formed blank, and then sinter. The method is capable of producing small pieces of porous titanium with great design flexibility, combining the properties of powder metallurgy (such as low cost, simplicity, flexibility in choosing components) and the characteristics of injection molding (such as the manufacture of complex parts and rapid production).
2.4 Preparation of porous titanium materials by infiltration casting combined with acid etching
The titanium liquid was injected into the wound molybdenum wire, and then the molybdenum wire was etched. The porosity of the prepared porous titanium material was 32-47%, the modulus was 23-62 GPa, and the strength was 76-192 MP.
