Motion Control And Preparation Technology Of Nano-ceramic Artificial Bone In Selective Laser Sintering System

Hydroxyapatite possesses predominate biological performance and is considered as a kind of the most promising bone replacement material. However, as a kind of ceramic material, there are limitations in the application of weight-bearing field for artificial bone due to its high brittleness, low hardness and strength, bad performance in reliability and anti-destroying property. Nano ceramics are regarded as the strategic path to overcome the brittleness of ceramics. To fabricate nano-HAP (n-HAP) artificial bone with complex shape and porous structure, the laser is used to control the grain growth due to its rapid heating and cooling. The process is carried out with nano HAP powders as raw material, micron spot laser as energy and selective sintering as technique. The main research and innovations in the paper are shown as follows:1. Based on NURBS theory, the motion of arbitrary complex space curves is realized in the self-developed selective laser sintering (SLS) system. Modeling is primarily done with NURBS curve in Rhino software according to the requirements of implantation. Then all the characteristic parameters, including control points, knots and weights, are calculated with Rhino software, and the selective sintering of artificial bone is eventually realized in the SLS system with these characteristic parameters.2. Studies are carried out on the influence of laser power and scanning speed on the microstructure of n-HAP artificial bone. It is found that the density of sintered n-HAP is improved with the increase of laser power (5-10W) and the decrease of scanning speed (300-50mm/min). Besides, HAP grains tend to be spherical-like from initial long needle-like with the weakening of preferred orientation, but still remain nanoscale.3. Influence of preheating temperature on the sintering properties of n-HAP artificial bone is investigated with modern test methods. It is discovered that the preheating process can effectively reduce the effects of temperature gradient inside and between layers, as well as thermal stress. This is good for preventing the cracks on the surface of sintered layer and improving sintering properties. More importantly, the heat conduction between powder particles is gradually enhanced with the increase of preheating temperature (0-600℃), which further inhibits the grain growth.4. It reveals the variation rule and formation mechanism of mechanical properties of n-HAP artificial bone. The mechanism of grain boundary diffusion and volume diffusion play a dominant role in the densification process when the energy density is relative low (1.6-3.4J/mm2). And the mechanical properties of artificial bone increase with the energy density. However, it begins to decrease when the energy density becomes too high (>3.4J/mm2), which attributes to the fast grain growth over nanoscale by grain boundary migration.