Investigation On Preparation Of SiC Particulates Performed By Selective Laser Sintering

Particulates reinforced light alloy matrix composites have a few advantages such as low density, high specific strength and stiffness, resistance property, low thermal expansion and size stabilities. They are potentially applied in aeronautics and astronautics, national defense, automobile industry and electronics fields etc. Among all the fabrication methods, vacuum pressure infiltration becomes into a main approach of the fabrication of MMCs due to excellent seepage, facile control of pressure, homogenous infiltration and soundness. However, the preparation of particulates preform with desired properties has been considered to be one of hard problems. Currently, there are very limited reports concerning ceramic powders fabrication by selective laser sintering (SLS), although it is regarded as a novel, fast and efficient way. To investigate the detailed molding process by SLS and corresponding mechanism of SiC ceramic perform, it will provide important theoretical significance and engineering value for the establishment of theory and experiment foundation about research on particulates reinforced composites.In this work, based on SiC particulates coupling modifications, we initiated the method of double binders composed of organic and inorganic moieties, focused on influence of different binders upon ceramic preform formability, studied laser transient sintering principle, and concentrated on effect of SLS parameters on ceramic powders forming accuracy and mechanical properties through optimization process. In addition, we performed vacuum pressure infiltration of aluminum experiment on ceramic powders after heat treatment by way of SEM and XRD characterization and analysis for confirming its microstructure or morphology. The primary research results are as follows:The SLS molding rigidity of SiC particles has been improved greatly after modification of KH-570 coupling silane agents. In tests of double binders, SLS treatments show that organic binder epoxy resin (EP) or Nylon 6 (PA6) plays a key role in sintering process, whereas inorganic compound NH4H2PO4 contributes to secondary function of binding.In light of study regarding laser sintering mechanism, SEM proved that EP is critical to combine particulates compared with MAP, but there occurred seamed problem within layers and agglomerates because of thermosetting properties of EP. For the choice of PA6 and MAP, as a thermoplastic binder, PA6 melted during laser scan and connected or infiltrated to inner particles, thus brought seamless binding and regular arrangement of particulates, finally made homogenous and smooth surface between SiC particulates and binders.Under the experiment of EP and MAP (6wt% and 8wt%), we got the optimized parameters through SLS orthogonal tests such as: laser power 42.5 W, scan speed 1400 mm/s, scan spacing 0.1 mm, layer thickness 0.2 mm, tensile strength 1.11 MPa, bending strength 0.74 MPa, shrinkage less than 3.6%. While for the choice of PA6 and MAP, the above parameters are decided to be laser power 15 W, scan speed 1200 mm/s, scan spacing 0.1 mm, layer thickness 0.1 mm, preheating temperature 175 oC, tensile strength 2.44 MPa, bending strength 2.22 MPa, shrinkage less than 2.2% respectively.We checked the preform after twice heat treatment, XRD indicated that organic binder decomposed completely under the high temperature, but new phase of phosphate formed by MAP's decomposers and binded with particulates. In detail, SiP2O7 phases binders were formed in the ceramics during EP and MAP test, the sample strength decreased slightly: tensile strength 0.17 MPa, bending strength 0.5 MPa. For PA6 and MAP, two kinds of phosphates such as SiP2O7 and 2SiO2·P2O7 were obtained with tensile strength 1.24 MPa, bending strength 1.05 MPa respectively. After sintering treatment of SiC ceramics, we conducted vacuum-pressure infiltration experiments, aluminum based composites with homogenous particulates dispersion, uniform size derived from precursor and clear shape were obtained upon 0.4-0.5 MPa pressure and infiltration.