Selective Laser Melting Fabrication Of Ti-Based Nanocomposites: Process, Microstructure And Properties

As a novel Rapid Prototyping （RP） technique, Selective Laser Melting （SLM） enables the quickfabrication of three-dimensional components with any complex shapes through selectively fusing andconsolidation of thin layers of loose powder materials in a layer-by-layer fashion by a high-energylaser beam, without post-processing requirements. In the present paper, the Ti, Ti-TiC, Ti-SiC powdersystem as raw materials was selected to successfully prepare the pure Ti, TiC/Ti, TiC/Ti₅Si₃bulk formby SLM process. The influences of the laser processing conditions on the phase, composition, surfacemorphology, and microstructure evolution were investigated. The analysis of densification levelmicro-hardness, wear and electrochemical properties of the SLM-processed parts in different laserprocessing parameters was completed. Furthermore, the mechanisms of wear and corrosion onSLM-processed materials were elucidated. The main conclusions were obtained in the paper asfollows:The SLM process using the pure titanium powder was performed. Too high or too low energyinput of laser heat-resource could lead to the occurrence of balling effect metallurgical defects andmicro-cracks. Consequently, the densification rate of the fabricated material decreased. With theincensement of the applied scanning speed, υ （≥200mm/s）, a martenstic transformation occurred inthe SLM-processed samples during the material solidification procedure. Meanwhile, themicrostructure of the formed martenstic phase, α, was refined. The refinement degree of α phase ispositively related to the growth of laser scanning speed. According to the optimization of laserprocessing parameters, the higher density and refinement degree of the α phase obtained in theprepared microstructure effectively improved the mechanical properties of the pure Ti specimens.TiC/Ti composites were prepared by SLM process with the addition of TiC reinforcement in Timatrix. The characteristics of the TiC reinforcement in the SLM-processed parts were distinctlydifferent from the raw particle morphology of the pre-processed TiC. With the increasing of theapplied υ, TiC reinforcement particles were gradually refined. The formation of nano-scale TiCreinforcement effectively improved both the micro-hardness and wear resistance of the substratematerial. However, with the excess of the applied value of υ （≥400mm/s）, the corrosion resistance ofthe SLM-processed parts decreased resulting from the reduction of forming densification. Under theoptimization of processing conditions, the TiC contents played an important role in the microstructureand performance of the laser forming material. With the TiC contents increasing, the grain of the TiCreinforcement coarsened. Consequently, the densification, wear performance and corrosion resistanceof the forming materials decreased.The SLM of SiC-Ti blended powder was completed aiming to prepare the in-situ TiC/Ti₅Si₃composite samples. Too low or too high input of laser energy resulted in the micro-crack and ball effect metallurgical defects, thus, the densification rate of the forming material decreased. The in-situTiC reinforcement exhibited a typical dendritic morphology. As the reasonably decreasing of theapplied υ, the dendrite microstructure was then gradually refined. Under a too low value of υ （100mm/s）, the TiC dendrite grew sufficiently and finally developed into the significantly coarseneddendrites due to the long duration of the laser molten pool. As a result, the densification, wearperformance and corrosion resistance of the forming material decreased.