Selección de objetivos y contribución al desarrollo de las Competencias

Surface morphology plays a critical role for the bone cells growth [162, 163]. Extensive level of researches has been carried out so far to understand the role of surface morphology for bone regeneration for titanium implants mostly on traditional titanium implants manufactured by casting process[164-167]. Even though some different research groups they have investigated the additively manufactured titanium implants pore geometry’s effect on in-vitro[168], changing the surface morphology by chemical treatment[169, 170], but still it is not so much explored for additively manufactured titanium surface morphology role without doing post- processing treatment and getting rid of partially melted particles for orthopaedic implants as the surface topography can be manipulated easily by changing the build inclination angle. Therefore prior to clinical application, it is so essential to observe the surface morphology of different inclined SLM plates for both upward and downward surface.

Fig.4.4.1 and Fig.4.4.2 represent the surface morphology of Ti6Al4V SLM plates of upper and lower surface from 5 degrees to 90 degrees incliantion angle varying 5 degrees by SEM images for lower and higher magnification respectively. In all occasions for both upward and downward surface we can observe the partially melted particles stuck on the SLM plates.The phenomena of partially melted particles occurs by three mechanisms:(1) thermal diffusion occurs due to the significant temperature difference between loose powder and solidified material, leading to local fusion of powder to the edge of the scan track of the SLM surface[171, 172]; (2) balling phenomenon in SLM process which is responsible for forming particles on the laser melted surface[144]; (3)the stair-stepping effect of the implant of varying inclination angles are partially built on the loose powder; and thus some metal particles below each layer will be totally or partially melted and then bonded on the bottom of the layer[173].

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The phenomena for balling is defined as its ability of breaking up the melt pool into smaller entities when the total surface of a molten pool becomes larger than that of a sphere with the same volume which causes several impediments on interlayer connection[174]. Marangoni convection theory supports the balling phenomena by explaining the thermal gradient which occurs due to balling and create a thermos-capillary flow of fluid within the melt pool from low surface tension region to high surface tension region[175]. Balling is the breakup of the melt pool into small spheres. It occurs when molten material does not wet well to the underlying substrate or material due to high surface tension differences generated as a result of variations in thermal properties within the melt pool [176-178].Balling is a severe impediment on interlayer connection, it decreases part density and increases top surface roughness and side roughness. However, the balling effect more dominantly affects the side roughness of parts due to the direction of balling scattering to either side of the melt pool rather than settling on the top surface.

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Figure 4.4.1: SEM micrograph shows the surface morphology of Ti6Al4V SLM plates of both upper and lower surface 5 to 25 degrees inclination angle with 5 degrees interval for lower (63X) magnitude.

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Figure 4.4.2: SEM micrograph shows the surface morphology of Ti6Al4V SLM plates of both upper and lower surface 30 to 50 degrees inclination angle with 5 degrees interval for lower (63X) magnitude.

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Figure 4.4.3: SEM micrograph shows the surface morphology of Ti6Al4V SLM plates of both upper and lower surface 55 to 75 degrees inclination angle with 5 degrees interval for lower (63X) magnitude.

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Figure 4.4.4: SEM micrograph shows the surface morphology of Ti6Al4V SLM plates of both upper and lower surface 80 to 90 degrees inclination angle with 5 degrees interval for lower (63X) magnitude.

It is observed from Fig.4.4.1 that with the increase of the inclination angle, there is a corresponding increase in the number of partially melted particles on the upward SLM support- free part from 5 to 90 degrees, and there is no regular trend was observed in terms of partially melted particles on downward surface. It is apparently seen from Fig.8 that there are some distinguishable spaces between particles melted particles from 5 degrees to 70 degrees whereas 75 to 90 degrees the partially melted particles are in dense fashion on the upper surface. We can clearly see that in case of 10 degrees inclination, powders are less densely located on the

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SLM plate but in case of 90 degree inclination, powders are quite densely located on the SLM plate. In case of lower surface, it observed that the particially melted particles are located in agglomerate fashion from 5 degrees to 35 degrees where 5 to 15 degrees are particularly highly agglomerated. From 40 to 90 degrees it can be observed that the partially melted particles located densly on SLM plates but there the aglomeration of particles are almost negligible. It is also observed from Fig.4.4.2 that the sharpness of step edge border is dimmed with the increase of the inclination angle for upper surface of SLM plates from 5 to 45 degrees and no step edge border was found from 50 to 90 degrees. From 5 to 20 degrees the step edge border is completely prominent. In case of lower surface of SLM plates no step- edge border is found in any of the inclination angle. We can also observe that the distance between two step edge borders are also shrinking from 10 degrees to 30 degrees for the upper SLM parts shown by red line in SEM images. The distance between two step edge borders is 335 µm, 235 µm, 219.28 µm, 191.21 µm, 136.84 µm for 10,15, 20,25,30 degrees inclination angle respectively.

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Figure 4.4.5: SEM micrograph shows the surface morphology of Ti6Al4V SLM plates of both upper and lower surface 5to 90 degrees inclination angle with 5 degrees interval for higher

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