LASER MICROWELDING OF TITANIUMMICROSPHERES FOR REPAIRING ORTHOPAEDICSURGICAL IMPLANTS

摘要

The present work tries to develop a technique to weld microspheres (powder) on orthopaedicrnimplants, only in some particular areas, using advanced techniques of laser processing. Thisrnway it will be avoided that the pieces undergo a high temperature cycle, reducing theirrnresistance, as the mechanical properties of the base material decrease.rnIn an attempt to improve the osteointegration of the prosthesis, these utilize porous coatings,rnbased on the sintering without pressure of titanium microspheres that produces a porousrnnetwork of a diameter of 80 to 250 microns. Sometimes, these coatings experience arnloosening of microspheres in some areas, due to the complexity of the areas or due to therndifficulty of the access to these areas with the tools applying the microspheres, so the lackingrnmicrospheres are replaced and microwelded by the means of laser. A Nd:YAG laser is used;rn1000 W of maximum power that allows pulsing mode, using as main variables of the processrnthe laser power between 130 and 300 W and the duration of the pulse between 400 and 4000rnms.rnA macroscopic and microscopic evaluation of the effect of the laser is done, in the surface ofrnthe microspheres as well as inside them. Due to the energy involved in the microweldingrnprocess allotropic changes in the titanium microstructure are produced; the fast cooling raterncan lead to a martensitic transformation, and the surface of the microspheres can becomernbrittle, deeply affecting the strength of the porous coating. To minimize these effects in thernmicrostructure the initial conditions of melting for each power has been determined,rncontrolling the exposition time or laser pulse.