An assessment of microstructure and properties of laser clad coatings of ultrafine eutectic beta Ti-Fe-Nb-Sn composite for implants

Abstract

[EN] High mechanical strength (1800¿2500 MPa), elastic modulus (50¿110 GPa) close to that of human bone and good corrosion resistance are some characteristics of ultrafine eutectic Ti-based nanocomposite alloys. This is explained due to a combination of soft ß-Ti (bcc) matrix and hard/refined TiFe and/or Ti3Sn intermetallic particles. The present study focuses on the production and characterization of Ti-Fe-Nb-Sn eutectic alloys using biocompatible ß-stabilizer elements, such as Nb, Fe and Sn. Different fabrication techniques based on rapid solidification may be highlighted considering the application of these alloys as implant materials. In the present investigation, the processing routes comprise single tracks and coatings (overlapped tracks) by laser melting of pre-alloyed powders of the Ti66Fe20Nb8Sn6 alloy deposited into a Ti substrate. To select this composition (i.e., the Ti66Fe20Nb8Sn6 alloy), three Ti-Fe-Nb based chemistries (Ti63Fe23Nb8Sn6, Ti60Fe23Nb8Sn9 and Ti66Fe20Nb8Sn6) were originally generated under bulk conditions by using a suction casting apparatus. These alloys were further evaluated. All samples were analyzed by metallography, X-ray diffraction (XRD), scanning electron microscopy (SEM-EBSD and SEM-EDS), microhardness, nanohardness and elastic modulus. The results showed that the proportions of the formed TiFe and Ti3Sn intermetallic particles dispersed within the soft ß-Ti matrix play a fundamental role on the final properties. Lower elastic modulus (E ~72 GPa) is associated with the Ti66Fe20Nb8Sn6 bulk alloy. The laser clad coatings showed a broad range of nanohardness (4.8¿8.0 GPa) and elastic modulus (98¿150 GPa) depending on the related laser power and scanning speeds.