Development of new laser-assisted titanium alloys for orthopedic applications

Abstract

Among metallic biomaterials Ti and its alloys exhibit the most suitable characteristics for biomedical applications due to their excellent biocompatibility, specific strength and corrosion resistance. This issue is becoming increasingly important as the consumption of biomaterials is increasing, with the increase in average age of human population. Ti and Ti alloys for implants and prostheses are required to have high strength, high fatigue resistance, ductility and an elastic modulus similar to that of cortical bone to avoid bone resorption. Thus, alpha and alpha+beta Ti alloys are preferred to beta alloys. Biocompatibility analysis showed that Nb, Ta, Zr and Mo are the safest alloying elements for biocompatible Ti alloys. Research on the development of Ti alloys with these elements has been done firstly in the USA and recently in Japan, and has lead to some alloys with interesting properties (lower Young's modulus than current Ti alloys). However, some of the alloys developed do not present the adequate levels of strength or ductility and further development is necessary to find solutions with improved balance between Young's modulus, strength, fatigue and ductility. The suitability of these alloys for biomedical applications is enormous and considerable efforts should be devoted to further improve their behavior. This work is part of a project that aims to develop Ti-M (M=Zr,Ta,Nb,Mo) binary and ternary alloys with microstructure and properties optimized for use in implants and prostheses, biocompatible, with a corrosion resistance at least as good as current alloys. The objective is to study the effect of these alloying elements in the structure and properties of the alloys. The proposed work plan intends to concentrate on the Ti-Nb-Zr alloys - a system for which some promising alloy compositions have already been found. The development of new materials using conventional methods is a relatively slow and costly process, as it requires the synthesis and analysis of extremely large numbers of discrete composition samples. A more radical and faster approach to alloy development is necessary. Combinatorial methods allow greatly accelerating materials discovery and optimization processes. These methods require the creation of large libraries of materials with compositions varying in wide ranges, which are scanned for the desired structure and properties using rapid evaluation techniques available. In this project a combinatorial alloy development method based on variable powder feed rate laser cladding previously developed by the team of Professor Rui Vilar will be used to design innovative Ti alloys for implant and prosthetic applications. The project will involve the rapid and exhaustive preparation of a range of alloys with compositions variable along a single clad, the screening of interesting compositions based on characterization of the microstructure, evaluation of mechanical and wear properties by microscale techniques. Alloys with promising properties will be selected for constant composition sample production followed by a detailed characterization of the structure, mechanical and corrosion behavior and biocompatibility. The Laser Materials Processing Group of Instituto Superior Técnico (Lisboa) has considerable background on alloy laser development. This Project constitutes a decisive step in the research of new titanium alloys for medical applications. (AU)