Microstructural Evolution and Mechanical Properties of a Modified Ti-5553 Alloy

The use of titanium and titanium alloys to produce from jet engines to orthopedic implants has increased consistently in the recent years. The need for materials with enhanced mechanical performance for structural applications, especially in aerospace field, has resulted in the design of new beta metastable titanium alloys. This class of alloys is able to retain the beta bcc phase at the room temperature in a metastable state. Usually, beta phase in titanium alloy has low yield strength and low elastic modulus, however, aging heat treatments may lead to the controlled alpha hcp phase precipitation, finely dispersed in the beta matrix, resulting in improvements in the mechanical behavior. The main goal of this study was to explore the possibility of replacing V by Nb in the metastable beta Ti-5553 alloy. Accordingly, in addition to Ti-5553 alloy, two other Ti alloy containing Nb were prepared. The alloys were prepared by arc melting, plastically deformed by hot swaging and submitted to two different aging heat treatments. Characterization was carried out by optical and scanning electron microscopy, measurements of elastic modulus, Vickers hardness and tensile tests. The results suggest that the replacement of V by Nb does not modify the main characteristics of the Ti-5553 alloy, particularly, its high tensile strength and the low kinetics of phase transformations. Application of the aging heat treatments resulted in reasonable ductility and high tensile strength values.