Nb modified Ti-5553 alloy: Effects of heating rate on mechanical properties, corrosion behavior, and crystallographic texture

Abstract

Ti–5Al–5Mo–5V–3Cr (Ti-5553) is a metastable β-type Ti alloy with excellent hardenability and high mechanical strength designed for aerospace applications. Previous studies have shown that the replacement of V with Nb, resulting in a Ti–12Nb–5Al–5Mo–3Cr (Ti-12553) alloy, can enhance the mechanical strength and hardenability. This study focuses on exploring the effects of V replacement with Nb in this alloy, aiming to evaluate the effects of the aging heating rate during aging heat treatment on the microstructure and its effect on hardness, tensile and compression strengths, corrosion resistance, and crystallographic texture development. The Ti-5553 and Nb-modified Ti-5553 (Ti-12553) alloys aged at 600 °C for 2 h resulted in a microstructure formed by α precipitates in a β matrix, with larger precipitates at a faster heating rate. This effect was more pronounced for the Ti-5553 alloy. The coarsening microstructure affected the mechanical behavior by decreasing the mechanical strength (hardness, ultimate tensile strength, and yield strength) while improving ductility and intergranular fracture mode in combination with a smaller region containing dimples. A decrease in hardness was observed at a faster heating rate, but it was still superior to that of the solution heat-treated samples. The textures formed in both alloys were similar and lacked any strong components. The replacement of V with Nb and the microstructure produced after aging heat treatment did not affect the samples’ corrosion resistance in a 3.5% NaCl solution. A stable passive protective layer with noble corrosion potential and reduced corrosion current density was observed.

Keywords

• Titanium alloys
• Phase transformation
• Aging heat treatments
• Corrosion resistance