Oxidation Effects on Short-Term Creep Response in Air of Commercially Pure Titanium (CP-2 Ti)

Abstract

The creep response in the air of commercially pure titanium was investigated at 550, 600, and 650 °C to assess the effect of oxidation on the mechanical response. Experiments demonstrated that prolonged exposures at high temperatures produced a marked reduction in the minimum creep rate under a given applied stress. Microhardness measurements showed that a hardened zone formed in proximity to the surface due to oxygen penetration into the metal. A simplified composite model was then used to describe the creep response. In this model, the sample consisted of two zones, the hard case that was enriched in oxygen and the soft pure-titanium core, both creeping with similar strain rates. Calculations led to an estimation of the dependence of the minimum creep rate on stress and temperature for the hard high-oxygen zone. The simplified composite model presented here provided a good description of the experimental creep data for pure titanium, tested in its air, and a reliable picture of the effect of oxidation on complex Ti alloys.

Effect of Friction Stir Welding on Short-Term Creep Response of Pure Titanium

“…Creep behavior of the base metal was shown to be strongly influenced by the growth of an oxygenrich layer on the surface of the creep samples, during the high-temperature exposition inside the creep testing furnace. In fact, a direct relationship was found between the thickness and the hardness of the formed outer oxide layer, with the temperature level and the exposure time, or rather the higher the temperature, the higher the dwell time, and the higher the hardness of the surface oxide layer [29]. The present study represents a further step of this articulated research since it aims to investigate the creep response of the same material after FSW.…”

“…The creep curves exhibited a conventional shape with a well-defined primary region, a minimum creep rate range, and a prolonged tertiary stage. The major difference with the creep curves observed by testing the samples with the same geometry machined from the Ti-CP 2 plate [29] is the lower elongation to fracture. In most cases, under high stresses, the CW samples ruptured at strains below 0.3, while the pure titanium samples accumulated higher deformation without visible damage.…”

“…Creep experiments were carried out in the air. To avoid the effect of oxidation, well documented in the previous paper [29], the experimental load was purposedly selected to obtain minimum creep rates above 1 × 10 −8 s −1 . The side view shows the macrostructure: the SZ is in light grey.…”

“…In addition, the availability of recent experimental data on the creep response of this pure metal remains another major issue. This led some of the authors of the present study to investigate the creep response in air of Ti-CP 2 at temperatures ranging from 550 to 650 • C [29]. Creep behavior of the base metal was shown to be strongly influenced by the growth of an oxygenrich layer on the surface of the creep samples, during the high-temperature exposition inside the creep testing furnace.…”

“…The present study represents a further step of this articulated research since it aims to investigate the creep response of the same material after FSW. All the details on the creep response of the unwelded material and the friction stir welded joints can be found in [23,29].…”