Effect of grain size on the very high cycle fatigue behavior and notch sensitivity of titanium

The very high-cycle fatigue performances of coarse-grained and ultrafine-grained titanium samples with different geometries at ambient temperature and various stress amplitudes were investigated. Severe plastic deformation improves monotonic strength of titanium at the cost of a loss in ductility. Ultrafine-grained titanium demonstrates a superior fatigue performance compared to that of coarse-grained counterparts in the high-cycle fatigue regime, however, suffers notch sensitivity. Furthermore, in the very high-cycle fatigue regime stress-life curves merge unexpectedly. Microstructural inhomogeneity in the ultrafine-grained titanium is expected to be the reason. Analysis of fracture surfaces reveals that the formation of fatigue slip marks is evident on the fatigued samples of both microstructural states. Ultrafine-grained titanium is more prone to the intergranular fracture.Hessen State Ministry of Higher Education, Research and the Arts - Initiative for the Development of Scientific and Economic Excellence (LOEWE

Effect of purity levels on the high-temperature deformation characteristics of severely deformed titanium

In the present investigation, high-temperature compression tests were conducted at strain rates of 0.001 to 0.1 s−1 and at temperatures of 873 K to 1173 K (600 °C to 900 °C) in order to study the hot deformation characteristics and dynamic softening mechanisms of two different grades of commercial purity titanium after severe plastic deformation. It was observed that the effects of deformation rate and temperature are significant on obtained flow stress curves of both grades. Higher compressive strength exhibited by grade 2 titanium at relatively lower deformation temperatures was attributed to the grain boundary characteristics in relation with its lower processing temperature. However, severely deformed grade 4 titanium demonstrated higher compressive strength at relatively higher deformation temperatures (above 800 °C) due to suppressed grain growth via oxygen segregation limiting grain boundary motion. Constitutive equations were established to model the flow behavior, and the validity of the predictions was demonstrated with decent agreement accompanied by average error levels less than 5 pct for all the deformation conditions.TÜBİTA