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2 Archives of Metallurgy and Materials

2 2017

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Mechanical and Microstructural Response of Near Beta Ti Alloys to Hot Tensile Testing

Abbasi S. M., Momeni A., Daraee M., Akhondzadeh A., Mirsaeed S. G.

Archives of Metallurgy and Materials

2017

Vol. 62, iss. 2A

815--823

Hot tensile tests were carried out on Timetal-125 and Timetal-LCB near beta Ti alloys at temperatures in range of 600-1000°C and constant strain rate of 0.1 s-1. At temperatures below 700-800°C, the homogenuous and total strains for Timetal-LCB were greater than those for Timetal-125. In contrast, at temperatures over 800°C, Timetal-125 showed better hot ductility. The yield point phenomena was observed in Timetal-LCB at all temperatures. Unlikely, for Timetal-125, it was observed only at temperatures over 800°C. The weaker yield point phenomena in Timetal-125 could be attributed to the negative effect of Al on the diffusion of V. At all temperatures Timetal-LCB exhibited higher strength than Timetal-125. It was found that there should be a direct relationship between the extent of yield point phenomena and strength and dynamic softening through hot tensile testing. It was observed that at temperatures beyond 800°C (beta phase field in both alloys) dynamic recrystallization can progress more in Timetal-125 than in Timetal-LCB. These results were in good agreement with the better hot ductility of Timetal-125 at high temperatures. At low temperatures, i.e. below 700-800°C, partial dynamic recrystallization occurs in beta and dynamic globularization in alpha phase. These processes progress more in Timetal-LCB than in Timetal-125.

Analytical Descriptions of Dynamic Softening Mechanisms for Ti-13Nb-13Zr Biomedical Alloy in Single Phase and Two Phase Regions

Quan G.-Z., Wang X., Li Y.-L., Zhang L.

Archives of Metallurgy and Materials

2017

Vol. 62, iss. 4

2029--2043

Dynamic softening behaviors of a promising biomedical Ti-13Nb-13Zr alloy under hot deformation conditions across dual phase α + β and single phase β regions were quantitatively characterized by establishing corresponding dynamic recovery (DRV) and dynamic recrystallization (DRX) kinetic models. A series of wide range hot compression tests on a Gleeble-3500 thermo-mechanical physical simulator were implemented under the strain rate range of 0.01-10 s−1 and the temperature range of 923-1173 K. The apparent differences of flow stress curves obtained in dual phase α + β and single phase β regions were analyzed in term of different dependence of flow stress to temperature and strain rate and different microstructural evolutions. Two typical softening mechanisms about DRV and DRX were identified through the variations of a series of stress-strain curves acquired from these compression tests. DRX is the dominant softening mechanism in dual phase α + β range, while DRV is the main softening mechanism in single phase β range. The DRV kinetic model for single phase β region and the DRX kinetic model for dual phase α + β region were established respectively. In addition, the microstructures of the compressed specimens were observed validating the softening mechanisms accordingly.