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High-efficiency and low-cost hot forming technologies for titanium alloys have been developed for producing complex-shaped, thin-walled tubular components under non-superplastic forming conditions. Under these forming conditions, there exist complex and highly integrated material evolution processes including microscopic heterogeneous deformation, microstructure evolution and damage behaviour. This paper presents an integrated crystal plasticity finite element model of near-α titanium alloys during non-superplastic hot deformation conditions considering grain boundary sliding (GBS), dynamic recrystallisation (DRX), as well as void evolution. The polycrystalline model of a near-α TA15 titanium alloy was established, containing α phase, β phase and grain boundary (GB) regions, in which the GB region was a visualised representation of GBS. The quantitative strength ratio between the GB regions and α phase was calculated according to the Zener–Holloman parameter Z and grain size, which determined the microscopic deformation behaviour. There were found to be two high microscopic strain regions in the α phase: intragranular deformation bands through the most favourable slipping and near the GBs through multiple slipping, which promoted continuous and discontinuous DRX, respectively. With the decrease in parameter Z or grain size, the activated dislocations accommodating GBS were found to no longer pile up inside the grain, but instead travel across the grain interior. Finally, methods to improve the macroscopic plastic formability were proposed for the difficult-to-form titanium alloys experiencing non-superplastic hot deformation. [ABSTRACT FROM AUTHOR]

This study investigated the features of grain boundary regions in a Ni-based superalloy which underwent creep deformation. Large grain boundary zones were denuded in fine γʹ precipitates but contained coarsened microscale γʹ rods. The coarsening direction of these rods was along the <110> of the γ matrix and γʹ precipitates. The orientation of the grain boundary zone was the same as that of the adjacent grain behind the migrating boundary. This result indicated that the formation of these zones was accompanied by the migration of the grain boundary. Then, numerous slip features were observed through detailed local disorientation analysis. It is proposed that the driving force for the grain boundary migration was the local stress induced by the dislocation creep. The dissolution–reprecipitation of the precipitates at the boundary migration front resulted in the directional coarsening of the γʹ rods. [ABSTRACT FROM AUTHOR]

Abstract: High temperature corrosion and microstructure deterioration phenomenon of KHR35H radiant tubes had been investigated after a service life of approximately 2years in annealing process. Analyses revealed that deterioration in mechanical properties of the radiant tube was caused primarily by significant growth of precipitates during high temperature service. Internal oxidation and simultaneously in situ carbides dissolution were responsible for the formation of large number of voids and microcracks at the inner wall of the tubes, which brought the reduction of effective thickness of the tube wall and may act as crack sources under either thermal shock or creep deformation. [Copyright &y& Elsevier]

In this article, the hot deformation mechanism of a laser-welded near α TA15 Ti-alloy joint was studied by hot tensile tests conducted at temperatures ranging from 800 °C to 900 °C with strain rates ranging from 1.0 × 10 − 1 s − 1 to 1.0 × 10 − 3 s − 1 . The results show that the main hot deformation mechanism of the laser-welded TA15 Ti-alloy joint is continuous globularization, but dynamic recrystallization (DRX) plays an important role during the globularization process. The morphology of α phase exerts considerable influence on the DRX mechanism. When the lamella microstructure is dominant in the weld seam, continuous dynamic recrystallization (CDRX) is the active mechanism; whereas with the increasing fraction of equiaxed grains in the weld seam, discontinuous dynamic recrystallization (DDRX) seems to be the dominant mechanism during the tensile deformation. The globularization process can be divided into three stages based on the characteristics of the microstructure. Under such a deformation mechanism, the laser-welded TA15 Ti-alloy joint tends to have a good formability at high temperature and small strain rate. A maximum elongation of 292% was achieved at 900 °C, 0.001 s − 1 , which exhibits superplastic characteristics. [ABSTRACT FROM AUTHOR]