Effect of High-Pressure Torsion Process on Precipitation Behavior of α Phase in β-Type Ti–15Mo Alloy

Abstract

Precipitation behavior of ¡ phase in Ti15Mo alloy during isothermal aging after straining by high-pressure torsion (HPT) was investigated and compared with that without HPT process. Upon isothermal aging, ultrafine equiaxed ¡ phase particles and acicular ¡ phase plates were obtained in HPT-processed samples, while only the coarse acicular ¡ phase plates were obtained in the samples without HPT process. The precipitation of equiaxed ¡ phase occurred faster than the precipitation of acicular ¡ phase in HPT-processed samples. It seemed that a high density of dislocations resulted in highly strained area and enhanced atomic diffusivity, promoting the formation of equiaxed ¡ phase. The HPTprocessed samples exhibited higher hardness and ultimate tensile strength but lower ductility than those of the specimens without HPT process.

Microstructure evolution in solution treated Ti15Mo alloy processed by high pressure torsion

“…Similar appearance was observed for central part of all samples after 1, 3 and 5 rotations. It is argued that lighter appearing bands are shear bands that are slightly Mo enriched [27,28]. The appearance of peripheral part in the sample after 10 rotations is very different as shown in Fig.…”

“…The samples after 3, 5 and 10 revolutions were observed by scanning electron microscopy using cross-section of the samples with horizontal direction in images parallel to radial direction in a sample after HPT similarly as reported in [27]. Two selected images are shown in Fig.…”

Influence of Cold Caliber Rolling on α Phase Formation in Metastable β Ti Alloys

“…These precipitates were thought to be nucleated on the shear bands introduced during cold caliber rolling. This type of microstructure was found in Ti-15Mo alloys after HPT processing [6]. These microstructural features in the DA sample show that cold caliber rolling is able to apply large deformation strain with relatively small area reduction of around 55 %.…”

“…Mechanical properties of metastable titanium alloys are strongly affected by phase precipitation behavior, such as amount, size, morphology and distribution [4]. Recently, utilization of severe plastic deformation (SPD) such as equal channel angular pressing (ECAP) [5] and high pressure torsion (HPT) [6] is reported to be very effective way to refine the precipitated phase through introduction of high density defect structure. However, both ECAP and HPT are somewhat complicated method and are so far difficult to apply for large components.…”

Investigation of Microhardness and Microstructure in Ultra‐Fine Grained Metastable Beta‐Ti Alloys Prepared by High Pressure Torsion

“…Lighter bands are also seen in disc periphery. These might be deformation bands or evenstabilizer enhanced areas as suggested in [15]. However, the mechanism of element partitioning and segregation remains unknown.…”