Yunlian Qi

Thermal Stabilities of Ti-600 Alloy Pancake

Thermal stabilities at ambient temperature were studied on Ti-600 alloy before and after being exposed at 600 °C for 100 h. Fractography morphologies were investigated, and fracture mechanism analyzed. The results indicated that the strength of the alloy sample after thermal exposure decreased 1% or so, the elongation decreased about 49%, indicating that the plasticity decreased abruptly during the exposure process. For the as-solutioned plus as-aged samples, the cracks originate from the center of the fracture, dimple typed fracture can be found in the fractographies. After thermal exposure, only cleavage facets can be observed in the fractographies, the fractures propagate along the interfaces of lamellar α phases. The fractography of the tensile specimen prior to and after thermal exposure presented the feature of intergranular fracture, transgranular plus intergranular rupture, respectively. These results are caused by the precipitation and the existence of the brittle oxidizing layers. The cracks formed in the oxidizing layers first and then propagated into the matrix during the tensile tests. Oxygen filtration in the surface layer was one of the important reasons for the decrease of plasticity. The major deformation mechanism for Ti-600 alloy without and with thermal exposure is dislocation slips pass-through α bundles, α/β phase boundary slips during the tensile deformation process at ambient temperature, respectively.

Effect of Upsetting and Cogging Technique on Microstructure and Mechanical Properties of β Titanium Alloy

The effect of upsetting and cogging Technique on Microstructure and mechanical properties of β-CEZ and Ti-38644 titanium alloys is studied in this paper. The results showed that β grain boundaries are not distinct and lath-shaped α phases precipitate in grains, for the β-CEZ and Ti-38644 alloys with single upsetting and cogging under the transus temperature. The grains are relatively coarse and their sizes are non-uniform. While for the β-CEZ and Ti-38644 alloys with multiple upsetting and cogging, the equiaxed microstructure become fine and uniform. β grain boundaries are very clear and small acicular and lath-shape α phase also precipitate in the equiaxed grains, and the microstructure difference is small between along transverse direction and longitudinal one. The multiple upsetting and cogging can significantly improve the reduction of area and the mechanical properties of β-CEZ and Ti-38644 titanium alloys with the refined and uniform grains.

Effect of B Content on the Microstructure and Properties of As-cast TC4/B

In this paper, the TC4 titanium matrix composite were fabricated by melting-casting process, the composite was reinforced with different content of B ranging from 0.2wt% to 1.0wt%. The microstructure and mechanical properties of as-cast TC4/B titanium matrix composite were investigated. The results indicate that the elastic modulus increase 15%-30% for TC4/B composite with 0.2wt% to 1.0wt%B. The microstructures of as-cast TC4/B are consisted of lamellar α, grain boundaries β and the second phase of TiB, and the second phase TiB aggregates at the prior-β grain boundaries with necklace-like arrangement. The microstructures of TC4/B would refine with the increath of B content. From the analysis of fractographies, it can be found that with the increasing of B content, the fracture model transforms from typical intergranular fracture to mixed fracture.

Creep behavior of Ti-600 alloy solutioned at and + region

Creep tests were carried out on one kind of near alpha titanium alloy named after Ti-600 at 550 ℃, 600 ℃ and 650 ℃ with the same stress of 300 MPa. The calculated activation energies for the alloy solutioned atβand α+β region are 490.1kJ/mol and 473.5 kJ/mol, respectively. Transformed β grains become coarsened and twisted, and the short primary α grains grow up, α plus β lamellar in transformed β grains elongate apparently after creep tests.