Chen Yongnan

Microscopic Characterization of Semi-Solid Ti14 Alloy

The microstructural evolution and the element distribution of Ti14 (a+Ti2Cu) alloy during semi-solid compression were investigated. Moreover, the Ti2Cu precipitate behaviors were discussed in detail. The results show that the microstructure, the number and distribution of Ti2Cu precipitates have significant dependence on the process parameters. More Ti2Cu will precipitate on grain boundaries at a higher deformation temperature, and/or a lower strain rate as well as deformation ratio, and finally a network structure is formed after deformation at 1100 °C. The precipitation on grain boundaries is found to be mainly controlled by peritectic reactions. The elevated temperatures resulted in more liquid along the prior grain boundaries, and a Cu-rich region is formed, finally. the “coarse” grain boundaries appear during re-solidification.

Effect of Temperature on Segregation and Deformation Mechanism of α+Ti2Cu Alloy during Semi-Solid Forging

Abstract The segregation behavior and the deformation mechanism of Ti14, a new typical burn resistant α+Ti2Cu alloy were investigated, during semi-solid forging at different temperatures. The results reveal that semi-solid temperature will affect the content and the distribution of liquid phase evidently. Upon increasing of temperature, the liquid phase distribution transforms from discontinuity to continuity at grain boundaries, and finally a type of net-structure is formed. Moreover, the macro-segregation of liquid and solid phases occurs during the semi-solid forging, which leads to a change of the main deformation mechanism from center to edge of the sample. The relationship of macro-segregation of liquid/solid phases and the main deformation mechanism was also discussed by a phenomenological model.

Influence of Processing Parameters on the Deformation Behavior of Ti14 Alloy Containing a Small Volume of Liquid

Abstract The effects of the processing parameters on the deformation behavior of Ti14 alloy containing a small volume of liquid have been investigated through compressive tests. Experiments were conducted at deformation temperatures from 1000 to 1150 °C, strain rates from 5×10−3 to 5 s−1 and deformation degrees from 40% to 70%. The results show that deformation temperature and strain rate have significant effects on the peak flow stress. The flow stress decreases with increasing of deformation temperature and/or decreasing of strain rate. The response time required by deformation is affected by the strain rate and liquid fraction is controlled by the temperature. As the temperature increases, deformation mechanism transforms from sliding between solid particles (SS) to the flow of liquid incorporating solid particles (FLS), which improves the semi-solid deformation behavior. In addition, the flow stress decreases with increasing of deformation degrees during the compression which is associated with lubricating effect of liquid during semi-solid deformation.

Effect of Cu Content on the Semi-Solid Formability and Mechanical Properties of Ti-Cu Alloys

Abstract The formability of Ti-Cu alloys and their mechanical properties after semi-solid forging were investigated. The formability was evaluated by upsetting and die forging tests. Tensile test was also performed to study the mechanical properties of Ti-Cu alloys after semi-solid forging. The results show that the semi-solid forging requires lower upsetting forces in the temperature range from 1000 °C to 1150 °C compared with conventional solid forging. Die forging tests show that the semi-solid forged Ti-Cu alloys have an excellent workability with a forging ratio of 75% in the temperature range from 1000 °C to 1050 °C. The Ti 2 Cu phase increases with the increase of Cu content, and more liquid precipitates during semi-solid deformation at higher temperatures and higher Cu content, which relaxes the stress concentration caused by solid deformation and improves the formability. Tensile test reveals that semi-solid forged Ti-Cu alloys exhibit higher strength and lower ductility than conventional forged alloys. The Ti-Cu alloys have lower ductility and higher strength with the increasing of Cu content. The difference in tensile properties is attributed to the change of Ti 2 Cu precipitates at different Cu contents and semi-solid forging temperatures.