Dynamic Softening and Hardening Behavior and the Micro-Mechanism of a TC31 High Temperature Titanium Alloy Sheet within Hot Deformation

TC31 is a new type of α+β dual phase high temperature titanium alloy, which has a high specific strength and creep resistance at temperatures from 650 °C to 700 °C. It has become one of the competitive candidates for the skin and air inlet components of hypersonic aircraft. However, it is very difficult to obtain the best forming windows for TC31 and to form the corresponding complex thin-walled components. In this paper, high temperature tensile tests were carried out at temperatures ranging from 850 °C to 1000 °C and strain rates ranging from 0.001 s−1 to 0.1 s−1, and the microstructures before and after deformation were characterized by an optical microscope, scanning electron microscope, and electron back-scatter diffraction. The dynamic softening and hardening behaviors and the corresponding micro-mechanisms of a TC31 titanium alloy sheet within hot deformation were systematically studied. The effects of deformation temperature, strain rate, and strain on microstructure evolution were revealed. The results show that the dynamic softening and hardening of the material depended on the deformation temperature and strain rate, and changed dynamically with the strain. Obvious softening occurred during hot tensile deformation at a temperature of 850 °C and a strain rate of 0.001 s−1~0.1 s−1, which was mainly caused by void damage, deformation heat, and dynamic recrystallization. Quasi-steady flowing was observed when it was deformed at a temperature of 950 °C~1000 °C and a strain rate of 0.001 s−1~0.01 s−1 due to the relative balance between the dynamic softening and hardening. Dynamic hardening occurred slightly with a strain rate of 0.001 s−1. Mechanisms of dynamic recrystallization transformed from continuous dynamic recrystallization to discontinuous dynamic recrystallization with the increase in strain when it was deformed at a temperature of 950 °C and a strain rate of 0.01 s−1. The grain size also decreased gradually due to the dynamic recrystallization, which provided an optimal forming condition for manufacturing thin-walled components with the desired microstructure and an excellent performance.

3D printed phantom to mimic dynamic softening of cervix during pre-labour

It is thought that through the development of more realistic training models for midwives and obstetricians it may be possible to reduce the overuse of labour induction. To this end we demonstrate a method for creating pneumatically-controlled phantom cervixes using thermoplastic elastomer, filled with a granular material. The maximum spring constant of the phantom cervix was measured to be 10.5 N/m at -20 kPa deflated air (vacuum) and the minimum spring constant measured was 5.3 N/m at 20 kPa inflated air. The true stress measured on these elastomeric phantom cervixes indicated a maximum stress of 133 kPa and a minimum stress of 94 kPa at 0.15 strain. Discrimination and threshold tests demonstrated that people can distinguish between the hard and soft states of the phantom. Future work will focus on increasing the softness of these devices.

3D printed phantom to mimic dynamic softening of cervix during pre-labour

It is thought that through the development of more realistic training models for midwives and obstetricians it may be possible to reduce the overuse of labour induction. To this end we demonstrate a method for creating pneumatically-controlled phantom cervixes using thermoplastic elastomer, filled with a granular material. The maximum spring constant of the phantom cervix was measured to be 10.5 N/m at -20 kPa deflated air (vacuum) and the minimum spring constant measured was 5.3 N/m at 20 kPa inflated air. The true stress measured on these elastomeric phantom cervixes indicated a maximum stress of 133 kPa and a minimum stress of 94 kPa at 0.15 strain. Discrimination and threshold tests demonstrated that people can distinguish between the hard and soft states of the phantom. Future work will focus on increasing the softness of these devices.

Dynamic Softening Mechanisms and Microstructure Evolution of TB18 Titanium Alloy during Uniaxial Hot Deformation

In this study, isothermal compression tests of TB18 titanium alloy were conducted using a Gleeble 3800 thermomechanical simulator for temperatures ranging from 650 to 880 °C and strain rates ranging from 0.001 to 10 s−1, with a constant height reduction of 60%, to investigate the dynamic softening mechanisms and hot workability of TB18 alloy. The results showed that the flow stress significantly decreased with an increasing deformation temperature and decreasing strain rate, which was affected by the competition between work hardening and dynamic softening. The hyperbolic sine Arrhenius-type constitutive equation was established, and the deformation activation energy was calculated to be 303.91 kJ·mol−1 in the (α + β) phase zone and 212.813 kJ·mol−1 in the β phase zone. The processing map constructed at a true strain of 0.9 exhibited stability and instability regions under the tested deformation conditions. The microstructure characteristics demonstrated that in the stability region, the dominant restoration and flow-softening mechanisms were the dynamic recovery of β phase and dynamic globularization of α grains below transus temperature, as well as the dynamic recovery and continuous dynamic recrystallization of β grains above transus temperature. In the instability region, the dynamic softening mechanism was flow localization in the form of a shear band and a deformation band caused by adiabatic heating.

Research on Hot Deformation Behaviors of 6061 Al Alloy

In this paper, the high temperature flow behaviors of 6061 Al alloy was studied by thermal compression experiments. The effects of temperature, strain rate and strain on the microstructure evolution and flow behavior of the alloy were investigated by experiments. The results show that the flow stress of the alloy increases with the increase of strain rate and it decreases with the increase of deformation temperature. The flow curve reaches the dynamic equilibrium under the interaction of work hardening and dynamic softening mechanism. The uprising deformation temperature promotes thermal excitation dynamic recrystallization of deformed microstructure. With the increase of strain, the microstructure of the alloy is transformed from equiaxed crystal morphology to fibrous structure and strain-induced dynamic recrystallization occurs. As strain rate increases, the action time of dynamic softening mechanism for the studied alloy is reduced, resulting in the fraction of dynamic recrystallized structure is reduced and the flow stress increases.