Research progress on microstructure evolution and hot processing maps of high strength β titanium alloys during hot deformation

High strength β titanium alloys are widely used in large load bearing components in the aerospace field. At present, large parts are generally formed by die forging. Different initial microstructures and deformation process parameters will significantly affect the flow behavior. To precisely control the microstructures, researchers have conducted many studies to analyze the microstructure evolution law and deformation mechanism during hot compression. This review focuses on the microstructure evolution of high strength β titanium alloys during hot deformation, including dynamic recrystallization and dynamic recovery in the single-phase region and the dynamic evolution of the α phase in the two-phase region. Furthermore, the optimal hot processing regions, instability regions,and the relationship between the efficiency of power dissipation and the deformation mechanism in the hot processing map are summarized. Finally, the problems and development direction of using hot processing maps to optimize process parameters are also emphasized.

A Single Central Pattern Generator for the Control of a Locomotor Rolling Wave in Mollusc Aplysia

Locomotion in mollusc Aplysia is implemented by a pedal rolling wave,a type of axial locomotion.Well-studied examples of axial locomotion(pedal waves in Drosophila larvae and body waves in leech,lamprey,and fish)are generated in a segmented nervous system via activation of multiple coupled central pattern generators(CPGs).Pedal waves in molluscs,however,are generated by a single pedal ganglion,and it is unknown whether there are single or multiple CPGs that generate rhythmic activity and phase shifts between different body parts.During locomotion in intact Aplysia,bursting activity in the parapedal commissural nerve(PPCN)was found to occur during tail contraction.A cluster of 20 to 30 P1 root neurons(P1Ns)on the ventral surface of the pedal ganglion,active during the pedal wave,were identified.Computational cluster analysis revealed that there are 2 phases to the motor program:phase I(centered around 168°)and phase II(centered around 357°).PPCN activity occurs during phase II.The majority of P1Ns are motoneurons.Coactive P1Ns tend to be electrically coupled.Two classes of pedal interneurons(PIs)were characterized.Class 1(PI1 and PI2)is active during phase I.Their axons make a loop within the pedal ganglion and contribute to locomotor pattern generation.They are electrically coupled to P1Ns that fire during phase I.Class 2(PI3)is active during phase II and innervates the contralateral pedal ganglion.PI3 may contribute to bilateral coordination.Overall,our findings support the idea that Aplysia pedal waves are generated by a single CPG.

Research progress on hot deformation behavior of high-strength β titanium alloy: flow behavior and constitutive model

High-strength β titanium alloys represented by near β titanium alloy and metastable β titanium alloy are preferred materials for large-scale load-carrying structures.In order to achieve the precise regulation of microstructure in the deformation process, massive efforts have been made to study the flow behavior and microstructure evolution of βtitanium alloy in the hot deformation process. This paper reviews the flow behavior of high-strength titanium alloy,including the effects of initial microstructure, deformation process parameters, work hardening, and dynamic softening on flow stress. Furthermore, the effects of deformation process parameters on the apparent activation energy for deformation and strain rate sensitivity coefficient are analyzed. The discontinuous yield phenomenon is discussed,and the constitutive models of flow stress are summarized.Furthermore, some microstructural evolution models are reviewed. Finally, the development direction and difficulties of the flow behavior and constitutive model are pointed out.