Microstructure of Hardened Steel at High Temperature and High Strain Rate

In high-speed machining,hardened steel materials are subjected to high temperatures and high strain rates.Under these conditions,the composition and microstructure of the material may change,and phenomena,such as thermal softening,emerge.These effects are difficult to detect by only observing the chip morphology.Here,using a microscopic detection method,the dynamic mechanical behavior and microstructure of SDK11 hardened steel(62HRC)is investigated at high temperature and high strain-rate,and the relationship between strain hardening,thermal softening,and strain-rate strengthening is determined.The metallographic phases of specimens treated using a split-Hopkinson pressure bar,and″chips″generated during high-speed machining at high temperature and high strain rate state are compared.The results indicate that the phase composition at low temperature and low strain rate differs from that at high temperature and high strain rate.It is further concluded that shear slip occurs at high temperature and high strain rate,and the shear behavior is more pronounced at higher strain rates.

Automated Silicon-Substrate Ultra-Microtome for Automating the Collection of Brain Sections in Array Tomography

Understanding the structure and working principle of brain neural networks requires three-dimensional reconstruction of brain tissue samples using array tomography method.In order to improve the reconstruction performance,the sequence of brain sections should be collected with silicon wafers for subsequent electron microscopic imaging.However,the current collection of brain sections based on silicon substrate involve mainly manual collection,which requires the involvement of automation techniques to increase collection efficiency.This paper presents the design of an automatic collection device for brain sections.First,a novel mechanism based on circular silicon substrates is proposed for collection of brain sections;second,an automatic collection system based on microscopic object detection and feedback control strategy is proposed.Experimental results verify the function of the proposed collection device.Three objects(brain section,left baffle,right baffle)can be detected from microscopic images by the proposed detection method.Collection efficiency can be further improved with position feedback of brain sections well.It has been experimentally verified that the proposed device can well fulfill the task of automatic collection of brain sections.With the help of the proposed automatic collection device,human operators can be partially liberated from the tedious manual collection process and collection efficiency can be improved.

Structural and Piezoelectric Properties of Sr_(0.6)Ba_(0.4)Nb_2O_6 Micro-rods Synthesized by Molten-Salt Method

Sr0.6 Ba0.4 Nb2 O6 micro-rods are prepared by the molten-salt method with K2 SO4,KCl-K2 SO4,and KCl as fluxes.It reveals that the Sr0.6 Ba0.4 Nb2 O6 synthesized with KCl as a flux exhibits a single phase with tetragonal tungsten bronze structure.The measurement of X-ray diffraction indicates that the Sr0.6 Ba0.4 Nb2 O6 micro-rods synthesized at 1 300℃are anisotropic.The morphology of the powers is examined by transmission electron microscope.It reveals that the length-diameter ratio of Sr0.6 Ba0.4 Nb2 O6 micro-rods increases with increasing annealing temperature from 900℃to 1 300℃.At 1 300℃,the rod possesses a large length-diameter ratio of 8∶1.Moreover,the analysis of the piezoelectric properties of single micro-rods using apiezo-response force microscope indicates that the domains of the material are arranged along its radial direction.