Development Of An In-situ Mechanical Testing Device In SEM

The mechanical properties of materials are determined by their microstructures.Revealing the influence mechanism of composition,structure and crystal orientation on the macro-mechanical properties by studying the evolution of various microstructures of superalloys in working condition is helpful for understanding how different factors effect on the microstructures.Thereby researchers can design high performance superalloys on the premise of understanding how and why,which has great significance for the development of national aviation industry.Nowadays,scanning electronic microscope(SEM)becomes an important and indispensable tool in scientific research field,by virtue of high resolution,good depth of field and simple operating procedure that no optical microscope can match.At present,in-situ high-temperature mechanical test device developed for SEM are mostly products of foreign companies,while seldom are developed independently interiorly.Moreover,the commercial test devices usually can't perfectly simulate the severe working condition of key components in aeroengines,trading off between temperature,accuracy and multi-functioning.The purpose of this paper is to develop a multi-functional high-temperature in-situ mechanical test device for scanning electron microscopes,which can simulate creep and fatigue conditions of key components in aero-engines,providing advanced technology and methods for studies of plastic deformation mechanism under micro-scale and the development of new materials.The specific research contents of this paper are as follows:1.This paper introduces the development of in-situ high temperature mechanical test devices for SEM,which are commercial products or laboratory-made at home and aboard.The advantages and disadvantages of these devices are compared.The design scheme of fixture heating with double screw drive is selected.The transmission,in-situ heating and in-situ measuring technologies adopted are analyzed and demonstrated.2.A design scheme which uses double reverse ball screw to apply load to sample is proposed,using motor and reducer as driving source,gear drive to pass power,and micro resistance strain tension/pressure load cell and optical grating displacement sensor as measuring device.It uses heating fixture as sample heater,takes circulating cooling to key components in the meantime.The heating fixtures can be installed in the middle of the double screw driving structure with heat insulation.In addition,they have a preset 25° tilting angle,cooperating with 45° tilting pedestal to facilitate EBSD experiment.3.The ANSYS finite element simulation(FEA)analysis of how the surface roughness and heat insulating material affect the temperature distribution of test device and pole shoe and EBSD probe was done.The result shows that the temperature of ambitus components in steady state such as sensors and ball screws can be greatly lowered by the reducing surface emissivity,lowering surface roughness by polishing.Therefore,it can also reduce the required heating power while keeping sample temperature unchanged,which is conducive to heat concentratation and further miniaturization of the testing device.Installing the sensor through zirconia ceramic insulation device to the test device can effectively lower the temperature at the root of load cell from 178? to 73.6?;4.Heat shields are equipped in order to reduce the temperature of pole shoe and EBSD probe,protecting the internal structure of SEM from effect of high temperature.The effect of thickness and installation position of heat shields to the temperatures of pole shoe and probes was simulated and analyzed by ANSYS.The result shows that 1.5 mm thick with 2 mm working distance is the best solution,while the temperature at bottom of the pole shoe and fluorescent screen of EBSD probe respectively are 51.62? and 83.05?,lower than no heat shield situation by 34.72? and 71.3?.