Development And Experiments Of Micro/Nano-indentation Testing Device For High Temperature

As we know,most of the materials serve in complex environments,and even some materials serve in extreme environments.However,at present,the research on evolution mechanisms of materials' mechanical properties in complex environments is in severe dearth.Especially for the materials which serve in high temperature environment,their mechanical properties' evolution mechanisms are not clear enough,affecting the assessment of materials' mechanical properties at high temperature.Micro/nano-indentation testing technique has currently become one of the most popular techniques for mechanical properties testing on materials,which is due to its advantages,such as simple testing procedure,high testing accuracy,simple preparation and fixation of the sample and so on.In recent years,an increasing number of researchers have begun to use micro/nano-indentation testing device to conduct the mechanical properties testing on all kinds of materials at room temperature.However,for the materials serving in the high temperature environment,such as super alloys,refractory metals,carbon/carbon composites and so on,their mechanical properties measured at normal temperature cannot characterize the real properties under actual serving conditions.Therefore,it is very important to develop the micro/nano-indentation testing device for high temperature and conduct the related experiments at high temperature.This paper summarized and analyzed the recent progresses at home and abroad in the testing techniques of micro/nano-indentation for room temperature and high temperature.Furthermore,in this paper,the characteristics and data analysis methods of micro/nano-indentation testing techniques were introduced,and several key techniques of micro/nano-indentation testing at ambient temperature as well as high temperature were detailed.Based on the above work,this paper designed a micro/nano-indentation testing device for high temperature,which contains precision driving technique,precision testing technique,precision changing position technique,temperature control technique,signal processing technique and so on.To verify the rationality of this device's design,the 3D model of the testing device's main body was established.Moreover,the flexure hinge and the main body of the testing device were analyzed by finite element method.Based on that,the whole machine integration work of micro/nano-indentation testing device for high temperature has been completed.The calibration of force and displacement sensors has been carried out.The performances of the temperature control module and the normal temperature indentation testing module have also been tested.The testing results indicated that the temperature control module can provide a stable and constant temperature environment for the indenter and the sample.Moreover,the water-cooled circulation unit designed in this paper can ensure that the components such as sensors,motors and bearings are in a reasonable working temperature range,which will not be damaged by high temperature.The response rate of the precision driving component is high enough,and the indenter can press into and out the surface of samples according to the given indentation loading mode as well as loading process.Besides,the indentation curve obtained from this device has a good repeatability.Then,after completing the calibration of the device,five groups of indentation tests were carried out on the standard hardness block by the calibrated device.The average values of hardness and elastic modulus measured were very close to those obtained by commercial indentation tester.The testing deviations were 0.91% and 2.86%,respectively,and the five groups of curves measured had a good repeatability.The testing results above verified the feasibility of the design scheme,and proved that the developed device has a good testing stability.The micro/nano-indentation testing device for high temperature developed in this paper had been used to test the mechanical properties of fused silica and TBCs at high temperature.The testing results showed that with the increase of temperature,the elastic modulus of fused silica increased,and the hardness decreased.With the increase of temperature,the reduced modulus and hardness of TBCs decreased.