To observe cracks formation and propagation of materials,an in-situ tensile test system integrated with AFM and CCD imaging tools is developed in the present study.A left-right combination precision ball screw which c...To observe cracks formation and propagation of materials,an in-situ tensile test system integrated with AFM and CCD imaging tools is developed in the present study.A left-right combination precision ball screw which can realize the equal motion of the sample’s two ends resulting in a constant position during imaging is employed.A linear encoder and a bridge circuit type strain gauge force sensor are used to measure the displacement and the force,respectively,which are utilized to calculate the strain and stress during the imaging.Based on this sytem,the mechanical properties of the sample and the deformation behavior of the materials can be obtained simultaneously.The magnetic tape is employed as the sample to be tensiled and observed by the developed system.AFM and CCD observation results verify that the in-situ tensile test system is feasible to observe the crack formation and propagation from micron to nano scale.This technique can also be used in other materials research fields such as failure of nano composites,local deformation of the sample surface under the tensile force and so on.展开更多
Severe plastic deformation is known to induce grain refinement and gradient structure on metals’surfaces and improve their mechanical properties.However,the fundamental mechanisms behind the grain refinement and micr...Severe plastic deformation is known to induce grain refinement and gradient structure on metals’surfaces and improve their mechanical properties.However,the fundamental mechanisms behind the grain refinement and micromechanical properties of materials subjected to severe plastic deformation are not still well studied.Here,ultrasonic surface rolling process(USRP)was used to create a gradient microstructure,consisting of amorphous,equiaxed nano-grained,nano-laminated,ultrafine laminated and ultrafine grained structure on the surface of TB8βtitanium alloy.High energy and strain drove element co-segregation on sample surface leading to an amorphous structure during USRP processing.In situ transmission electron microscope compression tests were performed in the submicron sized pillar extracted from gradient structure and coarse grain,in order to reveal the micromechanics behavior of different grain morphologies.The ultrafine grained layer exhibited the lowest yield stress in comparison with single crystal and amorphous-nanocrystalline layers;the ultrafine grained layer and single crystal had an excellent strain hardening rate.The discrepancy among the grain sizes and activated dislocation sources led to the above mentioned different properties.Dislocation activities were observed in both compression test and microstructure evolution of USRP-treated TB8 alloy.An evolution of dislocation tangles and dislocation walls into low angle grain boundaries and subsequent high angle grain boundaries caused the grain refinement,where twinning could not be found and no phase transformation occurred.展开更多
基金Funded by the Natural Scientific Research Innovation Foundation in Harbin Institute of Technologythe China Postal Doctoral Foundation(No.20070420161)the Heilongjiang Province Postal Doctoral Foundation(LBH-Z07123)
文摘To observe cracks formation and propagation of materials,an in-situ tensile test system integrated with AFM and CCD imaging tools is developed in the present study.A left-right combination precision ball screw which can realize the equal motion of the sample’s two ends resulting in a constant position during imaging is employed.A linear encoder and a bridge circuit type strain gauge force sensor are used to measure the displacement and the force,respectively,which are utilized to calculate the strain and stress during the imaging.Based on this sytem,the mechanical properties of the sample and the deformation behavior of the materials can be obtained simultaneously.The magnetic tape is employed as the sample to be tensiled and observed by the developed system.AFM and CCD observation results verify that the in-situ tensile test system is feasible to observe the crack formation and propagation from micron to nano scale.This technique can also be used in other materials research fields such as failure of nano composites,local deformation of the sample surface under the tensile force and so on.
基金financially supported by the National Natural Science Foundation of China(No.51771155)the National Science and Technology Major Project(No.J2019-I-0016)。
文摘Severe plastic deformation is known to induce grain refinement and gradient structure on metals’surfaces and improve their mechanical properties.However,the fundamental mechanisms behind the grain refinement and micromechanical properties of materials subjected to severe plastic deformation are not still well studied.Here,ultrasonic surface rolling process(USRP)was used to create a gradient microstructure,consisting of amorphous,equiaxed nano-grained,nano-laminated,ultrafine laminated and ultrafine grained structure on the surface of TB8βtitanium alloy.High energy and strain drove element co-segregation on sample surface leading to an amorphous structure during USRP processing.In situ transmission electron microscope compression tests were performed in the submicron sized pillar extracted from gradient structure and coarse grain,in order to reveal the micromechanics behavior of different grain morphologies.The ultrafine grained layer exhibited the lowest yield stress in comparison with single crystal and amorphous-nanocrystalline layers;the ultrafine grained layer and single crystal had an excellent strain hardening rate.The discrepancy among the grain sizes and activated dislocation sources led to the above mentioned different properties.Dislocation activities were observed in both compression test and microstructure evolution of USRP-treated TB8 alloy.An evolution of dislocation tangles and dislocation walls into low angle grain boundaries and subsequent high angle grain boundaries caused the grain refinement,where twinning could not be found and no phase transformation occurred.
