Research On The Microstructures And Mechanical Properties Of Fe-Ni-Al-Nb-B Based Polycrystalline Shape Memory Alloys

Ferro-based shape memory alloy is a new kind of functional and intelligent material.In this paper,the effects of Co additions on microstructure and properties in the Fe_41.5-xNi₂₈Co_xAl_11.5Nb₂B_0.05?x=0,6,12,18?alloys are investigated by metallurgical,X-ray diffraction,EDS,SEM,high-temperature dilatometer spectrometer and pressure test machine.At the same time,the effects of aging time and aging temperature on microstructure and mechanical properties of the alloys were investigated.The results show that:?1?The results are as follows after solid solution treatment and aging treatment to Fe_41.5-xNi₂₈Co_xAl_11.5Nb₂B_0.05?x=0,6,12,18?alloys:There are?phase and?phase in solid-soluble alloy,which has twin crystals.The grain size is smallest and hardness is biggest when the Co content is 12 at.%.The addition of B elements in the alloy can inhibit the generation of?phase.After aging treatment,?'phase precipitated in the alloy.The diffuse distribution of?'phase is beneficial to the strengthening of alloys.With the increase of Co additions in the alloys,the compressive strength,the recoverable strain and the hardness of the aging state alloys increases first and then decreases.When the Co content is 12.%,the alloy's compressive strength,recoverable strain and hardness reach its maximum value,which respectively 1594.4 MPa,488.68HV and 16.13%.?2?At the aging temperature of 600?,the alloys Fe_46.45Ni₂₈Co₁₂Al_11.5Nb₂ B_0.05were aged with different time.There are?phase,precipitation?phase and precipitation?'phase in the alloys.?'phase is distributed in grains and?phase is mainly distributed in grain boundary.The aging time influences the form and quantity of the two precipitations.With the increase of aging time,the quantity of the two precipitations increases.An appropriate amount of?'phase distributed in the alloy can enhance the strength of the alloy,and the overdose of?phase is not conducive to the strengthening of the alloy.With the increase of aging time,the compressive strength,recoverable strain and Vickers hardness of the alloy increase at first and then decrease.When the aging time is 60 h,the compressive strength,the recoverable strain and the hardness of the alloy all reach its maximum value.And at this moment,the pseudo-elasticity of alloy is the best.?3?The Fe_46.45Ni₂₈Co₁₂Al_11.5Nb₂ B_0.05.05 shape memory alloys were aged for 60 h at different temperature.There are?phase and?phase in the alloy when aging temperature is 520?.As the aging temperature increase,the?'phase is gradually precipitated in the alloys.With the increase of aging temperature,the quantity of the?'phase and?phase increases,the compressive strength,recoverable strain and Vickers hardness of the alloy increase at first and then decrease.When the aging temperature is600?,the recoverable strain and the hardness of the alloy reach its maximum value.And at this moment,the pseudo-elasticity of alloy is the best.