Study On Effects Of Fe And Co On Microstructure And Properties Of Ni₅₅Ti₄₅ Alloys

Ni-rich NiTi alloy has a variety of excellent properties,such as high hardness,super elasticity,low density,non-magnetic performance,wear resistance and corrosion resistance,which has become a candidate material for bearings.In order to improve the comprehensive properties of Ni Ti alloy,the alloy(Ni₅₅Ti₄₅)_100-xFe_xand(Ni₅₅Ti₄₅)_100-xCo_x（x=0.5,1,3,5 at.%）（x=0.5,1,3,5 at.%）were prepared by arc melting.By optical microscopy observation,X-ray diffraction analysis,scanning electron microscopic observation,transmission electron microscopic observation,microhardness test,wear properties test and corrosion resistance test,the effects of the content of alloying elements on microstructure,hardness,wear performance,and corrosion resistance of alloy were studied,and its mechanism was analyzed.The microstructure of solution treated(Ni₅₅Ti₄₅)_100-xFe_xalloy is mainly composed of Ni Ti matrix,Ti₃Ni₄phase,X phase and a small amount of Ti₂Ni phase.The structure of X phase is the same as that of Ni Ti matrix,but the composition is slightly different.A narrow matrix channel is formed between X phases,through which the matrix can be strengthened by Orowan mechanism.A small amount of Ti Ni₃phase is formed in(Ni₅₅Ti₄₅)₉₅Fe₅alloy.With the increase of Fe content,the microhardness of(Ni₅₅Ti₄₅)_100-xFe_xalloy increases,and the hardness of(Ni₅₅Ti₄₅)₉₅Fe₅alloy is the highest,which is 717HV.The microstructure of solution treated(Ni₅₅Ti₄₅)_100-XCo_xalloy is mainly composed of Ni Ti matrix phase,Ti₃Ni₄phase,X phase and a small amount of Ti₂Ni phase.A small amount of Ti Ni₃phase is formed in(Ni₅₅Ti₄₅)₉₇Co₃alloy and(Ni₅₅Ti₄₅)₉₅Co₅alloy,and the X phase in(Ni₅₅Ti₄₅)₉₅Co₅alloy disappears.With the increase of Co content,the microhardness of(Ni₅₅Ti₄₅)_100-XCo_xalloy also increases,and the hardness of(Ni₅₅Ti₄₅)₉₅Co₅alloy is the highest,which is 682 HV.At room temperature,with increasing frequency,the CoF curve fluctuation decreases and friction becomes more stable.With the increase of load,the wear weight loss of the alloy increases.(Ni₅₅Ti₄₅)₉₅Fe₅alloy and(Ni₅₅Ti₄₅)₉₅Co₅alloy show more stable friction curve,narrower wear mark width,lower wear quality and better wear resistance in the same series of alloys respectively.All the alloys exhibit typical adhesive wear,abrasive wear and oxidative wear mechanisms.The corrosion resistance test was carried out in 3.5%NaCl solution simulating the seawater environment.The results show that with the increase of Fe or Co content,the open-circuit potential of the alloy increases,the thermodynamic tendency of corrosion decreases,the capacitive arc diameter of the alloy increases,and the resistivity increases.(Ni₅₅Ti₄₅)₉₅Fe₅alloy and(Ni₅₅Ti₄₅)₉₅Co₅alloy respectively show the best corrosion resistance in the same series of alloys.