| NiTi alloy not only has the advantages of high specific strength,low elastic modulus,good wear resistance and corrosion resistance,high fatigue resistance,but also has excellent shape memory effect and superelasticity performance,in orthopedic,skull repair,orthodontics and cardiovascular stent and other aspects have been widely used.However,the surface of the alloy is not bioactive,it is difficult to form a long-term stable bone tissue with bone.The introduction of porous structure in NiTi alloy to form porous alloy not only significantly reduces the elastic modulus of the alloy,but also can form a good match with the biological hard tissue to improve the biological activity.However,when the porosity is higher than a certain level,the strength of porous alloy decreased significantly,can not meet the clinical requirements.Therefore,a novel NiTi surface porous gradient alloy is designed and prepared on the basis of SPS technology,which is based on the porous NiTi alloy with uniform pore size and no other impurity phase.The inner layer is NiTi alloy and the outer layer is porous NiTi alloy layer.The effects of SPS sintering temperature on microstructure,interfacial bonding,pore characteristics,mechanical properties and biocompatibility of NiTi surface porous gradient alloy were studied,the following conclusions were drawn:(1)The porous nickel-titanium alloy was prepared by spark plasma sintering.The sintering temperature was better in the range of 800??1050?,and the porosity decreased from 51.6%to 43.5%with the sintering temperature decreasing.NiTi surface porous gradient alloy was prepared by spark plasma sintering.At 650?,the sintered temperature was too low and the alloy phase was inhomogeneous.The diffraction peaks of Ti and Ni were dominated.With the increase of sintering temperature,Ti2Ni,Ni3Ti and the NiTi peak are weakened.When the sintering temperature reaches 750?,the diffraction peak of the elemental phase disappears completely,mainly composed of NiTi phase.At 650?,the interface between the matrix and the porous layer is poor.With the increase of temperature,the interface between the inner and outer surfaces gradually forms a stable metallurgical combination,and the grain refinement and sintering effect are good.At the same time,the increase of temperature makes the inner surface of the inner wall of the hole gradually become smooth,and the porosity of the porous layer on the surface decreases slowly.But the sintering temperature increased to 800?,the interface area is not uniform,can not meet the design requirements of gradient alloy.(2)The compressive elastic modulus of the porous NiTi alloy prepared on the NiTi surface is not obvious with the increase of the sintering temperature,and the elastic modulus is very close to the human bone.The compressive strength increases with the sintering temperature increasing.After immersion in the simulated human body for two weeks,there is no difference between the dense nickel-titanium alloy,the porous nickel-titanium alloy and the porous structure of the gradient alloy deposition of certain phosphate particles.Graded alloy nickel ion dissolution rate between the dense nickel-titanium alloy and porous alloy,and are lower than the human toxic dose.And this paper measured the maximum release of nickel ions were lower than the human toxic dose.Compared with dense porous nickel titanium alloy,nickel titanium alloy 750? sintering temperature for the preparation of porous gradient of the surface of the NiTi alloy not only has the good interface bonding and surface pore characteristics(porosity 46.1%,the average pore diameter 296 microns),higher compressive strength(1350 Mpa)and the lower modulus of elasticity(10.1 GPa),excellent properties of hyperelastic(cyclic loading unloading 27 times),but also has certain biological compatibility. |
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