Preparation And Mechanical Properties Of Biomedical Degradable Zinc-based Foam

Open-cell structure foamed metal is a key component in tissue engineering for bone implant,which is conducive to tissue inward growth,allows the transportation of body fluid and also shows the potential to serve as a platform for drug delivery,it is very promising as bone tissue transplantation materials.Metal zinc and its alloys have become one of the most potential biodegradable materials due to their degradation rate between iron and magnesium,and their porous structure is more promising for bone tissue transplant materials.However,there is few studies on the preparation process and properties of porous Zn and Zn-based alloys.Therefore,this paper explores the preparation process parameters of porous Zn-based foamed alloy,the macroscopic structure,microstructure,mechanical properties and corrosion resistance of Zn and Zn-based foamed alloys.It is of great significance for the development,research and application of porous Zn and Zn-based foamed alloy in biomedical materials.In this experiment,the alloys of Zn-5Al,Zn-1.5Mg and Zn-3Al-1Mg were first cast,and then three kinds of zinc alloys were used to prepare three kinds of zinc alloy foams with two pore sizes with self-designed vacuum infiltration casting device,and the technological parameters for preparing zinc alloy foams were determined.With three kinds of Zn-based foamed alloys as the research object,the microstructure and organization of Zn-based foamed alloys were characterized by Inductively Coupled Plasma Direct Reading Spectrometer(ICP),Metallographic Microscope(MM),X-ray diffraction(XRD),scanning electron microscope(SEM)and Energy dispersive Spectrometer(EDS)technique.The mechanical properties of three kinds of foamed metals were studied by compression test of foamed alloys.Corrosion resistance and corrosion mechanism of foam zinc alloy were studied by immersion corrosion experiment.This paper mainly obtains the following research results.The optimal process parameters for the preparation of open-cell foamed Zn-based alloy are as follows:Spherical calcium chloride particles were selected as space holder.the sintering temperature of the space holder is 680-710?,the sintering duration is 3h-5h,and the compression weight range is between 0.3kg and 0.8kg.The temperature rose to 550-620? in 40min.Vacuum degree is-0.090--0.098Mpa;Argon was pressurized to 0.45-0.55Mpa,and the pressurization time was 5min.With the furnace cooling to 300-350?,took out the crucible and air-cooled the foamed metal complex.The pore sizes of the prepared foamed alloy are concentrated in 1mm and 4mm respectively.The pore structure of the spherical foams is well connected internally,and the porosity of the foams with both pore sizes is 66.8%to 70.2%.The as-cast and homogenized Zn-5Al foamed alloys show a dual-phase structure,mainly composed of ?-Al phase and ?-Zn phase.However,after the homogenization heat treatment,the structure morphology changed from the original long lamellar structure to a coarse short bar eutectoid structure,and the segregated atoms in the alloy were uniformly diffused.The structure of as-cast Zn-1.5Mg foamed alloy includes three phases:?-Zn,Mg2Zn11,and MgZn2.After homogenization,the MgZn2 phase disappears,and coarsening of lamellar eutectic structure in microstructure.As-cast Zn-3Al-1Mg foamed alloy contains ?-Zn phase,?-Al phase,Mg2Zn11 phase and Mg2Al3 phase.After homogenizing the alloy foams,the non-equilibrium phase Mg2Al3 disappeared.Three zinc-based alloy spherical open-cell foams of as-cast large-pore Zn-5Al,Zn-1.5Mg,and Zn-3Al-1Mg showed obvious elastic and brittleness characteristics in the compression performance.The compressive strength and elastic modulus of as-cast large-pore foamed alloy are 16.5 MPa,13.5 MPa,19.6 MPa,and 1.06,1.07,and 1.06,respectively.The compressive strengths and elastic modulus of the as-cast small-pore foamed alloy are 11.5 MPa,8.5 MPa,13.8 MPa,and 0.73,1.01,and 1.01,respectively.It can be known that the compressive mechanical properties of large-pore alloy foams are better than those of small-pore foams.The homogenization heat treatment has a great influence on the elastic brittleness of as-cast Zn-5Al alloy foams,and it exhibits elastic-plastic compression characteristics after treatment.The homogenization heat treatment significantly improved the mechanical properties of the three alloy foams.The peak stresses of the three homogenized alloy foams with large pore sizes were 18.5MPa,26.5MPa,and 26.5MPa,and the elastic modulus were 1.99,1.58,and 1.15,it can meet the requirements of human cancellous bone mechanical properties.The corrosion rates on the first day of immersion corrosion of Zn-5Al,Zn-1.5Mg,and Zn3Al-1Mg small-pore foams are 2.01 mm/year,5.98 mm/year,and 11.72 mm/year,which are higher than the large pores,the corrosion rates were 0.81 mm/year,1.25 mm/year,and 3.44 mm/year.It can be known that the corrosion rate of alloy foams with the same pore size had a faster corrosion rate in the early stage.The corrosion rate of Zn-3Al-1Mg alloy foam was the fastest,and the corrosion rate of Zn-5Al alloy foam was the slowest.The corrosion rate in the initial period of immersion varies greatly.When the immersion time is about 10 days,the corrosion rate of the alloy foam tends to be stable between 0.15-0.45mm/year.Three Zn-based alloy foams have met the degradation rate conditions required for bone repair devices.The lamellar eutectic structure of ?-Al phase of Zn-5Al foamed alloy in simulated body fluid is firstly corroded due to galvanic corrosion effect.Zn-1.5 Mg foamed alloy in simulated body fluid,Mg2Zn11 phase before ?-Zn phase is corroded due to two different phase potential formation of galvanic corrosion effect.Observation of the microstructure showed that corrosion first occurred at the eutectic tissue junction.In foamed alloy Zn-3Mg-1Al,the corrosion resistance of three phase showed that as ?-Al phase corrosion resistance is best,followed by ?Zn phase,the most easily corroded phase is Mg2Zn11 phase.