| Background:Zirconia bioceramics have strong mechanical properties and good biocompatibility,but no bone induction activity.Although hydroxyapatite bioceramics have excellent biological activity,they are brittle and not suitable for the replacement of load-bearing bone tissue.In view of this,the synthesis of functionally gradient materials by combining the two materials has become a hot topic in the research of bioactive materials,and the microstructure and phase after the combination are important factors affecting the mechanical and biological properties of materials.ObjectiveUsing gradient functional technology,yttrium-stabilized nano-zirconia was used as the matrix layer,and yttrium-stabilized zirconia/nano-hydroxyapatite composite material gradient transition was applied in the middle,and the surface layer was pure nano-hydroxyapatite.The gradient functional material was pressed into shape and sintered into bioceramic specimen by high temperature sintering technology.Through the test of mechanical properties of the specimens,select the best design scheme and the sintering temperature,using scanning electron microscopy(sem)and X-ray diffraction analysis specimen interface morphology,crystal materials and components,etc.,discussing the new functionally gradient ceramic material interface morphology and phase of the relevant factors,material design and the sintering temperature and specimen interface morphology,physical and mechanical properties of relations.Methods1.Sample design,preparation and grouping:nHA and Y-ZrO2 powders were placed in the air-blast constant temperature drying oven for 2h for backup use;The nHA volume fraction of each gradient layer calculated according to the sample design was added to the corresponding Y-ZrO2 powder,and the ultrasonic oscillator was fully mixed for backup use.Y-ZrO2/nHA FGM was designed with a substrate layer of 100%Y-ZrO2,an intermediate layer of Y-ZrO2/nHA composite material gradient functional layer,and a surface layer of 100%nHA content(volume fraction).In order to facilitate the detection of mechanical properties and biological activity,the specimen was designed to have a unidirectional change in the number of gradient layers along the thickness.The total thickness of the sample powder D=5 0mm,Y-ZrO2 at the base layer is D1,Y-ZrO2/nHA at the gradient layer is D2,and the volume fraction of nHA content in each gradient layer is calculated according to f(x)=(x/n)pxf(s),x represents the number of gradient layers,and n represents the total number of gradient layers.p is gradient index 2.5;f(x)is 100%nHA.According to the different thickness of D1,it is divided into three groups:A,B and C,among which group A D1=40mm,D2=10mm,group B D1=30mm,D2=20mm,and group C D1=20mm,D2=30mm.According to the number of layers n,each group is divided into 3 groups.Each group produced 18 specimens,a total of 162 specimens.2.Place the weighed powders in a 40mm×60mm cylindrical steel mold,and lay them layer by layer.Y-ZrO2 powder was added first,and then gradient layers were added respectively.Y-ZrO2/nHA module was made by universal mechanical testing machine under 10Mpa pressure and lmm/min uniform one-side vertical pressure.Set 6 groups of different sintering temperature,which is 1300?,1350?,1400?,1450?,1500? and 1550?.After successful preparation of Y-ZrO2/nHA green specimens in the muffle furnace respectively,according to the two stages of sintering temperature,start with 10?/min uniform temperature to 300? warm after 2h,then at 5?/min speed to set temperature and heat preservation 2h,finally out with furnace cooling to room temperature.3.Detection of bending and shear strength:the high-temperature sintered Y-ZrO2/nHA cylindrical specimen was processed into a sample strip with a high-speed mobile phone,and the surface of the material was polished and polished with fine sandpaper,which was used for testing the mechanical properties of bending strength and shear strength.The vernier caliper is used to accurately measure each side of the specimen,and its specification is 10mm×4mm×xmm rectangular specimen(x is the height of the cylindrical specimen after high temperature sintering,that is,the height of the rectangular specimen;The sintering temperature of the specimen is different,so the height of each specimen is different.(1)bending strength detection:place the rectangular specimen side up into the universal testing machine fixture.The force measuring machine will vertically downward pressure at the speed of 1mm/min until the specimen breaks and breaks.Observe the maximum peak value displayed on the computer monitor,make statistics and calculate the bending strength.(2)shear strength detection:one end of the rectangular specimen is fixed in the mold,and the force measuring machine is applied vertically downward at a speed of 1mm/min until the specimen breaks and breaks.The maximum peak value is observed on the computer display,and the shear strength is calculated by statistical data.4.Electron microscope observation of interface microstructure:the rectangular specimen with functional gradient material of zirconia nanometer hydroxyapatite with a size of 10mm×4mmxxmm was polished and polished.After spraying gold,scanning electron microscope was used to observe the microstructure and layered structure of the surface on the side of the sample.5.Specimen of crystal phase and phase detection:1300? A3 group and 1550?A3 specimen with universal material testing machine repeatedly broken,placing agate mortar made into fine powder,with gauze after filtering screen size smaller powder XRD testing its crystal phase and phase.6.Data processing:SPSS 19.0 software was used for one-way anova of the data,and P<0.05 was considered statistically significant.Results1.The raw specimen of functional gradient material zirconia-based nanometer hydroxyapatite prepared by universal force measuring machine under lOMpa pressure has a complete appearance and smooth and hard feel.2.Zirconium oxide nanometer hydroxyapatite functionally graded material resistance to bending strength and shearing strength gradually increased with the increase of sintering temperature,when 1550?,the mechanical strength reaches the highest,compared with 1300? group,the difference is statistically significant(P<0.05).3.The thickness of matrix layer and the number of gradient layers affect the mechanical properties of zirconiaoxide nanometer hydroxyapatite functionally gradient materials.The basic zirconia layer is the main mechanical bearing area.As its thickness increases,the mechanical strength of functionally gradient materials gradually increases.The more gradient layers,the smaller the difference in the content of nano-hydroxyapatite between layers,the better the interface compatibility between layers and the change of continuity and gradient,and the mechanical properties also increased.The bending and shear strength of the 7-layer gradient layer group was significantly better than that of the 3-layer layer group(P<0.05).4.Observed under scanning electron microscopy(SEM)zirconium oxide nanometer hydroxyapatite functionally graded material surface microtopography,under the condition of same group,comparing different gradient layer microstructure morphology,when the gradient layer number n=3,nanometer hydroxyapatite content is large difference between layer and layer,can be observed between layer and layer is relatively obvious change of gradient,with the increase of gradient layers,differences between adjacent two layers of zirconia content gradually narrowed,boundary between the layers is more and more is not obvious.When D1=20mm and n=3,the gradient change between layers is the most obvious.When the number of gradient layers n=5,7,there is almost no obvious stratified interface,the transition between layers is gentle,the compatibility is good,the material density is good,the crystal distribution is uniform,the agglomeration and the gap is small.5.Of zirconium oxide nanometer hydroxyapatite function gradient material preparation of ceramics powder X-ray diffraction tests and the results show that 1550? group at 2 theta=30 diffraction peak for zirconia sifang phase characteristic peaks,at the same time found the beta tricalcium phosphate and calcium oxide diffraction peak,13000C group appear monoclinic phase and cubic zirconia crystals and nano hydroxyapatite characteristic peak.Conclusion1.Under the pressure of 10Mpa,the universal force measuring machine can be used to prepare raw samples with certain mechanical strength of zirconia based nanometer hydroxyapatite functionally gradient material,which can realize the design concept of functionally gradient material and meet the conditions for further experiments.2.Sintering temperature,gradient layer number and substrate thickness are the main factors affecting the mechanical properties of functional gradient materials.When the sintering temperature is 1550?,for 7,substrate thickness gradient layer is 40 mm,its structure is compact,equal distribution of crystal,crystal reunion and smaller crack gap,zirconia crystal phase for high mechanical strength,and it's part of the hydroxyapatite is decomposed into beta tricalcium phosphate and calcium oxide,the highest material mechanical strength.3.Using powder metallurgy technology and high temperature sintering method,the functional gradient material bioceramics of zirconia-based nanometer hydroxyapatite with better mechanical properties can be prepared. |
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