| Cobalt-chromium(CoCr)alloy has excellent mechanical properties,corrosion resistance and biocompatibility,and is widely used in dental metal porcelain restoration bottom crown.Due to the low bonding strength between the CoCr alloy crown and the ceramic layer on the surface,the ceramic layer is easy to fall off,metal ions precipitate out,causing oral inflammation and other problems.Al2O3 ceramic as the reinforcement phase added to the CoCr alloy matrix can prepare the metal matrix composite material with excellent performance.The bonding strength between the bottom crown and the porcelain layer processed by this composite material is greatly improved,and it has good wear resistance and biocompatibility.Aiming at the requirement of oral denture customization,Al2O3 ceramics were added to CoCr alloy and Selective Laser Melting(SLM)was used to produce dental Al2O3/CoCr metal matrix composites.The microstructure and bonding properties of Al2O3/CoCr metal matrix composites and Al2O3/CoCr interface were studied.The main research contents and conclusions are as follows:(1)The distribution of temperature field and variation of molten pool size during SLM fabricated Al2O3/CoCr metal matrix composites process were studied by finite element numerical simulation.The results show that higher laser power and lower scanning speed have lead to the higher temperature gradient and elongation of liquid time,which contributed to greater width and depth of the molten pool.In the meantime,it is found that the laser power exerted greater influence on the size of the molten pool than that of scanning speed.When the laser power increased from 100 W to 300 W,the molten pool width increased from 69.21μm to 71.71μm by 123.81%;the molten pool depth increased from 16.87μm to 154.90μm by325.07%.When the scanning speed decreased from 1100 mm/s to 300 mm/s,the width of the molten pool increased from 90.29μm to 135.26μm by 49.81%;the depth of the molten pool increased from 37.66μm to 58.44μm by 55.18%.The simulating results show that the most suitable laser power P was in the range of 150-250 W and the scanning speed V was in the range of 700-1100 mm/s for the SLM fabricated Al2O3/CoCr metal matrix composites.(2)On the basis of finite element simulation and experiment,the optimal forming process parameters of Al2O3/CoCr metal matrix composite formed by SLM were determined:laser power 200 W,scanning speed 700 mm/s,scanning line spacing 0.06 mm,powder thickness 0.03 mm.Al2O3/CoCr metal matrix composites with excellent microstructure and properties were prepared under the optimal process,and the microstructure morphology was mainly cell crystal morphology.The introduction of Al2O3 ceramic particles resulted in the weld pool width of the composite was shortened by about 20%and the weld pool depth increased by about 233.3%compared with CoCr alloy.The boundary and inner cell crystal size of molten pool are obviously refined.Compared with CoCr alloy,the mean microhardness of cross section and longitudinal section of Al2O3/CoCr metal matrix composite formed by SLM is increased by 12.45%and 24.58%,the mean friction coefficient is reduced by 12.9%,and the shear strength is 29.962 MPa,which can meet the requirements of the bottom crown of metal porcelain restoration.(3)The interface bonding properties of after Al2O3 was added to CoCr alloys was studied.Three interface models of Al2O3(111)/CoCr(100),Al2O3(111)/CoCr(110)and Al2O3(111)/CoCr(111)were constructed using first principles,and the work of adhesion,work of separation,the interface formation energy,fractional density of states and projected charge density distribution of these models were calculated.The results show that a covalent bond was formed between Co-O and Cr-O atoms at the Al2O3(111)/CoCr(111)interface,the Co-O bond length was 1.782?,the work of adhesion(Wad)was 2.33 J/m~2.The work of separation(Wsep)was 2.12 J/m~2,and the interface formation energy(Efor)was 0.11 J/m~2.The more electron clouds at the interface overlap,the stronger is the charge density,and the higher is bonding strength.(4)The corrosion resistance and biocompatibility of SLM fabricated Al2O3/CoCr metal matrix composites were studied.The results show that compared with CoCr alloy,Al2O3/CoCr metal matrix composites have higher corrosion potential,lower corrosion current density,higher corrosion resistance and less metal ion precipitation.The Al2O3/CoCr metal matrix composite extract had no toxic effect on the proliferation of human dental cyst stem cells,and had a significant effect on cell proliferation,and had osteogenic induction ability on human dental cyst stem cells.The hemolysis rate was less than 5%of the standard and did not cause acute hemolysis.The Al2O3/CoCr metal-matrix composites were implanted in SD rats for 4 weeks,8 weeks and 12 weeks,and showed good response to tissues without inflammatory reaction,showing good biocompatibility. |
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