Research On Preparation And Interfacial Reaction Of Ti-6Al-4V Alloy Prosthetic Joint Precision Casting

Four different types of mold shells have been developed using different sourcesof zirconia powder, ammonium zirconium carbonate and ludox blinder. Ti-6Al-4Valloy has been smelted in water jacketed copper crucible induction melting furnaceand eight prosthetic joints have been prepared by investment casting. The formationalpha-phase (-phase) layer on joint casting has been studied with opticalmicroscopy, scanning electron microscopy and microhardness tester. Tensileproperties has been investigated with universal testing machine. The cast fillingtime, the liquid flowing, the temperature field and the probable position ofshrinkage cavity and priority have been simulated using the ProCast software duringthe process of cast filling and solidification of titanium alloy.The reaction between molten titanium alloy and mold materials results in theformation of-phase enriched layer which is divided into recation layer andhardness layer. The thickness of-phase enriched layer is from100μm to300μm onthe surface of each titanium alloy casting. The size and the volume fraction ofphase in-phase enriched layer is much more than that in titanium alloy matrix. TheSEM micrographs show that the metal-mold reaction of casting3is the most violentand the rection layer is approximately20μm. Casting4has the weakest interfacialreaction and the reaction layer is about5μm. The reaction layers of casting1and2are respectively about15μm and10μm in thickness, so the metal-mold reactiondegree is between casting3and4. The Ti and Al contents have a trend to decrease,and a concentrated O contamination region has been detected in the reaction layer.The diffusion distance of Zr element in the-phase enriched layer of casting1,2,3and4is respectively45μm,55μm,60μm and30μm。The thickness of hardness layeron the surface of each casting is respectively200μm,215μm,160μm and170μm.The microhardness in hardness layer is much more than that of alloy matrix. Themain cause for the formation of hardness layer is zirconium solid solutionstrengthening and high concentration of oxygen.The casting filling and solidification of Ti-6Al-4V alloy were simulated withProCast software. The results show that the surface roughness is between Ra3.2andRa6.3according to the surface roughness comparison specimen. Gas cavity, sandinclusion and misrun exist in some region on the surface of casting. Two typical dimensional accuracies are respectively from CT2to CT4and from CT3to CT4.The size of shrinkage cavity of sample casting is smaller than1mm.The casting1and casting3have the same tensile properties. The fracturestrength, yield strength and elongation at break of casting1#is respectively833.61MPa,778.85Mpa and6.40%. The tensile properties of casting3#arefollowings: fracture strength831.34MPa, yield strength776.23MPa, elongation atbreak6.75%. The tesile fracture is charaterized by civility, permit cleavage andcleavage.