Study Of Microstructure Refinement Of TC4 Alloy Bars For Surgical Implant Application

At present,metallic materials used in surgical implants consist of stainless steels,Co-based and titanium alloys.Thereinto,titanium alloys are utilized in hard tissue loss,repairing and replacement.The research of titanium alloys for surgical implant application starts rather late in our country.Compared with imported TC4 alloy bars,TC4 alloy made in china is coarse microstructures and inhomogeneity in properties,and it is hard to meet the need of high-end medical apparatus.Hence,it is urgent to realize the technology breakthrough and end the long-term dependence on imports.The country's sole hot continuous rolling mill designed for titanium alloy bars was utilized to fabricate TC4 alloy bars,14 mm in diameter,which was proceeded twice hot rolling.The deformation amount was 78% and 96%,respectively.Based on practical production,the effects of rolling temperatures,rate,deformation amount and heat treatment on microstructures were estimated.Additionally,the high temperature performances were investigated,especially at 400?.The experimental results showed that the microstructures of TC4 alloy bars were refined definitely.It was improved that technological Parameters obviously affected the microstructures during the each-pass large deformation rolling.The one-pass rolling was performed above the ? transus,and the two-pass rolling in the two-phase field.The rolling rate was 3 m/s.At this case,coarse widmanstatten structures were broke,uniform and fine microstructures,about 2 ?m in size,were obtained in TC4 alloy bars of 14 mm in diameter.The rolling rate had an effect on microstructures.With the increase of rate,the microstructures were deteriorated seriously.Simultaneously,it was hard that heat diffused in the center of bars.This brought about the differences in microstructures between the center and edge.Based on the effect of heat treatment temperatures on microstructure morphologies,it was discovered that bars with fine microstructures gained uniform spheroidized microstructures,when heat treated at low temperatures.With the increase of treatment temperatures,the quantity of the primary ? phases decreased,that of the secondary ? and ? phases increased,and ? grains gradually coarsened.Up to the ? transus,widmanstatten structures were formed.The microstructure morphologies had an effect on tensile properties at room temperatures and 400 ?.Bars with fine microstructures exhibited the combination of high strength and high toughness,compared with ones with coarse microstructures.