Ti-Nb-Zr-Ta 합금계에서 냉각속도와 시효처리에 따른 미세조직의 변화가 내식성에 미치는 영향

Abstract

In recent years there has been a significant development of novel implant alloys based on β-Ti such as Ti-Nb-Zr and Ti-Nb-Zr-Ta alloy systems. Also, the use of titanium and its alloy as biomaterial is increasing due to its low modulus, superior biocompatibility and corrosion resistance when compared to conventional stainless steel and cobalt-based alloys. The purpose of this study is to investigate the microstructure variation, phase transformation behavior and corrosion characteristics of Ti-29Nb-4.3Zr-xTa alloys. Four kinds of alloys containing Ta concentrations of 5, 10, 15, and 20(wt%) were used to investigate the microstructure, corrosion resistance and others. The specimens were solution treatment in the β phase field of Ti alloy and followed by water quenching(WQ). Optical microscopy, FE-SEM(Field emission scanning electron microscope), X-ray diffraction, and a Vickers hardness test were performed to investigate the microstructure variation and corrosion resistance for each alloy under different cooling rate and Ta addition conditions. Concentrations corrosion resistance was studied by anodic polarization test. Fine needle-like traces of martensite were observed at the prior β grain boundary in the image of Ti alloys(Ti-29Nb-4.3Zr-xTa). Also, α´(hexagonal)martensite and β phase peaks were observed in the XRD profile; this, α´(hexagonal)martensite and β duplex phase structures were revealed. When aged at 780 ℃/WC, the hardness increased slightly. This was considered to be related to the βTa, βZr precipitation in the grain boundary. In addition, the anodic polarization curves of Ti-29Nb-4.3Zr-xTa(x=5, 10, 15) alloys which were age treated specimen at 780 ℃/AC move to the left and upwards. It causes excellent pitting resistance and corrosion resistance.