Ti-Zr-XNb합금계에서 냉각속도와 소려시효가 미세조직 및 내식성에 미치는 영향

Abstract

The purpose of this study is to investigate the microstructure variation, phase transformation behavior and corrosion characteristics of Ti-13Zr-xNb alloys. Five kinds of alloys containing niobium concentrations of 4, 6, 8, 10, and 12 (wt.%) were used. The specimens were solution heat treated in the β phase field of Ti alloy and followed by water quenching(W.Q). Optical microscopy, 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 niobium addition conditions. Corrosion characteristics of its alloy on the 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-13Zr-xNb). 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 ℃/W.C, the hardness increased slightly. This was considered to be related to the βNb, βzr precipitation in the grain boundary. In addition, the anodic polarization curves of Ti-13Zr-xNb(x=4, 6, 8) alloys which were age treated specimen at 780 ℃/W.C move to the left and upwards. It caused excellent pitting resistance and corrosion resistance.