Low temperature nitriding of commercially pure titanium with harmonic structure

Abstract

Commercially pure titanium with harmonic structure, which consists of a coarse-grained structure surrounded by a network structure of fine-grains, was produced by sintering mechanically milled powders to achieve high strength and high ductility. The effect of subsequent nitriding on the commercially pure titanium with harmonic structure was investigated. Nitriding was performed at relatively low temperatures of 773, 873 and 973 K (500, 600 and 700 °C). The surface microstructures of the nitrided specimens with harmonic structure were characterized using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and a non-contact scanning white light interferometry. The nitrided titanium specimen with harmonic structure had higher hardness than a nitrided-only titanium specimen because the fine-grained structure in the harmonic structure accelerated the formation of titanium nitrides during nitriding. Furthermore, fine grains created by mechanical milling were not coarsened during the nitriding process. These results indicate that low temperature nitriding is effective to increase the surface hardness of commercially pure titanium with harmonic structure while grain-coarsening is also suppressed.