Micro-XRD study of beta-titanium wires and infrared soldered joints

Objective: The purpose of this study was to investigate the metallurgical phases in beta-titanium soldered joints prepared by infrared soldering, using the Micro X-ray diffraction technique (Micro-XRD), and to characterize the Vickers hardness in the soldered beta-titanium wires. Methods: Beta-titanium wires with cross-section dimensions of 0.032 in. × 0.032 in. (TMA, Ormco), and both titanium-based solder (Ti-30Ni-20Cu, Selec) and silver-based solder (Ag-22Cu-17Zn-5Sn, Tomy) were selected. Soldering was performed using infrared radiation (RS-1, Morita) under argon atmosphere. Micro-XRD analyses were performed at room temperature. Micro-XRD spectra were obtained for the boundary region of the soldered beta-titanium wires using 50 μm and 10 μm diameter analysis regions. Hardness was measured at 30 μm intervals from boundary of the diffusion layer and beta-titanium wire. The Kruskal-Wallis test with the Bonferroni and Wilcoxson Mann-Whitney tests for nonparametric means were employed as statistical methods (P < 0.05). Results: For both types of soldered beta-titanium samples, the Micro-XRD spectra contained four major peaks for body-centered cubic (bcc) beta-titanium. Additional peaks at about 41 and 45 degrees are attributed to Cu-Ti intermetallic phase(s), which may be metastable under soldering conditions. The diffusion layer had greater hardness than bulk beta-titanium for both types of soldered specimens (P < 0.05). Significance: Soldering of beta-titanium orthodontic wire by infrared radiation may be acceptable for clinical use, since Micro-XRD spectra revealed that both types of soldered specimens largely retained the bcc beta-titanium structure. Further research is needed to investigate the mechanical properties and corrosion behavior of infrared-soldered beta-titanium wire.