Mechanical and structural characteristics of commercially pure grade 2 Ti welds and solder joints

This study aimed at determining whether data previously gathered for a lase r welds and IR brazings using a Au-Pd alloy were applicable to titanium joi nts. As to its resistance under fatigue loading, Au-Pd alloy had shown a po or response to pre-ceramic laser welding and post-ceramic brazing. The pres ent study was designed to assess the mechanical resistance, the microstruct ure and the elemental diffusion of laser welded, electric arch welded and b razed joints using commercially pure titanium as substrate metal. Mechanical resistance was determined by determining the joints' ultimate te nsile strength and their resistance to fatigue loading. Elemental diffusion to and from the joints was assessed using microprobe tracings. Optical mic rographs of the joints were also obtained and evaluated. Under monotonic tensile stress, three groups emerged: (1) the GTAW and the native (i.e. as received) substrate, (2) the annealed substrate and the las er welds and (3) the brazed joints. Under fatigue stress, the order was: fi rst the native and annealed substrate, second the brazings and laser welds, third the GTAW joints. No Au-filler brazing withstood the applied fatigue loading. The micrographs showed various patterns, an absence of HAZ crackin g and several occurrences of Widmanstatten structures. Elemental diffusion to and from the Ti substrate was substantial in the Ti filler brazings and virtually nil in the Au-based brazings. Under fatigue stress application, the titanium-based brazings as well as th e laser- and electric arc welds performed equally well if not better than a previously tested AuPd alloy. There was a definite increase in grain size with increased heat application. However, no feature of the microstructures observed or the elemental analysis could be correlated with the specimen's resistance to fatigue stress application. (C) 2001 Kluwer Academic Publish ers.