Direct observations of welding-induced solid-state phase transformations
- Lawrence Livermore National Lab., CA (United States); and others
A new diagnostic tool that uses time-resolved x-ray diffraction (TRXRD) for in-situ, spatially resolved, phase identification around a weld is presented for the purpose of mapping the location of phase fields during welding. In this investigation, TRXRD experiments were conducted at the Stanford Sychrotron Radiation Laboratory where a high-intensity tunable synchrotron x-ray `probe` was available. The high spatial resolution of the x-ray probe (1mm) allowed precise mapping of specific phase fields around the weld, while the high intensity of the beam (10{sup 11} photons/s) yielded high signal-to-noise ratio of the diffracted x-rays. These characteristics enabled the crystal structure to be characterized during a 1-s x-ray integration time, thus providing real-time data to be gathered about welding-induced phase transformations. Experiments were performed on unalloyed Grade 4 titanium (Ti, 0.28%Fe, 0.38%O), which has an allotropic phase transition that occurs at 922{degrees}C, where the low temperature hcp phase transforms to the high temperature bcc phase. Welds were made using a semi-automatic tungsten inert gas procedure to establish a quasisteady-state thermal profile on 4.5 in. diameter titanium bar, which was rotated at a speed of 0.5 rpm beneath a 3.5 kW arc. Characteristic hcp, bcc, and liquid diffraction peaks were measured along x-ray probe scans traveling from the base metal through the heat-affected zone and into the weld pool, respectively. The results of this study clearly demonstrate the feasibility of using TRXRD for in-situ investigations of welding-induced phase transformations, thus allowing verification of welding models, the creation of transformation diagrams during rapid thermal cycling of materials, and the ability for real-time investigations of the nucleation and growth behavior of solid-state phase transformations.
- OSTI ID:
- 115461
- Report Number(s):
- CONF-9404233-; TRN: 95:002927-0039
- Resource Relation:
- Conference: 75. American Welding Society (AWS) annual meeting, Philadelphia, PA (United States), 10-15 Apr 1994; Other Information: PBD: 1994; Related Information: Is Part Of 75th Diamond anniversary American Welding Society annual meeting; PB: 273 p.
- Country of Publication:
- United States
- Language:
- English
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