Perricone, M.J., “Advanced Milling Technology Helps Identify Phase Transformations”, Welding Journal, Vol. 84(10), pp. 44-49, 2005.
Understanding the microstructural development of alloys during weld solidification is centrally important to controlling fusion zone properties (Refs. 1–4). As technology continues to advance, new engineering alloys with complex compositions must often be designed to provide application-specific properties to maximize performance. Invariably, these alloys are subjected to some form of welding during manufacturing, where weld resolidification may cause chemical redistribution resulting in inhomogeneities in fusion zone properties, particularly when compared to the base metal. With the constant market pressure to make products smaller and cheaper, high-energy-density (HED) welding processes such as laser and electron beam welding become attractive options to increase productivity and minimize distortion, particularly when compared to conventional arc welding processes (Ref. 5). However, the extremely high cooling rates associated with HED welding (102–106 °C/s) (Refs. 3, 6) significantly reduce the scale of the fusion zone microstructure compared to conventional arc welding methods (100–103 °C/s)(Ref. 3). Even at these cooling rates, intermetallic phases that form in the fusion zone at the termination of solidification can also be extremely difficult to analyze due to their fine structures. This therefore presents a unique challenge for the welding engineer attempting to characterize the composition and the identity of the phases present.