Joining of Wrought Ni-Base Combustor Alloys Free

In many advanced combustor concepts, such as the RQL (rich-quench-lean) combustor, the requirement of low NOx emission makes film cooling of the hot gas path surfaces undesirable. Double-walled structures with relatively low aspect ratio (height/width) rectangular passages and with well-controlled thin hot gas side metal walls are an alternative to film cooling. The additional application of other cooling techniques, such as impingement and surface enhancements, make efficient use of the limited cooling air available. However, the use of cooling channels to increase heat transfer coefficients on the coolant side may ultimately require well-bonded structures. Alternate methods of bonding have been considered for Ni-base alloy HA230-to-HA230 joints in thin-walled structures, with emphasis on bonds produced by hot isostatic pressing and by laser welding. For hot isostatic pressed (HIPed) structures, mechanical strength and ductility have been measured as a function of temperature for structures prepared after a number of different surface cleaning treatments prior to joining. The surface cleanliness has been characterized by scanning electron microscopy, and the after-HIP bond line microstructure has been evaluated as formed and after mechanical testing. Characterization of laser welds produced at Laserdyne for Acraline Products has consisted of scanning electron microscopy of the weld surfaces and metallography of weld/substrate cross-sections, looking at solidification/heat affected features and defects.