Browsing by Author "Zhang, Z."
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Item Open Access An investigation into cracking in nickel-base superalloy repair welds(2010-12-31T00:00:00Z) Rush, M. T.; Colegrove, Paul A.; Zhang, Z.; Courtot, B.The nickel-base superalloy Rene 80 is considered very susceptible to liquation and strain-age cracking. Material in the solutionised condition is welded using the Cold Metal Transfer, or CMT process (with ductile filler alloy) and autogenously using a laser. Grain size is shown to have a significant effect on cracking. Using the CMT, welding power is shown to have high significance on the level of cracking, whereas welding speed has little effect. When welding using the laser, it is shown that the power and spot size are more crucial to the material cracking than the travel speed. It is indicated that the weld bead geometry has high significance over the occurrence of cracking, with a relationship between welding power, weld bead geometry, and stresses controlling the occurrence and magnitude of cracking. Further, some laser welds are analysed after post-weld heat treatment, and there is a significant increase in cracking after this. However, 34% of samples contained no cracking in both the as-welded and post-weld heat treated state.Item Open Access Liquation and post-weld heat treatment cracking in Rene 80 laser repair welds(Elsevier Science B.V., Amsterdam., 2012-01-31T00:00:00Z) Rush, M. T.; Colegrove, Paul A.; Zhang, Z.; Broad, D.An extensive experimental study on a nickel-based superalloy, Rene 80 using autogenous laser welding has been undertaken to determine the effect of the process parameters and weld bead geometry on cracking in the as-welded and post- weld heat treated conditions. Little cracking was observed in the as-welded condition with low powers and beam diameters around 2.5mm. Welding speed had little effect on the incidence of cracking in the as-welded condition. Investigation of the aspect ratio (penetration divided by width) indicated that little cracking occurred in the as-welded condition when the aspect ratio was approximately 0.5. The same effect was observed with the post-weld heat treated samples. An analysis of the microstructures indicated that the cracking was caused primarily by liquation in the as-welded condition and was exacerbated by post-weld heat treatment cracking during the subsequent heat treatment. Finally the study resolved some of the contradictory findings in the literature on the effect of process parameters on the incidence of cracking in the as-welded and post-weld heat treated conditions.