Evaluation of fatigue behaviour of laser beam welded aerospace superalloy haynes 282
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In 2005, a new, wrought, nickel-base superalloy Haynes 282 was developed. Characteristic of superalloys, Haynes 282 was produced to be used for components, specifically aero and land-based gas turbine engines, which are subjected to high temperatures. The manufacture and/or repair of aero and land-based gas turbine engines require the use of joining processes, an example being welding. However, it was observed that laser beam welding (LBW) of the new superalloy resulted in cracking in the heat affected zone (HAZ) of the alloy. Accordingly, an aspect of this research involves the development of a procedure for preventing or minimizing cracking of the alloy. This is achieved through microstructural modification of the alloy prior to welding through the use of appropriate heat treatment. However, at the core of this research is the main objective of methodically studying the effect of LBW on the high temperature fatigue crack growth (FCG) behaviour of Haynes 282, and how to mitigate any negative effects. Findings from this research show that LBW causes a deleterious effect on the FCG behaviour by increasing the FCG rate. Thus, although this research resulted in a procedure that minimizes cracking during welding of the new alloy, the minimized level of cracking is not tolerable under dynamic loading. Therefore, a procedure to make the minimized level of cracking tolerable during dynamic service is developed. This is achieved by developing two post weld heat treatments, including a new thermal treatment schedule developed in this work, which significantly improved the FCG resistance of the new alloy after LBW. Additionally, Low cycle fatigue (LCF) tests results indicate strong fatigue deformation resistance of Haynes 282. On the other hand, FCG tests results show that, in contrast to common assumption, the loading frequency was observed to have an effect on the FCG behaviour at room temperature. Prior to this research, there was limited publication on the fatigue behaviour of Haynes 282. Hence, the study of the cyclic deformation characteristics and growth behaviour of fatigue crack in Haynes 282 in this research provides valuable information that helps establish design criteria to safeguard against component failure by fatigue.