THERMALLY INDUCED GRINDING DAMAGE IN CAST EQUIAXED NICKEL-BASED SUPERALLOYS (MACHINING, METAL REMOVAL, AIRCRAFT ENGINES, MANUFACTURING)

The overall objective of this program was to increase the understanding and productivity of conventional grinding operations utilized in the finishing of cast equiaxed nickel-based superalloy components. To achieve this overall goal a four phase approach was employed. Initially, a grinding energy partition relationship for conventional grinding of superalloys was developed. Secondly, the mechanisms and conditions which influence superalloy microcracking during abusive grinding were determined. Third, building on the above relationships, a means of readily predicting the onset of grinding damage in cast Rene-77 and B-1900 superalloys was established. Finally, the results were implemented in production surface grinding operations to increase superalloy grinding quality and productivity.;It was then demonstrated that workplace damage would occur when the combined conducted and convected heat flux exceeded a critical limit. A hyperbolic quality threshold relationship, dependent upon alloy type, was established to readily predict incipient microcracking in production. By interactively using this power based quality threshold criterion, superalloy metal removal rates were increased an average of 60% over 12 production surface grinding machines.;Several series of laboratory grinding studies were conducted to determine key superalloy grinding energy components. Unlike previous ferrous alloy models, the abrasive type was shown to produce significant differences in the chip formation and plowing energy components of the superalloy grinding partition relationship. Two unique expressions, which depend upon abrasive type, were developed to predict the total specific grinding generated during superalloy surface grinding. Using simulated worst case production conditions, the combined effects of temperature dependent thermal properties, convective cooling within the wheel/workpiece interface, and increased contact length were identified. Finite element analyses were utilized to determine the superalloy grinding zone temperatures and residual stresses. The results indicated that Rene-77 microcracks are not formed by the residual stresses alone. The effects of constitutional liquation or weakening of the grain boundaries due to rapid heating to such temperatures were shown to be significant.