An investigation of cracking in laser metal deposited nickel superalloy CM247LC

McNutt, Philip Alexander (2015). An investigation of cracking in laser metal deposited nickel superalloy CM247LC. University of Birmingham. Eng.D.

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Abstract

A parametric investigation of the crack susceptibility of laser deposited nickel superalloy CM24 7LC was conducted, using Design of Experiments (DOE) methodology to correlate the laser deposition processing variables (laser power, scanning speed, deposit dilution, laser spot size) against the cracking response. Also investigated was the effect of tool path pattern, powder particle size and substrate preheating.

Results showed that cracking occurs during solidification, due to the presence of a low melting point eutectic composition liquid that forms due to elemental segregation of alloying elements, which resides at grain boundaries and other solidification boundaries, at temperatures below the solidus creating a weakened area that separates under an applied tensile stress.

Cracking was reduced, but not eliminated, by using a high heat input approach comprising of high laser power, slow scanning speed, large laser spot diameter and low dilution. Different toolpath patterns produced various microstructures, with the cross hatch toolpath producing the lowest cracking response due to the generation of competing stress fields that reduce the net tensile stress available to form cracks. Powder particle size range was also observed to influence the crack density, with finer powders increasing the number of cracks, but decreasing the average crack length.

Type of Work:

Thesis (Doctorates > Eng.D.)

Award Type:

Doctorates > Eng.D.

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