Additive manufacturing of nickel based superalloys for aerospace applications

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Parimi, Lakshmi Lavanya (2014). Additive manufacturing of nickel based superalloys for aerospace applications. University of Birmingham. Ph.D.

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Abstract

The aim of this work is to establish the influence of the many process variables on the microstructure and the nature of internal stress in IN718 samples produced directly from powder using direct laser fabrication, which enables production of solid samples directly from a CAD file. The process variables that have been studied include, specimen geometry, laser power, laser traverse speed, the detailed laser path and powder feed rate. It has been found that the detailed microstructure is strongly influenced by all of these variables with the propensity for the production of equiaxed or columnar grains being strongly influenced by laser power. The texture is correspondingly strongly influenced by changes in processing conditions. The extent of precipitation of the various phases expected in IN718 was also found to be influenced by the process conditions. The level and nature of the residual stress in the sample and in the substrate have been determined for a wide range of experimental conditions and using neutron diffraction. It has been found that the level of these stresses could be reduced to a minimum value of about 300 MPa, but could not be eliminated. A simple 3D thermo-mechanical model was developed to understand the residual stress distribution, which agreed closely with the experimental measurements.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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