Nauka i Obrazovanie (Jan 2016)
Structure Defects Interrelation of Heat-resistant Nickel Alloy Obtained by Selective Laser Melting Method and Strategy and Scanning Parameters
Abstract
The objective was to conduct a study of the surface morphology and a chemical composition analysis of the powder of different fractional composition of a heat-resistant Ni-Co-Cr-AlTi-W-Mo-Nb alloy, and to define the patterns of change in the quantitative parameters of the structure of samples obtained by selective laser melting (SLM) method with different parameters of power, laser speed, and a type of hatching (staggered, island diagonal, and solid diagonal).To study the surface morphology of the microstructure was used optical, laser-confocal and scanning electron microscopy. The elemental and local phase composition was performed by X-ray and miсro-X-ray spectrum analysis.The initial powder morphology study has found that the powder granules have a generally spherical shape, and the number of structural defects increases with increasing granule size. The microstructure of all granules has a dendritic structure. The superficial defects have a form of satellites, shapeless shield, round gas pores, and pores located in the inter-dendritic regions because of the shrinkage process.The study of the microstructure of the samples has been defined that dimensions of the structural components, pores, and micro-cracks depend on the parameters of the SLM process. With raising laser power within 160 - 190 W there is an increase in a fraction of pores and their average diameter. With further increase in laser power the volume fraction of pores is slightly reduced while their average size is, essentially, unchanged.It has been found that at the constant laser power and variable scanning speed the volume fraction of pores depends on the type of hatching. For staggered and solid diagonal hatching, at the constant laser power of 180 W with increasing scanning speed the volume fraction, at first, falls and then again grows, and for island diagonal hatching remains unchanged.When changing the laser power values within a range from 160 to 170 W for samples with staggered type of hatching the volume fraction of cracks decreases. For other samples, this range is from 160 to 180 W. With increasing laser power to 190 W the volume fraction of cracks gets growing. With further increase of the laser power to 200 W the volume fraction of cracks is unchanged for the solid diagonal hatching and is decreased for the staggered one. There were no cracks found in the sample obtained by the diagonal hatching. It has been found that at a constant laser power of 180 W the volume fraction of cracks gets decreasing with increasing scanning speed.
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