Microstructure and mechanical properties of direct laser deposited alloy IN718

Xia, Zhangwen (2017). Microstructure and mechanical properties of direct laser deposited alloy IN718. University of Birmingham. Ph.D.

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The microstructure and mechanical properties of direct laser deposited IN718 have been investigated and compared to forged IN718 base material (BM). Typical laser deposited microstructural features such as deposit layers, columnar grains and dendritic structures are observed in material addition (MA). Secondary phases such as γ’’, γ’, Laves phase, δ phase, carbides and α-Cr in MA are identified. Microhardness is measured throughout the deposit build - comparable hardness is obtained for both MA and BM.

Tensile tests are carried out at room temperature and 600 °C for both MA and BM. Higher yield stress and lower elongation to failure are obtained when the loading direction is parallel to the deposit layers.

Fatigue crack growth resistance tests at stress ratio of 0.1 and 0.7 have been carried out at 600 °C for MA. A higher threshold value and better fatigue crack growth resistance are found for crack growth direction perpendicular to the deposit layers. Both orientations in MA show higher threshold values and increased fatigue crack growth resistance to BM.

Fractography and cross-sections after tensile and fatigue crack growth resistance tests indicate that layer interfaces, columnar grains boundaries and interdendritic regions are weak regions in MA.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Metallurgy and Materials
Funders: Engineering and Physical Sciences Research Council
Subjects: T Technology > TJ Mechanical engineering and machinery
URI: http://etheses.bham.ac.uk/id/eprint/7578


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