Directed laser deposition of super duplex stainless steel: Microstructure, texture evolution, and mechanical properties

Navid Sayyar; Vidar Hansen; Wakshum Mekonnen Tucho; Mona Wetrhus Minde

doi:10.1016/j.heliyon.2023.e15144

Directed laser deposition of super duplex stainless steel: Microstructure, texture evolution, and mechanical properties

Heliyon. 2023 Apr 1;9(4):e15144. doi: 10.1016/j.heliyon.2023.e15144. eCollection 2023 Apr.

Authors

Navid Sayyar¹, Vidar Hansen¹, Wakshum Mekonnen Tucho¹, Mona Wetrhus Minde¹

Affiliation

¹ Department of Mechanical and Structural Engineering and Materials Science, University of Stavanger, 4036 Stavanger, Norway.

Abstract

Microstructure and texture evolution of directed-laser deposited super-duplex stainless-steel, in the as-received block, were characterized using light and electron microscopies and electron backscattered diffraction. Mechanical properties in different directions were studied. Local FCC-depleted and FCC-rich zones and extensive precipitation of oxides were detected at the matrix wherein the different types of reformed austenite were surrounded by the elongated coarse ferrite. A vertical gradient of austenite content, caused by overall change in cooling rate, generated a waning hardness distribution along the building direction. The texture of austenite across the different deposition layers was not as intense as that of the ferrite. A dominant $⟨ 001 ⟩$ ⫽ND fibre, embedding strong Cube ${001} ⟨ 100 ⟩$ , was calculated for ferrite on the layer away from the bottom while the Goss ${011} ⟨ 100 ⟩$ appeared in the layer near the building substrate due to the considerable epitaxially developed grains. The less intensified multi-component texture of austenite at the layer near the substrate changed to $⟨ 011 ⟩$ ⫽ND fibre adorned by Rotated-Goss and Goss components at the upper layers where an incomplete fibre ${001} ⟨ u v w ⟩$ with a major Rotated-Cube was also partially inherited from the parent phase. The inter-phase boundaries obeying Kurdjumov-Sachs orientation relationship were predominantly formed at all layers. A slight increase of Σ3 coincidence site lattice interfaces was observed in austenite across the build direction. The possible mechanical anisotropy was depressed due to complex and multi-component transformation texture of the austenite. The material showed brittleness corresponding to significantly high tensile strength and low impact toughness.

Keywords: Directed laser deposition; Mechanical properties; Microstructure; Super-duplex stainless steels; Texture.