Digital image correlation for microstructural analysis of deformation pattern in additively manufactured 316L thin walls

Abstract

In additive manufacturing, the process parameters have a direct impact on the microstructure of the material and consequently on the mechanical properties of the manufactured parts. The purpose of this paper is to explore this relation by characterizing the local microstructural response via in situ tensile test under a scanning electron microscope (SEM) combined with high resolution digital image correlation (HR-DIC) and electron backscatter diffraction (EBSD) maps. The specimens under scrutiny were extracted from bidirectionally-printed single-track thickness 316L stainless steel walls built by directed energy deposition. The morphologic and crystallographic textures of the grains were characterized by statistical analysis and associated with the particular heat flow pattern of the process. Grains were sorted according to their size into large columnar grains located within the printed layer and small equiaxed grains located at the interfaces between successive layers. In situ tensile experiments were performed with a loading direction either perpendicular or along the printing direction and exhibit different mechanisms of deformation. A statistical analysis of the average deformation per grain indicates that for a tensile loading along the building direction, small grains deform less than the large ones. In addition, HR-DIC combined with EBSD maps showed strain localization situated at the interface between layers in the absence of small grains either individual or in clusters. For tensile loads along the printing direction, the strain localization was present

High resolution digital image correlation for microstructural strain analysis of a stainless steel repaired by Directed Energy Deposition

“…Eventually, interlayers become regions with the highest local strain as displayed in Figure 3(c). For a similar loading on printed specimens, [4] equally observed localisation at interlayers and [11] reported that interlayers are a crack initiation area.…”

“…The SS316L powder used had a particle size between 45 − 90 µm. Further discussions concerning these process parameters are available in [4] .…”

“…Ex situ monotonic tensile tests were first performed for the three specimen configurations in order to determine the tensile properties. Then, a RS was prepared with a two-scale gold pattern deposited by lithography on its surface and loaded with a tensile machine inside a scanning electron microscope (SEM) (see [4] for additional details). A "micro grid" (2.2 mm × 1 mm) with a pitch of 3 µm was encompassing the interface and is used for local strain measurements.…”

Influence of interlayer dwell time on the microstructure of Inconel 718 Laser Cladded components

“…1. They consist of a thin plate acting as the substrate on top of which a single-track wall wall with a similar thickness is deposited by Laser Cladding as proposed initially in [24,25].…”

Plastic strain localization induced by microstructural gradient in laser cladding repaired structures

“…Other studies use DIC at a smaller scale to highlight spatial distribution of strain within grains [31][32][33][34]. A combination of these techniques were used in [35] to investigate strain localization pattern in additively manufactured 316 stainless steel and explain the observed macroscopic anisotropy of the material.…”