Columnar grain width control for SS316L via hatch spacing manipulation in laser powder bed fusion

Abstract

This study provides a quantitative way to tailor the grain structure in laser powder bed fusion (LPBF). Square-bottomed columnar grains (SCGs) were developed with a certain width roughly equal to the hatch spacing. The development of SCGs relied on different distinguishable regions, which were identified based on the differences in microstructural features between the melt-pool side and centreline. High lattice rotation accumulated at the melt-pool centreline, leading to grain boundaries forming at the centreline regions. The ultrasonic attenuation measurements and microhardness tests further validated the controllable properties. The findings indicated a novel approach to customise the material property. IMPACT STATEMENTA method to quantitatively control the columnar grain width in laser powder bed fusion was uncovered. The controllable properties were indicated, and the formation mechanism was revealed.

Epitaxial Growth and Stray Grain Control toward Single‐Crystal Metallic Materials by Additive Manufacturing: A Review

“…[55] Also, the effect of PBF process parameters, especially beam scanning strategy, on the resulting epitaxial growth of columnar grains has a profound effect on the epitaxy tendency and grain orientation across layers. [56][57][58] Depending on layer rotation (i.e., 0°, 67°or 90°), [59][60][61][62] point or line (raster) heat source, [63] fraction of remelting ratio (RR), [61,64] or specific hatch pattern [65][66][67] adopted in the scanning strategy, the epitaxial growth continuity of columnar grains can vary significantly. SLE process, as a descendant form of SLS process, has been employed to produce a crack-free, dense SX deposit (CMSX-4 alloy), that is, on top of investment-cast SX substrate of similar chemistry.…”

Microstructural Control of a Multi‐Phase PH Steel Printed with Laser Powder Bed Fusion

“…Recent progress in this field has shown a significant ability to locally control the grain size, shape, and texture, by manipulating the printing strategy in order to tune the direction of the temperature gradients upon cooling. [ 28–33 ] Mukherjee et al. have thoroughly reviewed and outlined the different approaches enabling the control of grain structures, phases, and defects in metal AM parts.…”

“…However, the work to date does not result in significant spatial gradation in mechanical properties nor the ability to generate local microstructures with competing properties (e.g., strong/brittle VS soft/ductile). [ 28,36,39 ]…”

“…However, the work to date does not result in significant spatial gradation in mechanical properties nor the ability to generate local microstructures with competing properties (e.g., strong/brittle VS soft/ductile). [28,36,39] In this manuscript, we propose an alternative approach for local microstructural control in LBPF, based on tailoring of volume fractions in multi-phase alloys. We demonstrate the potential of this approach on 17-4 precipitation hardening (17-4PH) stainless steel (Type 630, or UNS S17400).…”

“…Recent progress in this field has shown a significant ability to locally control the grain size, shape, and texture, by manipulating the printing strategy in order to tune the direction of the temperature gradients upon cooling. [28][29][30][31][32][33] Mukherjee et al have thoroughly reviewed and outlined the different approaches enabling the control of grain structures, phases, and defects in metal AM parts. [34] Most notably, Sofinowski et al have introduced highly controllable layer-wise engineering of grain orientation (LEGO) microstructures, where the crystallographic grain orientation in LPBF 316L steel [35] and Ti-Nb [36] can be locally manipulated with great accuracy, by using the laser scan speed and printing strategy to tune thermal gradients.…”