TY - JOUR

T1 - Strengthening control in laser powder bed fusion of austenitic stainless steels via grain boundary engineering

AU - Sabzi, H.E.

AU - Hernandez-Nava, E.

AU - Li, X.-H.

AU - Fu, H.

AU - San-Martín, D.

AU - Rivera-Díaz-del-Castillo, P.E.J.

PY - 2021/12/15

Y1 - 2021/12/15

N2 - A new approach to modelling the microstructure evolution and yield strength in laser powder bed fusion components is introduced. Restoration mechanisms such as discontinuous dynamic recrystallization, continuous dynamic recrystallization, and dynamic recovery were found to be activated during laser powder bed fusion of austenitic stainless steels; these are modelled both via classical Zener-Hollomon and thermostatistical approaches. A mechanism is suggested for the formation of dislocation cells from solidification cells and dendrites, and their further transformation to low-angle grain boundaries to form subgrains. This occurs due to dynamic recovery during laser powder bed fusion. The yield strength is successfully modelled via a Hall–Petch-type relationship in terms of the subgrain size, instead of the actual grain size or the dislocation cell size. The validated Hall–Petch-type equation for austenitic stainless steels provides a guideline for the strengthening of laser powder bed fusion alloys with subgrain refinement, via increasing the low-angle grain boundary fraction (grain boundary engineering). To obtain higher strength, dynamic recovery should be promoted as the main mechanism to induce low-angle grain boundaries. The dependency of yield stress on process parameters and alloy composition is quantitatively described.

AB - A new approach to modelling the microstructure evolution and yield strength in laser powder bed fusion components is introduced. Restoration mechanisms such as discontinuous dynamic recrystallization, continuous dynamic recrystallization, and dynamic recovery were found to be activated during laser powder bed fusion of austenitic stainless steels; these are modelled both via classical Zener-Hollomon and thermostatistical approaches. A mechanism is suggested for the formation of dislocation cells from solidification cells and dendrites, and their further transformation to low-angle grain boundaries to form subgrains. This occurs due to dynamic recovery during laser powder bed fusion. The yield strength is successfully modelled via a Hall–Petch-type relationship in terms of the subgrain size, instead of the actual grain size or the dislocation cell size. The validated Hall–Petch-type equation for austenitic stainless steels provides a guideline for the strengthening of laser powder bed fusion alloys with subgrain refinement, via increasing the low-angle grain boundary fraction (grain boundary engineering). To obtain higher strength, dynamic recovery should be promoted as the main mechanism to induce low-angle grain boundaries. The dependency of yield stress on process parameters and alloy composition is quantitatively described.

KW - Grain refinement

KW - Laser powder bed fusion

KW - Mechanical properties

KW - Microstructure

KW - Stainless steel

KW - Austenite

KW - Austenitic stainless steel

KW - Dynamics

KW - Grain boundaries

KW - Grain size and shape

KW - Recovery

KW - Strengthening (metal)

KW - Yield stress

KW - Dislocation cells

KW - Dynamic recovery

KW - Grain boundary engineering

KW - Hall-petch

KW - Laser powders

KW - Low angle grain boundaries

KW - New approaches

KW - Powder bed

KW - Subgrains

U2 - 10.1016/j.matdes.2021.110246

DO - 10.1016/j.matdes.2021.110246

M3 - Journal article

VL - 212

JO - Materials and Design

JF - Materials and Design

SN - 0261-3069

M1 - 110246

ER -