Decoupling strength-damage trade-offs in additively manufactured alloys via engineered strain gradient

doi:10.1007/s10483-026-3386-8

Abstract

Abstract:

The strength and damage tolerance of additively manufactured (AM) alloys are significantly influenced by their heterogeneous microstructures. However, establishing quantitative relationships between these microstructural characteristics and the resulting mechanical properties remains a challenge. Here, a microstructure-based mechanical model is established based on the heterogeneous grain distribution within the melt pool, with particular emphasis on the strain gradient effect arising from the deformation incompatibility between distinct grain regions. The strengthening mechanisms and local deformation response of AM alloys are elucidated with the finite element method (FEM). The strain gradient effect generated by the deformation incompatibility between the columnar and equiaxed grain regions enhances the local stress near the equiaxed-columnar interface, which is an important reason for the overall work hardening. Concurrently, the local stress concentration makes it easier to reach the critical stress for microcrack nucleation at the interface, leading to failure and a lack of synergy between the strength and damage tolerance. The prediction of the crack initiation location based on the simulation results is consistent with the previous experiments. By further quantitatively predicting the comprehensive effects of melt pool size on strength, strain hardening, and damage rate, small-melt-pool structures produce high strength, but microcracks originate early, whereas large-melt-pool structures have weak strengthening effects but fast damage evolution in the later stages of deformation. This study provides a pathway to predict the optimal melt pool size for achieving superior combinations of strength and damage tolerance in AM alloys.

Key words: additive manufacturing, strain gradient, strain hardening, damage tolerance, microcrack nucleation

2010 MSC Number:

Jing PENG, Hui FENG, Hong WU, Jia LI, Qihong FANG. Decoupling strength-damage trade-offs in additively manufactured alloys via engineered strain gradient. Applied Mathematics and Mechanics (English Edition), 2026, 47(5): 1041-1064.

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URL: https://www.amm.shu.edu.cn/EN/10.1007/s10483-026-3386-8

https://www.amm.shu.edu.cn/EN/Y2026/V47/I5/1041

Figures/Tables 16

Fig. 1

Fig. 2

Table 1

Constitutive parameters of AM-fabricated CuNiSn alloys[33,35,43]"

Parameter	Symbol	Equiaxed crystal	Columnar crystal
Shear modulus/GPa	G	58	58
Poisson’s ratio	ν	0.326	0.326
Taylor parameter	M	3.06	3.06
Burgers vector/nm	b	0.256	0.256
Hall-Petch constant/(MPa·m^1/2)	k_HP	356	356
Taylor constant	α	0.3	0.3
Geometric factor	k₁	0.1	0.1
Proportionality factor	k₂	0.035	0.038
Dynamic recovery constant	k₃	8	4.3
Reference strain rate/s^-1	$ε ˙ 0$	1	1
Rate sensitivity coefficient	m	20	20
Dynamic recovery parameter	n₀	21.26	21.26
Initial dislocation density/μm^-2	ρ	280	200
Reference grain size	d_def	0.9	0.8
Grain size/μm	d	5	22
Effective radius of GND/μm	R	1	1
Average radius of nanoprecipitate/nm	d_p	72	72
Volume fraction of nanoprecipitate	f_p	2.24	2.24

Table 1

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8

Fig. 9

Fig. 10

Fig. 11

Fig. 12

Fig. 13

Fig. 14

Fig. A1

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