AM Part Qualification by Meltpool, Material, and Grain Boundary Engineering

Abstract

Additive Manufacturing (AM) achieves significant cost savings and enables complex geometries that are otherwise impossible to fabricate using conventional manufacturing processes. 3D-printed parts produced by Laser Power Bed Fusion (LPBF) need to be qualified and may suffer from: (i) defects (micro, macro), (ii) net-shape warpage, (iii) high residual stresses, (iv) surface roughness, (v) inconsistent density, (vi) anisotropic microstructures, (vii) scatter in mechanical properties, and (vii) poor fracture and fatigue performance. AM defects (e.g., unfused powder, balling, humping, and keyholing) are affected by variations in power and speed as well as hatch spacing that result in pores, thermal cracks, rough surface finish and warping. The objective is to minimize the trial-and-error prints using a building block qualification strategy. An Integrated Computational and Material Engineering (ICME) tool is proposed to perform: 1) melt pool engineering (MPE) and predict the process thermal map and density map, as well as temperature time history to establish print road map, 2) Grain boundary engineering (GBE) to perform micro scale material modeling of alloy composition and predict the grain size, mechanical strength, fracture, fatigue crack growth properties due to defects and precipitates; and 3) thermal-structural analysis incorporating MPE and GBE to evaluate part quality. This includes: i) void prediction at the coupon level, ii) print error macro void calculations at element level along with scatter in material strength and allowables, iii) prediction of fracture control plan, iv) computing part distortion due to different print strategies, and v) net shape and warpage measurements.