Process-Structure-Properties-Performance Modeling for Selective Laser Melting

Abstract

Selective laser melting (SLM) is a promising manufacturing technique where the part design, from performance and properties process control and alloying, can be accelerated with integrated computational materials engineering (ICME). This paper demonstrates a process-structure-properties-performance modeling framework for SLM. For powder-bed scale melt pool modeling, we present a diffuse-interface multiphase computational fluid dynamics model which couples Navier-Stokes, Cahn-Hilliard, and heat-transfer equations. A computationally efficient large-scale heat-transfer model is used to describe the temperature evolution in larger volumes. Phase field modeling is used to demonstrate how epitaxial growth of Ti-6-4 can be interrupted with inoculants to obtain an equiaxed polycrystalline structure. These structures are enriched with a synthetic lath martensite substructure, and their micromechanical response are investigated with a crystal plasticity model. The fatigue performance of these structures are analyzed, with spherical porelike defects and high-aspect-ratio cracklike defects incorporated, and a cycle-amplitude fatigue graph is produced to quantify the fatigue behavior of the structures. The simulated fatigue life presents trends consistent with the literature in terms of high cycle and low cycle fatigue, and the role of defects in dominating the respective performance of the produced SLM structures. The proposed ICME workflow emphasizes the possibilities arising from the vast design space exploitable with respect to manufacturing systems, powders, respective alloy chemistries, and microstructures. By digitalizing the whole workflow and enabling a thorough and detailed virtual evaluation of the causal relationships, the promise of product-targeted materials and solutions for metal additive manufacturing becomes closer to practical engineering application.to be modified to maintain similar properties achieved with traditional techniques such as casting or wrought parts. Compared to traditional manufacturing methods, due to local powder fusion in rapid solidification conditions and solid-state heat cycling, the resulting microstructures present unique features such as metastable phases, smaller scale microsegregation, formation of unexpected secondary phases, spherical or high-aspect-ratio pores, oxide inclusions, microstructural residual stresses, melt pool boundaries, grains with complex morphology, and strong texture.The aforementioned structural features in SLM lead to properties and performance that are unexpected [1]. For example, stainless steel 316L can achieve remarkably high hardness and ductility [2] but has a susceptibility to pitting corrosion [3]; Inconel 625 nickel superalloy contains detrimental intermetallic and carbide phases [4]; Ti-6-4 tends to produce hard needlelike α martensite which leads to high hardness but low ductility; tool steels are extremely difficult to fabricate with SLM due to their complex metallurgy, including a tendency to form brittle martensite and high volume fractions of ...

Ongoing Challenges of Laser-Based Powder Bed Fusion Processing of Al Alloys and Potential Solutions from the Literature—A Review

“…Finally, a body of literature has attempted to overcome the challenge to rapidly identify the adequate parameters by combining simulations and experiments to obtain reliable data that can help optimise the production process [ 67 , 68 , 69 , 70 ]. Among others, Letenneur et al [ 69 ] evaluated the melt pool dimensions through an analytical model of a thermal field.…”

Processing metallic materials far from equilibrium

“…They outline a field that draws much of its appeal to the processing-structure paradigm of materials science. For example, in their article in this issue, Pinomaa et al 26 focus on solute trapping in rapid solidification (Figure 1[IV]) and its impact on solidification morphology and the emergent length scales. They introduce the phenomenological theories of solute trapping, which generally prescribe a velocity-dependent partition coefficient k(V) (i.e., the ratio of the solid composition to the liquid composition at the interface), as well as a velocity-dependent interface temperature T(V).…”

Advanced Simulation Technologies of Metallurgical Processing

“…Equally or even more important are processes on a micro-scale in the rapidly growing field of additive manufacturing, for which the modelling of process-structure-properties-performance is a key loop [8]. Again, additive manufacturing underpins both the multi-physics behavior and multi-scale aspects, because the grain structure after solidification determines the performance such as mechanical strength to a large extent and depends heavily on process conditions such as laser speed, power or hatch size [7][8][9][10][11][12].…”

“…Equally or even more important are processes on a micro-scale in the rapidly growing field of additive manufacturing, for which the modelling of process-structure-properties-performance is a key loop [8]. Again, additive manufacturing underpins both the multi-physics behavior and multi-scale aspects, because the grain structure after solidification determines the performance such as mechanical strength to a large extent and depends heavily on process conditions such as laser speed, power or hatch size [7][8][9][10][11][12]. Solidification was also addressed by a volume-averaged approach for multiphase flow during alloy solidification, indicating that a full 3D calculation with the multiphase volume-averaged solidification will be available in the not too far future due to the development in computer power.…”