Laser Powder-Bed Fusion as an Alloy Development Tool: Parameter Selection for In-Situ Alloying Using Elemental Powders.

Leonardo Shoji Aota,Eric Aimé Jägle,Priyanshu Bajaj,Hugo Ricardo Zschommler Sandim

doi:10.3390/ma13183922

Abstract

The design of advanced alloys specifically tailored to additive manufacturing processes is a research field that is attracting ever-increasing attention. Laser powder-bed fusion (LPBF) commonly uses pre-alloyed, fine powders (diameter usually 15–45 µm) to produce fully dense metallic parts. The availability of such fine, pre-alloyed powders reduces the iteration speed of alloy development for LPBF and renders it quite costly. Here, we overcome these drawbacks by performing in-situ alloying in LPBF starting with pure elemental powder mixtures avoiding the use of costly pre-alloyed powders. Pure iron, chromium, and nickel powder mixtures were used to perform in-situ alloying to manufacture 304 L stainless steel cube-shaped samples. Process parameters including scanning speed, laser power, beam diameter, and layer thickness were varied aiming at obtaining a chemically homogeneous alloy. The scientific questions focused on in this work are: which process parameters are required for producing such samples (in part already known in the state of the art), and why are these parameters conducive to homogeneity? Analytical modelling of the melt pool geometry and temperature field suggests that the residence time in the liquid state is the most important parameter controlling the chemical homogeneity of the parts. Results show that in-situ alloying can be successfully employed to enable faster and cost-efficient rapid alloy development.

Highlights

Additive manufacturing (AM), unlike conventional processing methods, is based on the addition and consolidation of small portions of powder feedstock, layer by layer, aimed at producing dense parts with complex shapes [1,2]
We aimed to show that in-situ alloying in Laser Powder Bed Fusion (LPBF) can be successfully employed by choosing suitable process parameters, enabling faster and less cost-intensive alloy development in the future
Dense and chemically homogeneous AISI 304 L steel samples were obtained from in-situ alloying of elemental powders mixtures after process parameter optimization

Summary

Introduction

Additive manufacturing (AM), unlike conventional processing methods, is based on the addition and consolidation of small portions of powder feedstock, layer by layer, aimed at producing dense parts with complex shapes [1,2]. Laser Powder Bed Fusion (LPBF), termed Selective Laser Melting (SLM), is an AM process based on the melting of a thin powder layer [1] under inert gas atmosphere (at atmospheric or reduced pressure) by scanning a high-power laser beam across the powder bed in a pre-defined scanning strategy. Materials 2020, 13, 3922 convection [6,7,8,9] and recoil pressure from the metal vapor above the melt pool [6,7] generated by the laser. Surface roughness, and particle size distribution affect how the laser radiation is absorbed, and how deep the melt pool becomes [10,11,12]. Spherical particles with a smooth surface and Gaussian size distribution are preferred for better powder flowability, resulting in a uniform and more packed powder beds [1,13]

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