Session: 02-02-02: Characterization of Additively Manufactured Metal Parts

Paper Number: 71777

Start Time: Wednesday, 01:20 PM

71777 - Investigation of Microstructure and Mechanical Properties of Additive Manufactured AISI - 420 Martensitic Steel Developed by Directed Energy Deposition Method 

The traditional way to produce engineering materials having complex alloy systems is to melt the homogeneous raw materials mixes into the liquid, then cool the liquid metal down until it completely solidifies. The solidified alloyed metal can be subjected to a series of processing treatments, including but not limited to reheating, hot forming, transformation, machining, and joining depending on the final geometry and required application in the industrial world. These series of processing steps are necessary to manufacture engineering components. Moreover, the traditional manufacturing approach to produce engineering components can have a high energy cost, high material waste, longer delivery times, and certain geometries may be unattainable. The recent manufacturing developments on additive manufacturing might provide the opportunity to produce complex engineering components, reduced manufacturing costs, and reduced delivery times. Direct Energy Deposition offers great possibilities such as the fabrication of metal components with complex geometries, repair of high-value equipment, development of functionally graded materials, and large-scale additive fabrication or repair. 

This work focuses on the fabrication of AISI 420 stainless steel using DED for the application of the aerospace, automotive, and medical industries. AISI 420 martensitic stainless steel (12.7%Cr, 0.4%C in wt.%) was successfully deposited onto 316L substrate by a Laser Engineered Net Shaping (LENS®) process. The process was carried out in an open atmosphere, thus the center purge of the deposition head was solely responsible for shielding of the additive process.  The relative density of the deposited sample was about 98%, calculated through the Archimedes method. The microstructure, phase composition, and hardness were characterized using scanning electron microscopy, X-ray diffraction, and a micro-Vickers hardness tester, respectively. The cross-sectional examination by electron microscopy and XRD confirms the dual-phase microstructure of martensitic needles in random orientation and approximately 20 wt. % of austenite by Rietveld refinement and quantitative phase analysis. There were no cracks observed throughout the materials.  Preliminary mechanical characterization by micro-Vickers hardness tests shows uniform hardness about 725 (HV) trend across the build. However, The area fraction of porosity as DED manufactured material was found to be 0.4% with the max size of 2µm. There is a large number of processing parameters involved in the DED process such as laser power, travel speed, material feed-rate, beam diameter, hatch spacing, and layer thickness. These parameters affect directly the mechanical properties, thermal gradient, and final solidification structure; therefore, they must be optimized and tuned accurately to achieve high-quality parts. Besides microstructure, the chemical composition of the phases, the mechanical properties, and corrosion resistance of the steel could be affected by the post-heat treatment which is very sensitive. The team investigates to optimize the heat-treating method to improve its mechanical properties.

Presenting Author: Md Mehadi Hassan University of New Mexico

Authors:

Md Mehadi Hassan University of New Mexico
Madhavan Radhakrishnan University of New Mexico
David Otazu University of New Mexico
Tom Lienert Optomec
Osman Anderoglu University of New Mexico