Microstructure Development in Dual Phase Stainless Steel Parts Made by Laser Bed Powder Fusion
Thomas F. Murphy, FAPMI, Hoeganaes Corporation
Dual phase stainless steel alloys are characterized by a ferrite-martensite microstructure that is usually formed through a secondary heat treatment after creation of the part. The heat treatment requires reheating the part into the ferrite-austenite region of the phase diagram, creating partitioning of the alloying elements into the two phases. This is followed by rapid cooling, which transforms the austenite at high temperature to martensite. It will be demonstrated that the as-built parts made by laser bed powder fusion do not have the dual phase microstructure because, when building parts by heating with the laser, the cooling rate experienced by the parts in the powder bed is too rapid for the alloy partitioning to occur and consequently, the dual phase microstructure is not transformed. In order to create the desired two-phase microstructure, experiments are made with several heat treatments, which result in variations in the proportions of the ferrite and martensite phases after cooling. The resulting differences in microstructure and alloy distribution are investigated with the corresponding changes in physical and mechanical properties caused by variations in heat treatment temperature.
Highlights of Copper Development for Binder Jet: Porosity Control for Metal Filters, Nanoparticle Enhancements, Isostatic Pressing and Oxidation Control
Patrick Dougherty, ExOne
Binder jet additive manufacturing (AM) has a number of unique advantages compared to other AM techniques including more traditional microstructure , ability to handle a wider range of materials, and faster throughput which leads to much lower cost at production volumes. Pure copper is a high-value material due to its thermal and electrical conductivities, and recently also due to its antiviral properties in light of the COVID-19 virus. While the sintering process inherent to binder jet should make processing easier than with other AM techniques like EBM and DMLS, copper has its own unique challenges in the green state which have so far prevented fully dense binder jetting of copper. In this work, several techniques will be presented for enhancing the density and material properties of binder jet copper, as well as an application in which the unique aspects of copper can be to create a partially sintered, porous metal filter for airborne particulates.
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