Material Development for EBM: Ferrium C64, Part 1

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On August 1, 2017, Posted by , In Material Development,Research & Development, With No Comments

Ferrium C64 powder from Carpenter Technology

At Addaero we pride ourselves on providing flexible solutions to our customers.  For many additive manufacturing projects, this means using standard materials like Ti6Al4V to produce production hardware.  In the case of Ti6Al4V the OEM provides the machine software, also known as process themes, to manufacture parts out of this material.  For new materials like Ferrium C64, process themes do not exist and must be developed.   Through a series of blogs in the coming weeks we’ll look at one such project, documenting Addaero’s development of Ferrium C64 for the EBM (Electron Beam Melting) process. This week’s blog will introduce the material, equipment and the first step in the material development process.

Material:

Ferrium C64 is a high quality carburizing steel developed by QuesTek Innovations LLC and manufactured and supplied by Carpenter Technology (the datasheet can be found here). The alloy is known for providing high grade core strength and surface hardness, making it ideal for aerospace gear applications.  The material used in this research project was gas-atomized and had a size distribution of 45-150 microns.

Equipment:

The material development was performed in Addaero’s Arcam A2X EBM system, which was designed with high temperature alloys in mind.  A 150mm start plate was used throughout the development process.

Arcam A2X Build Table – Ferrium C64 Powder Loaded in Machine

Technical Approach:

The EBM process is controlled by multiple variables including layer height, scan strategy and process temperatures.  To develop a new material, these variables must be set and fine-tuned to find a combination that will result in fully dense material which can be supported to allow for the complex geometries common in additive manufacturing.

Each layer in the EBM process includes three steps: Preheat, Melt and Wafer (Supports). The preheat step loosely sinters the powder on the bed, improving the conductivity of the powder, increasing the structural support of the part within the build and preparing the bed for the subsequent melt step.  During the melt step, the electron beam melts the areas of the layer identified by the computer model using the process theme selected by the operator.  Finally, a wafer step is performed where support material is melted to support the part and draw heat away from the melt surfaces.  Themes unique to Ferrium C64 will be developed for each of these steps.  Prior to starting development of the preheat, theme tests are run to determine the flowability, density and other properties of the powder.

Process Tests – Preheat Theme:

  1. Smoke and Sinter Test:  In the EBM process, a ‘smoke’ event occurs when powder particles on the bed become oppositely charged, causing the powder around these particles to become excited and fill the build area with loose powder.  Process themes should be developed to mitigate the occurrence of smoke events.  This can be done by adjusting preheat parameters including the beam speed, current, iterations and focus offset the beam.  Initial trials are used to find an operating window of parameters where the material does not ‘smoke’.  These trials are run at room temperature to test the parameters in the most difficult conditions possible.  We’ve included some images below to better illustrate the Smoke and Sinter Test.  In this instance, a test matrix made up of 7 different variables attempts to identify a preheat setting that would allow the powder to sinter but not smoke.

Smoke and Sinter Test

 

  1. Start Plate Heating Test:  The goal of this test is to determine the start temperature which facilitates the powder sintering below the plate and informs us on the process operating temperature for Ferrium C64.  Highlighted in the pictures below, a build plate was inserted into the machine and the plate was pre-heated and held at temperature. Trials at varying temperatures were run until a suffiicent sintered block was observed under the start plate. The powder underneath needed to be firm enough to hold the plate but loose enough to be blasted away in the PRS and recycled.

Start Plate Heating Test

 

Next Steps:

Following the development of a pre-heat and start plate theme, we will begin trials to melt the Ferrium C64 material.  In our next blog, we will go into the DOE (Design of Experiments) builds used to determine the optimal melt parameters and move towards printing the first parts made of EBM Ferrium C64.

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