NIST logo
*

Materials Standards for Additive Manufacturing

Summary:

This project provides the measurement science for the additive manufacturing industry to measure material properties in a standardized way.  Determining the properties of the powder used for metal-based additive manufacturing, as well as the resulting bulk metal material, is a necessary condition for industry to be able to confidently select powder and produce consistent parts with known and predictable properties.

Description:

Objective:

By 2014, develop and deliver enhanced measurement techniques that support new, standardized methods for quantifying the material properties of both the powders used for additive manufacturing and the resulting manufactured products.

What is the new technical idea?

Currently, the additive manufacturing (AM) industry does not have the confidence, and is unable to rigorously verify, that nominally identical metal powders used in AM are in fact identical, resulting in unconfirmed powder properties.  This lack of confidence in material properties is also true for parts produced by AM.  The new idea is to develop enhanced material characterization test methods for the raw powder materials used in additive manufacturing as well as the final products fabricated by the process. Current test methods used for the determination of properties of materials made through conventional processes may not be suitable for materials made through additive manufacturing techniques. This is due, in part, to the anisotropic build patterns inherent to the layer-wise nature of additive manufacturing processes, but also to the quality and characteristics of the powder material used in the additive process. The powder batch could consist of an assortment of all virgin, unprocessed particles, a collection of reused particles that have already been subjected to the build environment, or a mixture of both. Another challenge to material property characterization of parts made via additive manufacturing processes is the fact that each AM equipment vendor makes available their own, proprietary set of powders which are to be used in their specific machines. Therefore, if a user purchases Ti-6-4 powder from one OEM and additional Ti-6-4 powder from a different OEM, there is no guarantee that the two batches of powder are identical, nor is it assured that parts made with the two different powders will have the same material properties.

The adoption of parts made via AM processes into mission critical applications such as aerospace engine components is hampered by a lack of consensus material properties for AM part materials, which are required for many procurement specifications.  Industrial round-robin testing, which includes both the fabrication and mechanical property measurements of test specimens, is a required step for developing consensus properties of AM part materials to be accepted into authoritative material databases.

What is the research plan?

The research plan is to first assess the current state-of-the-art testing methods for determining properties of both bulk metal materials and raw metal powder, including those methods used in powder metallurgy. These methods may include mechanical testing (including indentation and fracture testing to determine tensile strength), non-destructive techniques (to determine porosity and modulus), and X-ray diffraction (to determine powder composition).  For powder characterization measurements of particle homogeneity, size distribution and morphology will also be examined.  These powder characterization methods will leverage the current expertise and instrumentation in the IMS Shape Metrology project, as well as that in the EL Materials and Structural Systems Division.  These methods will then be evaluated and enhanced for use on additively manufactured parts and raw additive powder. NIST’s new Direct Metal Laser Sintering (DMLS) machine will be utilized to make parts, and these new methods will be rigorously implemented. Using these enhanced methods, the sensitivity of part material properties to variations in initial powder properties will be determined.  This is a critical step necessary for the production of AM parts with consistent properties.

The project will also coordinate an industry round-robin testing study of processed-part material properties for a selected AM material and AM process.  This will be the first step for acceptance of that material into an authoritative material database.  The round robin will leverage existing industrial groups that have interest in this type of testing.

This project will provide the technical foundation and required leadership necessary to develop new consensus-based standards.  This will be done via ASTM Committee F42 on Additive Manufacturing Technologies and the newly formed ISO TC261 on Additive Manufacturing.

Major Accomplishments:

Recent Results: 
  • Output: EL staff provided technical comments and feedback on ASTM F42 work item WK30522 - New Standard Additive Manufacturing Titanium-6 Aluminum-4 Vanadium with Powder Bed Process, which became ASTM Standard F2924.
  • Output: Completed all training requirements for running EOS AM system.
  • Output: Completed FY12 Project Hazard Assessment.
  • Output: Completed NISTIR 7847, assessing current state-of-the-art methods for material property testing of bulk metal materials. (Slotwinski, Cooke, Moylan.)
  • Output: Completed NISTIR XXXX assessing current state-of-the-art methods for characterizing metal powder.  (Slotwinski, Cooke.)
  • Output: Determined the applicability of current state-of-the-art methods assessed in Q1 and Q2 for AM parts and AM powder and document conclusions in group report. (Slotwinski, Cooke, Moylan.)
  • Outcome: Project staff joined ASTM F42 and became task group lead in F42.01 Test Methods sub-committee.
  • Output: Initiated powder sampling study to determine both batch-to-batch variability, and effects of multiple builds (e.g., build chamber exposure) on powder properties.  This study applies what has been learned in powder sampling techniques.
  • Output: In collaboration with NIST Metallurgy Division, initiated materials study to determine both the mechanical properties of tensile bars made via AM and the degree of anisotropy in the AM process, as well as the uniformity of the build process as a function of position in the build chamber.  Preliminary results show that there is little variability across the build chamber.  The initial tensile tests measured material strengths that are generally in agreement with vendor-supplied data, but have stress-strain behavior that is atypical for similar, conventionally made material.
  • Output: Established technical collaborations with NIST Metallurgy Division, Morris Technologies (the leading domestic producer of metal parts made with AM,) and Lawrence Livermore National Laboratory.
  • Output: Became part of organizing committee for 2012 National Summit on Additive Manufacturing.
 In addition, there are several on-going activities that will also be completed by the end of FY12:
  • Output: In collaboration with industry, complete plans and procedures for conducting and analyzing results of industry round robin for standard material property data and initiate round robin testing (Jurrens, Slotwinski)
  • Output: Based on Q2 and Q3 results, devise and submit draft ASTM F42 powder characterization standard. (Slotwinski, Cooke.)
  • Output: Based on available round robin results, prepare initial report on design allowable material properties (Slotwinski, Jurrens).
Standards and Codes:

Currently there is only one consensus-based standard in this area (ASTM F2924 Standard Specification for Additive Manufacturing Titanium-6 Aluminum-4 Vanadium with Powder Bed Fusion) except for standards pertaining to terminology and data file formats.  This project, in conjunction with the Fundamental Measurement Science for Additive Processes project, will provide the technical foundation and required leadership necessary to develop new consensus-based standards for metal AM powder characterization and mechanical test methods for AM parts.  This will be done via ASTM Committee F42 on Additive Manufacturing Technologies and the newly formed ISO TC261 on Additive Manufacturing.

Metal powder, and resulting metal parts (insert, paperclip is for scale) made from metal additive manufacturing process
Metal powder, and resulting metal parts made from metal additive manufacturing process

Start Date:

October 1, 2011

Lead Organizational Unit:

el
Contact

General Information:

John Slotwinski
301 975 2171 Telephone

100 Bureau Drive, M/S 8220
Gaithersburg, MD 20899-8220