New Test Method for Additive Manufacturing -- Measurement of grain size distribution in additively manufacture materials
1. Scope
The existing standards related to grain measurements such as ASTM E112, E930, E1181, and E1382 will be studied to determine the most realistic method with reported low scattering results. This information, combined with inputs from the AM industry on measurement methodology, attributes, and relationships will be leveraged to down select a recommended grain size measurement methodology. To demonstrate the efficacy of the selected measuring methodology, a round-robin test will be carried out on four different material systems, among different laboratories and measurement systems. Samples will be from heat-treated laser powder bed fusion AM builds. To account for the human errors, the intra-laboratory analysis will be conducted. Determination of the scattering data ranges in the measured values as a function of measurement techniques of a range of representative microstructures for different materials will be statistically analyzed. The statistical analysis results will be used to develop a protocol to enable higher-confidence, low-scatter measurements for grain size and distributions. Based on the above, a methodology for the measurement of grain size distribution in AM materials will be developed.
There is a general requirement for R&D to improve the guidelines for the measurement of
grain size distribution in the case of AM materials to ensure robust and consistent material
characterization. The properties of manufactured components are significantly dependent on
the grain size and size distribution of the underlying microstructures.
There is an inherent heterogeneity in the microstructure of metallic alloys made by AM that
requires a standard for identification and quantification of the spatial variability of various
microstructure features. Gaps identified by the Additive Manufacturing Standardization
Collaborative (AMSC) include:
ASTM E112 - Does not acount for heterogeneous microstructure
ASTM E930 - Does not account for spatial location of ALA grain and the alignment relative to the build direction
ASTM E1181 - It may partially work for TiAl alloys but not for the gradient from surface to the core of AM parts
