Additive manufacturing is a production technique that builds a component layer by layer, to the specification of a 3D model. This enables intricate parts to be made at a small scale without the need for large investment in rarely used manufacturing equipment.
However, using this manufacturing process affects the texture of metal alloys in a different way to conventional techniques. As the mechanical properties of a material are very dependent on this internal texture, it's important to understand the details of how the method of production influences what's happening inside the alloy.
One type of additive manufacturing is laser powder bed fusion (LPBF), where an initial powder is applied to a substrate and then a laser melts this powder into a given shape. There are many different parameters that can be controlled, each influencing the microstructure and texture of the end component.
In this study, published in Materials & Design, a Canadian research collaboration including Siemens Energy and scientists from the University of Western Ontario used neutron diffraction on Engin-X to understand the microstructural changes caused by altering different parameters during this type of additive manufacturing. They focussed on components made from a nickel-based superalloy known as Hastelloy‑X, which is used to make gas turbines.
As neutrons can penetrate up to several centimetres into these materials, they are an ideal tool to use to study their internal structure. The specialised setup on the Engin-X beamline meant that the researchers were able to study the internal structure at the same time as compressing them, to test how they would behave in a real-world scenario.
By studying samples made using a variety of laser powers and scanning speeds, the team were able to determine that both of these parameters influence the microstructure, with increasing laser power inducing a preferred orientation of the grains in the alloy.
This initial study confirms that it is crucial to control the individual parameters of this production method, as this will determine the structure, and therefore properties, of the end component.
“The laser powder-bed fusion (LPBF) additive manufacturing process produces an intense temperature gradient within the fabricated components as a result of the fast thermal and cooling cycles that occur during the process. Therefore, residual stresses and deformations are inevitable in the manufactured parts. In order to minimize deformation, residual stresses must be measured and analysed to optimise the LPBF process parameters. Due to the capabilities available at ENGIN-X, we were able to measure residual stresses precisely."
Ali Bonakdar - Siemens Energy
The full paper can be found online at DOI: 10.1016/j.matdes.2022.111030