Abstract
Developments in additive manufacturing technology are serving to expand the potential applications. Critical developments are required in the supporting areas of measurement and in process inspection to achieve this. CM247LC is a nickel superalloy that is of interest for use in aerospace and civil power plants. However, it is difficult to process via selective laser melting (SLM) as it suffers from cracking during rapid cooling and solidification. This limits the viability of CM247LC parts created using SLM. To quantify part integrity, spatially resolved acoustic spectroscopy (SRAS) has been identified as a viable non-destructive evaluation technique. In this study, a combination of optical microscopy and SRAS was used to identify and classify the surface defects present in SLM-produced parts. By analysing the datasets and scan trajectories, it is possible to correlate morphological information with process parameters. Image processing was used to quantify porosity and cracking for bulk density measurement. Analysis of surface acoustic wave data showed that an error in manufacture in the form of an overscan occurred. Comparing areas affected by overscan with a bulk material, a change in defect density from 1.17% in the bulk material to 5.32% in the overscan regions was observed, highlighting the need to reduce overscan areas in manufacture.
Highlights
Owing to the increasing interest in using additive manufacturing (AM) in high-value industries, there is a drive to employ novel materials in AM processes that yield parts with tailored properties [1,2]
It has been shown that microstructure information gained through Electron backscatter diffraction (EBSD) can differentiate between skin scan and bulk scan areas [20], and that, under certain process parameters, grains form with a high aspect ratio in the Z-axis, yielding very fine grains in the X–Y section [21]
Analysing the layer integrity is useful for assessing the impact of AM process parameters; in this case, the hatching pattern and its rotation
Summary
Owing to the increasing interest in using additive manufacturing (AM) in high-value industries (i.e. aerospace, medical, tooling), there is a drive to employ novel materials in AM processes that yield parts with tailored properties [1,2]. It exhibits poor weldability due to a high content of the γ -phase forming elements aluminium and titanium Research conducted on this superalloy for use in SLM has attempted to reduce cracking by implementing ‘island’ scanning techniques [17]. Destructive interrogation methods to measure microstructure are regularly used for parts created using traditional manufacturing techniques (e.g. forging or casting), and AM parts will be required to undergo the same interrogation for use in service Methods such as EBSD and X-ray micro-computed tomography have been used to evaluate AM-produced parts destructively in order to gain statistical information about process parameters and feed materials [19]. Since the grain sizes of AM parts are expected to be much smaller than the effective resolution of SRAS, the acoustic scans reveal microstructural texture information
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