Pyrometric-Based Melt Pool Monitoring Study of CuCr1Zr Processed Using L-PBF.

Katia Artzt,Joerg Riccius,Martin Siggel,Jan Kleinert,Guillermo Requena,Jan Haubrich

doi:10.3390/ma13204626

Abstract

The potential of in situ melt pool monitoring (MPM) for parameter development and furthering the process understanding in Laser Powder Bed Fusion (LPBF) of CuCr1Zr was investigated. Commercial MPM systems are currently being developed as a quality monitoring tool with the aim of detecting faulty parts already in the build process and, thus, reducing costs in LPBF. A detailed analysis of coupon specimens allowed two processing windows to be established for a suitably dense material at layer thicknesses of 30 µm and 50 µm, which were subsequently evaluated with two complex thermomechanical-fatigue (TMF) panels. Variations due to the location on the build platform were taken into account for the parameter development. Importantly, integrally averaged MPM intensities showed no direct correlation with total porosities, while the robustness of the melting process, impacted strongly by balling, affected the scattering of the MPM response and can thus be assessed. However, the MPM results, similar to material properties such as porosity, cannot be directly transferred from coupon specimens to components due to the influence of the local part geometry and heat transport on the build platform. Different MPM intensity ranges are obtained on cuboids and TMF panels despite similar LPBF parameters. Nonetheless, besides identifying LPBF parameter windows with a stable process, MPM allowed the successful detection of individual defects on the surface and in the bulk of the large demonstrators and appears to be a suitable tool for quality monitoring during fabrication and non-destructive evaluation of the LPBF process.

Highlights

Copper alloys such as CuCr1Zr are used for the inner lining of rocket engine combustion chambers due to their high thermal conductivity and strength
Copper alloys have been processed by electron beam melting (EBM) [3,4], in which larger powder sizes and high layer thicknesses (e.g., Reference [5]) commonly result in structures coarser than those achieved from laser powder bed fusion (LPBF)
Uhlmann et al reported a total porosity of 0.5% in CuCr1Zr for a low laser power of 350 W [11] at a high layer thickness of 50 μm, which we included in our parameter variations

Summary

Introduction

Copper alloys such as CuCr1Zr are used for the inner lining of rocket engine combustion chambers due to their high thermal conductivity and strength. Copper alloys have been processed by electron beam melting (EBM) [3,4], in which larger powder sizes and high layer thicknesses (e.g., Reference [5]) commonly result in structures coarser than those achieved from laser powder bed fusion (LPBF). The LPBF of copper alloys is being explored, leading to major challenges due to the high thermal conductivity of the powder, poor absorption. Densities for LPBF copper alloys achieved with common 200–400 W lasers are inferior to those obtained using EBM; the latter being in the range of 93.7% for Cu-4Sn [8] to

Methods

Results

Conclusion