In Situ and Ex Situ Characterization of the Microstructure Formation in Ni-Cr-Si Alloys during Rapid Solidification-Toward Alloy Design for Laser Additive Manufacturing.

Xiaoshuang Li,Dario Ferreira Sanchez,Adriaan B Spierings,Konrad Wegener,Daniel Grolimund,Kai Zweiacker,Christian Leinenbach

doi:10.3390/ma13092192

Abstract

Laser beam-based deposition methods such as laser cladding or additive manufacturing of metals promises improved properties, performance, and reliability of the materials and therefore rely heavily on understanding the relationship between chemical composition, rapid solidification processing conditions, and resulting microstructural features. In this work, the phase formation of four Ni-Cr-Si alloys was studied as a function of cooling rate and chemical composition using a liquid droplet rapid solidification technique. Post mortem x-ray diffraction, scanning electron microscopy, and in situ synchrotron microbeam X-ray diffraction shows the present and evolution of the rapidly solidified microstructures. Furthermore, the obtained results were compared to standard laser deposition tests. In situ microbeam diffraction revealed that due to rapid cooling and an increasing amount of Cr and Si, metastable high-temperature silicides remain in the final microstructure. Due to more sluggish interface kinetics of intermetallic compounds than that of disorder solid solution, an anomalous eutectic structure becomes dominant over the regular lamellar microstructure at high cooling rates. The rapid solidification experiments produced a microstructure similar to the one generated in laser coating thus confirming that this rapid solidification test allows a rapid pre-screening of alloys suitable for laser beam-based processing techniques.

Highlights

Laser-aided manufacturing processes involving deposition of alloy powders on substrates have gained increasing interest in the recent past
The broad peaks are still distinguishable from the background in the 1D profile of Intensity vs. Q spacing pattern seen in Figure 3a for the Ni21Cr11Si alloy
In both the Ni7Cr11Si and the Ni21Cr11Si alloy, peaks associated with two phases simultaneously appeared out of the melt which is an indication of an eutectic reaction

Summary

Introduction

Laser-aided manufacturing processes involving deposition of alloy powders on substrates have gained increasing interest in the recent past. Typical techniques include laser cladding or additive manufacturing (AM) technologies such as laser Direct Metal Deposition (DMD) or Selective. Laser-consolidated parts undergo complex thermal histories including rapid solidification of small material volumes with cooling rates in the range of 103 –104 Ks−1 during cladding or DMD [1,2], and up to 106 –107 K s−1 during SLM [3,4]. The properties–performance relationship of laser-deposited coatings and laser-manufactured parts are determined by the complex interrelationships between the alloy composition, the processing parameters, and the resulting microstructure. The processing parameters in SLM are typically optimized to achieve dense and defect-free parts and are usually determined in a trial-and-error approach based on the Volume Energy Density (VED)

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Results

Discussion

Conclusion