Session: 16-02-01: Microstructure II

Paper Number: 167015

Pyrolytic Carbon Formation on Additively Manufactured Inconel 718 for Enhanced Surface Characteristics 

Inconel 718 is a great nickel-based metal alloy used in industries were enhanced material properties often at elevated temperatures is required. Typically, high temperatures are an issue with non-refractory materials, such as aluminum and iron alloys; their properties begin to be unfavorable at such temperatures. Inconel 718’s high strength and excellent corrosion resistance make it a good choice for aerospace and energy applications, such as turbine blades and nuclear reactors. However, the process-born poor surface characteristics of additively manufactured components results in poor surface characteristics of Inconel 718. Surface characteristics for Inconel 718 are crucial to control and understand as to enhance the material’s tribological, mechanical, and thermal performance for a range of applications. Wear reduction, improved creep and fatigue resistance, and corrosion resistance are notable investigated properties of Inconel 718 by improving its surface quality. Usually, additional surface treatment or coating is applied to enhance surface properties and thus improve service life and consistency of the application of products.

In this study, we demonstrate the formation of pyrolytic carbon on Inconel 718 coupons additively manufactured using Laser Powder Bed Fusion (LPBF) and analyze their surface characteristics. The coupons were 3D printed using EOS M290 LPBF system with the recommended optimized process parameters provided by the system: 285W laser power, 960mm/s laser speed, 0.11mm hatch distance, and 40µm layer thickness. After that, about 10 nm layer of carbon formation was achieved through chemical vapor deposition (CVD) at 1000 ^oC for 30 minutes.  The samples (with and without carbon coating) were analyzed using Scanning Electron Microscopy and Raman spectroscopy. The Raman measurements were conducted using a Jasco Raman spectrometer, which enabled the observation of various carbon peaks on the metallic surface. The D-band, G-band, and 2D-band peaks have been clearly identified in a Raman spectrum. Notably, the G-band peak is the most prominent, indicating the hybridization of sp² carbon atoms and reflecting a well-ordered arrangement of these carbon structures. Furthermore, the 2D-band peak is slightly tilted, suggesting that the coated carbon bears a likeness to pyrolytic carbon.

The surface hardness studies on LPBF samples, carbon-coated through CVD, have also been explored. The results show a significant improvement in surface hardness for the pyrolytic carbon coated samples compared to as-built Inconel 718 samples. For a given part location on the powder bed, a sample’s orientation with respect to the recoater blade motion results in different surface roughness due to blade’s interaction with the top edges of different planes; a maximum Vickers’ hardness value of 835.5 HV was achieved for one of the planes. The ease of processing and scalability of the proposed method has great potential for improving tribological properties of metal additive components.

Presenting Author: Jorge Barron Jr University of Texas at Rio Grande Valley

Presenting Author Biography: Enrolled in the University of Texas at Rio Grande Valley, pursuing my Phd in Material Science and Engineering. Trailing research and internship opportunities to further employ myself in additive manufacturing, focusing in Laser-Powder Bed Fusion and Laser-Direct Energy Deposition, and metal alloys.

Authors:

Jorge Barron Jr University of Texas at Rio Grande Valley
Muhammad Shahbaz Rafique University of South Florida
Luis Jimenez University of Texas at Rio Grande Valley
Ali Ashraf University of South Florida
Farid Ahmed University of Texas at Rio Grande Valley