ICMCTF 2022 Session B1-1-ThM: PVD Coatings and Technologies I

Boron carbide is a material of interest as an ablative layer for inertial confinement fusion (ICF) applications due to its robust physical properties and uniform amorphous structure. However, growing boron carbide films to thicknesses of >50 μm, as needed for ICF, presents many challenges. Our approach to the optimization of two main process parameters (the target-to-substrate distance and Ar gas pressure) for the deposition of boron carbide coatings by RF magnetron sputtering is based on a combination of film characterization, plasma diagnostics, and modeling. Monte Carlo simulations of ballistic sputtering and gas-phase atomic transport are benchmarked by selected measurements of the deposition rate, residual film stress, and plasma parameters monitored with an electrostatic probe. We describe results of this study of parameter space and ultimately demonstrate the deposition of >50 μm-thick boron carbide coatings with close-to-zero residual stress.

This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.

Physical Vapor Deposition (PVD) technologies offer a suite of methods for surface engineering, where the broad range controls of the deposited flux chemical composition, density, ionization state and energy allow for the growth of wear reducing materials with complex compositions and structures tailored for an adaptive behavior in variable environments and temperatures.For example, the hybridization of magnetron sputtering and pulsed laser deposition had led possibility to embed transition metal dichalcogenides into hard ceramic matrices which had open a range of adaptive coating capable to operate over the broad range of environment humidity and temperature by self-changing the contact surface chemistry and structure in response to the environment change. The hybrid processes for the formation of adaptive wear protective coatings were further expanded to include combinations of PVD methods with other methods, e.g. laser texturing and electro-spark deposition, had led to additional avenues for realization of robust wear protective coatings with adaptive behavior to operate under high contact loads and speeds.The presentation reviews developments of adaptive wear protective coatings produced with hybrid PVD methods and places perspectives for future opportunities.

Rotating cylindrical magnetrons have several important benefits in comparison with widely used planar magnetrons, making them interesting for large-scale industrial applications. Due to their rotation, target erosion is uniform that results in a much higher target utilization (70% or more) and a high stability during reactive sputtering processes. Moreover, better cooling efficiency allows one to use higher power densities and, consequently, higher deposition rates can be achieved. This makes cylindrical magnetron sputtering (CMS) well adapted for HiPIMS.

In the present work, we investigated the use of CMS for the fabrication of Ti_0.5Al_0.5N as a model hard coating extensively used for the protection against harsh environments such as those seen in aerospace and manufacturing. We studied the effect of pulsed-DC and HiPIMS deposition conditions (frequency of 0.91 kHz, duty cycle of 91% and 9.1%, respectively) on the microstructure, mechanical properties, residual stress and stress depth profiles. In addition, in situ real-time plasma monitoring by optical emission spectroscopy (OES) was applied for the study of the process and of the film growth conditions.

By applying the substrate bias, the coating hardness increased from 20 GPa (no bias) up to 30 GPa for a bias of -60 V without any additional heating. This increase in hardness is in good correlation with the increase in compressive stress from -0.9 GPa to -5.5 GPa and corresponding decrease in the grain size (from 16 nm to 9 nm). The stress depth profiles clearly show a steep gradient in compressive stress increasing from the substrate interface towards to the coating surface.

Substrate heating results in further enhancement of the mechanical properties, accompanied by a considerably lower compressive stress and its gradient. Consequently, when combining substrate heating with substrate biasing, hard TiAlN coatings with even lower compressive stress can be produced (-2.3 GPa).

The results clearly show that the substrate bias and heating can effectively be used to tune the mechanical properties and residual stress and stress depth profiles of TiAlN coatings.

Transition metal carbides are known to feature high thermal and mechanic stability as well as high melting points, sometimes above 3500 K, and can be regarded as ultra-high temperature ceramics (UHTC). The huge downsides to those materials is the high inherent brittleness.

Superlattice architecture describes the alternation of coherently grown nanolayers of two or more materials. By creating such superlattices, optical, magnetic, electronic, tribological, or mechanical properties can be influenced. The hardness but also the toughness of superlattice materials can be significantly higher than their monolithically grown components.

Therefore, we developed superlattice structures of selected transition metal carbides combined with VC as well as performed bilayer period variations between 2 and 50 nm.

The selected carbide combinations are based on density functional theory simulations, which revealed VC containing films as most promising candidates to have an improved toughness behavior due to the superlattice structure.

All coatings are developed via DC magnetron sputtering using the respective ceramic targets. Their characterization includes X-ray diffraction, scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, elastic recoil detection analysis, nanoindentation and in-situ micromechanical investigations.

Owing to their amorphous structure, metallic glasses (MGs) have emerged as a new class of materials with remarkable properties compared with their crystalline counterpart. Using physical vapor deposition methods such as sputtering, MGs can be prepared in the form of thin film metallic glasses (TFMGs). Thus, the microstructural control inherent to the sputtering process can be exploited to tailor the properties of TFMGs. Meanwhile, laser irradiation is a well-established technique for surface functionalization, allowing the generation of ripples known as laser-induced periodic surface structures (LIPSS).However, a lack exists on the laser-induced surface functionalization of MGs, most of the studies are focused on the laser irradiation-crystalline material interaction.