Coating Material Development by Pulsed Laser Deposition for JIS SKD61 Steel Insert Pins Used in Aluminum Casting Industry

A Pulsed Laser Deposition (PLD) technique is a type of physical vapor deposition (PVD) technology. This research is one of a series of PVD studies aimed at determining the best PLD coating that can minimize the damage of steel pins made of SKD61 with a hardness of 48±1 HRc. The study began with the dummy blocks from SKD61 as research samples, followed by PVD-PLD with three coating materials as alternatives: Al/Cr (70:30), Al/Ti1 (50:50), and Al/Ti2 (63:37), all without active gases (N and C). The procedures used to test the research findings were FESEM, SEM, XRF, EDS, Vickers, and Rockwell Microhardness. The experiments were conducted at the BRIN Fotonic Research Center and the PT AHM Laboratory. The PLD process lasted for 10 minutes and employed an Nd: YAG laser with a wavelength of 1064 nm, a Q-switch with a time delay of 180 s, a pulse energy of 70 mJ, and a vacuum pressure of 1.161.35 Torr.Based on the results of the coating study, an AlTi1 coating was found to be the most effective material coating. The coating consisted of amorphous particles with a size range of 10 nm to 20 nm The coating had a thickness of 23 µm, and the surface hardness was measured to be 474-523 mHv for the single-layer coating and 477-501 mHv for the multilayer coating. The materials in both single-layer and multilayer coating samples have the same hardness in ascending order: AlCr, AlTi2, AlTi1, with a Ti concentration rise from 0.7% to 3.7%. The impact of the Ti element is also crucial in increasing hardness, wear resistance, and roughness.

Coating material; Minimize damage; Pin SKD 61; PLD process

    Physical Vapour Deposition – Pulse Laser Deposition ( PVD-PLD ) is a coating process that has been widely used since 1987 to generate superconductive thin films with high-temperature resistance, which are employed in superconductors, medical applications, and electric, magnetic, and protective layers (Bruncko et al., 2019; Duta and Popescu, 2019;  Lorusso et al., 2015; Krebs et al., 2003). It is sensitive to the target condition, pulse energy, wavelength, vacuum process, target lens focus distance, and gas condition (Subramaniam, 2015). A typical PLD process experimental setup includes five key elements: target, substrate, laser, plasma plume, and vacuum condition (Masood, 2014). PLD has been developed in the last 10 years to manufacture crystalline layers for ceramic oxide, nitride films, and metallic multilayers, as well as to synthesize nanotubes, nanopowder, and quantum dots.
     Pulse Laser Deposition – Neodymium-doped yttrium aluminum garnet (PLD-NdYAG) uses a laser beam to ionize the target material, which is then dispersed through a plasma arc generated during the laser irradiation process. The released ions are then deposited on a substrate as a thin layer made of 10-9 m nanosized particles, together with reactive gases (Katase et al., 2012; Eason, 2007). Some physical and chemical material characteristics can change dramatically on the nanoscale from those of bulk-structured materials with the same composition. For example, the theoretical strength of nanomaterials can be achieved, or quantum effects can appear; nanosized crystals have a low melting point (up to a 1000°C difference with bulk structures) and reduced lattice constants because surface atoms or ions form a significant fraction of the total number of atoms or ions, and surface energy plays a significant role in thermal stability (Balaskas et al., 2012; Katase et al., 2012; Pokropivny et al., 2007). Laser irradiance, Pulse Repetition Rate, and Liquid or Gas media also have important role for the deposition process (Khumaeni, Sutanto and Budi, 2019).
     Scholars have been intrigued by current research and uses of superconductive materials, prompting them to investigate their potential usage for protective coatings (Yang et al., 2018; Willmann et al., 2008). Furthermore, the aluminum casting industry has seen an increase in the demand for protective layers to deal with die soldering. Die soldering occurs when aluminum welds to the dies or mold surface, leading to die damage and component defects and thereby halting production. Repairs are expensive and add more than an hour to production time. Die soldering is scientifically described as a chemical reaction that occurs during die casting between molten aluminum and the die surface. This reaction happens due to the washout or removal of a protective layer, such as a coating or lubricant, on the die. At sufficiently high temperatures and pressures, a protective layer is broken when liquid aluminum comes into contact with the die surface (Han, 2015). There are several alternatives method to minimize die soldering. Researchers have been studying to use of alloying material (Kohlhepp et al., 2021), dies treatment method (Mochtar and Aldila, 2020), and coating method (Serekpayeva et al., 2022; Kukuruzovic et al., 2021).

Regarding the dimensional need of the automotive aluminum casting – machining component, which has a tolerance of +/- 50 m, the PVD and CVD coating method became good alternatives because of their coating result, which max 20 m thickness. PVD is chosen between these two methods because it has a lower working temperature, unnecessary to use toxic gases, has less process cost, and provides better coating properties (Oerlikon, 2012). PVD – PLD is being challenged to become a good alternative for a protective layer. This study attempts to determine which coating material has the highest performance for creating a protective layer on the surface of SKD 61 tool steel by using the PVD - PLD process. 

       The samples were divided into groups to investigate the impacts of Al, Ti, and Cr and compare their alloy compositions with mechanical properties, i.e. the hardness of the coating layer (Figure 4). They were also divided into two groups based on coating processes (single-layer and multilayer) to see how the number of layers affected the same mechanical qualities. Table 1 shows the classification.

Figure 4 Visual examination of the SKD61 plates after PLD
Table 1 Sample grouping by coating materials and techniques