Effect of Substrate Heat Treatment on the Tribological Performance of $MoS_{2}$+Ni and DLC Coatings Deposited on Tool Steels

Imagine the world of manufacturing as a giant, high-stakes dance floor where metal tools and hot plastic are constantly spinning, grinding, and pressing against each other. In this chaotic ballroom, the tools are the lead dancers, and if they get too hot, too scratched, or too sticky, the whole show falls apart. This is the world of tribology, the science of how surfaces rub against one another. To keep the dance going smoothly, engineers use coatings—thin, invisible layers of special materials sprayed onto tools to make them harder or slicker. Think of these coatings like a new pair of dance shoes: some are made of super-tough leather to protect your feet from getting bruised (wear resistance), while others are coated in a slippery wax to help you glide without tripping (low friction). But here's the catch: even the best shoes won't work if the floor beneath them is wobbly or uneven. The "floor" in this story is the metal tool itself, and how it's been treated before the shoes are put on matters just as much as the shoes themselves.

This paper dives into a specific dance-off between two types of "shoes" (coatings) and four different ways of preparing the "floor" (the tool steel). The researchers wanted to see which combination would keep the tools dancing the longest without stumbling. They tested two famous coatings: DLC (Diamond-Like Carbon), which is like a super-hard, diamond-encrusted boot designed to crush anything in its path, and MoS2+Ni, a molybdenum disulfide mix that acts like a solid lubricant, letting surfaces slide past each other with almost no resistance. They tried these on two common tool steels (AISI P20+Ni and AISI 420) that had been treated in different ways: left alone, baked hard (quenched), chemically hardened (Tenifer), or both.

The results were a tale of two different strengths. The study found that if you want your tool to be incredibly slippery and reduce friction to the bare minimum, the MoS2+Ni coating is the undisputed champion. When placed on a tool that had been both baked hard and chemically treated, it achieved a friction coefficient as low as 0.0710 on the P20 steel and 0.0851 on the 420 steel. It was like putting the tool on an ice rink; it just glided. However, if your goal is to stop the tool from getting scratched or dented when it gets hit hard, the DLC coating is the hero. Thanks to its hardness, which was about 50% higher than the MoS2+Ni mix, the DLC coating resisted deep scratches much better, especially when the tool underneath was hardened.

Interestingly, the paper suggests that the "floor" (the substrate treatment) matters more than the "shoes" when it comes to stopping scratches. The researchers measured the depth of scratches and found that simply hardening the steel through quenching reduced scratch depth by about 65% for the P20 steel and 70% for the 420 steel compared to untreated tools. While the Tenifer chemical treatment helped a little, it wasn't as effective as the heat treatment. The study concludes that there isn't one single "perfect" tool. Instead, if you need to minimize friction and energy loss, you should choose the slippery MoS2+Ni coating on a well-treated steel. But if you need to prevent the tool from getting physically damaged by heavy loads, the tough DLC coating on a hardened steel is the better choice. The paper doesn't claim to have solved all manufacturing problems, but it clearly maps out which tool to pick for which job, proving that the secret to a long-lasting tool is matching the right coating to the right foundation.