Applying a screen protector to a phone is probably one of the most universally accepted consumer habits of modern times.
Spend a few dozen yuan, buy a thin layer of tempered glass, protect a screen worth two or three thousand yuan—the logic holds, which is why phone screen protector stalls have been a mainstay at subway exits for years.
But there is a type of coating that is dozens of times harder than a phone’s tempered glass. It can extend the life of metal cutting tools by several times. It can keep precision optical lenses transmissive under extreme conditions. It can enable ultra-low-friction, coating-free lubrication on surgical instruments. It is not a screen protector. It is called DLC.
Diamond-Like Carbon coating—DLC for short.
What Is DLC, and Why Is It So Special?
Diamond is the hardest naturally occurring material known, ranking 10 on the Mohs scale. DLC is an amorphous carbon film whose structure sits somewhere between diamond and graphite. It exhibits hardness approaching that of diamond—with Vickers hardness typically ranging from 1500 to 3000HV (compared to steel, which typically ranges from 100 to 900HV)—while also having an exceptionally low coefficient of friction—approximately 0.05 to 0.15 under dry sliding conditions, far below the 0.5+ of steel-on-steel.
Hard and slippery at the same time—these two properties combined make DLC capable of things that steel simply cannot do.
What’s more, DLC has excellent optical transmittance across a broad spectral range, especially in the infrared band. This means it not only provides mechanical protection but can also safeguard precision optical components without compromising their optical performance—something that metal coatings and traditional hard coatings cannot achieve.
In Infrared Optics, DLC Solves a Long-Standing Dilemma
The lenses and windows of infrared optical systems are typically made from materials such as germanium, zinc sulfide, zinc selenide, and magnesium fluoride. These materials have excellent transmittance in the infrared band, but their mechanical properties are generally soft, with limited resistance to sand, dust, rain, and chemical corrosion.
Outdoor thermal imaging cameras have lenses exposed to wind, sand, and rain every day. Military and automotive infrared systems need to maintain stable optical performance under vibration and shock. Industrial windows need to withstand long-term service in high-temperature and corrosive gas environments. In all these scenarios, windows that have excellent optical performance but fragile mechanical properties present a persistent engineering challenge.
The value of DLC coating here is that it achieves two things simultaneously: surface hardening that improves wear and scratch resistance, while barely affecting infrared transmittance. A germanium window coated with DLC can have its surface hardness increased from the material’s inherent 700–800HV to over 1500HV, with the loss in infrared transmittance typically kept within 1 to 2 percentage points.
MULTI IR’s DLC coating processes cover optical windows, filter substrates, optical lenses, and various other components, with process parameters tailored for different substrate materials and application environments. The adhesion and stress state of the DLC film are extremely sensitive to the substrate material—the same process parameters can yield completely different results on germanium versus zinc sulfide. This is the part of DLC coating with the highest technical barriers, and the hardest to control for production consistency.
DLC’s Applications Extend Far Beyond Optics
Cutting tools and molds represent the largest industrial application volume for DLC. High-speed cutting tools coated with DLC, when machining aluminum and copper alloys, can see tool life extended by 3 to 5 times, with better surface finish quality as well—thanks to DLC’s low friction coefficient reducing built-up edge formation.
Medical devices represent another critical application area. Surgical scalpels, orthopedic implants, and minimally invasive surgical instruments require good biocompatibility, resistance to bodily fluid corrosion, and low surface friction. DLC has natural advantages across all these dimensions—and as a carbon-based film, its biocompatibility is superior to metal coatings.
The automotive sector has seen rapid growth in DLC usage in recent years. Engine piston rings, camshafts, and precision components in fuel injection systems—DLC coatings applied to these high-friction, high-load contact surfaces significantly reduce wear rates and extend engine service life.
The logic of a phone screen protector is to use an inexpensive sacrificial layer to protect an expensive screen.
The logic of DLC coating is to enable expensive and precision components—already costly in their own right—to survive longer in harsh environments while maintaining their original performance.
Both approaches start from the same premise, but the latter addresses problems that the former simply cannot reach.
If you are working with infrared optical systems, precision cutting tools, medical devices, or any application that demands both optical performance and mechanical durability, DLC coating is worth a serious look—not just as a high-sounding process term, but as a practical engineering solution.
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MULTI IR – National-level “Little Giant” Specialized and Sophisticated Enterprise. Over 10,000 types of infrared sensitive components in stock. Top 3 globally in comprehensive strength. Lead drafter of the infrared filter industry standard.
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