FAQs about PVD Coatings

Inert, biocompatible PVD coatings enhance the appearance and performance of medical devices, including drills, needles, and wear parts utilized in various device assemblies. Photo Credits: Surface Solutions

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Physical Vapor Deposition (PVD) is a vacuum coating technique primarily used to improve the performance of cutting tools. Mike Schultz, co-founder of Surface Solutions, states that cathodic-arc PVD coating services offered by his Fridley, Minnesota-based company can extend a tool's lifespan by as much as 10 times compared to an uncoated tool, providing a harder, more lubricious, and wear-resistant surface.

Moreover, PVD coatings are increasingly utilized by medical device manufacturers to enhance the aesthetic differentiation of their products and improve performance. The hard, inert coatings are biocompatible and do not react with bone, tissue, or bodily fluids. The company coats various medical devices, including distractors, drills, needles, and wear parts used in device assemblies, along with applications in dentistry.

Schultz explains that PVD coatings improve edge retention, ensuring coated surgical instruments remain sharp. They can also minimize galling between mating stainless steel components and help prevent oxidation and corrosion.

Below, he addresses some frequently asked questions about PVD coatings:

What is a Cathodic-Arc PVD Process?

Cathodic-arc PVD is a method where various metals are evaporated from a solid source material inside a vacuum chamber using an arc welder. Metals such as titanium, chromium, zirconium, aluminum, and various alloys are evaporated and reacted with a gas (usually nitrogen and/or a carbon-containing gas) to create a coating material that condenses on the target parts.

This process generates high levels of metal ionization (over 95%), which ensures excellent coating adhesion to the substrate material. The process typically has wide operating windows, allowing for quality coatings to be deposited across various parameters. In contrast, other methods, such as sputtering or ion plating, have limited operating windows and struggle to produce consistent quality coatings.

What Preparation is Necessary Before Coating?

To ensure a well-adhered coating, it is crucial that the parts to be coated are clean. Surfaces must be free from oxides, EDM recast, and organic films, as contaminants can significantly affect coating quality.

Proper masking ensures that PVD coating is applied only where needed.

Coating companies utilize techniques such as polishing, tumbling, acid etching, and sand or glass-bead blasting to remove contaminants. Some processes may alter the surface finish of the part being coated, so coating companies often collaborate with customers to establish a process that meets expectations for quality and appearance.

Are Sharp Edges Affected by the Coating Process?

For parts with sharp edges, cleaning processes that may compromise edge sharpness are avoided. If delicate or fragile components are involved, modifications to coating processes can be applied to reduce heat and coating rates, ensuring that sensitive features are not overheated and that the coating thickness remains appropriate.

What Surface Finishes Yield the Best Results?

PVD coatings are extremely thin, typically ranging from 0.1 to 0.3 microns, and generally replicate the part’s original finish, unless an abrasive cleaning method is employed. Smooth surfaces usually yield the best results; therefore, ground or polished surfaces often perform better compared to bead-blasted or matte finishes.

If a specific area requires a matte finish, it is advisable to allow the coater to produce the texture, preventing potential contamination from the part supplier’s texturing process, which could lead to rework and negate anticipated savings.

What Temperatures are Used in the Coating Process?

The typical coating temperature for all Surface Solutions PVD coatings is around 800°F. This temperature can influence the hardness of parts or cause distortion (shrinkage or expansion). To mitigate these effects, we suggest tempering heat-sensitive parts at 900 to 950°F before coating.

What Types of Materials Can Be Coated?

PVD coatings can be applied to most metals that can endure heating up to 800°F. Commonly coated materials in the medical sector include 303, 440C, and 17-4 stainless steels; titanium alloys; and select tool steels. However, PVD coatings are generally not applied to aluminum, as the coating temperature approaches its melting point.

What Coatings Are Commonly Used for Medical Devices?

Surface Solutions provides four types of PVD coatings for medical devices. The most popular is titanium nitride (TiN), which has a thickness ranging from 0.1 to 0.3 microns, a Vickers hardness between 2,400 and 2,600 Hv, and a gold hue.

This multilayer coating includes zirconium nitride (ZrN) as the top layer, yielding a silver-gold color and high hardness.

The second most prevalent medical coating is aluminum titanium nitride (AlTiN), often referred to as black nitride or black titanium coating. It has a thickness of 0.1 to 0.3 microns, hardness ranging from 4,000 to 4,200 Hv, and a charcoal black finish.

Additionally, the company offers chrome nitride (CrN) and Alpha coatings. CrN features a thickness of 0.1 to 0.3 microns, hardness between 2,200 and 2,400 Hv, and a silver finish. Alpha is a multilayer coating with zirconium nitride as the top layer that results in a silver-gold color. It ranges in thickness from 0.1 to 0.3 microns and offers maximum hardness, ranging from 4,400 to 4,600 Hv. This coating can last two to four times longer than TiN due to its superior hardness, lubricity, and abrasion resistance.

What Advantages Does PVD Have Over CVD?

In comparison to chemical vapor deposition (CVD), PVD coatings are applied at significantly lower temperatures, eliminating the need for post-coating heat treatment. PVD also replicates the original surface finish, while CVD results in a matte finish unless polished afterward.

What Advantages Does PVD Have Over Anodizing?

Surface Solutions specializes in coating titanium alloys and asserts that PVD is more wear-resistant than anodizing and tends to retain color better over time.

PVD coatings are frequently used for cutting tools, significantly increasing tool life by up to 10 times compared to uncoated tools.

In addition to medical devices and cutting tools, PVD coatings are commonly utilized to enhance the performance and durability of punching tools, forming tools, and injection-molded wear components. Schultz suggests that medical manufacturers considering PVD coating should engage with the coating company to ensure they achieve a functional coating on components where needed or desired, along with optimal appearance.

All Questions and Answers About PVD Coating