PVD stands for Physical Vapor Deposition. It is a thin-film coating process. This is a process applied in a vacuum chamber to deposit thin-film coatings on component surfaces.

PVD coating is carried out in a vacuum chamber at an extremely low-pressure range (typically 10^-3 to 10^-9 Torr. Standard atmospheric pressure is 760 Torr) where in the component to be coated is placed in front of a high purity target source in a plasma environment (ionized gas). A target is the primary material source used for the coating (for example: Titanium for Titanium Nitride, Chromium for Chromium Nitride, etc.) This process involves three critical steps:

1. Evaporation: Removal of material (atom-by-atom) from the target source using sputtering, cathodic arc, electron-beam or other methods.
2. Transportation: Transfer of material from the target source to the component surface under plasma due to potential difference between the target and substrate.
3. Condensation: Nucleation and growth of the coating on the component surface by combining the transferred target source atoms with reactive gases to form the ceramic (non-metallic) coating compound.
4.  

PVD coatings can be applied on components using different methods such as arc evaporation, magnetron sputtering to name a few. HEF specializes in plasma enhanced magnetron sputtering, CAM (coating assisted by microwaves) and modified arc evaporation coating technologies.

Yes. There are different types of PVD coatings that can be offered depending on the application requirements. Titanium Nitride (TiN), Chromium Nitride (CrN), Titanium Aluminum Nitride (TiAlN), Titanium Boron Nitride (TiBN) are some examples of PVD coatings.

PVD coatings offer the following benefits:

• High hardness
• Excellent wear resistance
• Reduced frictional properties
• Low deposition temperatures (120°C-350°C)
• Maintaining dimensional tolerances for precision components
• Excellent adhesion to substrates

In general, PVD coatings are thin film and are in the range of 1 to 5 microns. For reference, 25 microns equals 0.001 inches. Red blood cells are around 8 microns in diameter, while human hair is around 80 microns in diameter. Thus, PVD coatings are extremely thin-film coatings with thickness specification defined within this 1 to 5-micron range depending on the application requirement.

PVD coatings have a hardness value around 1500 – 4500 HV (Vickers) depending on the type of coating offered. Vickers (HV) is a microhardness unit for measuring thin film coatings. For reference, 900 HV corresponds to 67 HRC (Rockwell C) hardness. Generally, carbon steels have a hardness range around 250 HV (25 HRC), nitrided or nickel and chrome plated steels fall in the range of 600 HV to 1000 HV surface hardness. Thus, PVD coatings are extremely hard and hence, very durable and wear resistant.

CERTESS^® NITRO is a tradename of HEF Group for Nitrogen based PVD coatings. Depending on your application, there are different options that can be provided within the family of CERTESS^® NITRO coatings. Some of these include:

CERTESS NITRO FAMILY

• CERTESS Ti (TiN)
• CERTESS X (CrN)
• CERTESS T (TiAlN)

Yes. PVD is a line-of-sight process. Only the surfaces of the components exposed to the target source can be coated. Depending on the size and shape of the components, they are subjected to a planetary motion (part rotation along an axis for uniform exposure to the target source) within the vacuum chamber to ensure uniformity of the coating across external, exposed surfaces.

A general thumb rule or ratio with this line-of sight process is 1:1 in terms of coating penetration to the diameter of the opening. This ratio can vary depending on the orientation of the component in the vacuum chamber and the critical surfaces requiring the coating. HEF can evaluate this case-by-case based on component geometry.

Yes. It is possible to mask certain surfaces that do not require PVD coating. Components are also held on certain surfaces using special tools within the vacuum chamber that do not get exposed to the coating. Customers are requested to specify on part drawings the following:

• Surfaces that must have the coating – critical surfaces
• Surfaces where coating is not allowed – requirement for masking
• Surfaces where coating is optional – non-critical surfaces

Non-critical surfaces will be utilized to fixture the part for the coating process.

Yes. PVD coatings can be applied on steel, titanium, copper-beryllium, aluminum alloys as well as certain plastics, elastomers and glass.

Absolutely! Pre-cleaning is essential and an important step of this process in order to ensure a good adhesion of the PVD coating on the component surface. HEF offers cleaning solutions for parts shipped to us with light rust preventative oils or machining coolants as part of the process.

Surface finish primarily depends on the application and performance requirements of the component. Ra, Rpk and Rz are typical surface roughness parameters that are looked into depending on the application. However, it is important to ensure that the parts are provided in a good surface condition without any imperfections/defects and contamination (rust, scaling/oxides).

PVD coatings generally duplicate the incoming surface finish of the parts. However, HEF offers certain pre-blasting and pre-polishing capabilities for applications that require a specific finish.

Yes. PVD coatings (depending on the type) can be offered in different colors such as gold, silver, grey and black to list a few.

Yes. PVD coatings can be removed or stripped if required. This requires components to be immersed in a special chemical solution for a certain time period to ensure the entire coating thickness has been removed. However, special attention needs to be given to ensure these de-coating chemicals do not affect the substrate material. The components may require additional polishing before recoating. This is generally discussed with the customer on a case-by-case basis. HEF has the capabilities to offer these services, if required.

Electroless nickel plating is an auto-catalytic chemical process that deposits a nickel phosphorus alloy on metallic substrate materials; this process does not use an electric current.

Key advantages are excellent corrosion resistance, improved wear resistance, and a uniform coating thickness with the ability to evenly coat complex geometries

Most metallic materials to include steel, aluminum, copper, and brass.

Electroless nickel is typically classified by its phosphorus content: Low (2 – 5%), Medium (6-9%), and High (10-12%). Each class offers different properties in terms of hardness, corrosion resistance, and ductility.

Yes. Post-plating heat treatment can be used for hydrogen embrittlement relief or an increase in hardness. Hardness values can get up to roughly 64 HRc.

Electroless nickel plating uses a chemical process, while electroplating uses an electric current. Electroless nickel offers much better uniformity, while electroplating tends to be more cost effective for simple shapes.

Electroless nickel is used in a wide variety of industries to include aerospace, automotive, oil & gas, industrial equipment, automation and many more.

Yes. Many electroless nickel coatings can be stripped and replated without significant changes to the substrate surface or dimensions.

Absolutely. Modern electroless nickel baths use advanced formulations and strict process control to ensure consistent, high-quality plating deposits.

Liquid Nitriding (LN) is a common term for a diffusion process that is actually liquid nitrocarburizing; a thermo-chemical reaction whereby nitrogen, primarily, and some carbon are diffused into the surface of iron-based materials. The nitrogen combines with the iron to form an iron-nitride compound layer that provides improved surface properties; e.g., resistance to wear, friction, corrosion, and fatigue.

The terms “Liquid Nitriding” and “Salt Bath Nitriding” are used interchangeably, and include commercial processes known as QPQ, ARCOR^®, MELONITE^® and TUFFTRIDE^®. All are actually nitrocarburizing processes that use molten salts as a source of nitrogen (+ some carbon). Different trade names are used due to differences in the chemistry of the nitriding chemicals and the secondary processing steps.

Nitriding provides only nitrogen to the surface of the work piece, and is normally accomplished in gas or plasma atmospheres, using much longer cycles to achieve deep diffusion depth. Nitrocarburizing supplies both nitrogen and some carbon; can be performed in either liquid (salt bath) or gas atmospheres; and uses much shorter time cycles to produce comparatively shallow diffusion depth.

MELONITE^®, TUFFTRIDE^® and ARCOR^® are all liquid nitrocarburizing processes, and trademarks of the HEF Group, MELONITE^® and TUFTRIDE^® are identical processes – the former term is prevalent in North America, and the latter term in the rest of the world. However, ARCOR^® represents a family of LN processes, including ARCOR^® C, V, N, DT, and others, which were developed to address specific applications and/or materials. These ARCOR^® treatments provide a more robust and consistent compound layer; are operationally easier to control and environmentally friendlier than other liquid nitriding treatments.

“QPQ” stands for “Quench-Polish-Quench”, which describes a sequence of secondary steps following the liquid nitriding step. These steps entail the sequence: (1) OXIDATION: 2-3 microns of the surface layer is transformed to an iron oxide. This is done by immersing the parts in specially formulated ‘salts’ between 400°C – 425°C (750°F -800°F); (2) POLISHING: to improve surface finish and (3) RE-OXIDATION: to recover the oxide layer thickness that may have been lost during the polishing step. QPQ is prescribed when a smooth surface finish and maximum corrosion protection are required.

Nitriding, or nitrocarburizing, can be accomplished using four different media: 1) Liquid; 2) Gas; 3) Plasma; and 4) Fluidized Bed. All methods are intended to accomplish similar – though not identical – results. However, liquid is considered the benchmark for uniformity, consistency, and flexibility. Liquid Nitriding also provides the best combination of wear and corrosion protection and the shortest processing times.

Liquid Nitriding is not a coating or plating: it is a diffusion process that modifies/transforms the surface of the treated component. This modified surface layer is well integrated with the bulk material – hence it is not susceptible to flaking or peeling.

Liquid Nitriding is often referred to as a heat treatment; but this is technically incorrect. True heat-treating processes operate at higher temperatures and transform the crystal structure of the steel to produce the desired mechanical properties. Liquid Nitriding achieves results by means of a chemical reaction (at temperatures lower than conventional heat treatment) that leads to the formation of a hard nitride compound on the surface of the component.

A compound layer is the outermost surface layer, or zone, formed during the nitrocarburizing process, and consists mostly of an iron nitride compound. This hard compound layer provides most of the desired wear and corrosion properties. The diffusion zone contains much less nitrogen, and forms immediately below the compound layer. The diffusion zone is the source of improved strength and fatigue properties. The “case” formed by Liquid Nitriding is composed of the compound layer, plus all or most of the diffusion zone.

Liquid nitriding may be performed at temperatures as low as 500°C (932°F), and as high as 630°C (1166°F). Typically, however, the temperature range is between 540°C – 590°C (1000°F -1090°F). HEF NA uses specially formulated nitriding chemistries whereby nitriding can be performed at 510°C (950°F) for certain types of steels, without compromising compound layer depth or quality and without any reduction in process productivity.

Both compound layer depth and hardness is dependent upon the composition of the material being treated. Hardness will increase with the amount of nitride-forming alloys (e.g. chromium, vanadium etc.), and depth will decrease with overall alloy content, including carbon. With ARCOR^® Liquid Nitriding, compound layer depth can range from 0.0001 inches for stainless steels to 0.001 inches for plain carbon steels (0.003 mm – 0.025 mm OR 3 to 25 microns); and hardness from 600 HV for low carbon steels up to 1200+ HV for stainless steels (55 – 70+ HRC). Similarly, diffusion zone depths will also vary with alloy content, including carbon. These can range from 0.001 inches (0.025 mm) for austenitic stainless steels to 0.040 inches (1 mm) for plain carbon steels. It should be noted that austenitic materials, and certain martensitic PH grades, do not produce a typical compound layer. Rather, it is a relatively thin total “case” – usually 0.001 – 0.0025 inches – that consists of multiple layers of varying hardness and composition.

All surface treatments will change part dimensions to some degree, but Liquid Nitriding produces comparatively little growth; typically 0.0002-0.0003 inches (5 – 8μm) on the diameter.

Only ferrous materials (materials whose major ingredient is the element iron), i.e. all steels, including stainless steels and cast irons, are considered candidates for Liquid Nitriding. However, other materials containing minor percentages of iron may also produce some benefit from Liquid Nitriding.

Liquid Nitriding is intended for use on ferrous materials only; that is, materials whose largest constituent is iron. But, if the material contains even a small amount of iron, some nitriding may occur – as is the case with some grades of high-nickel alloys such as Inconel 600.

Ferrous materials manufactured using a Powder Metallurgy (PM) processing route can be effectively treated by ARCOR^® Liquid Nitriding, provided the density of the part the part is above a certain minimum threshold. For details, please contact us.

Masking to prohibit nitriding in specific areas is technically possible using plating, or, certain masking compounds; however, this typically not done due to cost, and/or marginal effectiveness in the liquid bath environment.

No nitriding or nitrocarburizing process can nitride small holes and deep cavities with complete uniformity. However, Liquid Nitriding is by far the most capable of generating a uniform compound layer in these regions of a component.

Hardness levels produced by gas, plasma, or Liquid Nitriding are similar, ranging from between 600-1200 HV (60-70+ HRC). Hardness produced by nickel plating may be between 60 -65 HRC; hard chrome plating is around 70 HRC. Please note that surface hardness is usually measured on the Vickers scale (HV) rather than the conventional Rockwell C (HRC) scale.

The corrosion resistance produced by Liquid Nitriding will exceed that of gas or plasma nitrided parts, as well as chrome and nickel plated parts, assuming equivalent layer depths. Hence, ARCOR^® Liquid Nitriding/ QPQ processes are preferred by industries such as Oil & Gas where components experience both harsh erosion and corrosion environments. Also, automotive and industrial machinery components operating with minimal lubrication can experience significant performance improvements when treated with ARCOR^® Liquid Nitriding.

Post-nitriding surface roughness will depend upon the specific nitriding process/chemistry, component material, cooling method, and nitride layer depth. However, typically, a Ra increase of 8-15 μin (0.4 μm) may be expected. Certain ARCOR^® treatments result in lower surface roughness than conventional liquid nitriding.

DLC stands for Diamond-Like Carbon. This is a special family of thin-film coatings that provide the high hardness like diamond (due to its tetragonal structure) and low lubricity like graphite (due to its hexagonal structure). DLC though, is amorphous in nature i.e. it does not have a crystal structure, however, offers combined advantages in spite of its overall random arrangement of carbon atoms.

DLC coatings are deposited using a Plasma Assisted Chemical Vapor Deposition (PACVD) method. Unlike PVD method that involves physically depositing the solid target material source on the component surface, PACVD on the other hand involves a precursor gas source (hydrocarbon) that is broken down into carbon and hydrogen atoms in plasma, deposited as DLC on the component surface in an amorphous fashion.

DLC coatings are generally applied after a PVD underlayer such as Ti, Cr, CrN or WCC or a combination of them has first been deposited on the component surface. The selection of the underlayer depends on various factors such as hardness of the component surface (substrate), bonding characteristics with the substrate, load bearing requirements of the application, etc. The choice of underlayer is determined case by case primarily based on the application and performance requirements.

DLC coatings are deposited at relatively low temperatures below 200°C. HEF’s specific deposition technology allows us to deposit these coatings at around 170°C. With our plasma enhancement technology, HEF is able to deposit at such low temperatures to ensure no distortion or change in core properties of the component being coated. Thus, precision components with tight dimensional tolerances can be DLC coated without any concerns.

Total coating thickness including the underlayer is uniform and generally in the range of 2 to 5 microns. The exact coating thickness within this range is determined based on the application and performance requirement.

DLC coating hardness can range from 2500 HV to 4500 HV depending on the type of DLC coating including the choice of underlayer.

DLC coatings offer the following benefits

1. High hardness (2500-4500 HV)
2. Excellent wear resistance
3. Friction reduction
4. Thin, uniform film (precision coating)
5. Excellent aesthetics

Coefficient of friction is a system property. It is generally the ratio of the frictional force to the normal force when two bodies interact with each other. Deposition of DLC coatings helps with friction reduction of the system for applications involving smooth, interacting surfaces. Lubrication plays a key role in this property as well. Typical friction coefficient range for such systems with DLC coated surfaces can be around 0.1 to 0.2 in a dry-condition and less than 0.1 in a lubricated condition.

Yes. DLC coating can be removed or stripped if required. While the DLC layer can be removed within the same coating chamber using a reactive plasma-based process, removal of the PVD underlayer(s) requires components to be immersed in a chemical solution for a certain time period. The components may require additional polishing before recoating. This is generally discussed with the customer on a case-by-case basis. HEF has the capabilities to offer these services, if required.

DLC is a family of ultra-hard, thin-film, carbon-based coatings that can be broadly classified into:

1. Hydrogenated DLC, represented as a-C:H (amorphous carbon, hydrogenated). In this category there are several coatings with different underlayers – but all of them have the same a-C:H top layer. The full range of hardness for coatings within this family is 1000-2800 HV, but the typical range is 2000-2200 HV. For further details, please refer to the DLC Coatings overview section on our website.
2. Non-Hydrogenated DLC, represented as ta-C (tetrahedral amorphous carbon). This coating is deposited from solid carbon sources, rather than a gaseous hydrocarbon (as for the a-C:H coatings) precursor. The specific arrangements of the carbon atoms within the ta-C coatings results in them being at least 20% harder than the standard a-C:H coatings and can withstand operating temperatures of up to 450° C – which is about 100° C higher than the maximum temperature resistance of a-C:H coatings.

CERTESS^® CARBON is a tradename of HEF Group for DLC coatings. Depending on your application, there are different options that can be provided within the family of CERTESS^® CARBON coatings. Some of these include:

1. CERTESS DT (WCC)
2. CERTESS DDT
3. CERTESS DCX
4. CERTESS DCY
5. CERTESS DCZ
6. CERTESS TC