The purpose of this FAQ page is to address, in the broadest sense, some of the most basic questions that come up with our customers. By its very nature, this page cannot hope to delve deeply into the nuances of every customer’s application. While this page is a good starting point, we strongly encourage you to contact us directly for better information specifically related to your application.
- What is PVD coating?
- What is CVD coating?
- What is TD coating?
- Why should I use PVD, CVD and/or TD coatings?
- How do PVD, CVD and TD coatings improve tool life and performance?
- How much of an increase in tool life should be expected after PVD, CVD, or TD coating?
- Which coating process is best for my application?
- Is it possible to mask certain areas on parts to prevent them from being coated?
- Is it possible to coat assembled parts?
- What is the average thickness of your coatings?
- What are the processing temperatures for PVD, CVD, and TD coatings?
- What materials are suitable for PVD, CVD, and TD coating processes?
- What are the average turn-around times for your coating processes?
- Are you able to remove your PVD, CVD, and TD coatings?
What is PVD coating?
Physical Vapor Deposition, or PVD, is a term used to describe a family of coating processes. The most common of these PVD coating processes are evaporation (typically using cathodic arc or electron beam sources), and sputtering (using magnetic enhanced sources or “magnetrons”, cylindrical or hollow cathode sources). All of these processes occur in vacuum at working pressure (typically 10-2 to 10-4 mbar) and generally involve bombardment of the substrate to be coated with energetic positively charged ions during the coating process to promote high density. Additionally, reactive gases such as nitrogen, acetylene or oxygen may be introduced into the vacuum chamber during metal deposition to create various compound coating compositions. The result is a very strong bond between the coating and the tooling substrate and tailored physical, structural and tribological properties of the film.
The potential applications for PVD coatings are constantly expanding. That being said, PVD coatings can be separated into two very broad categories: functional and decorative coatings.
Functional PVD coatings are engineered to improve the life and overall performance of a tool or component; thereby, reducing the cost-per-part in manufacturing. Examples of functional PVD coating would be Titanium Nitride (TiN) on a HSS end mill.
Decorative PVD coatings are deposited to improve the appearance of a part, as well as to provide some wear resistance characteristics: improvements to both form and function. An example of decorative PVD coating would be the deposition of a Zr-based film onto a stainless steel door handle in order to provide a brass colored coating, but with a wear and tarnish resistance greater than real brass.
Richter Precision Inc. is always working on improvements to PVD processes and coatings. We have developed new coating compositions, new “Super Lattice” nano-layered coating structures, expanded our family of carbon coating processes (DLC), and implemented new technological advancements such as Filtered Arc technology. We are devoted towards maintaining our position as a leader in PVD coating technology.
What is CVD coating?
Chemical Vapor Deposition (CVD) is an atmosphere controlled process conducted at elevated temperatures (~1925° F) in a CVD reactor. During this process, thin-film coatings are formed as the result of reactions between various gaseous phases and the heated surface of substrates within the CVD reactor. As different gases are transported through the reactor, distinct coating layers are formed on the tooling substrate. For example, TiN is formed as a result of the following chemical reaction: TiCl4 + N2 + H2 1000° C → TiN + 4 HCl + H2. Titanium carbide (TiC) is formed as the result of the following chemical reaction: TiCl4 + CH4 + H2 1030° C → TiC + 4 HCl + H2. The final product of these reactions is a hard, wear-resistant coating that exhibits a chemical and metallurgical bond to the substrate. CVD coatings provide excellent resistance to the types of wear and galling typically seen during many metal-forming applications.
What is TD coating?
Thermoreactive Diffusion (TD or TRD) is a high temperature coating process for producing metal carbides (typically vanadium carbide) on the surface of a carbon-containing substrate. This is a multi-stage coating process which utilizes a pre-heat cycle, a coating segment, ultra-sonic cleaning, heat-treating, and post-coating polishing. The coating segment is performed in a molten bath [typically consisting of a solute (Borax), a metal source, and a reducing agent]: carbide-forming compounds in the bath react with carbon in the substrate and produce metal carbides on the substrate surface. TD coatings exhibit a diffusion type bond, thereby providing superb adhesion between the metal carbide layer and the substrate. This bonding characteristic, combined with the coating’s high micro-hardness, provides excellent resistance to the types of wear and galling often seen in many metal-forming processes.
Why should I use PVD, CVD and/or TD coatings?
When using PVD, CVD, or TD coatings in a tooling application, the primary motivation is very simple: to lower your cost-per-part manufacturing costs. Our customers consistently experience longer tool life while also being able to operate at increased speeds and feeds. The savings calculation becomes very easy: reduced down-time for PM and/or tool changes + increased production rates + decreased tooling costs due to increased tooling life with coating = significant and tangible savings for your company. The savings generated by the use of these coatings fall right to the bottom line as profit for the company.
How do PVD, CVD and TD coatings improve tool life and performance?
While all of our coatings have some variation in their properties in order to augment their performance in specific applications, there are two main properties that are fundamental to all of our coatings: high micro-hardness and lubricity (low coefficient of friction).
The average relative micro-hardness of our PVD, CVD, and TD coatings would be well over 80 Rc. When this hardness is compared to 58-62 Rc of tool steel, 62-65 Rc of HSS, or 70-76 Rc of carbide, one gets a clearer picture of the comparative hardness of our coatings. This higher hardness gives cutting tools, forming tools, and wear components much greater protection against abrasive wear.
As for lubricity, the Coefficient of Friction of our coatings can be significantly lower than un-coated tool substrates. For forming tools, this lowered Coefficient of Friction means that tools work with less force due to reduced resistance. In cutting applications, reduced friction means less heat is generated during the machining process, thereby slowing the breakdown of the cutting edge. In slide wear applications, the coatings greatly reduce the tendency of materials to adhere: this reduces friction and allows for more unrestricted movement.
How much of an increase in tool life should be expected after PVD, CVD, or TD coating?
In many applications, conservative estimates would range from 2-3 times the life of an un-coated tool; however, some applications have shown increases in tool life that exceed 10 times that of an un-coated tool. When a customer works with our experienced staff to match the appropriate coating with their substrate and application, dramatic improvements follow.
Which coating process is best for my application?
This is a question without an “easy” answer. There are many variables that must be taken into consideration when choosing the best coating process and composition for a customer’s application: workpiece material, failure mode, tool substrate, and tool tolerances are just a few.
Broadly speaking, when the materials and tolerances allow, CVD and TD coatings have proven to be superior in many applications. This is especially true for metal-forming applications where “sliding friction wear-out” and galling are pervasive. CVD and TD processes create a metallurgical and diffusion type bond between the coating and the substrate which is much stronger than the physical bond created through the PVD process. A potential area for concern with CVD and TD coating is their high processing temperatures: 1925°F and 1875°F, respectively. This high processing temperature can limit the use of CVD and TD coatings in some applications due to tolerance concerns.
PVD coating, due to its relatively low processing temperatures, is suitable for a much wider range of substrates and applications. This is largely due to its lower processing temperatures (385°F-950°F) and average coating thicknesses of 2-5 microns. These characteristics, among others, make PVD coatings a better choice for applications where close tolerances need to be held, and for base materials that are sensitive to higher temperature ranges. For example, a HSS end mill would likely end up with straightness and concentricity issues if process in a high temperature CVD coating process, whereas it would be an ideal application for PVD coating. Lower process temperatures mean zero distortion will be observed on most materials, as long as proper draw temperatures are utilized.
Of course, there are many other factors that may be important to consider when choosing the appropriate coating process and composition. Please contact your Richter Precision Inc. representative for assistance in making the best choice for your application.
Is it possible to mask certain areas on parts to prevent them from being coated?
PVD is a line-of-sight process; therefore, it is possible to mask areas in order to prevent them from receiving coating deposition. When custom masking fixtures are required, our in-house machine shop is able to respond quickly in order to meet the customer’s needs.
The CVD process uses various gases during the coating process; therefore, coating will deposit anywhere the gas can contact the substrate. Due to the nature of this process, it is extremely difficult to mask areas during CVD coating. Leaving extra material in order to grind critical dimensions after CVD coating using a diamond or CBN wheel is usually a better option.
The TD process uses a molten salt bath during the coating process; therefore, coating will deposit anywhere the liquid can contact the substrate. As with CVD, it is extremely difficult to mask areas during TD coating. Leaving extra material in order to grind critical dimensions after TD coating using a diamond or CBN wheel is a better option.
Please contact us regarding feasibility and costs related to masking for your particular application.
Is it possible to coat assembled parts?
Assembled parts cannot be coated with any of our coating processes. Parts must be fully disassembled prior to sending for coating. There can be no plastic, rubber, nylon, glue or tape in or on any part. Polishing compounds and excessive oil or lubricants must also be removed.
What is the average thickness of your coatings?
The average thickness of our various PVD coatings is 2-5 microns (.00008-.0002”). The average thickness of our various CVD coatings is 5-10 microns (.0002-.0004”). The average thickness of our TD coating is 6-9 microns (.0002-.00035”).
What are the processing temperatures for PVD, CVD, and TD coatings?
The standard processing temperatures for our PVD coatings can range from 385°F-750°F depending upon the particular coating being deposited. Please note that we recommend draw temperatures of 750°F+ in order to avoid distortion or hardness changes. If these draw temperatures are not possible for your parts, then we recommend you contact us for special instructions in order to provide for the safe processing of your parts.
CVD processing temperatures will reach 1925°F; therefore, any tool steels or HSS being CVD coated will be annealed during coating. After coating, we will vacuum heat-treat all steels in order to achieve the customer’s required hardness.
The process temperature for TD coating will generally be about 1875°F; therefore, any tool steels or HSS being TD coated will be annealed or partially annealed during coating. After coating, we will vacuum heat treat all steels in order to achieve the customer’s required hardness.
What materials are suitable for PVD, CVD, and TD coating processes?
High Speed Steels, carbides, and a wide variety of tool steels and stainless steels are among the most commonly coated materials for all of these processes. A more detailed list is available by accessing the Material Compatibility page of this website.
What are the average turn-around times for your coating processes?
The average turn-around time for functional PVD coatings range from 2-5 working days, depending upon the specific coating composition. The average turn-around time for decorative PVD coatings range from 2-3 weeks. The average turn-around time for CVD coatings is 5-7 working days. The average turn-around time for TD coating is 4-6 working days.
Are you able to remove your PVD, CVD, and TD coatings?
We have de-coating processes available for removing all of our coatings. These processes remove only the coating layers and, in most cases, do not adversely affect tool substrates. There may be some limitations to de-coating certain compositions from carbide substrates. Contact your Richter Precision, Inc. representative for more information.