Frequently Asked Questions01. 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.
Richter Precision Inc. is constantly 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.
02. 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.
03. 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.
04. Why should I use PVD, CVD and/or TD coatings?
Regardless of the tooling application, the primary reason for using these coatings is very simple: to lower your cost-per-part. 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 = significant and tangible savings for your company.
05. How do PVD, CVD and TD coatings improve tool life and performance?
Although all of our various 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 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 low 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.
06. How much of an increase in tool life should be expected after PVD, CVD, or TD coating?
Conservative estimates would range from 2-3 times the life of an un-coated tool; however, many 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 improvement is the resulting outcome.
07. Which coating process is best for my application?
There are many variables that must be calculated when considering this question, such as application, substrate, and tool tolerances.
The simple answer is that when the tolerances and materials allow, CVD and TD coatings have proven to be superior in many applications, especially in high stress metal-forming applications where “sliding friction wear-out” and galling are pervasive. These “hot” processes create a diffusion type bond between the coating and the substrate which is much stronger than the bond created through the PVD process. A potential area for concern with CVD and TD coating is the 1925°F and 1650°F processing temperatures. This characteristic can limit CVD coating in some applications.
The PVD coating process has been successful in a wider range of substrates and applications. This success is largely due to its lower process temperatures (385°F-750°F) and average coating thicknesses of 2-5 microns. These characteristics, among others, make PVD coatings ideal for HSS and carbide cutting tools (no excessive coating build-up on cutting edges) as well as parts with tight tolerances, such as plastic injection molding components and fine blanking tools. In addition, the lower process temperatures mean zero distortion will be observed on most materials, as long as proper draw temperatures are maintained.
Of course, there are numerous other factors that may be important to consider when choosing the appropriate coating process and composition. Please contact your Richter Precision Inc. representative if you have further questions.
08. 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 deposits. 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, post-coating grinding of critical dimensions using a diamond 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. Due to the nature of this process, post-coating grinding of critical dimensions using a diamond wheel is usually a better option.
Please contact us regarding feasibility and costs related to masking your particular application.
09. 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 4-15 microns (.00016-.0006”).
10. What are the processing temperatures for PVD, CVD, and TD coatings?
The process 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.
The process temperature for CVD coating 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 1650°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.
11. What materials are suitable for PVD, CVD, and TD coating processes?
High Speed Steels, carbides, and a wide variety of tool steels are among the most commonly coated materials for both these processes. A more detailed list is available by accessing the “Material/Coating Compatibility” page of this website.
12. What are the average turn-around times for your coating processes?
The average turn around time for PVD coatings range from 2-5 working days, depending upon the specific coating composition. The average turn-around time for CVD coatings is about 5-7 working days. The average turn-around time for TD coating is about 5 working days.
13. 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 while not affecting a majority of tool substrates. There may be some limitations to de-coating certain compositions from carbide substrates. Contact your Richter Precision, Inc. representative for more information.