Anodizing and bluing are performed to prevent corrosion, however these methods can scratch off, and anodizing processes do not strengthen the surface much. An alternative that has been used is chrome plating, but chrome-6 is toxic, and can still wear, spall, and pit.
The Challenge
Duralar, a vacuum deposition system manufacturer, wanted to find a solution by creating a rapid, diamond-like coating method, using physical vapor deposition, that is harder and more durable than the previously mentioned methods. It can be applied to prevent erosion, corrosion, and wear on metal parts.
Just like Duralar, if a physical vapor deposition innovator wanted to create a method, time, money and plenty of testing will be required. The testing will require modification of flow ratios and gases, while maintaining a precise flow to ensure reproducibility.
However, a new vacuum flow controller cannot be purchased for every test, and the cost to have them recalibrated for each recipe would be high.
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Figure 1. After the diamond-hard PVD vacuum coating, plain steel shows as black.
Alicat’s Solutions
Duralar built a general vacuum deposition system, but calibration was not complete for any of the six integrated thermal controllers for their special gas, tetramethylsilane (TMS). However, recalibration is essential for these controllers to accurately change the gases, resulting in downtime.
Therefore, Duralar decided to take the assistance of Alicat. Despite not having TMS in its standard list, Alicat were able to engineer a corrosion resistant flow controller equipped with a custom gas calibration for TMS (Figure 2).
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Figure 2. Alicat provided Duralar with a corrosion resistant flow controller with a custom gas calibration for TMS.
Using the Alicat controller (it's a drop-on replacement) Duralar retrofitted its system. The TMS flow will be accurate whether turned down to 0.5% of the full scale or flowing full scale, due to Alicat’s gas selection. It offers a full performance curve based on NIST’s viscosity tables, eliminating the issue of inaccuracies caused by changing pressures or temperatures in its factory.
Unlike the original thermal controllers, the closed-loop sensor fitted in the controller compensates for the volumetric changes, and helps to prevent inaccuracies.
Duralar was producing coated parts using the chamber as a vacuum, flowing precise amount of gases, adding material vapor, and converting it to plasma, which bonds to the components. The vacuum is required in physical vapor deposition because the chemistry will not work when there is atmospheric gases.
A new process to deposit thin coatings inside pipes and tubes is being developed. Coating the inside of the pipe can reduce corrosion and abrasive wear, ensuring a smooth flow of abrasive liquids in a pipe, or the protection of the inside of a rifle barrel from rusting.
The method is intelligent; the tubes ends are sealed and the tube’s interior becomes a vacuum chamber. The challenge now is varying the location of the plasma-producing electrical discharge within a thin tube to obtain a total coating.
Alicat provided the solution. With the aid of an MCS flow controller for the corrosive TMS, and two more Alicat MC mass flow controllers, they were able to alter the gases whenever required. Providing the choice of up to 20 user-customizable mixes and 98 built-in types.
Alicat’s downloadable LabVIEW drivers were used to construct the vacuum process steps, managing the MFCs and their shut-off solenoids from a remote laptop.
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Figure 3. A vacuum pump and three mass flow controllers for prototyping.
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Figure 4. Alicat’s LabVIEW downloads customized to run a prototype system
Conclusion
Over time the process has been improved, and customized coating systems are now available. Customers can place orders for diamond-like coatings for metal parts, or the systems to offer the service for others.
The vacuum coating is highly durable compared to anodizing, and quicker and harder compared to chrome plating. The adaptability of Alicat’s flow controller provide constant improvement for the physical vapor deposition process.
Download the brochure for more information about Alicat's Mass Flow Controllers
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This information has been sourced, reviewed and adapted from materials provided by Alicat Scientific.
For more information on this source, please visit Alicat Scientific.