- What coating suits what type of metal? And why?
Reference the coating overview page for detailed coating descriptions, the coating selection varies depending many factors including the base material, application parameters and other, please consult our application engineers for details.
- There are many PVD coating companies, everyone seems to offer a number of similar coatings and a few unique ones; How should I choose a PVD coating provider?
First, you should determine whether the need for PVD coating is once in a while requirement or if it is a ongoing, long term project.
In the scenario that, this is a once in a blue-moon need, and the coating requirement is one of the standard commercial coatings of TiN, TiAlN, AlTiN, CrN or equivalent; any PVD coating companies should be able to perform the service, and it is matters of comparing pricing and turnaround time.
In the case of long term requirement, then in depth interview should be conducted; use a list of performance measurable and evaluate the supplier based on the criteria.
The age and sophistication of the equipment does not directly translates to superior quality; because pretreatment/cleaning of the parts directly affects the quality of the coating. These are dictated through know-hows, experience and R & D.
There are no single criteria to find the best suited supplier, but you must first determine your requirements and measurable indicators; then rank them in descending order, and use this to help with the selection process. Feel free to contact us for assistance.
- What are steps or pre-treatment does the parts undergo before they are coated?
- Upon receiving customer package, the package condition and inventory of the contents are electronically documented, so that the parts can be repackaged to the arrival condition after they are coated.
- Detail inspection of the contents is performed and documented, customers are notify of any questions and concerns as they arise throughout the process
- the parts are un-packaged, loaded onto fixtures and put through a multi-step ultrasonic cleaning line.
- bead blasting and polishing are performed as needed (additional charges may apply), to ensure that the parts are prepped with suitable fresh surface for the coating process
- Why is the pricing based on the largest dimensions of the parts, I only need small portion of it to be coated? Why do parts need to be fixtured? Can the coat be selectively applied to area(s) of the part?
Physical Vapor Deposition (PVD Coating) or Vacuum deposition is a line of sight operation, and the entire part(s) need to be placed inside of the vacuum chamber to be coated. The parts will need to be held (fixtured) somehow in order to be placed into the vacuum chamber, Therefore the entire part(s) need to be prepped and priced based on the largest dimensions.
In order to achieve uniform coating, the parts need to rotate within the vacuum chamber. A turning table is used to achieve this, see below, this can be top or bottom mounted to the chamber, depending on the equipment configuration.
The coating is formed by
- the ionized target material
- reactive gas(s) (Nitrogen, hydrocarbon, Oxygen, and/or other reactive gas(s) of choice)
= forms the coating that is being deposited onto the negatively biased parts
Vacuum deposition, like the name needs to be performed under vacuum setting, in order to control the inputs to the coating process. Anything other than the 3 native components outlined below, are contaminants to the process and adversely product varying levels of undesired results.
Even though the requirement may on need a small portion of the part to be coated, the entire part still need to be cleaned and prepped to ensure that only the native materials are put into the coating process, the oxides, rust, and other foreign matters are neutralized and removed.
- What is heat treatment?
Heat treating is the controlled heating and cooling of metals to alter their physical and mechanical properties without changing the shape of the object or product. Heat Treatment is often associated with increasing the strength of the material, but it can also be used to alter certain manufacturability objectives such as improve machining, improve formability, and restore ductility after a cold working operation.
- What is the lowest temperature the tool is under during the coating process and what is the highest?
The temperature that the parts are exposed are accumulation of initial heating during the pump down stage (room temperature to 500F), and the higher temperature are added/accumulated during the coating process.
The temperature generated during the coating process is result of the coating being deposited onto the surface of the part. formation the ions, reactive gases and their reactants bombarding (hitting) the surface of the parts.
Usually during the tooling PVD coating of a typical part depending upon shape, size and material will experience temperatures anywhere from 300F to about 950F. In addition, the temperature is and can be controlled according to difference in coating and application. In decorative coating, the coating temperature is controlled within 300 to 600F due to lower working temperature of ABS plastic, magnesium alloy, and other similar materials.
- What other coatings are out there besides PVD and what are the advantages and disadvantages?
The most common surface treatment methods utilized are PVD, CDV, electroplating, powder coating, Teflon coating, and black oxide. Electroplating, powder coating, and black oxide offer similar enhanced oxidation resistance, a more enhanced appearance, and some abrasion resistance as well. PVD and CVD offer 50% or more increase in life time of the part, abrasion resistance, and corrosion resistance. Furthermore properties can be modified according to different applications. PVD is applied under half the pressure and temperature of the CVD process which drastically reduces annealing or any other property altering.
- Why is TiN coating the most common?
TiN coating has been around the longest, and it is a base coating that is offered by every PVD coating. Therefore it is priced very competitive, in turn it is most likely the economical return in term of improved functionality or appearance per dollar. Other coatings may offer a longer life time, however, they may be more application specific and possibly more costly.
- What are the most common surface treatment methods
- Electro-chemical Treatments
Electro-chemical coatings are produced by electrolysis of an aqueous solution of a salt of the coating metal, the component to be coated being the cathode. For good wear resistance, chromium is the most widely used coating metal as it combines high hardness (about 1000 Hv) with corrosion resistance and a low coefficient of friction against steel if the load is not excessive. Chromium coatings are limited in thickness to 0.5 mm because of internal stresses. Thicker coatings may be obtained using nickel, but the deposit is relatively soft (about 250 Hv) so it is not normally used for wear resistance. Hard particles of carbides (e.g. SiC, Cr2C3) and oxides, (e.g. Al2O3) can be incorporated in electro-chemical coatings of nickel and cobalt during plating to give a hardness of 600 Hv.
- Chemical Treatments
Chemical coatings are produced by the immersion of the component in a solution of a salt of the coating metal, no current being used. Coatings of nickel, phosphorus, and nickel boron alloys are produced by the reduction of a nickel salt by sodium hypophosphite or sodium borohydride respectively. After heat treatment, coatings have a hardness of up to 1000 Hv and good adhesive wear resistance. Electrolysis nickel coatings are more expensive than electro-chemical chromium coatings but they have superior corrosion resistance and uniform thickness can be obtained on complex shaped components. Hard particles, e.g. of SiC, can also be incorporated in the nickel during deposition to give a composite coating with a hardness of about 1300 Hv. Thin (0.01 mm) coatings of metal phosphates are also formed chemically on steel components to provide a low friction surface and resistance to adhesive wear, usually to aid running in.
- Chemical Vapor Deposition
Chemical vapor deposition (CVD) is a process whereby compounds are reacted in the gas phase to form a dense layer on a heated substrate. The most widely used wear resistant materials deposited by CVD are titanium carbide and titanium nitride. With these materials the coating thicknesses are limited to about 10 micro m by interfacial stresses. Temperatures in the range 800C to 1000C are required for deposition, at these temperatures thermal distortion and chemical reaction between coating and substrate limit the choice of substrate. In wear resistance applications, only cemented carbides and some tool steels are used and in these cases the reaction that takes place results in very high bond strengths. Compared to PVD processes, CVD has much better ‘throwing power’ i.e. the ability to coat complex shaped components with a coating of uniform thickness.
- Physical Vapor Deposition
Physical vapor deposition (PVD) processes are performed at sub-atmospheric pressures, the coating atmosphere being generated by thermal evaporation or electrical sputtering of a suitable source material, possibly with the addition of a reactive gas. For titanium nitride, the most widely used wear resistant material deposited by PVD, the coating rate is limited to a few microns per hour with a thickness range of 1 – 10 micro m. Coatings are dense and with appropriate techniques, good adhesion to the substrate is achieved. Substrate temperatures do not exceed 500C.
In this procedure, a large chamber is loaded with parts to be coated. The chamber is then closed and air is pumped out creating a vacuum. Then argon, an inert gas, is fed into the chamber. Subsequently, a high current is applied to create an arc across a gap between the chamber walls and a solid metal rod. The intense, dense energy from the arc evaporates the metal rod (changing the metal from a solid state to liquid to gas). Charged atoms ejected from the metal rod collide with the argon atoms creating plasma matter in an energetic, gas state. The plasma creates a conductive path that sustains the arc in the vacuum. As the evaporation occurs, parts (such as faucets) are rotated in front of this evaporating source. The gas condenses on the parts growing a thin solid film atom by atom. There are various other surface treatment methods commonly employed by the application and decorative.
- Spraying Processes
A number of processes have been developed in which particles of the coating material are heated to a molten or plastic state and projected at the substrate which is relatively cold (less than 200C). Coating density and strength of the bond with the substrate increase with projection velocity. This may be about 100 m/s in a simple combustion gun; 500 m/s in a plasma gun in which gases, usually argon and hydrogen, are heated in an electric arc to 15,000C; and 800 m/s in a gun in which metered quantities of acetylene and air are detonated. Most metals and ceramics can be sprayed onto a wide range of metallic substrates. All sprayed coatings are porous to some extent, the porosity varying from about 20% for application by a combustion gun to less than 1% for detonation gun coatings. The bond between the coating is mainly mechanical and is usually much less strong than those obtained by other coating processes.
- Welding Processes
All of the various welding methods can be used to deposit wear resistant coatings (hard facing). Coating materials range from low alloy steels to tungsten carbide composites. Rates of deposition are high and good bond strengths are obtained because of alloying at the coating – substrate interface. There is no easily defined upper limit to coating thickness, although there is a tendency for some of the harder materials to crack if deposited too thickly. These cracks are not usually harmful since they are perpendicular to the surface and do not usually reach the interface. It is ,however, impracticable to produce coatings less than 2 or 3 mm thick. Most hard facing materials are based on:
Micro structurally, most hard facing alloys consist of hard phase precipitates such as borides, carbides, or intermetallics bound in a softer iron, nickel, or cobalt base alloy matrix. Carbides are the predominant hard phases in iron and cobalt base hard facing alloys. Borides and carbides are the main hard phases in nickel base hard facing alloys. The matrix alloys in most cobalt, nickel and high alloy iron base hard facing alloys generally contain up to 35% Cr, up to 30% Mo and up to 13% W, with smaller amounts of silicon and manganese.
PVD Coating Information Links
- What is PVD coating and why is it important? From <https://www.borgandoverstrom.com/en/blog/what-is-pvd-coating/>
- PVD Coating Process Background, From <http://www.hefusa.net/pvd_coating/PVD-Coatings-FAQ.html>
- What Is PVD Coating & How It Works, From <https://alcadyne.com/what-is-pvd-coating-how-it-works/>
External links for more information on PVD coating and material properties.
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