In terms of PVD principles, tungsten (W) can be deposited using various methods, such as magnetron sputtering, multi-arc ion plating, HiPIMS, or ion-beam-assisted deposition. The real question is: what is the intended application for the tungsten? Are you looking to create a pure tungsten layer, tungsten carbide (WC), a minor dopant within a W-DLC coating, or a high-load-bearing transition layer?
The most suitable method varies depending on the objective.
The biggest advantage of magnetron sputtering for W is "easy control"
The W target is a conductive target and can be used for magnetron sputtering. Ar ions bombard the W target, knock out W atoms, and then deposit them on the surface of the workpiece.
The advantages of using magnetron sputtering to deposit tungsten (W) are clear: fewer particulates, a smooth film surface, and easily controllable composition. This method is particularly well-suited for W-DLC coatings, where precise control over the tungsten content is required.
In W-DLC, tungsten is generally not the primary functional component. The carbon network is what actually provides low-friction properties; the tungsten serves to tune internal stress, enhance load-bearing capacity, and improve the stability of thicker films. However, adding too much tungsten disrupts the low-friction carbon network characteristic of DLC.
Therefore, W-DLC is most afraid of the W content getting out of control.
Herein lies the benefit of magnetron sputtering. You can slowly bring the W content to the target window by adjusting the W target power, carbon source flow rate, bias voltage, and air pressure. For example, if you compare low W, medium W, and high W, the trends in friction, hardness, and stress can be clearly seen.
Therefore, magnetron sputtering is a very common and stable route for fine W doping, W-C transition layer, and W-DLC main layer.
Multi-arc ion plating can be used for tungsten (W), but it presents greater challenges.
It is not impossible to process tungsten using multi-arc ion plating.
The arc spots in cathodic arc processes possess extremely high energy; theoretically, they can vaporize a wide range of high-melting-point metals, including refractory metals like W, Mo, and Ta. The fact that tungsten has a high melting point does not mean it cannot be vaporized by the arc spot.
However, just because it is possible does not mean it is easy to achieve.
Tungsten (W) is a material characterized by a high melting point and high hardness; consequently, processes such as target machining, clamping, cooling, and maintaining arc ignition stability are more challenging than with standard titanium (Ti) or chromium (Cr) targets.
When using multi-arc deposition for tungsten, special attention must be paid to arc spot movement, target surface ablation, localized overheating, particle formation, and film surface roughness.
The characteristics of multi-arc are high metal ionization rate, strong deposition energy and good bonding force, but it is also easy to bring droplets and large particles.
For conventional arc targets such as Ti and Cr, particles are already a common problem in multiple arcs. If it is replaced by a high melting point material such as W, the arc spot state and target surface ablation are not well controlled, and film surface defects may also be obvious.
Therefore, while multi-arc technology can be used to deposit tungsten (W), it is better suited for applications requiring intense metal ion bombardment, high adhesion, and the reinforcement of transition or load-bearing layers; it is not necessarily ideal for producing the highly refined W-DLC surface layers that demand low particulate levels and precise control over tungsten content.
Why do more people prefer magnetron sputtering when producing W-DLC?
Because the key to W-DLC lies not merely in "incorporating tungsten," but in determining how much to add, where to distribute it, and whether the addition disrupts the carbon network.
By using a magnetron-sputtered tungsten (W) target in conjunction with a carbon source-such as a graphite target, acetylene, methane, or other carbon plasma-it is relatively easy to maintain a low tungsten content, allowing it to disperse within the DLC matrix as fine W-C structures or nano-carbides.
In this way, the tungsten serves to enhance load-bearing capacity and reduce stress, while the carbon network remains continuous, ensuring that low-friction properties are preserved.
When using a tungsten (W) source in a multi-arc process, the flux of tungsten metal ions can be quite intense, making it easy for the local tungsten content to become excessively high.
High tungsten levels tend to promote the formation of significant amounts of WC or W₂C phases, effectively locking the carbon into carbide structures. Consequently, the resulting coating may end up as a tungsten-containing carbide composite hard coating rather than a low-friction DLC coating.
In other words, while it is certainly possible to use a tungsten source in multi-arc deposition, the window for controlling tungsten content is narrower and more difficult to manage; furthermore, close attention must be paid to surface particulates and the continuity of the carbon network.
Where is the multi-arc W better suited to be placed?
If it is W-DLC, I prefer to understand multi-arc W as a tool for "enhancement layer" or "transition layer", rather than directly using it to make a whole layer of high W-content DLC.
For example, close to the substrate, a W or WC transition layer can be used to improve load-bearing and bonding; a W-C gradient can be made in the middle to allow a gradual transition from metal to carbon; the most surface still maintains carbon-rich DLC to ensure low friction and anti-adhesion.
This design is more rational than using a monolithic tungsten (W) layer.
If the objective is not low-friction DLC but rather a high-hardness, wear-resistant layer of W, WC, or W-C, the multi-arc approach is also valuable. This is because multi-arc deposition generates high-energy metal ions, resulting in dense coatings with strong adhesion-ideal for creating robust, wear-resistant layers.
However, if the client requires an exceptionally smooth surface, minimal particulates, and a low coefficient of friction, one should exercise caution when relying solely on multi-arc deposition for tungsten.
If you are producing W-DLC coatings-particularly where the focus is on low friction, anti-sticking properties, sliding components, or smooth mold surfaces-prioritize using magnetron sputtering or HiPIMS to deposit the tungsten (W) component, combined with a carbon source for deposition. This approach allows for better control over the tungsten content, results in a finer coating surface, and makes it easier to preserve the carbon network structure.
If you need to produce a W-C transition layer that is thicker, offers higher load-bearing capacity, and requires strong adhesion, you might consider using a multi-arc W source or a hybrid source combining multi-arc and magnetron sputtering.
If you aim to produce pure W or WC-type wear-resistant layers, the multi-arc method is also an option, though you must be prepared to deal with challenges such as particulates, internal stress, target surface ablation, and surface roughness.
The conclusion is therefore simple:
Tungsten (W) coatings can be produced not only via magnetron sputtering but also through multi-arc ion plating.
However, magnetron sputtering is better suited for precisely controlling tungsten content and achieving a surface with minimal particulates, whereas multi-arc plating is superior for creating W or W-C transition layers characterized by high ionization, strong adhesion, and high load-bearing capacity. The optimal approach often involves a hybrid strategy rather than choosing one method over the other: using a tungsten layer at the base to enhance load-bearing capacity while retaining a low-friction DLC carbon layer on the surface.
