Hard PVD ceramic coatings – What are they made of?
Unlike other techniques such as powder coatings, PVD coatings are extremely hard. Materials suitable for these thin film coatings are usually carbides, nitrides, borides and silicides of the IVth, Vth and VIth groups of the periodic table. The materials are formed by depositing metals in a nitrogen, hydrocarbon, or silicide atmosphere. It is thought that the ceramic compound is formed at the surface of the substrate. An example of such a hard ceramic is titanium aluminium carbo-nitride, TiAlCN.
This website concentrates on the PVD vacuum surface coating technique magnetron sputtering as this is the most widely used PVD surface coating technique as it is suitable for that is many applications. However the basics of arc evaporation and pulsed laser ablation can be viewed by clicking the links.
The arc evaporation coating deposition process
This PVD surface coating process takes place in a vacuum deposition chamber. The arc evaporation coating deposition process begins with the striking of a high current, low voltage arc on the surface of a cathode that gives rise to a small (usually a few microns wide) highly energetic emitting area known as a cathode spot. The localised temperature at the cathode spot is extremely high (around 15000 °C), which results in a high velocity (10 km/s) jet of vapourised cathode material, leaving a crater behind on the cathode surface. Read more.
High power pulsed magnetron sputtering (HPPMS/HIPIMS)
High power pulsed magnetron sputtering (HPPMS/HIPIMS) has the ability to produce thin film coatings with excellent adhesion, density, and low surface roughness. This is primarily due to the intense pulsed plasma producing a high density of metal ions. Read more.
Pulsed Laser Deposition (PLD)
Pulsed Laser Deposition (PLD) is a reliable, if extremely expensive, vacuum based PVD coating technique that allows the room temperature deposition of a wide range of target materials such as high-temperature superconductors, ferroelectrics, metals, polymers, and ceramics. Read more.
Nucleation and Growth
During PVD coating processes such as magnetron sputtering and arc evaporation the film material is usually deposited atom by atom on a substrate by condensation from the vapour phase to the solid phase. This condensation step is not a random impingement of atoms that stick on the surface at the point of impact, due to the development of interatomic attractive forces, thermal mobility considerations and surface defects. Read more.
Effect of Pressure and Temperature
Two factors that greatly affect the coating quality during deposition are pressure and temperature. The first published work in this area was carried out by Movchan and Demchishin and is known as the Structure Zone Model (SZM). This model was subsequently built upon by other researchers. The present day model is shown below. [CMN V2, Issue 3 1992]. Read more.