How Do We Choose Between PVD And CVD?

PVD and CVD are the most commonly used surface treatment methods for tools and moulds, CVD is based on chemical vapour deposition and PVD is based on physical vapour deposition, as they differ in principle, the final coating results are different and each has its own focus in application.

PVD is thinner than CVD, with a coating thickness of 10-20μm for CVD and only 3-5μm for PVD, and the processing temperature for PVD is around 500°C, while the furnace temperature for CVD is 800-1000°C. This shows that because of the high temperatures, CVD requires high temperature resistance for the material being treated. We hardly ever see anything other than carbide on CVD-treated tools, as the only mainstream cutting material that can withstand such high temperatures is carbide.

In addition to this, CVD coatings, due to their thickness and high processing temperatures, are susceptible to tensile stresses on the surface during cooling, resulting in the formation of fine cracks. These cracks tend to expand when subjected to external impacts (e.g. milling) and once they have expanded to the point where they run through the entire coating, the coating flakes off and the tool substrate is left without protection from the coating. Therefore, CVD coated tools are used in large numbers on turning inserts, as turning is subjected to uniform and continuous cutting forces throughout the cutting process, where the wear resistance of the CVD coating due to its thickness is clearly evident.

On the contrary, interrupted cutting represented by milling. The low processing temperature of PVD (around 500°C) causes compressive rather than tensile stresses to develop during the cooling process, which has the effect of preventing the formation and expansion of cracks. In addition, due to the thin thickness of the PVD coating, the geometry of the cutting edge is not altered much, which preserves the sharpness of the cutting edge to a large extent and reduces the generation of cutting forces and cutting heat. As a result, PVD is more suitable for interrupted milling operations and for almost all monolithic tools.

To be fair, CVD has another advantage over PVD that is difficult to surpass with the current common PVD technology, namely the most commonly used CVD coating material, aluminium trioxide (Al2O3). Al2O3 has very good physical and chemical stability, is hard wearing and extremely low cost, but the constraints of the production process make it very difficult to implement on normal PVD. However, due to the many other advantages of PVD and the recent expansion in coating materials, its performance has become increasingly superior to that of CVD in many respects. Its current share of the world tool market has gradually increased from 20-30% a decade ago to over 50% today.

In response to the convenience that PVD coating can bring to our customers, Enijor wants to improve the coating business. We will provide our customers with cost-effective coating services in a timely and convenient manner.