PVD coating of cutting tools

Application:
The PVD (Physical Vapour Deposition) coating can be applied as the last step in the production of a tool with no loss of hardness, distortion or change to the microstructure of the steel or carbide. The significant advantage of the PVD method, in contrast to the CVD method, is the low coating temperature of less than 500 °C, which is thus below the tempering temperature of high-speed steels.

Technology:
All PVD methods take place in a high vacuum, in which a metal (such as titanium) is converted to its vapour state. The addition of a reaction gas (such as nitrogen) then creates a thin, hard and extraordinarily firmly-attached layer on the tool surface (e.g. TiN = titanium nitride).

The individual PVD methods differ only in the type of metal vapour deposition.

The length of the coating cycle depends on the size and shape of the tool. It generally lasts between 4 and 8 hours.

Precleaning:
For the coating to be successful, the tool surface must be clean. So, before coating, the tools undergo intensive cleaning in which oil, grease, inorganic salts and anticorrosion residues are removed. The cleaning line essentially consists of an ultrasound-based, multistage degreasing process with alkaline baths, a cascaded water rinsing module and finally stain-free drying.

Properties of the carbide coatings

	Properties / features
PVD layers	Hardness in HV	Practical coating thickness in µm	Friction coefficient of pin on disk test system steel on steel = 0.8	Coating temperature in °C	Max. temperature for use	Thermal conductivity (compared to steel)	Resistance to chemicals	Colour	General characteristics	Preferred application
TiN Titanium nitride	2300 +/-200	2 - 4	0,6	250° - 450°	500°C	Relatively low	Good	Golden	All-round coating	Cutting iron-based materials; plastic-forming; metal-forming
TiCN Titanium carbonitride	3500 +/-500	2 - 4	0,2	400° - 450 °	400°C	Relatively high	Good	Blue-grey	High hardness, excellent wear-resistance, improved viscosity	Cutting of hard to machine steel alloys; high-performance cutting when there are moderate temperatures at the cutter; excellent for metal-forming
EXXTRAL TiAlN monoblock	3300 +/-300	2 - 3	0,7	400° - 450°	80°C	Very low	Good	Anthracite	Excellent oxidation resistance	For machining hardened steel and high-speed cutting; semi-dry (MMS) or dry machining
EXXTRAL-Plus TiALN stacked	3300 +/-300	1 - 3	0,6	400° - 450°	800°C	Very low	Good	Anthracite	Excellent oxidation resistance	Machining hardened steel; high-speed cutting with lubrication. Excellent for stainless steels and nickel-based high-temperature alloys.
EXXTRAL-silver TiALCrN	3300 +/-500	2 - 3	0,6	400° - 450°	800°C	Very low	Good	Silver	Resistant to oxidation and wear	Cutting of aluminium, copper and other NF metals; for aluminium and magnesium die-casting
Sistral ALTiN nanostructured	3500 +/-500	2 - 4	0,7	400° - 450°	900°C	Very low	Good	Anthracite	Oxidation resistant, high hot hardness and wear-resistance	Cutting under extreme conditions of use; high-speed milling of very abrasive or hard materials (steel > 55 HRc)
Variantic TiALCN multilayer	3500 +/-500	2 - 4	0,2	400° - 450 °	800°C	Very low	Good	Copper-coloured	Very low friction; high oxidation-resistance	For a wide range of carbide, Cermet and HSS tools; all types of steel for MSS and wet-coating
Formatic TiN/TIC multilayer	3700 +/-200	3 - 5	0,3	400° - 450°	400°C	Very low	Good	Silver-grey	Low friction; very high hardness and wear-resistance	For machining CrNi steels and all stainless grades
CrN / CrCN chromium (carbo)nitride mono/multilayer	2000 (2300) +/-200	2 - 6	0,2 - 0,4	400° - 450°	600°C	Relatively high	Excellent	Silvery-grey	Low-stresses; high adherence and higher corrosion-resistance	Cutting copper and other NF metals. Metal and plastic-forming (improved demoulding)

Which PVD coating should be used with which material?

Cutting	TIN	TICN	Variantic	Exxtral Plus TIALN	Sistral	CrN	CrCN	Exxtral Silver
Normal-strength steels with conventional cutting parameters	++	+++	+++		++
Increased-strength steels and higher cutting parameters		++	++	+++	+++
Hard and high-speed cutting (HSP and HPC)		+	++	+++	+++
Cast iron, cast steel, hard alloys, titanium and nickel alloys	+	++	++	+++	+++			+++
Aluminium, aluminium and non-ferrous metal alloys	++			++	++	+++	+++	+++
Dry-cutting			++	+++	+++

+        = may be suitable
++      = suitable
+++    = particularly suitable