Nanolock Black: An unbreakable bond for milling

From the law of gravity to x-rays and penicillin - the story of some of the most important discoveries often owes thanks to coincidence. And the development of the world's first nano-structured coating for indexable inserts fits neatly into this pattern: the real breakthrough that led Boehlerit's expert engineers to the development of Nanolock some two years ago remained unnoticed at first.

On the search for greater hardness

We first need to appreciate that LMT's alliance partner Boehlerit wanted to use chemical vapor deposition (CVD) to develop a particularly hard titanium-carbon nitride (TiCN) coating. Instead of attempting to prepare the chemical coating at medium temperatures – generally between 700 and 900 degrees Celsius – like other manufacturers, the developers risked trying a high-temperature process in the range between 900 and 1000 degrees Celsius. The reason for this was that the new TiCN coating needed not only to be extremely hard and to have good adhesion, but it was hoped that it would not become brittle as quickly as other CVD surface treatments. TiCN coatings are most often used to bond a ceramic covering layer, such as aluminum oxide, to the tool or to the cutting edge.

Needle structure at the nano-scale

The experts were at first unable to explain why this effect was significantly reduced in the new Boehlerit range. Only examination under an electron microscope provided insight: the elements carbon and nitrogen had mixed together in the titanium carbon nitride layer. This had not just happened at the microscopic scale, but at the scale of the nano-structure. The Nanolock coating has an extraordinarily fine, needle-shaped surface. Like a zip-fastener, this nano-structure improves the bond with the outer layer that is deposited on top.

Protecting tools from heat

Since then, indexable inserts from Boehlerit with the Nanolock coating have proven their performance in a more than 1000 applications around the world – although most of these have been in the turning field. In order to be able to give this innovation greater prominence in the milling field, the needle-shaped TiCN coating has now been combined with a black, heat-resistant ceramic layer, known as a kappa-Al2O3 coating. There are several reasons for this. To begin with, cutting edges coated in this way have, of course, all the advantages we now expect from Nanolock: the adhesion between the black ceramic covering layer and the TiCN layer is particularly tight. This offers, moreover, high protection against wear and, due to its special structure, has an elastic, damping effect. In addition, the black ceramic layer only has a low thermal conductivity. This protects the ceramic substrate of the tool from heat. On top of this, special dopings (the inclusion of other types of atom) in the carbide substrate reduces the tendency to form thermal "comb" cracks. Altogether, Nanolock Black is well able to withstand the impact stresses typically encountered in milling. In addition, it is resistant to oxidation when used for dry machining. And one more thing: the CVD layers in Nanolock Black are only a few thousandths of a millimeter thick. This means that their application has no effect on the rounding of the tool's edges.

Economy in dry milling

The result of this research effort can be seen in the performance figures: The new, universal LC230E milling material with Nanolock Black gives the tool, above all, long-term protection from abrasion when dry-milling steel. The enormous benefits of this coating technology can be seen in particular at higher cutting speeds between 120 and 300 m/min. Nanolock Black has already been able to prove its capability, and its economy in a large number of applications, some of which have placed extreme demands on the material. This includes machining the plate edges of the steel plates for pipelines or of worn out rails of manganese steel – again at cutting speeds of up to 300 m/min.