New high-quality wear-resistant coating improves cutting tool performance

Challenge: Improve cutting tool performance by developing better wear resistant coatings.

Solution: A new quality coating that significantly reduces wear.

Chemical coating (CVD) is a key technology used to produce high quality coatings to improve the performance of cutting tools. The continuous evolution of tool coatings and processes has greatly increased the efficiency of tool production, and chemical coatings are a major contributor to this development.

The history of Sandvik Coromant's involvement in chemical coatings dates back to the original introduction of coated blade grades in 1969. This GC125 grade has only a few microns thick titanium carbide coating, but it increases cutting speed and extends tool life.

Chemical coating is an extremely versatile technology for the production of hard-wearing hard coatings such as titanium carbonitride, aluminum oxide and diamond, as well as semiconductor products. It is another auxiliary technology for the widely used tool coating technology, Physical Coating (PVD). The chemical coating forms thick aluminum oxide (Al2O3), titanium carbide (TiC), titanium carbonitride (TiCN) and titanium nitride (TiN) coating (5-25 microns) on the tool insert to provide the pole High wear resistance and suitable for use in the presence of large amounts of abrasive wear. In contrast, the thinner coatings produced by the physical coating process have high compressive stress and are therefore more suitable for cutting applications that emphasize toughness.

Chemical coating technology is constantly improving and perfecting. One reason for the development of chemical coatings is that it allows engineers to optimize each coating, and today it is still the only coating process that deposits a high quality alpha-Al2O3 crystalline layer.

The latest coated carbide inserts have up to 10 coats, each with a different function. In multi-coated grades, a thin layer of titanium nitride is used for the wear mark; underneath it is usually an aluminum oxide layer that provides chemical and abrasion resistance. Below are several layers of ductile carbonitride and nitride layers that provide a high degree of flank wear resistance. The blade base consists of a cemented carbide bottom and a cobalt binder phase, while in the region near the coating, the matrix on some of the cemented carbide substitutes has been removed to enhance edge fracture resistance.

The blade may have multiple different chemical coatings, each with different functions.

The first grade of Sandvik Coromant to use precision chemical coating technology is the GC3020 for cast iron milling. It was introduced in 1994 with a medium temperature chemical coating (MTCVD – Titanium Carbonitride (TiCN) on the inner layer and a unique patented alumina (Al2O3) for excellent wear resistance and coating adhesion. The GC2025 grade for stainless steel cutting is an example of the latest technology available today.

In practice, chemical coatings involve a series of processes, including the use of a gas phase to deposit solid materials. In the simplest form, for example, the chemical coating system consists primarily of a heated reaction chamber (on which the blade to be coated is placed on the carrier), a gas delivery system, and a vacuum pump system. This pump is used to maintain low pressure in the reactor and to remove various excess and incidental gases. At a preheating temperature, gases such as aluminum chloride, carbon monoxide, carbon dioxide, hydrogen, nitrogen, and titanium tetrachloride are introduced into the reaction chamber. As they pass over the heated surface of the blade, a reaction occurs and a solid coating is formed. Process parameters such as gas flow, gas pressure and reaction temperature are critical. Deposition of alumina requires a temperature of around 1,000 degrees Celsius; while titanium carbonitride provides the best results in the range of 800 to 950 degrees Celsius. A chemical coating process can take up to 24 hours.

to sum up

Chemical coatings (CVD) are likely to remain important in the future. It has had a major impact on tool performance, so that more than 80% of today's blade grades are coated. Nearly 70% of the coating grades currently offered by Sandvik Coromant use chemical coatings.

Chemical Coating (CVD) grades at a glance:

——SO5F CVD coated cemented carbide: suitable for high-speed finishing of high-temperature alloys or low-speed long cutting.
——GC3215 CVD coated cemented carbide: suitable for difficult interrupted cutting. Suitable for all cast iron machining.
——GC3210 thick coating CVD coated carbide: suitable for high speed turning applications of ductile iron.
-- GC4235 Low Stress MTCVD TiCN Coating: Suitable for steel turning and stainless steel applications.
-- GC4215 MTCVD TiCN coated grade: with a thick, low-stress alumina layer for maximum protection.
——GC2025 CVD coated carbide: suitable for semi-finishing to roughing.
——GC3205 thick coating CVD coated carbide: suitable for high-speed turning applications of gray cast iron.
——GC4225 CVD coated cemented carbide: suitable for a wide range of applications.
——GC2015 CVD coated carbide: suitable for stainless steel finishing and roughing, and provides chemical protection.

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