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During high pressure die casting (HPDC), molten metal is injected into the tool cavity where it reaches high velocities that cause substantial wear of the tool components. In order to mitigate this problem, different surface treatments are sometimes employed for high production tools. The most common treatments are nitriding and physical vapor deposition (PVD) of hard coatings. Within this study, effectiveness of two duplex PVD hard coatings, CrN and TiAlN, was tested on core pins, which are the most endangered elements of high pressure die casting tools. Core pins were tested in four industrial production runs of an automotive component. In every run, the tool was mounted with one pin that was PVD-coated, and one that was gas-nitrided. Nitrided core pins were used as a base standard since the nitriding is the most commonly used surface treatment. TiAlN-coated pins were able to complete a full production run of 22,000 shots without significant damage. CrN coating showed somewhat higher soldering tendency and erosion rates. Considering that the untreated core pins were able to withstand only 5500 shots, it can be concluded that duplex PVD coatings can significantly improve tool lifetime. Additionally, results indicate that often disregarded variances in casting temperature or in cleanliness of ingots used in production can significantly influence wear performance of HPDC tools. Analysis of the production costs has shown that the application of duplex TiAlN coating on the core pins can lead to significant savings for tested automotive components.

The Inconel 718 superalloy is one of the most-used nickel based superalloys in the aerospace industry due to its superior mechanical properties, for instance, high thermal and chemical resistance, and high strength at elevated temperatures. However, the work hardening tendency, low thermal conductivity and high hardness of this superalloy cause early tool wear, leading to the material to be called as a hard-to-cut material. Therefore, deposition of a wear resistant hard coating on carbide cutting tools has a critical importance for longer tool life in milling operations of the Inconel 718 superalloy. In this study, carbide cutting tools were coated with multilayer nanocomposite TiAlSiN/TiSiN/TiAlN coating using the magnetron sputtering technique, and wear behavior of the coated tool was investigated during face milling of the Inconel 718 superalloy under dry conditions. Abrasive and adhesive wear mechanisms were founded as main failure mechanisms. The nanocomposite TiAlSiN/TiSiN/TiAlN coated carbide cutting tool gave better wear resistance, and thus it provided 1.7 times longer tool life and a smoother surface (Ra<0.18 μm) on the Inconel 718 material than the uncoated one.

Titanium and its alloys are widely used in aerospace and aviation industries because of their high strength-to-weight ratio, high fracture resistance and corrosion resistance at elevated temperatures. However, chemical reactivity and low thermal conductivity of these alloys lead to adhesion and diffusion wears on carbide tools, respectively. In addition, fluctuations in cutting forces occur during the cutting process due to chip shear band formation; and chipping wear is observed at the tool cutting edge as a result. Therefore, machining of these alloys is a challenge for researchers. A common method to increase the lifetime of carbide tools is to coat them with a thin hard coating. In this study, a nanolayer AlTiN/TiN coating was deposited on carbide cutting tools using an industrial magnetron sputtering system in order to enhance their wear resistance and lifetime in milling of Ti6Al4V. The cutting tests with the coated tools were performed at a cutting speed of 50 m/min, feed rate of 0.1 mm/tooth and depth of cut of 1 mm under dry conditions. Tool wear and surface roughness on the workpiece were measured and recorded as a function of cutting distance. Wear mechanisms and types were revealed using optical and scanning electron microscopy and energy dispersive spectroscopy. It was found that the nanolayer AlTiN/TiN coated tools provide higher wear resistance and 4 times longer lifetime when compared to uncoated ones. The main observed wear types are notch wear and build-up edge formation on the cutting edge. A slight improvement in surface roughness of the workpiece was observed with the nanolayered coating.

Thin hard coatings are widely used in the protection of cutting tools, dies and molds to prolong their wear resistance and lifetime. Superior properties of different coatings can be combined with multilayer design, and especially a higher microhardness can be obtained by nanocomposite structures. In this study, a multilayer design composing of TiAlSiN, TiSiN and TiAlN layers was applied on carbide cutting tools. The top TiAlSiN layer has a nanocomposite structure of crystalline fcc-TiAlN and amorphous Si3N4 phases. The multilayer nanocomposite TiAlSiN/TiSiN/TiAlN coating was deposited on the carbide cutting tool using an industrial magnetron sputtering system. Wear behavior of the coated tools was investigated in the milling of hardened AISI D2 steel (~55 HRc). The changes in tool wear and surface roughness as a function of cutting distance were recorded. Wear mechanisms and types were investigated using optical and scanning electron microscopy in combination with energy dispersive spectroscopy. It was found that the multilayer nanocomposite TiAlSiN/TiSiN/TiAlN coating provides at least 1.2 times higher wear resistance and a longer lifetime than single layer TiN and TiAlN coatings. Main wear mechanisms are abrasion and adhesion of the workpiece material on the cutting edge. As a result, wear types are notch wear and build-up-edge formation.

Three-types of diamond-like carbon (DLC) coatings were prepared by employment of an anode layer source on stainless steel substrates (316L). The DLC films show an amorphous structure and their thickness ranges between 1.1 to 1.5 um. An interlayer of sputtered Cr was used as buffer between the DLC and stainless steel substrate in order to enhance adhesion. The corrosion properties of DLC-coated stainless steel in Hank's solution (pH=7.2) were studied using electrochemical methods. Results show that all DLC-coated substrates have up to one order of magnitude better corrosion resistance than a bare substrate.

A comparative tool life test of protected tools was made in aluminium die-casting of driving wheels for automobiles with two types of cores in one casting plate. One set of cores was improved with plasma nitriding process, while another one was improved with duplex treatment (plasma nitriding + PVD CrN coating). After 2700 and 4150 shots, surfaces on both types of tools were analysed using optical and scanning electron microscopes to identify damages of tool working surfaces. The performance tests, made under real manufacturing conditions, showed that wear of duplex treated tool is smaller compare to only plasma nitrided tool.

Three-types of diamond-like carbon (DLC) coatings were prepared by employment of an anode layer source on stainless steel substrates (316L). The DLC films show an amorphous structure and their thickness ranges between 1.1 to 1.5 μm. An interlayer of sputtered Cr was used as buffer between the DLC and stainless steel substrate in order to enhance adhesion. The corrosion properties of DLC-coated stainless steel in Hank's solution (pH=7.2) were studied using electrochemical methods. Results show that all DLC-coated substrates have up to one order of magnitude better corrosion resistance than a bare substrate.