Halil Çalışkan

Monitoring of Wear Characteristics of TiN and TiAlN Coatings at Long Sliding Distances

TiN and TiAlN thin hard coatings have been widely applied on machine components and cutting tools to increase their wear resistance. These coatings have different wear behaviors, and determination of their wear characteristics in high-temperature and high-speed applications has great importance in the selection of suitable coating material to application. In this article, the wear behavior of single-layer TiN and TiAlN coatings was investigated at higher sliding speed and higher sliding distances than those in the literature. The coatings were deposited on AISI D2 cold-worked tool steel substrates using a magnetron sputtering system. The wear tests were performed at a sliding speed of 45 cm/s using a ball-on-disc method, and the wear area was investigated at seven different sliding distances (36–1,416 m). An Al2O3 ball was used as the counterpart material. The wear evolution was monitored using a confocal optical microscope and surface profilometer after each sliding test. The coefficient of friction and coefficient of wear were recorded with increasing sliding distance. It was found that the wear rate of the TiAlN coating decreases with sliding distance and it is much lower than that of TiN coating at longer sliding distance. This is due to the Al2O3 film formation at high temperature in the contact zone. Both coatings give similar coefficient of friction data during sliding with a slight increase in that of the TiAlN coating at high sliding distances due to the increasing alumina formation. When considering all results, the TiAlN coating is more suitable for hard machining applications.

A Comparative Study of the Microabrasion Wear Behavior of CoNiCrAlY Coatings Fabricated by APS, HVOF, and CGDS Techniques

The current study focuses on the microabrasion wear and microstructural properties of CoNiCrAlY coatings fabricated on nickel-based superalloy substrates using atmospheric plasma spraying (APS), high-velocity oxygen fuel (HVOF), and cold gas dynamic spraying (CGDS) methods. The microabrasion tests were performed on the samples for different durations in order to understand the wear mechanism of thermally sprayed coatings and influence of the coating microstructure on the wear mechanism. The microstructures of as-sprayed coatings and wear mechanisms on the worn coatings were investigated. Initial surface topography was examined using a surface profilometer. Coating hardness measurements were performed with a microhardness tester. The lateral fracture was observed as the wear mechanism on the samples. The wear resistance of the coatings has changed with the surface features of the samples depending on the coating production process.

Wear Behavior of Multilayer Nanocomposite TiAlSiN/TiSiN/TiAlN Coated Carbide Cutting Tool during Face Milling of Inconel 718 Superalloy

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.

3.16 Hard Coatings on Cutting Tools and Surface Finish

Performance of a machined part surface depends mostly on surface finish obtained on that part. Surface roughness, residual stress, microstructure, and hardness are some characteristics of the machined surface to be taken into account. Deposition of a hard coating on cutting tools improves the quality of surface finish by means of protection of the tool’s cutting edge geometry together with decreasing friction coefficient and cutting temperatures. The subject of this chapter is hard protective coatings, deposited by physical vapor deposition and chemical vapor deposition methods. An extended overview of fundamental effects of hard coatings on surface finish is performed.

Effect of Multilayer Nanocomposite TiAlSiN/TiSiN/TiAlN Coating on Wear Behavior of Carbide Tools in the Milling of Hardened AISI D2 Steel

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.

Effect of Boron Nitride Coating on Wear Behavior of Carbide Cutting Tools in Milling of Inconel 718

Boron nitride based tribological coatings promise hope in tribological applications thanks to their excellent lubrication and heat resistance properties. However, the applicability of these coatings on cutting tools in machining applications is not well known and it needs to be revealed. Therefore, in this study, a boron nitride (BN) coating was deposited on carbide milling tools. Inconel 718 was used as workpiece material in face milling tests to determine the wear behavior of the BN coated carbide tools. Surface roughness and tool wear was recorded in relation with cutting length. Wear mechanisms on the coated carbide tools were determined using scanning electron microscopy in combination with energy dispersive spectroscopy. Abrasive and adhesive wear was found as main failure mechanisms on the worn tools. Approximately two times longer tool life was obtained with the BN coated carbide tools.

Study of Nanolayer AlTiN/TiN Coating Deposition on Cemented Carbide and its Performance as a Cutting Tool

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.