Papers by Keyword: Hard Coating

Abstract: Chemical vapour deposited HfN can be utilised as a component of multilayer systems in protective coatings on cutting tools. In this study, related AlHfN coatings were synthesized through a reaction of metallic hafnium and aluminium with HCl gas forming gaseous HfCl₄ and AlCl₃, which were subsequently transported into a heated coating reactor. Via high temperatures and separately introduced NH₃ and N₂ as reaction gases, AlHfN coatings were deposited on hardmetal inserts. By varying the ratio between AlCl₃ and HfCl₄, compositionally different AlHfN coatings were examined. Additionally, surface morphology, composition as well as crystalline phases of the obtained coatings were analysed by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Finally, the microstructure of the cross section of a coating was investigated via transmission electron microscopy. The observations revealed a great impact of the gas composition on the morphology and crystal structures of the coatings. Within the layer, the growth of columnar microstructures was detected. Additionally, the formation of an amorphous HfN intermediate layer between the substrate and the AlHfN with a thickness of approximately 2 nm was found.

Abstract: Ternary transition metal nitrides are commonly used as protective coatings on cutting tools, owing to their excellent mechanical and wear properties. While AlTiN is a very well-studied material, little is known about AlZrN, in part due to the large miscibility gap in the phase diagram of AlN-ZrN. In this study, AlZrN thin films were prepared using chemical vapor deposition. By the reaction of metallic aluminum and zirconium with HCl gas under elevated temperature, AlCl₃ and ZrCl₄ were produced in situ and subsequently transported into a heated coating reactor with a carrier gas. Due to the high temperatures and the separately introduced mixture of NH₃ and N₂, AlZrN coatings were deposited. By varying the experimental conditions, such as the ratio between ZrCl₄ and AlCl₃, we studied the influence of these parameters on the coating thickness and morphology as well as the microstructure. Additionally, the impact of different sample positions in the coating reactor on the deposited coatings was investigated. Furthermore, the generated samples were characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy and transmission electron microscopy.

Abstract: Finite element modelling (FEM) and eXtended FEM (XFEM) combined with the experimental nanoindentation and scratch tests have been used to simulate the process of cohesive cracking in W-C coating on softer and more ductile steel substrate during nanoindentation and scratch testing. The formation of single and multiple circular “frame” cohesive cracks in the sink-in zone during nanoindentation were explained by the development of high local tensile stresses in the coatings controlled by the plastic deformation of the substrate. Analogous mechanisms were successfully applied to the simulation of multiple Chevron type cracking during scratch testing. Thus, the ability of XFEM to predict the formation of different types of cohesive cracks was confirmed. It was also demonstrated that both nanoindentation and scratch tests in combination with XFEM can be used as the methods to determine the strength and fracture toughness of thin coatings.

Abstract: Nanocrystalline CrAlN thin films were deposited on silicon substrates by reactive DC magnetron co-sputtering technique. The effect of deposition time on crystal structure, chemical composition, thickness, microstructure and hardness of the thin films were characterized by XRD, EDS, AFM and FE-SEM and Nanoindentation, respectively. The as-deposited films were formed as a (Cr,Al)N solid solution with (111), (200) and (220) plane. The lattice constants were in range of 3.9916 - 4.0455 Å. The as-deposited films exhibited a nanostructure with a crystallite size in range of 15-35 nm. The thickness and roughness increased from 197 nm to 998 nm and 1.6 nm to 8.1 nm, respectively, with increasing the deposition time. The chemical composition of the films varied with the deposition time. The cross section analysis by FE-SEM showed columnar structure and dense morphology. The film hardness decreased from 39 GPa to 25 GPa with increasing the deposition time and crystallite size.

Abstract: Aluminum chromium nitride (AlCrN) coatings and aluminum chromium oxynitride (AlCrON) coatings were successfully fabricated through cathodic arc deposition with pulsed bias. The results indicated that both AlCrN and AlCrON coatings had a lower coefficient of friction against AISI 52100 bearing ball under dry conditions than CrN coating. The hardness of the AlCrN coating was in the range of 30 GPa, two times higher than that of the AlCrON coating. Thermogravimetric and differential scanning calorimetry analyzer (TGA/DSC) confirmed the best thermal stability of the AlCrON coating during the test.

Abstract: It is well known fact that materials play an important role in engineering design. Nowadays over a hundred thousand available materials can be distinguished with constant tendency for increasing the novel designed materials. Therefore material selection process becomes a complex and time consuming task. Selection of the most suitable material for a given application can be regarded as a multi-criteria decision making (MCDM) problem with conflicting and diverse objectives. New MCDM methods have been developed, and existing methods improved, showing that research in the decision-making is important and still valuable. This paper describes the use of recently developed MCDM methods, i.e. Complex Proportional Assessment (COPRAS) and Weighted Aggregated Sum Product Assessment (WASPAS) for selecting the most suitable hard coating material.

Abstract: This paper presents the applications of advanced CVD Tungsten Carbide coating to extend the life of tooling used for forming abrasive and corrosive materials.Hardide nanostructured Tungsten Carbide coating combines high hardness (70-77Rc) with excellent toughness. Unlike other hard coatings Hardide can produce a conformal coating layer on complex-shaped tools, including internal surfaces of extrusion die cavities and moulds. In ASTM G65 test the Hardide coating abrasion resistance exceeded WC/Co (9%) cemented carbide by a factor of 4X, and D2 tool steel by 10X. Thus the coating can significantly increase the life of D2 steel tooling used for forming abrasive materials and by maintaining better dimensional tolerances and surface finish of the tool it will manufacture better quality products.The Hardide coating has enhanced resistance to corrosion and aggressive media, including acids; this makes the coating especially suitable for the tooling used in forming uPVC, PTFE and other corrosive materials.The Hardide coating has been tested on extrusion and pelletizing dies processing abrasive and corrosive slurries and typically showed a 3X increase in the life of the tooling. Similar results were achieved by the coating of powder compaction punch/die sets for pharmaceuticals tableting.

Abstract: Fracture behavior of hard nanocrystalline coatings decisively influences the lifetime and performance of coated tools. In this work, residual stresses in as-deposited and annealed CrN coatings deposited at 350 °C using bias voltages of −40 V and −120 V were evaluated using synchrotron X-ray diffraction coupled with four-point bending. The stress development during the bending experiments was used to analyse fracture properties of the coatings. The results indicate that an annealing at 550 °C does not deteriorate the fracture behavior of the coatings prepared using −40 V bias. In the case of −120 V bias coatings, the residual stress relaxation after the thermal treatment is accompanied by a fracture strain decrease and a fracture stress increase. The as-deposited and annealed CrN coatings deposited using −120 V bias exhibit significantly large fracture strains in comparison with −40 V samples. Finally the results document that the fracture stress may not be the only relevant parameter when comparing different coating systems. Also the strain at fracture can be considered as significant indicator of the coating fracture response. Methodologically, the results indicate that in-situ X-ray diffraction coupled with four point bending can be effectively used to evaluate macroscopic fracture behaviour of hard coatings.

Abstract: Pressure-pushing method of evaluation for adhesion strength of high performance coatings material and substrate is presented. This method, based on the pressure-testing device of high performance bond strength test sample patent, is one that the sample is cracking along the interface by putting the static load. According to the sample’s stress boundary conditions, the formula of the adhesion strength is given. The surface coating/substrate interface stress distribution is analyzed by using the finite element method, which provides the theory basis for the correct evaluation of coating/substrate strength. The experiments are conducted on the strength of common coating substrate materials as well. All the results show that pushed method can test the adhesion strength of high performance coatings and substrate, whose data is smaller than the international standard and A STMC633-79. And the experimental data of the pushed method are free from the influence of random factors.

Abstract: CrAlN/BN nanocomposite coatings were deposited on mirror-polished silicon wafer and high-speed steel (HSS) substrates using reactive cosputtering, i.e., pulsed dc and rf sputtering of CrAl and h-BN targets, respectively. Further, the oxidation resistance of the obtained coatings was investigated. The CrAlN/BN coating exhibited superior oxidation resistance properties when compared with those of the CrAlN coatings; after annealing the sample at 800 °C in air for 1 h, the plastic hardness value of the CrAlN coatings decreased to 50% of the as-deposited hardness value; in contrast, the CrAlN/BN coatings exhibited self-hardening phenomena from 700 to 800 °C in the range of 5 to 30%. In particular, the CrAlN/18 vol% BN coatings showed an increase of approximately 30% in hardness values, and a maximum hardness value of approximately 50 GPa was reached after annealing the sample at 800 °C in air. The plastic hardness value hardly changed when the sample was annealed up to 800 ^°C in nitrogen and argon; this result was contrary to the result obtained for the sample that was annealed in air. The radiofrequency glow discharge optical emission spectroscopy (rf-GD-OES) analysis of the CrAlN/18 vol% BN coating annealed in air revealed that the coating has an oxide layer deposited on the surface to a depth of ~200 nm. Conventional transmission electron microscopy (TEM) observations of the same coating indicate that the columnar structure was disrupted by a thin layer (30–40 nm) of the coating annealed in air. The indentation hardness value of the annealed coating was measured using Ar ion sputtering before and after etching of the annealed surface. Subsequently, when the oxide layer was etched to a depth of 200 nm from the surface, the hardness value decreased from approximately 48 GPa to 43 GPa; this result was similar to the results obtained for the as-deposited coating.