Hard Ceramic Coatings Research Articles

Study on the sand erosion resistance of ZrN and ZrAlSiN coatings

Brittle spalling is a crucial problem for hard ceramic coatings under high-angle sand erosion, especially for traditional binary nitride coatings such as ZrN. Here, we deposited the ZrAlSiN coating by co-doping Al and Si into the ZrN coating to improve the toughness and erosion resistance. ZrN coating was also prepared on Ti6Al4V substrates by magnetic filtration cathode vacuum arc technology (FCVA) under the same process for contrast. The microstructure, mechanical properties, and sand erosion resistance of ZrN and ZrAlSiN coatings were studied. The ZrAlSiN coating contains nanocrystalline ZrAlN and amorphous Si3N4. The results show that the ZrAlSiN coating exhibits the highest H, H/E, H3/E2, and Welastic/Wplastic among as-deposited coatings with the value of ~30.8Gpa, ~0.12, ~0.43Gpa, and 2.19, respectively. The erosion rate of the ZrAlSiN coating is about half that of the ZrN coating. The dopping of Si element is conducive to inhibition of the grain growth. The enhanced toughness while maintaining high hardness is one of the main reasons for the better anti-sand erosion performance of ZrAlSiN coatings. The research helps promote the application of ZrN-based coatings in the field of anti-sand erosion.

Study on the Optimization of the Preparation Process of ZM5 Magnesium Alloy Micro-Arc Oxidation Hard Ceramic Coatings and Coatings Properties

Hard ceramic coatings were successfully prepared on the surface of ZM5 magnesium alloy by micro-arc oxidation (MAO) technology in silicate and aluminate electrolytes, respectively. The optimization of hard ceramic coatings prepared in these electrolyte systems was investigated through an orthogonal experimental design. The microstructure, elemental composition, phase composition, and tribological properties of the coatings were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and tribological testing equipment. The results show that the growth of the hard ceramic coatings is significantly influenced by the different electrolyte systems. Coatings prepared from both systems have shown good wear resistance, with the aluminate electrolyte system being superior to the silicate system in performance. The optimized formulation for the silicate electrolyte solution has been determined to be sodium silicate at 8 g/L, sodium dihydrogen phosphate at 0.2 g/L, sodium tetraborate at 2 g/L, and potassium hydroxide at 1 g/L. The optimized formulation for the aluminate electrolyte solution consists of sodium aluminate at 5 g/L, sodium fluoride at 3 g/L, sodium citrate at 3 g/L, and sodium hydroxide at 0.5 g/L.

Indentation and sliding contact testing of three laser-textured and PVD-coated cemented carbide tools

A new concept for cemented carbide tools was presented with laser-generated abrasive-like protrusions on their machining surfaces that mimic the surface features of diamond or cubic boron nitride abrasives commonly used on honing tools. In this study, the surface structure on the new tools were protected by three different PVD ceramic hard coatings. All three nitride-based coatings, i.e., TiSiN-AlTiN, TiSiN-AlTiN-CrN and AlTiN-CrN, differed in the adhesion layer and coating structure. The coating-substrate systems were assessed by means of indenting and sliding contact testing in order to find out an appropriate one for the textured tools. Experimental methodology included (1) ‘passive’ Vickers indentation hardness tests, and (2) ‘active’ machining tests. In both cases, the resulting surface integrity was inspected by using FIB/SEM/EDS. It is found that both laser texturing and coating deposition changed the hardness. The tool coated by the two-layer film (TiSiN-AlTiN) achieved the best performance, in terms of both hardness enhancement and damage prevention experienced under both tests. Meanwhile, improvement was much less pronounced by the two-layer (AlTiN-CrN) coated tool. Here, cracks appeared under the Vickers indentations and the film was completely or partially spalled-off at some protrusion tops (cutting fronts), due to the concentrated stress during the machining. Finally, the three-layer coating with the TiSiN on the top (TiSiN-AlTiN-CrN) exhibited an intermediate response, where moderate hardness increase was combined with some wear – although less severe than for AlTiN-CrN film - taking place at critical points, such as cutting fronts.

State-of-the-Art Developments in Advanced Hard Ceramic Coatings Using PVD Techniques for High-Temperature Tribological Applications

Hard and wear-resistant coatings created utilizing physical vapor deposition (PVD) techniques are extensively used in extreme tribological applications. The friction and wear behavior of coatings vary significantly with temperature, indicating that advanced coating concepts are essential for prolonged load-bearing applications. Many coating concepts have recently been explored in this area, including multicomponent, multilayer, gradient coatings; high entropy alloy (HEA) nitride; and functionally modified coatings. In this review, we highlighted the most significant findings from ongoing research to comprehend crucial coating properties and design aspects. To obtain enhanced tribological properties, the microstructure, composition, residual stress, hardness, and HT oxidation resistance are tuned through doping or addition of appropriate materials at an optimized level into the primary coatings. Such improvements are achieved by optimizing PVD process parameters such as input power, partial pressure, reactive gas flow rates, substrate bias, and temperature. The incorporation of ideal amounts of Si, Cr, Mo, W, Ag, and Cu into ternary and quaternary coatings, as well as unique multilayer designs, considerably increases the tribological performance of the coatings. Recent discoveries show that not only mechanical hardness and fracture toughness govern wear resistance, but also that oxidation at HT plays a significant role in the lubrication or wear failure of coatings. The tribo-induced metal oxides and/or Magnéli phases concentrated in the tribolayer are the key governing factors of friction and wear behavior at high temperatures. This review includes detailed insights into the advancements in wear resistance as well as various failure mechanisms associated with temperature changes.

Effects of ceramic-based CrN, TiN, and AlCrN interlayers on wear and friction behaviors of AlTiSiN+TiSiN PVD coatings

In this study, the wear and friction behavior of cathodic arc physical vapor deposited AlTiSiN+TiSiN coatings on H13 tool steels were investigated by using CrN, TiN and AlCrN interlayers with tribometer tests both under unlubricated and boundary lubricated conditions. 6 mm alumina balls were used as counter surfaces to test ceramic hard coatings. Surface coatings were characterized through nanoindentation, scanning electron microscopy coupled with an energy-dispersive X-ray spectrometer (SEM/EDXS), optical profilometry, and atomic force microscopy (AFM) techniques. The results showed that especially AlTiSiN+TiSiN coating with TiN interlayer resulted in a much more enhanced tribological performance of the tool steels at both unlubricated and the boundary lubricated conditions even at elevated contact pressures.

Method for tribological experiment to study scuffing initiation on AISI 52100 steel and hard ceramic coatings

Though many models of wear have been proposed, the design of the lab-scale experimental procedures to reproduce and characterize a particular wear regime, scuffing, has been difficult to generalize and more limited in scope. In this study, we used a high-frequency reciprocating tribometer to determine a set of tribological experimental parameters that instigate material scuffing and yield reliable and repeatable results by varying grinding lay orientation, temperature, counter body material, substrate hardness, contact load, stroke length, and frequency. The onset of scuffing in through-hardened 52100 steel substrates lubricated with low viscosity fuels was most repeatable with a perpendicular grinding lay and alumina counterface, while no effect was observed with substrate temperature. The experimental method using a load progression from 1 N to 18 N was then used on several protective coatings to determine their effectiveness in inhibiting scuffing initiation.

Supersensitive Sm2+‐Activated Al2O3 Thermometric Coatings for High‐Resolution Multiple Temperature Read‐Outs from Luminescence

AbstractThe introduction of additional functionalities to materials is exceptionally important as it opens new applications for them. Aluminum, one of the most abundant and important materials, is coated with luminescent Sm2+‐doped γ‐aluminium oxide to impart thermometric functionality. Considering the potential industrial applications, two of the most widely used aluminum alloys, 6061 and 7075, are also coated. For this purpose, plasma electrolytic oxidation (PEO), an effective technique for producing hard ceramic coatings on various metal surfaces, is used. It is shown that thermometric coatings can be produced on aluminum in one‐step process by adding the raw precursor to the electrolyte. The valence reduction of Ln3+ to Ln2+ is achieved during the PEO process. The intense and broad (orange to deep red) emission from the coating shows supersensitivity to temperature changes over the 100–648 K range. The temperature is obtained from the coating emission using i) the emission intensity ratio method, ii) emission lifetime, and iii) emission band position with sensitivities of 4.8% K−1, 1.2% K−1, and 8 cm−1 K−1, respectively. Several applications would benefit from the thermometric coating's excellent temperature resolution of 0.04 K and the choice of three temperature read‐outs that facilitate the coating's use in different luminescence thermometry setups.

Review of the fatigue behavior of hard coating-ductile substrate systems

With the wide application of coating materials in aerospace and other fields, their safety under fatigue conditions in service is important. However, research on the fatigue properties of ceramic hard coatings started late, and a unified standard is yet to be established to evaluate the fatigue life of hard coating-ductile substrate systems. Studies also present different opinions on whether coatings can improve or reduce the fatigue life of substrates. In this paper, the influence of the properties of ceramic coatings on fatigue performance is reviewed, and the effects of coating on the mechanism of fatigue crack initiation in substrates are discussed, aiming to help readers understand the fatigue behavior of hard coating-ductile substrate systems.

Effect of TiN, TiAlCN, AlCrN, and AlTiN ceramic coatings on corrosion behavior of tungsten carbide tool

Hard ceramic coatings are widely used for cutting and forming applications because these coatings on the surface of the tools considerably improve the oxidation, wear, and corrosion resistance of the materials. The aim of this study is to investigate the electrochemical corrosion behavior of TiN, TiAlCN, AlCrN, AlTiN, and multi-layered coat of AlTiN on tungsten carbide (WC) at different mediums. Coatings were performed using the cathodic arc evaporation-physical vapor deposition (CAE-PVD) method. The corrosion behaviors of the coated and uncoated WC materials were carried out with potentiodynamic polarization curves which used to calculate the corrosion rate of the tested materials at the pH values of 2, 7, and 10 at the room temperature. The surface morphologies of the uncoated and coated samples were examined by a scanning electron microscopy (SEM) before and after the corrosion testing. The corrosion experiment results indicated that the corrosion rate (114.7 × 10–6 mpy) of TiAlCN coating was much lower than WC substrate material (38.83 mpy) in pH = 7. The highest corrosion rate (1.559 mpy) was obtained for TiN coating, although the corrosion rate (490.8 × 10–9 mpy) of AlCrN coating was lower in pH = 10. The corrosion resistance of AlCrN coating was also the highest, even if in acidic environment.

Wear mechanisms identification using Kelvin probe force microscopy in TiN, ZrN and TiN/ZrN hard ceramic multilayers coatings

Mechanical and tribological properties of titanium nitride, zirconium nitride, and (TiN/ZrN)n multilayers were studied to examine the potential of Kelvin probe force microscopy (KPFM) to identify wear mechanisms. Crystalline structure, chemical composition, residual stress, and the mechanical properties showed that the coatings are iso-structural polycrystalline multilayers, with a reduction of grain size, crystallite size, and compressive stress; however, hardness increased with increase in the number of the bilayers. Pin-on-disc test was used for tribological evaluation, and wear tracks were analyzed using field-emission scanning electron microscopy/energy dispersed spectroscopy (FE-SEM/EDS) and KPFM. The increase in mechanical properties generated predominantly abrasive wear mechanisms. Abrasive and adhesive wear mechanisms differentiated by KPFM demonstrated that fragile wear mechanisms presented differences in capacitance and surface potential and that the method is sensitive when the adhered material presents differences in chemical composition. We have demonstrated KPFM to be a promising technique to study tribo-oxidation processes, providing experimental evidence to understand the wear mechanisms at nanometric scales.

Properties of Tool Steels and Their Importance When Used in a Coated System

The introduction of new light-weight high-strength materials, which are difficult to form, increases demands on tool properties, including load-carrying capacity and wear resistance. Tool properties can be improved by the deposition of hard coatings but proper combination and optimization of the substrate properties are required to prepare the tool for coating application. The aim of this paper is to elaborate on tool steel substrate properties correlations, including hardness, fracture toughness, strength and surface quality and how these substrate properties influence on the coating performance. Results show that hardness of the steel substrate is the most influential parameter for abrasive wear resistance and load-carrying capacity, which is true for different types of hard coatings. However, high hardness should also be accompanied by sufficient fracture toughness, especially when it comes to very hard and brittle coatings, thus providing a combination of high load-carrying capacity, good fatigue properties and superior resistance against impact wear. Duplex treatment and formation of a compound layer during nitriding can be used as an additional support interlayer, but its brittleness may result in accelerated coating cracking and spallation if not supported by sufficient core hardness. In terms of galling resistance, even for coated surfaces substrate roughness and topography have major influence when it comes to hard ceramic coatings, with reduced substrate roughness and coating post-polishing providing up to two times better galling resistance.

Grinding of hard and brittle ceramic coatings: Force analysis

In this work, a grinding force model has been proposed and a correlation between the analytical model and the experimental grinding forces obtained during finishing of plasma sprayed ceramic coatings has been investigated. Thermally sprayed ceramic coatings have low fracture toughness and develop micro brittle fracture under moderate mechanical loading. In this investigation, grinding of air plasma sprayed alumina, zirconia, and titania coatings were studied theoretically and experimentally. It was observed that the ground surface contained micro-cracks and debris of irregular fragmented chips owing to the micro-brittle fracture. A grinding force model is proposed to incorporate the fracture behavior of the ceramic coating. This was substantiated through experimental values showing low grinding forces.

Effect of Si content on functional behavior of nanostructured coatings of Zr–Si–N

Nanostructured coatings have been widely investigated due to their excellent physical and chemical features that surpass those of conventional materials. Hard ceramic coatings doped with silicon are part of nanostructured coatings used to modify the surface of solid materials and thus enhance their physical properties. In this investigation, a series of zirconium nitride (ZrN) coatings with different silicon (Si) contents (Zr–Si–N) were deposited on common glass and 316 l stainless steel substrates using pulsed-DC reactive magnetron sputtering, and the influence of the silicon content on the nanohardness, optical transmittance, and corrosion resistance was investigated using nanoindentation, UV–vis-IR spectrophotometry, and electrochemical impedance spectroscopy, respectively. The results indicated that as the silicon content increases, the nanohardness values decrease from 29.6 GPa (0 at% Si) to 15.9 GPa (15 at% Si), but as the silicon content increases (>15 at%), the nanohardness value increased to 28.1 GPa. Optical measurements showed that the transmittance is higher in the infrared wavelengths as the silicon content increases, and the corrosion resistance of the 316 L stainless steel substrate was improved with the addition of silicon.

Reactive ion beam stripping process for diamond coated cutting tools reconditioning

Cemented carbide cutting tool reconditioning and reuse approach gives a significant benefit to the subtractive manufacturing industry by saving tool manufacturing and material costs. Successful reconditioning requires wear resistant coating to be stripped off prior to the edges resharpening. Electro-chemical stripping of ceramic hard coatings is a well established process. However, it is not applicable to diamond coatings due to diamond's chemical stability. In this work we are reporting an ion beam based stripping process, showing excellent results in the CVD diamond coated drills and end mills. Erosion rates were measured for micro-, nano- and ultra nanocrystalline diamond films. It was shown that suggested stripping methods provides 10 times higher erosion rate of the diamond films compared to the cemented carbide. Spatial distribution of the erosion rate along the perimeter of transverse cross-section of a drill was shown to be rather uniform, with deflection ~20% of max value. Raman spectroscopy was utilized in order to facilitate a discussion on the diamond erosion mechanisms.

Wear Resistant Coatings with a High Friction Coefficient Produced by Plasma Electrolytic Oxidation of Al Alloys in Electrolytes with Basalt Mineral Powder Additions.

To achieve a better performance of engineering components, modern design approaches consider the replacement of steel with lightweight metals, such as aluminum alloys. However, bare aluminum cannot satisfy requirements for surface properties in situations where continuous friction is needed. Among the various surface modification techniques, plasma electrolytic oxidation (PEO) is considered as promising for structural applications, owing to its hard and well-adhered ceramic coatings. In this work, the surfaces of two Al alloys (2024 and 6061) have been modified by PEO coating (~180 µm) reinforced with basalt minerals, in order to increase the coefficient of friction and wear resistance. A slurry electrolyte, including a silicate-alkaline solution with addition of basalt mineral powder (<5 µm) has been used. The coating composition, surface morphology, and microstructure were studied using X-ray diffraction, scanning electron, and optical microscopy. Linear reciprocating wear tests were employed for the evaluation of the friction and wear behavior. It was found that the coatings reinforced with basalt mineral showed that the wear and friction coefficients reached values 10−6–10−7 (mm3 N−1 m−1) and 0.7–0.85, correspondingly (sliding distance of 100 m). In comparison with the characteristics of resin-based materials (10−5–10−4 (mm3 N−1 m−1) and 0.3–0.5, respectively), the employment of thin inorganic frictional composites may bring considerable improvement in the thermal stability, durability, and compactness, as well as a reduction in the weight of the final product. These coatings are considered an alternative to the reinforced resin composite materials on steel used in frictional components, for example, clutch disks and braking pads. It is expected that the smaller thickness of the active frictional material (180 μm) reduces the volume of the wear products, extending the service intervals associated with filter and lubricant maintenance.

Effect of ion peening and pulsed plasma nitriding on the structural properties of TiN coatings sputtered onto 100Cr6 steel

Ion peening with noble gas is typically used to generate lattice imperfections and a nanostructure within the bombarded metal surfaces. This might have therefore an impact on subsequent plasma nitriding, thus allowing for enhancing the adhesion and wear resistance of hard ceramic coatings deposited onto steel surfaces. In this work, the influence of pre-treating a 100Cr6 steel surface by Xe+ ion bombardment and pulsed plasma nitriding was investigated with respect to surface roughness, wear resistance and residual stresses of thin TiN coatings deposited by reactive ion beam assisted deposition.Xe+ ion bombardment was carried out using a 400 eV acceleration energy produced by a broad Kaufman cell and subsequent thermo-chemical nitrogen diffusion was accomplished at 520 °C. The results show that Xe+ ion bombardment intensifies nitrogen diffusion without inducing significant changes in the substrate topography. The combined pre-treatment with Xe+ ion bombardment and subsequent pulsed plasma nitriding leads to a reduction of compressive stresses in the TiN coatings. The presence of porosity in the white layer diminished the wear resistance.

Mechanical failure of CrN/Cu/CrN interfacial regions under tensile loading

Quantitative assessment of the adhesion strength of ceramic hard coatings on substrates is a subject of great technological and scientific relevance, the achievement of which has proven difficult over the past two decades. Here we show that a micro-pillar tension testing protocol may serve as an effective method for this purpose, and demonstrate its effectiveness through a combination of micro tension testing and crystal plasticity finite element analysis (CPFEA). Tensile loading perpendicular to the interfaces, as well as accompanying CPFEA simulations, was conducted on CrN/Cu/CrN/Si micro-pillar tensile specimens fabricated from vapor phase deposited thin film sandwich structures. All tensile loading induced fracture were observed to occur within the Cu interlayer and near one Cu/CrN interface of the CrN/Cu/CrN sandwich structure. Observations, measurements, and discussions were made regarding the fracture surfaces, fracture stresses, and primary fracture mechanisms. Fracture surface examinations indicated ductile tensile fracture, induced by the formation of voids. It is shown that, due to the geometric constraint imposed by the ceramic layers in the current testing configuration, interlayer plasticity and the critical fracture stress display a strong dependence on the Cu interlayer thickness. It is postulated as a failure criterion that cooperation of deviatoric and hydrostatic stress components is needed to induce the nucleation and growth of voids. The relevance of the present work to the interfacial mechanical integrity of other metal/ceramic interfaces is discussed.

Dry Progressive Stamping of Copper-Alloy Snaps by the Plasma Nitrided Punches

The dry progressive stamping was strongly required to make mass production of clothing parts and beverage cans. The duplex coating was one of the most reliable means to protect the dies and punches from wear and friction and to prolong their life time. In this coating, the die and punch was first surface-treated to have sufficient hardness in compatible to the hard ceramic coatings. In the present study, the low temperature plasma nitriding at 673 K was employed to harden the six kinds of punches and dies for progressive stamping of copper alloyed fucks. The micro-structure and nitrogen mapping were investigated by SEM with EDS to demonstrate that the hardening took place by nitrogen super saturation into SKD11 matrix without nitride precipitations. These nitrogen super-saturated punches and dies were fix into the progressive die set for dry stamping. No significant wear of tools as well as reduction of stamping loads even after a million shots proved that the low temperature plasma nitriding should be suitable to make hardening of dry stamping die substrates even without use of hard ceramic coatings.

First principles study of ceramic materials (IVB group carbides) under ultrafast laser irradiation**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474207 and 11374217).

Group IVB carbides have been applied in extreme aerospace environments as hard ceramic coatings; ZrC is being considered as a replacement for SiC in nuclear reactors. Therefore, a thorough understanding of the laser irradiation response of group IVB carbides is of clear significance. However, the existing knowledge on the fundamental properties of IVB group carbides is limited and insufficient with regard to both irradiated and non-irradiated characteristics. We investigate the effect of ultrafast laser irradiation on the lattice stability of ceramic materials (IVB group carbides) using the density functional perturbation theory (DFPT). The calculated phonon frequencies of TiC and ZrC at the ground state are in good agreement with previous calculations and experimental values. The phonon frequencies of IVB group carbides are positive, even though the electronic temperature reached 5 eV. Thus, IVB group carbides are more stable under ultrafast laser irradiation, which has greater benefits in nuclear and aeronautical applications compared to metals (W, Na), semimetals (Bi), and semiconductors (Si, SiC). The thermodynamic properties of ZrC are calculated as functions of their lattice temperature at different electronic temperatures. The elastic shear constants of IVB group carbides satisfy the Born stability criteria at Te = 5 eV. In addition, a comparison of the predicted melting temperatures of IVB group carbides, reveal that HfC is better suited for extreme high-temperature environments.

Characterization and machining performance of laser-textured chevron shaped tools coated with AlTiN and AlCrN coatings

Owing to increased demands of more efficient cutting tools for machining difficult to cut materials and environment friendly cutting operations, laser textured tools have become necessary. The characterization and machining studies with such laser textured tools coated with hard ceramic coatings are the prime motivation for this present work. The main aspect of the study is to evaluate two different PVD coated (AlTiN and AlCrN) laser textured tools. In the first stage, laser textured tools were prepared with novel chevron shaped textures on tool rake face using nanosecond pulse laser. This stage is followed by PVD coatings of AlTiN and AlCrN coatings by cathodic arc evaporation (CAE) technique. Coating characterization studies were conducted considering coating morphology, surface roughness, coating elemental analysis and phase analysis of coated and coated textured tools. The performance of the different tools thus manufactured was evaluated by carrying out suitable turning experiments on cylindrical Ti6Al4V work material under dry cutting environment. Machining results were evaluated in terms of cutting force, flank wear progress, rake surface analysis, and chip underside study. Further, static diffusion couple test (SDCT) has been conducted to understand diffusion wear mechanism in plain and textured tools. A new concept of derivative cutting or interfacial multipoint micro-cutting (IMP-μC) on chip underside surface due to texture patterns and a reduction of derivative cutting due to coatings on the textured tools have been proposed.