Thermal and thermo-mechanical properties of Ti–Al–N and Cr–Al–N coatings

Metastable Ti–Al–N and Cr–Al–N coatings have been proven to be an effective wear protection due to their outstanding mechanical and thermal properties. Here, a comparative investigation of mechanical and thermal properties, for Ti–Al–N and Cr–Al–N coatings deposited by cathodic arc evaporation with the compositions (c-Ti_0.52Al_0.48N, c/w-Ti_0.34Al_0.66N and c-Cr_0.32Al_0.68N) widely used in industry, has been performed in detail. The hardness of Ti_0.52Al_0.48N and Ti_0.34Al_0.66N coatings during thermal annealing, after initially increasing to the maximum value of ~ 34.1 and 38.7 GPa with T_a up to 900 °C due to the precipitation of cubic Al-rich and Ti-rich domains, decreases with further elevated T_a, as the formation of w-AlN and coarsening of precipitated phases. A transformation to Cr₂N and finally Cr via N-loss in addition to w-AlN formation during annealing of the Cr_0.32Al_0.68N coating occurs, and thus results in a continuous decrease in hardness. Among our coatings, the mixed cubic-wurtzite Ti_0.34Al_0.66N coating exhibits the highest thermal hardness, but the worst oxidation resistance. The Cr_0.32Al_0.68N coating shows the best oxidation resistance due to the formation of dense protective α-Al₂O₃-rich and Cr₂O₃-rich layers, with only ~ 1.4 μm oxide scale thickness, after thermal exposure for 10 h at 1050 °C in ambient air, whereas Ti–Al–N coatings are already completely oxidized at 950 °C.     

A comparative study of microstructure,oxidation resistance,mechanical, and tribological properties of coatings in Mo–B–(N), Cr–B–(N) and Ti–B–(N) systems

M–B–(N) (M = Mo, Cr, Ti) coatings were obtained by the magnetron sputtering of MoB, CrB₂, TiB, and TiB₂ targets in argon and in gaseous mixtures of argon with nitrogen. The structure and composition of the coatings have been investigated using scanning electron microscopy, glow-discharge optical emission spectroscopy, and X-ray diffraction. The mechanical and tribological properties of the coatings have been determined by nanoindentation, scratch-testing, and ball-on-disk tribological tests. The experiments on estimating the oxidation resistance of coatings were carried out in a temperature range of 600–1000°С. A distinctive feature of TiB₂ coatings was their high hardness (61 GPa). The Cr–B–(N) coatings had high maximum oxidation resistance (900°С (CrB₂) and 1000°С (Cr–B–N)) and possessed high resistance to the diffusion of elements from the metallic substrate up to a temperature of 1000°С. The Mo–B–N coatings were significantly inferior to the Ti–B–(N) and Cr–B–(N) coatings in their mechanical properties and oxidation resistance, as well as had а tendency to oxidize in air atmosphere after long exposure at room temperature. All of the coatings with nitrogen possessed a low coefficient of friction (in a range of 0.3–0.5) and low relative wear ((0.8–1.2) × 10^–6 mm3 N^–1 m^–1.     

Influence of Al on the microstructure and mechanical properties of Cr–Zr–(Al–)N coatings with low and high Zr content

Low Zr (S1) and high Zr (S2) quaternary Cr–Zr–(Al–)N coatings with increasing Al content were deposited by d.c. reactive magnetron sputtering. The structure, fracture cross-section morphology and mechanical properties of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), nanoindentation, scratch testing and Vickers micro-indentation testing. All the coatings present an fcc NaCl-type B1 structure; in the low Zr content coatings, the diffraction peaks shift towards higher angles as the Al content increases. The grain size is approximately constant in a range from 6 to 8 nm, except for high Zr content films where a significant decrease in crystalline order is observed (grain size ~ 2.5 nm). In both series, the microstructure changed from equiaxed to columnar with increasing Al content. The highest hardness and strongest adhesion values were achieved in coatings with lower Zr and Al content. Conversely, the coatings with high Zr and the highest Al content exhibited an abrupt decrease in hardness, adhesion strength and toughness.     

Comparative investigation of oxidation resistance and thermal stability of nanostructured Ti–B–N and Ti–Si–B–N coatings

Nanostructured Ti–B–N and Ti–Si–B–N coatings were deposited on silicon substrate by ion implantation assisted magnetron sputtering technique. To evaluate the oxidation resistance and thermal stability the coatings were annealed on air and in vacuum at 700–900°C. As-deposited and thermal-treated coatings were investigated by transmission electron microscope, selected area electron and x-ray diffraction, atomic force microscopy, Raman and glow discharge optical emission spectroscopy. Nanoindentaion tests were also performed. Obtained results show that Si alloying significantly improves the thermal stability of Ti–B–N coatings and increases their oxidation resistance up to 900°C. It was shown that formation of protective amorphous SiO₂ top-layer on the coating surface plays important role in the increasing of the oxidation resistance.     

Elevated-temperature tribological behavior of Ti–B–C–N coatings deposited by reactive magnetron sputtering

Quaternary Ti-B-C-N coatings with various carbon contents were deposited on high-speed steel(HSS)substrates by reactive magnetron sputtering(RMS) system.The elevated-temperature tribological behavior of Ti-BC-N coatings was explored using pin-on-disk tribometer,scanning electron microscopy(SEM),and energy-dispersive X-ray spectroscopy(EDX).The present results show that the steady-state friction coefficient value and the instantaneous friction coefficient fluctuation range of TiB-C-N coatings decrease as carbon content increases at100 and 300 ℃,while the steady-state friction coefficient value of all Ti-B-C-N coatings becomes higher than 0.4 at500 ℃.As ambient temperature increases,the running-in periods of all Ti-B-C-N coatings become shorter.Wear damage to Ti-B-C-N coatings during sliding at elevated temperature is mainly caused by adhesive wear,and adhesive-wear damage to Ti-B-C-N coatings increases as ambient temperature increases;however,higher carbon content is beneficial for decreasing the adhesive-wear damage to Ti-B-C-N coatings during sliding at elevated temperature.     

Increased adhesion of diamond-like carbon–Si coatings and its tribological properties

A pre-activation process on substrate surface has remarkably improved the poor adhesion strength of diamond-like carbon (DLC)–Si coatings on steels which is the largest obstacle in achieving a widespread application of the coatings onto machine components. The activation process consists of preliminary nitriding followed by ion etching under the selected condition. Very fine protrusions formed by the processes provide large adhesion strength to the coatings that were made continuously within the same DC-plasma-assisted chemical vapor deposition (PACVD). No intermediate layers are necessary. The critical load of DLC–Si coatings thus treated reached over 50 N in the scratch tests. The coatings with the critical load over 50 N showed much improved rolling fatigue life. The DLC–Si coating with over 50 N critical load endured a rotationa1 stress of 10⁸ cycles at a contact pressure of 3.4 GPa, whereas the DLC–Si coatings with 10 N spalled at 10⁶ cycles.     

Erosion and Abrasion Resistance,Mechanical Properties,and Structure of the TiN,Ti–Cr–Al–N and Cr–Al–Ti–N Coatings Deposited by CFUBMS

Protection of Metals and Physical Chemistry of Surfaces - The results of structural studies and mechanical, abrasion, and erosion tests of single-layer and multi-layer TiN,...     

Thermal treatment effect on structural and mechanical properties of Cr–C coatings

In the present study, the effect of thermal treatment on the mechanical and structural properties of chromium carbide coatings with different thicknesses is evaluated. The coatings were deposited by cathodic magnetron sputtering on XC100 steel substrates. Samples were annealed in vacuum, at different temperatures ranging from 700 to 1000°C for 1?h, resulting in the formation of chromium carbides. X-ray diffraction (XRD), microanalysis X/energy-dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy analysis were used to characterise the samples. Mechanical properties were evaluated by nano-indentation tests and the residual stress was calculated with the Stoney formula. The XRD analysis suggests the formation of the Cr₇C₃, Cr₂₃C₆ carbides at 900°C. For thin films, they transformed totally to ternary (Cr, Fe)₇C₃ carbides and their partial transformation has been observed in the case of thick films at 1000°C, without the formation of Cr₃C₂. The EDS and XPS showed the diffusion mechanism between the chromium film and the steel substrate for the Cr, Fe, C, O elements during the annealing treatment. The increase of chromium film thickness from 0.5 to 2.64?µm, contributed to the significant enhancement of mechanical properties such as hardness (H) (from 12 to 26.3?GPa) and Young's Modulus (E) (from 250 to 330?GPa), respectively.     

Corrosion and tribological properties of nanocrystalline pulse electrodeposited Ni–W alloy coatings

Ni–W alloys with different tungsten content and grain size under 50?nm were prepared by means of pulse current and pulse reverse current electrodeposition. The alloys were analysed using various methods (EDX, SEM and XRD). The electrochemical (open circuit potential, corrosion current density) and tribological (coefficient of friction and wear rate) characteristics were evaluated. Tungsten content in the alloys influences grain size which is responsible for the quality of the coating and the corrosion and tribological properties. When the content of tungsten in the Ni fcc lattice is lower than 5?at.-% W, the corrosion resistance increases. When the content of W is higher than 5?at.-%, the corrosion resistance decreases. The relationship between tribological properties and W content is the reverse of that experienced with corrosion properties.     

Effect of number of layers on erosion,corrosion, and wear resistance of multilayer Cr–N/Cr–Al–N coatings on AISI 630 stainless steel

In the present study, multilayered Cr–N/Cr–Al–N coatings were prepared by cathodic arc physical vapor deposition (PVD) with different numbers of layers and the same total thickness on AISI 630 steel in an attempt to improve the wear and erosion–corrosion resistance. Structural analysis of the coatings was performed by field scanning electron microscopy, X-ray diffraction (XRD), and energy-dispersive spectroscopy. Depth profiles and roughness parameters of worn surfaces were calculated after erosion and wear tests. XRD indicated that nitride compounds were formed in multilayer coatings by PVD. The Cr–N/Cr–Al–N coating exhibited superior corrosion resistance compared with AISI 630 substrate. The erosion–corrosion results revealed that the smoothest wear track with the minimum erosion rate and wear depth was obtained for five- and seven-layered coatings. The failure mechanism of the bare substrate was influenced by plastic deformation via cutting and plowing, while the failure mechanism for coated samples was chipping and delamination. According to the wear results, the multilayer coatings showed a lower friction coefficient and better surface morphology that demonstrated their high ability for wear protection.     

Microstructure and properties of Fe–Cr–C hardfacing alloys reinforced with TiC–TiB2

Abstract

Different amounts of TiB₂ powder were added to flux cores of wear resistant hardfacing flux cored wires for the preparation of new flux cored wires. Fe–Cr–C hardfacing alloys reinforced with TiB₂ were produced by arc hardfacing. The microstructure, hardness and wear resistance behaviour of the hardfacing alloys were investigated using an optical micrograph, scanning electron micrograph (SEM), X-ray diffractometer, macrohardness tester, microhardness tester and abrasive wear tester. The results showed that, among the hardfacing alloys, a new hard phase, i.e. TiC–TiB₂ composite compound particles, was formed and dispersed in the primary carbides and matrix structures. The TiC–TiB₂ reinforced Fe–Cr–C hardfacing alloys imparted greater hardness and better wear resistance. The presence of TiC–TiB₂ hard phase particles is the main reason for the improvement in hardness and wear resistance of Fe–Cr–C hardfacing alloys.     

The Influence of H,W, H/E,H 3/E 2, Structure and Chemical Composition on the Resistance of Ti–B–(N), Mo–B–(N), Cr–B–(N), and Zr–B–(N) Coatings to Cyclic Impact Loading

Protection of Metals and Physical Chemistry of Surfaces - Coatings based on transition metal borides (Ti, Mo, Cr, Zr) were obtained by magnetron sputtering of ceramic targets in Ar and Ar–15%...     

Extrusion and selected engineering properties of Mo–Si–B intermetallics

In this study, an extrusion process has been developed to produce defect free, high-density rods of Mo–Si–B material. An initial powder composition (53.5 vol.%, 91 wt.%) of 66 vol.% Mo₅Si₃B_x (T1)–16 vol.% MoB–18 vol.% MoSi₂ was mixed with a paraffin-wax based binder (46.5 vol.%, 9 wt.%) and extruded using a twin-screw extruder. Following binder removal by a combination process of wicking and thermal degradation, the material was sintered at 1800°C. The bulk density of the sintered material was 90–92% of theoretical. Thorough binder removal was evidenced by low impurity levels: 258±6 ppm carbon and 772±10 ppm oxygen. The material demonstrated excellent high temperature oxidation resistance. The calculated parabolic rate constant is 1.1×10⁻² mg²/cm⁴/h at 1600°C. The extruded material was also successfully tested as a resistance heating element. These materials show promise for the development of heating elements with enhanced performance compared to current MoSi₂-based heating elements.     

(Ti,Al)N–Ni nanostructured coatings: Thermal stability,heat resistance,electrochemical behavior,and adhesive strength with a substrate

In this work, thermal stability and oxidation resistance at temperatures up to 800°C are studied for (Ti,Al)N–(8–10 at %)Ni coatings with a thickness on the order of 4 µm and a crystallite size below 20 nm, which have been prepared via ion–plasma vacuum arc deposition. The composition and structural characteristics of coatings remain stable during 1-h heating in vacuum of 10_–4 Pa at temperatures of 600 and 700°C. Heating at a temperature of 800°C leads to an increase in the crystallite size and a decrease in microstrains of a ceramic phase, which is accompanied by a reduction in the hardness of the coating from 51–53 to 31–33 GPa. The coatings are heat resistant up to 800°C and characterized by cohesive failure in scribing. The adhesive strength of coatings with a substrate exceeds 85 N. Studying electrochemical behavior reveals the high efficiency of (Ti,Al)N_0.87–Ni coatings in corrosion protection of cutting tools in acid and alkaline environments.     

Characterization and oxidation behavior of MTCVD Ti–B–N coatings

In this work, Ti–B–N coatings have been prepared by moderate temperature chemical vapor deposition (MTCVD). The effect of a varying boron concentrations (9.6 and 55.4 at.%) on the chemical composition and the oxidation behavior was investigated by XRD, SEM, WDS, XPS and Raman spectroscopy. The results clearly demonstrate a good correlation between the different techniques. The same transition trends were observed in the examined Ti–B–N system in the progression from TiN to TiB₂ by the addition of boron. At boron concentrations ≥ 18 at.%, the coatings reveal a two phase structure comprising a nanocrystalline TiN phase embedded in an amorphous TiB₂ matrix. In Ti–B–N coatings with boron concentrations ≤ 18 at.%, the high sensitivity of Raman spectroscopy enabled the identification of an amorphous TiB phase.The oxidation behavior of Ti–B–N coatings was found to be affected by the boron concentration as well. Boron concentrations ≤ 18 at.% improve the thermal stability compared to TiN, most likely due to the TiB phase present in these coatings. Ti–B–N coatings with a high boron concentration show a higher degree of oxidation compared to TiN manifested in a higher oxide layer thickness. In addition, these coatings tend to form boron oxides on their surface, which lead to the formation of metastable anatase rather than the thermodynamically stable rutile.     

Influence of metalloids and annealing on the fundamental magnetic properties of bulk Fe–(Cr,Mo,Ga)–(P,B,C) metallic glasses

Although bulk ferromagnetic metallic glasses have been synthesized in many alloy systems, the dependence of fundamental magnetic properties – saturation moment and Curie temperature – on annealing treatments and the content of alloying metalloids has not been well understood. In the present work, bulk ferromagnetic glassy alloys of Fe_77.5−x(Cr_0.33Mo_0.33Ga_0.33)_xP₁₂B_5.5C₅ (x = 8–14), (Fe₆₆Cr₄Mo₄Ga₄P₁₂C₅)_(100−x)/95B_x (x = 3–7), and (Fe₆₆Cr₄Mo₄Ga₄P₁₂B₅) _(100−x)/95C_x (x = 3–8.5) were prepared by a flux-melting and water-quenching technique. The effects of alloying metals (Cr, Mo, and Ga), metalloids (P, B, and C), and annealing treatments on the saturation moment and Curie temperature of these bulk glasses were investigated. The saturation moment and Curie temperature decrease linearly with increasing metals content. However, the saturation moment and Curie temperature change complicatedly with metalloids content. The Curie temperature increases with both annealing temperature and annealing time. The dependence of magnetic properties on the composition and annealing treatment for our bulk glasses was compared with that for glassy ribbons. The results suggest that the dependence found in our bulk glasses can be explained by the theoretical models proposed for glassy ribbons.     

Microstructure and physical properties of PVD TiN/（Ti, Al）N multilayer coatings

Magnetron sputtered （Ti, Al） N monolayer and TiN/（Ti, Al） N multilayer coatings grown on cemented carbide substrates were studied by using energy dispersive X-ray spectroscopy （EDX）, scanning electron microscopy （SEM）, nanoindentation, Rockwell A indentation test, strength measurements and cutting tests. The results show that the （Ti, Al）N monolayer and TiN/（Ti, Al）N multilayer coatings perform good affinity to substrate, and the TiN/（Ti, Al）N multilayer coating exhibits higher hardness, higher toughness and better cutting performance compared with the （Ti, Al）N monolayer coating. Moreover, the strength measurement indicates that the physical vapour deposition （PVD） coating has no effect on the substrate strength.     

Structural characteristics and high-temperature tribological behaviors of laser cladded NiCoCrAlY–B4C composite coatings on Ti6Al4V alloy

In order to improve the hardness and tribological performance of Ti6Al4V alloy, NiCoCrAlY–B₄C composite coatings with B₄C of 5%, 10% and 15% (mass fraction) were fabricated on its surface by laser cladding (LC). The morphologies, chemical compositions and phases of obtained coatings were analyzed using scanning electronic microscope (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD), respectively. The effects of B₄C mass fraction on the coefficient of friction (COF) and wear rate of NiCoCrAlY–B₄C coatings were investigated using a ball-on-disc wear tester. The results show that the NiCoCrAlY–B₄C coatings with different B₄C mass fractions are mainly composed of NiTi, NiTi₂, α-Ti, CoO, AlB₂, TiC, TiB and TiB₂ phases. The COFs and wear rates of NiCoCrAlY–B₄C coatings decrease with the increase of B₄C content, which are contributed to the improvement of coating hardness by the B₄C addition. The wear mechanisms of NiCoCrAlY–B₄C coatings are changed from adhesive wear and oxidation wear to fatigue wear with the increase of B₄C content.     

Microstructure and properties of Al2O3-13%TiO2 coatings sprayed using nanostructured powders

The microstructure and wear performance of M203-13% TiO2 coatings prepared by plasma spraying of agglom- erated nanoparticle powders were investigated. SEM analysis showed that the as-sprayed Al2O3-TiO2 coatings comprise of two kinds of typical region： fully melted region and unmelted/partially melted nanostructured region, which is different than the conventional coating with lamellar structure. It is shown that the microhardness of the nanostructured coatings was about 15%-30% higher than that of the conventional coating and the wear resistance is significantly improved, especially under a high wear load. The nanostructured coating sprayed at a lower power shows a lower wear resistance than the coatings produced at a higher power, because of the presence of pores and microstructural defects which are detrimental to the fracture toughness of the coatings.     

Corrosion properties of CVD grown Ti(C,N) coatings in 3.5 wt-% NaCl environment

The corrosion behaviour of Titanium carbonitride (Ti(C,N)) films grown by chemical vapour deposition was analysed in artificial sea water environment. From potentiodynamic polarisation curves, two passivation zones were detected, which originated from an initial oxidation of TiC and TiN to TiO₂ followed by growth of the TiO₂ layer upon increased polarisation. X-ray photoelectron spectroscopy analyses verified the mechanism by detecting a gradual decrease in Ti(C,N) peaks accompanied by a gradual increase of oxidised Ti (e.g. TiO₂). It was likewise found that carbon in TiC mainly decomposes into carbonate species while the nitrogen in TiN remains elemental and likely escapes as nitrogen gas. Accordingly, Ti(C,N) behaves like a superposition of TiC and TiN with their individual oxidation behaviour, resulting in a highly corrosion resistant material.