Structure,Mechanical Properties,and Oxidation Resistance of MoSi<Subscript>2</Subscript>, MoSiB,and MoSiB/SiBC Coatings

Single-layer MoSi₂, MoSiB, and multilayer MoSiB/SiBC coatings are fabricated by magnetron sputtering. Coating structures are investigated using X-ray diffraction, a scanning electron microscopy, and glow-discharge optical emission spectroscopy. Mechanical properties of coatings are determined by nanoindentation. The thermal stability of coatings is studied in a temperature range of 600–1200°C and oxidation resistance is studied upon heating to 1500°C. It is established that single-layer MoSiB coatings possess a hardness of 27 GPa, elasticity modulus of 390 GPa, and elastic recovery of 48%. They can also resist oxidation up to 1500°C inclusively, which is caused by the formation of the SiO₂-based protective film on their surface. The MoSi₂ coatings can have hardness comparable to the hardness of MoSiB coatings, but they are somewhat worse than them in regards to oxidation resistance. Multilayer MoSiB/SiBC coatings have hardness 23–27 GPa and oxidation resistance restricted by 1500°C, but they herewith have higher elastoplastic properties when compared with MoSiB.     

Formation and Stability of Equiatomic and Nonequiatomic Nanocrystalline CuNiCoZnAlTi High-Entropy Alloys by Mechanical Alloying

Nanocrystalline equiatomic high-entropy alloys (HEAs) have been synthesized by mechanical alloying in the Cu-Ni-Co-Zn-Al-Ti system from the binary CuNi alloy to the hexanary CuNiCoZnAlTi alloy. An attempt also has been made to find the influence of nonequiatomic compositions on the HEA formation by varying the Cu content up to 50 at. pct (Cu _x NiCoZnAlTi; x = 0, 8.33, 33.33, 49.98 at. pct). The phase formation and stability of mechanically alloyed powder at an elevated temperature (1073 K [800 °C] for 1 hour) were studied. The nanocrystalline equiatomic Cu-Ni-Co-Zn-Al-Ti alloys have a face-centered cubic (fcc) structure up to quinary compositions and have a body-centered cubic (bcc) structure in a hexanary alloy. In nonequiatomic alloys, bcc is the dominating phase in the alloys containing 0 and 8.33 at. pct of Cu, and the fcc phase was observed in alloys with 33.33 and 49.98 at. pct of Cu. The Vicker’s bulk hardness and compressive strength of the equiatomic nanocrystalline hexanary CuNiCoZnAlTi HEA after hot isostatic pressing is 8.79 GPa, and the compressive strength is 2.76 GPa. The hardness of these HEAs is higher than most commercial hard facing alloys (e.g., Stellite, which is 4.94 GPa).     

Calculation-experimental study of the aging of casting high-strength Al-Zn-Mg-(Cu)-Ni-Fe aluminum alloys

The effects of natural aging and steplike aging on the hardness and the electrical conductivity of the following high-strength casting aluminum alloys are studied and compared: experimental alloys ATs6N4, ATs7NZh, and ATs6N0.5Zh based on the Al-Zn-Mg-(Cu)-Ni-Fe system (nicalins) and a commercial AM5 alloy based on the Al-Cu system. It is found that, during 3-day natural aging, the hardness of the nicalins increases to HV 1.4–1.55 GPa, which is higher than their hardness in the as-quenched state by a factor of 1.6–1.7. The hardness of the AM5 alloy is almost unchanged during natural aging and is retained at the level of the as-quenched state (HB ～ 0.8 GPa). After quenching and natural aging for 1 day, the alloys are subjected to steplike aging in the temperature range 100–250°C at a step of 25°C on holding for 3 h at each temperature. Upon steplike aging, hardness HB of the nicalins reaches a maximum (～2.1 GPa for the ATs7NZh and ～1.9 GPa for the ATs6N4 and ATs6N0.5Zh alloys) at a temperature of 150°C. The hardness of the AM5 alloy reaches a maximum (HB ～ 1.3 GPa) at a temperature of 175°C.     

Structural changes in the surface of titanium carbide and tungsten carbide hard alloys with nickel binder upon exposure to laser radiation

Pulsed laser action on cemented titanium carbide with nickel—chromium binder yields deep changes in its structure; and in the case of cemented tungsten carbide with nickel binder, the structural change is accompanied by phase transformations in the heat-affected zone. As a result of these changes, layers with thickness 30–60 µm and 30–60% greater hardness are formed. When the energy density of the laser radiation is higher than 200 J/cm², thermal failure of cemented carbide surfaces occurs (observed as crack formation).     

Surface Treatment of S355JR Carbon Steel Surfaces with ZrB<Subscript>2</Subscript> Nanocrystals by CO<Subscript>2</Subscript> Laser

To improve mechanical properties of S2355JR carbon steel, pre-synthesized ZrB₂ nanocrystals were used to coat the metal surface by laser cladding using 2000 W CO₂ laser. ZrB₂ nanocrystals were synthesized by mechanochemical process. The effect of laser power on the coating layers was examined for optimizing the most effective coating conditions. Microstructural studies were carried out using optical microscope, scanning electron microscope and X-ray diffraction to analyze phase structures of the coated layers. Mechanical characteristics of the laser coated layers were evaluated by studying microhardness, wear and scratch resistance properties. Maximum hardness of the coated layers was observed while cladding with 75 and 125 W laser powers, when other processing parameters and conditions were kept at optimum levels. EDS analysis of these laser cladded layers indicated the formation of complex boro-nitrides, nitrides and carbides of Zr and Fe that contributed to vast increase in hardness of the laser-clad coating on S2355JR steel. Depending upon the laser powers used, the thickness of the coated layers was found to be in the range of 15–37 µm. The wear and micro-scratch tests results revealed significant improvement in wear properties.     

Structure and properties of H-beams after accelerated water cooling

The structure and properties of the surface of DP155 H-beams made of 09G2S low-carbon steel are determined on the basis of materials physics, before and after thermomechanical strengthening—that is, accelerated water cooling. Such H-beams are used in monorail tracks. Highly defective structure in the surface layer is created by accelerated cooling of the beam in the line of the 450 bar mill at AO EVRAZ Zapadno-Sibirskii Metallurgicheskii Kombinat, in the following conditions: rolling speed 6 m/s; water pressure in the crosspiece-cooling section 0.22–0.28 MPa; temperature before cooling about 800°C. As a result, the hardness, wear resistance, and scalar dislocation density are higher than in the steel without strengthening. Without thermal strengthening, the microhardness of the samples is 2.70 ± 0.33 GPa, while the Young’s modulus is 269.2 ± 27.1 GPa. Thermomechanical strengthening increases its microhardness to 3.30 ± 0.29 GPa, and decreases the Young’s modulus to 228.2 ± 25.7 GPa. In addition, the microhardness range is increased from 2.20–3.80 GPa to 2.64–4.60 GPa, while the Young’s modulus range is reduced from 208.0–403.0 GPa to 184.1–278.2 GPa on thermomechanical strengthening. It is found that thermomechanical strengthening increases the wear resistance of the steel’s surface layer by a factor of ~1.36 (decrease in wear rate from 5.3 × 10^–5 to 2.9 × 10^–5 mm³/N m) and increases the frictional coefficient by a factor of 1.36 (from 0.36 to 0.49). Without thermal strengthening, the structure observed is dislocational chaos; the scalar density of the dislocations is (0.9–1.0) × 10¹⁰ cm^–2. High-temperature rolling and subsequent accelerated cooling of the samples produces dislocational substructure of band type in the ferrite grains and of reticular type in the martensite grains: the mean scalar density of the dislocations in the surface layer is 4.5 × 10¹⁰ cm^–2. Possible explanations for such behavior are discussed.     

Properties of nanostructured TiN-Ni ceramic-metal coatings obtained by ion-plasma vacuum-arc method

Physicomechanical and tribological properties of TiN-Ni ceramic-metal coatings prepared by ion-plasma vacuum-arc deposition are investigated. It is established that the hardness (H) increases from 23 to 54 GPa with the Ni content from 0 to 12 at %, which is determined by the influence of the nanostructured nitride component of coatings. Coefficients HE ^?1 and H ³ E ^?2, which characterize the material resistance against the elastic and plastic failure deformation, reach 0.104 and 0.567 GPa, respectively. The further increase in the nickel concentration in coatings to 26 at % leads to a decrease in H to 23–25 GPa, which is associated with the influence of the increasing amount of soft plastic metal and the formation of noticeable porosity in the bulk of coatings. The friction coefficient of studied coatings is 0.45, against 0.58 (for the TiN coating) and 0.72 (for the hard-alloy base). The cohesion failure mechanism of TiN-Ni nanostructured coatings (C _Ni = 2.8–12 at %) is established, and critical loads which characterize the appearance of the first crack (13.5–14.2 N) and the local coating attrition up to the substrate (61.9–64.4 N) are determined. The complete attrition of coatings does not occur up to a load of 90 N, which points to their high adhesion strength. The developed nanostructured ceramic-metal coatings are characterized by high heat resistance up to 800°C.     

Ultrafine high-cobalt VK40 hard alloy. I. Structure and properties

Ultrafine WC-41 wt.% Co powders (VK40) are densified under 1000–1200 MPa at 950–1250 °C and in 0.13 Pa vacuum. It is examined how the pressing temperature and annealing at 1190 °C influence the density, structure, physical and mechanical properties of VK40 alloy. It is shown that high-pressure sintering produces dense samples with ultrafine structure (L_WC = 0.35–0.45 µm) and low degree of contact for carbide particles (contiguity C_WC = 0.08–0.1) in solid phase. The highest mechanical properties are exhibited by samples densified at 1150–1250 °C or by samples annealed after preliminary pressing at 1050–1150 °C. The alloy has the following properties: transverse rupture strength (TRS) of 3200–3400 MPa, fracture toughness of 25–33 MPa · m^1/2, Vickers hardness of 7.5–7.7 GPa under 300 N, compressive strength of 2600–2800 MPa, compressive offset yield stress σ_0.2 = 2200–2400 MPa, compressive plastic strain of 6.5–7.0%, and fracture energy of 180–200 MJ/m³. These mechanical properties of ultrafine VK40 alloy differ from those of standard impact-resistant coarse-grained hard metals in higher TRS, fracture toughness, and yield stress.     

Electric-discharge sintering of TiN-AlN nanocomposites

The structurization and properties of TiN-AlN and TiN-AlN-Y₂O₃ nanocomposites consolidated by electric-discharge sintering are examined. TiN-AlN composites with a relative density of about 98 to 99% are produced. Their structure is not homogenous and consists of TiN and AlN grains of about 200 nm in size. There are also large spherical grains of titanium nitride of 2 to 10 µm. This effect is probably caused by microdischarges between particles of the conducting phase and subsequent meltback of the interacting surfaces. The effect of yttrium oxide additives on the material structure and properties is investigated. It is shown that TiN-AlN composites consolidated by electric-discharge sintering have high hardness (HV ～ 25 GPa) and fracture toughness (K_1c ～ 6 MPa · m^1/2).     

Evaluation of Microstructure and Mechanical Properties of Nano-Y2O3-Dispersed Ferritic Alloy Synthesized by Mechanical Alloying and Consolidated by High-Pressure Sintering

In this study, an attempt has been made to synthesize 1.0 wt pct nano-Y₂O₃-dispersed ferritic alloys with nominal compositions: 83.0 Fe-13.5 Cr-2.0 Al-0.5 Ti (alloy A), 79.0 Fe-17.5 Cr-2.0 Al-0.5 Ti (alloy B), 75.0 Fe-21.5 Cr-2.0 Al-0.5 Ti (alloy C), and 71.0 Fe-25.5 Cr-2.0 Al-0.5 Ti (alloy D) steels (all in wt pct) by solid-state mechanical alloying route and consolidation the milled powder by high-pressure sintering at 873 K, 1073 K, and 1273 K (600°C, 800°C, and 1000°C) using 8 GPa uniaxial pressure for 3 minutes. Subsequently, an extensive effort has been undertaken to characterize the microstructural and phase evolution by X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive spectroscopy. Mechanical properties including hardness, compressive strength, Young’s modulus, and fracture toughness were determined using micro/nano-indentation unit and universal testing machine. The present ferritic alloys record extraordinary levels of compressive strength (from 1150 to 2550 MPa), Young’s modulus (from 200 to 240 GPa), indentation fracture toughness (from 3.6 to 15.4 MPa√m), and hardness (from13.5 to 18.5 GPa) and measure up to 1.5 through 2 times greater strength but with a lower density (~7.4 Mg/m³) than other oxide dispersion-strengthened ferritic steels (<1200 MPa) or tungsten-based alloys (<2200 MPa). Besides superior mechanical strength, the novelty of these alloys lies in the unique microstructure comprising uniform distribution of either nanometric (~10 nm) oxide (Y₂Ti₂O₇/Y₂TiO₅ or un-reacted Y₂O₃) or intermetallic (Fe₁₁TiY and Al_9.22Cr_2.78Y) particles' ferritic matrix useful for grain boundary pinning and creep resistance.     

Microstructure and Mechanical Properties of Yttria-Stabilized Zirconia Coatings Produced by Eletrophoretic Deposition and Microwave Sintering

Y₂O₃-stabilized zirconia coatings were deposited on superalloy K17 substrates at room temperature by the eletrophoretic deposition technique followed by two different sintering methods. Scanning electron microscopy, X-ray diffraction (XRD), and nanoindentation techniques were employed to characterize morphological, structural, and mechanical properties of the coatings. Finer and more uniform microstructures were observed in the microwave sintered coatings. For the conventionally sintered coatings, the monoclinic phase was observed. The microwave sintered coatings of Y₂O₃-stabilized zirconia contain mainly cubic/tetragonal phases with some metastable phase present. In comparison with the hardness of 3.1 GPa and elastic modulus of 83.5 GPa for conventional sintered coating, the hardness and elastic modulus for microwave sintered coating rapidly increased to 4.3 and 172.7 GPa, respectively. Such coatings have potential in being used as thermal barrier coatings (TBCs) on superalloy substrates.     

Trying out spraying modes and properties of wear-resistant flame Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> coatings fabricated using a flexible cord material

Samples of Al₂O₃–TiO₂ coatings are fabricated by the flame spraying of a flexible cord. The influence of process parameters and composition of the sprayed material on the structure, composition, and mechanical properties of coatings is investigated. It is shown that an increase in the spraying distance and feed rate of the sprayed material leads to a decrease in their density. An increase in the concentration of the low-melting TiO₂ component predetermines a decrease in the coating porosity and has no significant effect on the coating hardness. Being subjected to measuring scratching, Al₂O₃–TiO₂ flame coatings formed with minimal porosity (Π = 3.2%) are characterized by cohesion fracture behavior and no substrate opening under an indenter load of up to 90 N. The friction factor of coatings under study varies from 0.2 to 0.78 after 2800 counterbody revolutions (44 m of the friction path). This is associated with the accumulation of fatigue cracks in the coating material and its subsequent cohesive fracture by the formation of large fragments serving as an abrasive.     

Hardness,adhesion strength,and tribological properties of adaptive nanostructured ion-plasma vacuum-arc coatings (Ti,Al)N–Mo<Subscript>2</Subscript>N

The properties of nanostructured multilayered coatings of the composition (Ti,Al)N–Mo₂N, which were fabricated by the ion-plasma vacuum-arc deposition (arc-PVD), are investigated. The thickness of coating layers is comparable with the grain size, which is about 30–50 nm. The coating hardness reaches 40 GPa with relative plastic deformation work of about 60%. It is established by measuring scratching that the cohesion destruction character of the coating occurs exclusively according to the plastic deformation mechanism, which evidences its high fracture toughness. The local coating attrition to the substrate takes place under a load on the order of 75 N. The coating friction coefficient in testing conditions according to the “pin-on-disc” layout using the Al₂O₃ counterbody under a load of 5 N is 0.35 and 0.50 at temperatures of 20 and 500°C, respectively. The coating is almost unworn because of the formation of MoO₃ oxide (the Magneli phase) operating as the solid lubricant in the friction zone. An increase in the friction coefficient and noticeable wear are observed with the further increase in the testing temperature, which is associated with the sublimation intensification of MoO₃ from the working surfaces and lowering its operational efficiency as the lubricant.     

Ceramic-metallic (TiN-Cu) nanostructured ion-plasma vacuum-arc coatings for cutting hard-alloy tools

The structure and properties of TiN-Cu coatings with a broad range of copper concentrations (C _Cu = 0.6–20 at %), which were fabricated by the ion-plasma vacuum-arc deposition on a TT10K8B hard-alloy tool, including its cutting resistant tests, were investigated. The introduction of copper into the coating composition diminishes crystallites of the nitride phase from 100 to 20 nm. The hardness of coatings increases from 20 to 40 GPa, with an increase in C _Cu to 7–8%. The further increase in the copper content, which is accompanied by diminishing crystallites of the nitride phase, is characterized by a decrease in hardness to 14–15 GPa, which is associated with the influence of soft plastic metal. Resistant cutting tests of steel 35KhGSA of removable multifaceted plates (RMP) with the TiN-Cu coatings indicate that the optimally selected composition (TiN-7-8 at % Cu) increases RMP resistance more than by a factor of 6 and 2.5 as compared with tools without the coating and with the TiN coating deposited according to the basic technology, respectively.     

Effect of focused solar power on the structure and phase composition of a copper-based material

The change in the content, structure, and microhardness at a depth of the scale layer, which forms on the copper-based material under focused solar radiation, is studied. The formation of a structure with an external layer of CuO, Fe₂O₃, NiO oxides and mixed Cu₃WO₆ oxide (spinel type) with high microhardness H_μ = 29.4 GPa is shown. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 20–25, 2007.     

Microstructural analysis and oxidation behavior of laser-processed Fe-Cr-AI-Y alloy coatings

Dense crack-free coatings of Fe-Cr-Al-Y quaternary alloy were produced on stainless steel 316L substrates using a continuous wave Nd-YAG solid-state laser coupled with a fiber optic beam delivery system. Experiments were performed at a laser power between 0.6 and 2.4 kW, process speed in the range 0.053 to 0.423 cm/s, powder feed rate fixed at 0.083 g/s, and focused multimode laser beam with a diameter of 0.5 cm. Various microanalysis techniques demonstrated that the coatings were metallurgically bonded to the substrate and possessed thicknesses between 0.35 and 4.64 mm, refined columnar microstructures with grain sizes of 15 to 150 μxm, increased concentration of key alloying elements, and appreciably high microhardness up to 409 kg/mm². The laser-processed microstruc-tures comprised a body-centered cubic (bcc) ferrite(α phase) crystal structure with a relatively large lattice parameter compared to α-Fe due to the enhanced dissolution of varying amounts of Cr, Al, Ni, and Y, depending on the dilution from the substrate material. Oxidation tests conducted in air at temperatures of 1100 ° to 1200 ° for 95 hours revealed the formation of an approximately 5-μm-thick dense α-Al₂O₃ oxide scale of a rhombohedral (hexagonal) crystal structure. The α-Al₂O₃ scale exhibited remarkable high-temperature resistance and strong adherence to the coating surface. Extensive oxidation of the uncoated stainless steel substrate produced a porous and heavily spalled alloy oxide scale about 60-μm thick consisting of FeCr₂O₄ and NiCr₂O₄ with cubic and tetragonal crystal structures, respectively. The retention of the bcc α phase and the insignificant grain growth after oxidation are indicative of the thermal stability of the laser-processed coating microstructures. The obtained results demonstrate that Fe-Cr-Al-Y alloy coatings exhibiting fine-grained hard mi-crostructures, high-temperature oxidation resistance, and strong adherence to stainless steel can be developed by means of laser processing.     

Effect of scandium on the phase composition and hardening of casting aluminum alloys of the Al–Ca–Si system

The phase composition of the Al–Ca–Si–Sc system is investigated in aluminum corner uisng computational (Thermo-Calc) and experimental (optical microscopy, scanning electron microscopy, and electron probe microanalysis) methods. The influence of annealing on the structure and hardness of alloys containing 0.3 wt % Sc is investigated in the region up to 550°C. It is shown that the maximum in the hardening curve caused by the isolation of nanoparticles of the Al₃Sc (L1₂) is attained after annealing at temperatures of 300–350°C in alloys belonging to the phase region (Al) + Al₄Ca + Al₂Si₂Ca ((Al) is the aluminum-based solid solution). Scandium completely enters the (Al) composition in alloys of this region, while the silicon concentration is minimal in it. On the other hand, hardening is almost absent in alloys from the (Al) + (Si) + Al₂Si₂Ca phase region. The possibility in principle to form the casting alloys based on the (Al) + Al₄Ca + Al₂Si₂Ca eutectic hardened without quenching is substantiated.     

Structural features and properties of the laser-deposited nickel alloy layer on a KhV4F tool steel after heat treatment

The study and application of the materials that are stable in the temperature range up to 1000°C are necessary to repair forming dies operating in this range. Nickel-based alloys can be used for this purpose. The structural state of a nickel alloy layer deposited onto a KhV4F tool steel and then heat treated is investigated. KhV4F tool steel (RF GOST) samples are subjected to laser deposition using a pulsed Nd:YAG laser. A nickel-based material (0.02C–73.8Ni–2.5Nb–19.5Cr–1.9Fe–2.8Mn) is employed for laser deposition. After laser deposition, the samples are subjected to heat treatment at 400°C for 5 h, 600°C for 1 h, 800°C for 1 h, and 1000°C for 1 h. The microstructure, the phase composition, and the microhardness of the deposited layer are studied. The structure of the initial deposited layer has relatively large grains (20–40 μm in size). The morphology is characterized by a cellular–dendritic structure in the transition zone. The following two structural constituents with a characteristic dendritic structure are revealed: a supersaturated nickel-based γ solid solution and a chromium-based bcc α solid solution. In the initial state and after heat treatment, the hardness of the deposited material (210–240 HV_0.1) is lower than the hardness of the base material (400–440 HV_0.1). Only after heat treatment at 600°C for 1 h, the hardness increases to 240–250 HV0.1. Structure heredity in the form of a dendritic morphology is observed at temperatures of 400, 600, and 800°C. The following sharp change in the structural state is detected upon heat treatment at 1000°C for 1 h: the dendritic morphology changes into a typical α + γ crystalline structure. The hardness of the base material decreases significantly to 160–180 HV_0.1. The low hardness of the deposited layer implies the use of the layer material in limited volume to repair the forming surfaces of dies and molds for die casting. However, the high ductility of the deposited layer of the nickel-based material is a prerequisite for a high stability under thermocycling loading conditions.     

Structure, mechanical properties, and hydrogen permeability of Pd-Cu and Pd-Ru membrane foils prepared by magnetron sputtering

Magnetron sputtering is used to prepare thin (down to 7 μm) Pd-Cu and Pd-Ru membrane foils deposited on the surface of a SiO₂/Si heterostructure at 300 and 700 K. Condensed foils (CFs) of an ordered Pd-Cu solid solution (β phase with a CsCl-type structure) and a Pd-Ru solid solution (fcc lattice) are synthesized for the first time. The foils of both alloys are characterized by a gradient granular structure due to selective development of 〈110〉 and 〈112〉 textures and a 〈111〉 texture in the Pd-Cu and Pd-Ru foils during their deposition, respectively. The hardness of the free surface of both foils removed from the substrate is determined by nanoindentation. The hardness is 3.0–3.6 GPa and is 20–50% lower than that of the contact surface (at the interface with the substrate) owing to the gradient structure. The hydrogen permeability of the Pd-Cu CF (β phase) is higher than that of the Pd CF by almost an order of magnitude (effect of a less dense crystal lattice) and is 5–7 times higher than those of the Pd-Ru CF and the Pd-Cu foil prepared by rolling.     

Thermal Stability of Cathodic Arc Vapour Deposited TiAlN/AlCrN and AlCrN/TiAlN Coatings on Tungsten Carbide Tool

TiAlN/AlCrN and AlCrN/TiAlN bilayer coatings were deposited on tungsten carbide cutting inserts using the plasma enhanced physical vapour deposition process. Their thermal stability was varied by annealing the specimens at different temperatures and time durations. The thermal stability was evaluated from hardness measurement, oxygen absorption and X-ray diffraction (XRD) patterns. TiAlN/AlCrN coating initially shows an increase in hardness, but it decreases when the annealing temperature is increased. A high hardness of 46 GPa is measured in the TiAlN/AlCrN coating annealed at 600 °C for 08 h. But, AlCrN/TiAlN coating displays a decrease in hardness after annealing at 600 °C, and the hardness increases to 47 GPa on increasing the annealing temperature further (1000 °C for 6 h). From weight measurements, it is clear that the TiAlN/AlCrN bilayer coating results in weight reduction initially, but it increases with a further increase in the annealing temperature. In contrast, in the AlCrN/TiAlN coating, the weight increases monotonically, but gradually, with increasing temperature of annealing. The XRD results are discussed with reference to the different oxide phases formed in the two bilayer coatings during annealing.