L. Swadźba

Influence of coatings obtained by PVD on the properties of aircraft compressor blades

Abstract In this paper, the results of investigations to increase aircraft compressor blade durability were presented. The blades were made of the martensitic steels. The coatings were obtained by the physical vapour deposition (PVD) method. TiN and (Ti, Al)N coatings on a titanium nitride base and CrN and Crue5f8CrN multilayer coatings on a chromium nitride base were used in the tests. Low corrosion resistance of the TiN coatings was shown in laboratory tests. The (Ti,Al)N coatings, particularly CrN and CrN modifications, behaved better. Coating density and chemical interaction of the coating and steel in the corrosive medium were shown to have an influence on the blade properties. A significant increase in the corrosion resistance was achieved by using the diffusion and chemical treatment of coatings obtained by the PVD method. Investigations of coatings in a humid atmosphere containing SO2 showed very low resistance of the steel. The resistance of the coatings was increased significantly by additional chemical treatment.

Erosion- and corrosion-resistant coatings for aircraft compressor blades

Abstract In this paper the comparative test results of protective properties of several coatings for aircraft engine compressor blades are presented. Erosion and corrosion tests for the base metals and coatings were carried out. Corrosion test for base materials and anodic coating was made in neutral salt spray. For cathodic coatings a modified corrosion test was performed. It has been determined that the coatings obtained by physical vapour deposition (PVD), particularly (Ti, Al) N and TiN(Pt) are the best in the erosion and corrosion test conditions. The electroplated Ni-Cd coatings do not show satisfactory erosion resistance, but they have good corrosion resistance. It seems that PVD coatings fulfil the requirements for the protection of aero engine compressor blades.

Characterization of Alumina Scales Grown on a 2nd Generation Single Crystal Ni Superalloy During Isothermal Oxidation at 1050, 1100 and 1150 °C

This paper concerns microstructural characterization of alumina scales formed on a 2nd generation single crystal Ni superalloy during isothermal oxidation in dry oxygen at 1050, 1100 and 1150xa0°C for 100xa0h. Samples for high resolution characterization of Al2O3 scales were prepared usingxa0a focused ion beam (FIB) method. High resolution TEM and S/TEM techniques were used for a detailed characterization and a direct comparison of the phase composition and chemistry of the oxide scales formed during high temperature oxidation. The growth of transient θ-Al2O3 and its transformation to α-alumina is addressed for each oxidation temperature along with the differences in the diffusion of reactive elements, such as Hf, Zr and Y, through grain boundaries of the α phase. The θ to α transformation front was proven to move from the metal-scale to the scale-gas interface. The results presented in this paper indicate that after 100xa0h of oxidation at 1050 and 1100xa0°C there are still some θ-alumina grains remaining and even in the regions where the transformation to α was finished the surface retained the whisker-like morphology.

Degradation of the TBC system during the static oxidation test

This study was done on the IN‐738 type alloy with thermal barrier coatings. On the basic surface of the NiCoCrAlY superalloy, VPS‐sprayed powder was applied as the bond‐coat. In addition, ZrO2× 8%Y2O3 powder was used for a deposition outside the top surface of a ceramic layer by the APS method. Appropriate control of the spraying process parameters permitted to obtain a gradient of porosity on the thickness of the ceramic coating. Then a static oxidation test at 1100°C and for 1100 h was performed. The basic conclusions of that testing showed that main degradation modes of the gradient thermal barrier coating system were connected with formation of porous NiAl2O4 oxides in the thermally grown oxide area and, consequently, formation of micro‐cracks, delamination of a ceramic layer and final spallation of a ceramic top‐coat.

Characterization of TiAlSi Coating Deposited by Arc-PVD Method on TiAlCrNb Intermetallic Base Alloy

Results of microstructural investigations of aluminide coatings modified by Si are presented in this work. Protective coating (TiAlSi type) was deposited by Arc-PVD. Thickness of the outside layer of deposited coating was 35µm and it contained TiAl3 phase modified by Si as a main component. The second layer was found as a transition area between the TiAl3 outside layer and the surface of TiAlCrNb substrate. Thickness of the inside sublayer was 5 µm. The diffusion treatment caused the progress of coating homogenisation from the point of view of phase and chemical composition. It was found that the coating consisted of the dominant TiAl3 phase and Ti5Si3 in thick outer sublayer and only TiAl2 phase in transition thin sublayer. Below the transition area, on the surface of TiAlCrNb substrate alloy, the layer of g−TiAl was found. The amount of silicides was increased in comparison with the coating only after the Arc-PVD process and the area of its presence had been removed in the outside direction of the coating.

Corrosion damage and regeneration of aluminide coatings on aircraft turbine blades

Abstract The corrosion-induced microstructure changes associated with the successive stages of damage of the protective layers on nickel-base alloys have been studied up to complete layer penetration. The microanalytical investigations performed on the distribution of the alloying elements show increased contents of chromium and sulphur in the corrosion attack front zone. However, the microstructure of the diffusion zone, enriched with molybdenum, tungsten and chromium, remains practically unchanged. Attempts at regeneration of the corrosion-worn protective layers of the blades by removing the corrosion products and remnants of the coating with a subsequent new layer deposition have been also described. Two methods of blade recoating are presented in the paper: 1. (a) chemical-vapour-deposited chromoaluminizing either in low- or high-activity processes with the analysis of the effect of processing parameters on the layer microstructure and properties and 2. (b) diffusion annealing of the sprayed silicoaluminizing suspension. The purpose of regeneration is to regain the initial properties of the blades after a period of service. Some of blades formerly rejected for their inadequate structure or defects in the protective layer would be also regenerated in this way. The criteria of surface quality assessment and verification of the blades in successive stages of surface coating regeneration have been worked out.

Microstructure wear resistance and erosion resistance of plasma-sprayed boride coatings

Abstract The paper presents both material and technological concepts of coatings containing selected borides (FeB, CrB2, (TiCr)B2) and carbides (B4C, B4C−CrB). The selected borides and powder compositions were prepared by diffusion synthesis (chemically) and then were electrolytically covered with a nickel layer. The plasma spray parameters were determined. X-ray analysis was carried out to investigated the chemical compositions of the coatings. From the X-ray analysis results, we determined the phase transformations in the coatings after plasma spraying. Both the wear and erosion resistances of the coatings obtained were determined and compared with those of WC–Co, NiCrSiB and 45 VFNS (Metco) coatings. The results obtained in the tribological tests were applied to a selection of highly wear-resistant boride coatings.

Characteristics of Phenomena in Powders Type RE2Zr2O7-Al2O3 in High Temperature Annealing Conditions

The paper presents test results and characterizes the structural stability of powders, which form a mixture of aluminium oxide (Al2O3) and gadolinium, based on rare earth zirconates. This mixture is provided to create thermal barrier coatings (TBCs) by spraying. The purpose of the tests was to determine the influence of temperature on reactions, occurring between those powders within a temperature range from 25°C to 1500°C, while such conditions were to simulate the conditions, which occur during creation of TBCs and they give an answer to the question concerning mutual reactivity of the powders. The requirements for new materials, provided to spray the TBCs, indicate the necessity to prepare the materials, which do not show tendency towards reactions with the Al2O3, formed during oxidation of Ni (Co) CrAlY, while this reaction is of type bond coat. The tests included differential scanning calorimetric (DSC) analysis and differential thermal analysis (DTA) of powder mixtures. Diffraction analysis was also performed before and after the tests have been finished. The DSC analysis results, obtained at a range of high temperature, did not show any thermal effects, which indicate a low level of mutual reactivity of the powders. However, the DTA analysis suggests presence of such effects at temperature close to 1300°C, and it indicates the necessity to verify exactly the obtained results. Results of the XRD measurement showed that after annealing process already at 1100°C the perovskite oxide of GdAlO3 was present.

Evaluation of Hot Corrosion Resistance of Directionally Solidified Nickel-Based Superalloy

The turbine blades made of directionally solidified nickel-based superalloys are exposed to combination of high temperature and aircraft environment, in which appear corrosive elements like sulphur, sodium and vanadium (hot corrosion). Corrosion resistance of superalloys is mainly dependent on their structure and chemical composition. Therefore, it is important to be aware of the correlation between the hot corrosion and changes in chemical composition and morphology of a surface of the material. The following paper presents the influence of sulphur on the microstructure of directionally solidified nickel-based superalloy. The research was carried out in Na2SO4 environment at two temperatures of 850oC and 900oC (below and above the melting point of salt, 884°C). The results show scale morphology on material surface and changes in chemical composition of surface of nickel superalloy.

Degradation of Si-Al aluminide coating after service of turbine blades made of ZhS6K superalloy

Aero engine turbine blades made of nickel-based superalloys are characterized by very good mechanical properties, but their hot corrosion resistance is insufficient. Therefore, various protective coatings must be applied. These coatings are typically made of diffusive aluminide coatings based on the β-NiAl intermetallic phase. Although the oxidation resistance and hot corrosion resistance of these coatings are very good, their thermal resistance is relatively poor. As a result, turbine blades with aluminide coatings are prone to degradation in case of overheating. In this paper we study the degradation of the Si-Al aluminide coating on turbine blades made of ZhS6K superalloy during overheating in the DV2 jet engine.