High-speed Rubbing Research Articles

Investigation of High-Speed Rubbing Behavior of GH4169 Superalloy with SiC/SiC Composites

The silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC), ceramic matrix composite (CMC) and nickel-based superalloy GH4169 can be utilized in high-temperature applications due to their high-temperature performance. The SiC/SiC composites are commonly used in turbine outer rings, where they encounter friction and wear against the turbine blades. This high-speed rubbing occurs frequently in aircraft engines and steam turbines. To investigate the tribological behavior of these materials, rubbing experiments were conducted between the SiC/SiC and the GH4169 superalloy. The experiments involved varying the blade tip speeds ranging from 100 m/s to 350 m/s and incursion rates from 5 μm/s to 50 μm/s at room temperature. Additionally, experiments were conducted at high temperatures to compare the tribological behavior under ambient conditions. The results indicated that the GH4169 superalloy exhibited abrasive furrow wear during rubbing at both room temperature and high temperature. Furthermore, at elevated temperatures, some of the GH4169 superalloy adhered to the surface of the SiC/SiC. The analysis of the experiments conducted at ambient temperatures revealed that the friction coefficient increased with higher blade tip velocities (100~350 m/s). However, the coefficient was lower at high temperatures compared to room temperature. Furthermore, significant temperature increases were observed during rubbing at room temperature, whereas minimal temperature changes were detected on the rubbing surface at high temperatures.

High-Speed Rubbing Behavior of Abrasive Coating Coated on Titanium Alloy Blade Tips

High-Speed Rubbing Behavior of Abrasive Coating Coated on Titanium Alloy Blade Tips

High-Speed Rubbing Behavior Between Nickel-Based Superalloy Blades and Ceramic-Based Abradable Coatings

High-Speed Rubbing Behavior Between Nickel-Based Superalloy Blades and Ceramic-Based Abradable Coatings

Phenomenological modeling of wear mechanisms between nickel-based superalloy blades and ceramic-based abradable coatings in turbomachines

The tribological behavior and wear mechanism between K417G nickel-based superalloy blades and 8 wt% yttria-stabilized zirconia poly-p-hydroxybenzoate ceramic-based abradable coatings were investigated using a high-speed rubbing test machine simulating actual operating conditions. Two main influencing factors (linear velocity and incursion rate) were varied, and their effects on the system were determined. The wear mechanism of the system was attempted to be characterized. A significant correlation was found between all test results and the linear velocity, indicating that the linear velocity was the primary influence driving the friction. The incursion rate became a secondary factor. A linear mathematical model based on the proposed wear mechanism was developed to explain the wear mechanism and to predict the test results. The excellent fit and normally distributed residual results indicated the excellent performance of the model. This work can be used as an aid to understanding the present results and as a basis for further research on these phenomena in the future.

Anti-adhesion Mechanism of TiB2-Deposited Ti6Al4V Blade Tip Against Al-hBN Seal Coating During High-Speed Rubbing

Anti-adhesion Mechanism of TiB2-Deposited Ti6Al4V Blade Tip Against Al-hBN Seal Coating During High-Speed Rubbing

Experimental and Numerical Study on the Influence of Rubbing Force on Radial Crack Initiation in Labyrinth Seal Fins

Radial cracks appear in the labyrinth seal fins of the shrouded turbine blade of an aero-engine during service. To clarify the influence rule of rubbing force on crack initiation, a high-speed rubbing test bench and a numerical calculation model are established, and the research is carried out through experiment and numerical calculation. It is found that cracks can be initiated when the rubbing force is greater than 20 N with a high rubbing temperature at high speed. It is verified by numerical calculation and shows that pure mechanical load will not cause crack initiation, while the thermal load is the main reason for the radial crack initiation of fins. With the increase of rubbing force, the time of crack initiation increases, and the number and length of cracks decrease. At high rubbing temperatures, rubbing force will lead to radial crack initiation, which mainly affects the position of crack initiation.

Experimental Study on the Effect of Rubbing Mode on Radial Crack Initiation in Labyrinth Seal Fins of Shrouded Turbine Blade

The labyrinth-honeycomb seals have been widely used in aero-engine. However, radial cracks appear on labyrinth seal fins of shrouded turbine blade in use. To clarify the rubbing mode of radial crack initiation, a high-speed rubbing test bench was designed. The effects of five rubbing modes on crack initiation were studied. Through the test, it is found that cracks would be formed at the junction of the fin tip and side of the labyrinth seal fins under all five modes. When two successive rubbing modes are different, the temperature of the last rubbing can be lower than that of it alone rubbing, and simultaneous radial and axial rubbing can inhibit each other. Radial rubbing mainly affects the initiation of cracks on fin tip, while axial rubbing mainly affects the initiation of cracks on the side. Moreover, the rubbing temperature is mainly affected by radial force.

Investigation of the Al-adhesive transfer mechanism on Ti6Al4V blade tips under high-speed rubbing in an aero-turbine engine

The Al-hBN seal coating invariably transfers to the tip of the Ti6Al4V blade under high-speed rubbing, resulting in the deterioration of the power and the reliability of the developed aero-engine. The Al-adhesion phenomenon was reproduced using a high-speed rubbing test rig at 90 m/s and 300 m/s. The results showed that the coverage rate and thickness of the Al-adhesive transfer layer were higher at 300 m/s than at 90 m/s, which could be attributed to the Ti-Al interface reaction. The interface microstructure and the thermal stress distribution model were proposed to reveal the mechanism of the Al-adhesive transfer under conditions of high-speed rubbing. A gradient interface reaction interlayer composed of TiAl3 and γ-TiAl between the Al-adhesive transfer layer and the Ti6Al4V blade tip was observed only at 300 m/s. This interface reaction interlayer could release the thermal stress and enhance the adhesion between the Al-adhesive transfer layer and the Ti6Al4V blade tip.

Effect of the Corrosion of Seal Coatings Used in Aero Engines on Their High-Speed Wear Behaviour

As the number of aircraft that park in ocean environments increases, the corrosion of coatings used in their engines becomes inevitable. Previous studies have focussed on the abradability of as-sprayed seal coatings in high-speed rubbing tests with a blade. This study deals with the investigation of the effect of corrosion on the abradability of seal coatings. It uses metallographic analysis and hardness, bonding strength and high-speed rubbing tests conducted on as-sprayed and corroded Al-hBN coatings. The results have shown the appearance of additional pores in the corroded coatings and a decrease in the coating mechanical properties. Compared with the as-sprayed coatings, the corroded coatings caused an increase in blade wear and severe overheating of the blade tip during the high-speed rubbing test when the rubbing speed and single-pass depth were high. The unfavourable thermal properties of the corroded coatings were considered as the probable reason for these results.

Effect of microstructure on the adhesion strength of TiBx coating on Ti6Al4V substrate

TiBx coatings were deposited on Ti6Al4V and Si (100) wafer substrates by D.C. magnetron sputtering with various target-to-substrate distances (T.S. distances) from 50 mm to 200 mm. The influence of T.S. distance on the microstructure, hardness and adhesion strength of TiBx coatings and Ti6Al4V substrate system was investigated. Results showed that the microstructure of TiBx coatings transformed from dense to fibre columnar grain with the increase in T.S. distance, whilst the hardness decreased from 20.9 GPa to 9.4 GPa. The Rockwell-C indentation adhesion strength grade was also improved from HF6 to HF1. An adhesion evaluation factor G, which is related to the mechanical properties and the microstructure of TiBx coating, is proposed based on the test results. The adhesion strength increased with G, which corresponded well with the results of indentation test. The high-speed rubbing test with a sliding speed of 300 m/s was performed to check the Al-adhesion resistance of the TiBx coating against Al–hBN seal coating.

A novel method to evaluate the densification of abradable seal coatings

In order to further accurately evaluate the densification degree and investigate the densification mechanism of the abradable seal coating, X-ray Tomography (XRT) was used to quantitatively and qualitatively characterize the 3-D distributions of pores in the Al/hBN abradable coating before and after rubbing. Moreover, through comparing with the calculation of the densification factor, it was found that the experimental results of the two were consistent, which indicated that this novel method is proved to be an effective criterion. Furthermore, it was found that the densification of the Al/hBN abradable coating mainly occurred in the subsurface layer below the worn surface, and the effect of the high-speed rubbing on deeper areas was inconspicuous.

Quasi-Static Thermal Modeling of Multiscale Sliding Contact for Unlubricated Brush Seal Materials

Prediction of contact temperature between two materials in high-speed rubbing contact is essential to model wear during unlubricated contact. Conventionally, assumptions of either a steady or an annular heat source are used for slow and high speed rotation, respectively. In this paper, a rotating heating source is solved using an in-house finite element method code. This captures the full geometry and rotating speed of the rubbing bodies. Transient heat transfer is modeled quasi-statically, eliminating the need for a transient 3D simulation. This model is shown to be suitable for contact temperature prediction over a wide range of rotating speeds, anisotropic thermal conductivity, and nonuniform thermal boundary conditions. The model calculates heat partition accurately for a thin rotating disk and short pin combination, which cannot be predicted using the existing analytical solutions. The method is validated against ansys mechanical and experimental infrared thermography. Results demonstrate that the annular source assumption significantly underpredicts contact temperature, especially at the rubbing interface. Explicit modeling of a thin disk results in higher heat partition coefficients compared with the commonplace semi-infinite length assumption on both static and rotating components. The thermal anisotropy of tuft-on-disk configurations is evaluated and compared to a uniform pin-on-disk configuration. Despite the effective thermal conductivity (ETC) in the bristle tuft being approximately 1 order of magnitude lower than along the bristle length (treating the bristle pack as a porous medium), its impact on heat partition and contact temperature is shown to be limited.

Effects of blade material characteristics on the high-speed rubbing behavior between Al-hBN abradable seal coatings and blades

Abradable seal coatings have been widely used in aero engines to reduce gas path clearance. Research has been performed to evaluate the abradability of the seal coating. In addition, the high-speed rubbing test rig has been employed to simulate the interaction between the seal coating and blade. However, almost all previous studies tested blades made of one type of material. In real engines, the blade material for a seal coating is changeable. In this work, blades made of different titanium alloys were tested and rubbed against the same Al-hBN seal coating. Macro-morphology and micro-morphology observations with scanning electron microscopy (SEM) were employed to examine the wear behavior of the blade-coating couple. The results indicated that the Ti6Al4V blade exhibited the most severe coating adhesions and almost no blade wear; the Ti-8Al-1Mo-1V blade experienced less coating adhesions; and the Ti-5Al-2Sn-2Zr-4Cr-4Mo blade exhibited the least coating adhesions. The mechanical strengths at room and high temperatures and the rub performances during the single pendulum scratch test were checked to find the relationship between the mechanical properties and high-speed rub performances. Unfortunately, high mechanical strength did not appear to guarantee the absence of blade wear, and the thermal properties of the different materials blades were identified as the main reason for the different wear behaviors.

Material Transfer Behavior between a Blade and Two Types of Coating during High-Speed Rubbing

ABSTRACTThe material transfer behaviors of Al-hBN and NiAl-hBN coatings rubbed by a Ti6Al4 V blade at different linear speeds and single pass depths were studied using a high-speed rubbing tester. The blade height variation analysis, morphologies, energy-dispersive spectroscopy, and X-ray diffraction studies of the blade and the coating wear scars indicated that the coating material transferred to the blade during rubbing with the Al-hBN coating. For the NiAl-hBN coating, the blade material transferred to the coating. The temperature differences at the interface, varying melting points of the coatings, and blade plastic flow softening under high temperatures were regarded as factors for different material transfer behaviors.

Effect of thermal–physical properties on the abradability of seal coating under high-speed rubbing condition

The tribological behaviours of two seal coatings (NiAl-hBN and Al-hBN) against Ti-6Al-4V blade were investigated under high-speed rubbing conditions by a self-developed tribology tester. The wear behaviour and the mechanism of the blades and seal coatings were studied. The maximum possible temperature (MPT) and the temperature rising rate (TRR) at the rubbing surface, which were both directly related to the mechanical strength of coating and blade, were identified as two key factors influencing the blade wear performance and the coating abradability. The MPT of Al-hBN coating was limited to a rather low level and the coating temperature resistance was poor. Hence, the coating was initially softened and blade wear was reduced or even replaced by adhesion of Al-hBN coating. The MPT of NiAl-hBN coatings could be relatively high and the TRR of NiAl-hBN was much smaller than the blade. Hence, the blade lost its mechanical superiority over the coating and was severely damaged. A dimensionless number NT was proposed based on the thermal-physical parameters of blade and coating to represent MPT and TRR and predict the degree of blade wear. The theory agreed well with the wear performance of blades coupled with NiAl-hBN and Al-hBN, as well as with other seal coatings, such as Ni-Cg and AlSi-polyester.

Investigation and simulation of the shear lip phenomenon observed in a high-speed abradable seal for use in aero-engines

Abradable seals are used in the compressor sections of aero-engines, and their performance affects engine efficiency and durability. The sliding-induced surface damage between a type GH4169 turbine blade and a CuAl-NiG seal coating was investigated under simulated working conditions using an improved high-speed rubbing test rig. The influence of different linear speeds (150, 300m/s), incursion rates (5, 50, 500µm/s) and environment temperatures (300, 450°C) were researched. According to variations in weight and height measurements of the blade test samples, and based on observations of the blade wear scar macro-morphologies, it was found that blade wear with a prominent shear lip increases with linear speed and temperature but decreases with incursion rate. The surface and cross-section morphologies, phase components of the blade and coating wear scars were analyzed using SEM, EDS and XRD. The formation mechanism of the shear lip was revealed for the first time. It was found that a double-layer shear lip was produced by the combined action of a shear mixed layer and blade matrix softening, both of which resulted from high-intensity frictional heating.

Ti6Al4V Blade Wear Behavior During High-Speed Rubbing with NiAl-hBN Abradable Seal Coating

The high-speed rubbing wear behavior between a Ti6Al4V blade and a NiAl-hBN seal coating was studied with a high-speed rub test rig. Blade wear behavior, which had not received enough attentions, was the key concern of this study. The rub tests conducted at different linear speeds and single-pass depths indicated that although wear distance was constant and rub forces decreased at high linear speed, blade wear increased with the increment of linear speed when single-pass depth was invariable. According to scanning electron microscopy, x-ray diffraction, electron probe microanalysis and microhardness analyses of the wear scars, different blade and coating wear mechanisms were observed when rubbed at different linear speeds. Remarkably, when rubbing was done at high linear speed, there was severe blade oxidation with the generation of oxidation layer full of cracks and high-hardness transfer layer in the coating wear scar, and these were identified as reasons of aggravated blade wear.

Investigation of high-speed rubbing behavior of labyrinth-honeycomb seal for turbine engine application

The labyrinth-honeycomb seal has been widely used in gas turbine engines as an abradable gas path seal to protect the rotor from wear and damage in rubbing interaction. It usually works with a stepped labyrinth because the knife-edged tips could produce a special dynamic sealing system, and then the minimum clearance is possible between the rotor and stationary component. To investigate the high-speed rubbing behavior between a Hastelloy-X honeycomb material and a GH4169 double stepped labyrinth, nine rubbing tests were conducted using a high-speed abrasion test rig while the blade tip speed varied from 150 to 450 m/s, and the incursion rate from 120 to 360 µm/s. The abradability of honeycomb made from Hastelloy-X was fully verified by analyzing the visual rubbing observations, rubbing forces, and impact acceleration. It is shown that compression deformation happens to the honeycomb material during the rubbing process with the labyrinth blade except for a simple cutting mechanism, which is mainly affected by the parameter of incursion rate. Thermal ablation and oxidation were the main damage occurring on the labyrinth tip and appeared more obviously at a higher blade tip speed. Rubbing forces and impact acceleration were obtained from a piezoelectric dynamometer and acceleration sensor during the rubbing process. At a blade tip speed of 300 m/s and incursion rate of 360 µm/s, radial and tangential forces show their maximum values of 716 N and 871 N, respectively. The peak value of acceleration presents 341g with the highest blade tip speed of 450 m/s and the highest incursion rate of 360 µm/s. All testing results provide a great deal of effective information on high-speed rubbing behavior for the abradablility evaluation of a honeycomb.

Study on the High-Speed Rubbing Wear Behavior Between Ti6Al4V Blade and Nickel–Graphite Abradable Seal Coating

The wear behavior of Ti6Al4V blade rubbed against nickel–graphite (Ni–G) abradable seal coating was studied with a high-speed rub test rig. According to the test results acquired at different incursion per passes and linear speeds, blade wear increased with the increment of linear speed at a fixed incursion per pass. With incursion per pass increasing, blade wear increased when linear speed was fixed at 30 m/s, while decreased at 90 and 150 m/s. Referring to the macromorphology observation, scanning electron microscopy (SEM) and dispersive X-ray spectroscopy analyses of the wear scars, rubbing at 30 m/s, microcutting and microploughing with coating adhesion was the main blade wear mechanism while spalling accompanied by densification was the main coating wear mechanism. Rubbing at 90 and 150 m/s, plastic deformation was the main blade wear mechanism while transfer mixed layer that resulted from blade transferred was identified as the main coating wear mechanism. Quantitative analysis of coating densification and microhardness detection of the transfer mixed layer indicated that high coating densification made great contribution to low blade wear at 30 m/s and aggravated blade wear at high linear speed was due to the high frictional heat and the resultant high-hardness transfer mixed layer. It could therefore be concluded that high linear speed guarantees enough frictional heat output while low incursion per pass is responsible for the accumulation of frictional heat.

Tribological behaviors of turbofan seal couples from friction heat perspective under high-speed rubbing condition

Abstract The tribological behaviors of two types of seal coatings, nickel–graphite and aluminum–hexagon-boron nitride (Ni–Cg and Al–hBN, respectively) versus a Ti–6Al–4V blade used in turbofan engines were investigated using a high-speed rubbing test. The wear status and damage mechanism of the friction couples were studied and the abradability of the seal coatings was evaluated. By analysis of the coating properties and damage mechanism of the seal couple, the friction heat effect was identified as the key factor influencing blade wear forms as well as coating abradability. A one-dimensional heat conduction model was established to estimate the effect of increasing temperature on the friction interface. The results indicated that in the Ni–Cg and Ti–6Al–4V seal couple, the temperature rising rate (TRR) of the Ti–6Al–4V blade was faster than that of the Ni–Cg coating, and so the Ti–6Al–4V blade softened earlier than the Ni–Cg coating, causing the blade to suffer severe wear. In the Al–hBN and Ti–6Al–4V seal couple, the TRR of the Ti–6Al–4V blade was slower than that of the Al–hBN coating, and so the Al–hBN coating softened first; thus, blade damage was reduced or even replaced by coating adhesion. The square root ratio of thermal diffusivity between the blade and the coating could be taken as an indicator of the ratio of TRR between the blade and coating to predict blade wear status as well as damage mechanism. The results of the model agreed well with the experiment results of the two seal couples used in this study.