| The application of aluminum-based seal coating in aero-engine compressor can significantly improve its gas path sealing performance.The titanium alloy blade will be protected at the cost of sacrificial wear of the Al-based sealing coating.However,the Al-based sealing coating is prone to adhesive transfer onto the blade tip and enlengthen the blade during the high-speed rubbing,which will deteriorate the stability of the rotating system in the compressor.It is an effective method to inhibit the adhesive wear of the Al-based sealing coating by deposition an adhesive-wear resistance coating on Ti alloy blade tips.The closed-field unbalance magnetron sputtering was used to deposit TiB2 coatings on Ti alloy substrates.The coating structure and property were optimized by controlling the deposition parameters.The mechanical properties and tribology behavior of the coatings were further improved by multilayer structure design.After that,the Al-adhesive transfer behavior between TiB2 deposited Ti alloy substrate and Al-based sealing coating(industrial pure aluminum)was investigated on the tribology test rigs which could simulate the high-temperature and high-sliding speed tribo-condition in an aero-engine compressor.By the experiment results and analysis,the main conclusions are obtained as follows:The target-to-substrate distance(T.S.distance)in sputtering could affect the composition,microstructure and hardness of the TiB2 coatings.With the increase of T.S.distance from 50 mm to 200 mm,the coating changed from a dense featureless structure with(001)orientation to a columnar structure with(101)orientation,and the coating hardness decreased.Meanwhile,the adhesion strength grade measured by Rockwell-C indentation was improved from HF5 to HF1 grade.Under different sputtering power and bias voltage,the deposition coating always follows the principle of minimal total free energy.When the sputtering power increased or bias voltage decreased,the TiB2 coating orientation changed from(001)to(101),with alteration of coating microstructure,residual stress and hardness.Moreover,there was an influence of sputtering power and bias voltage on the adhesion strength and fracture toughness of the coatings which changed the coating tribology performance finally.When the sputtering power was 500 W and bias voltage was-60 V,TiB2 coating on Ti alloy substrates showed a better fracture toughness(1.99 MPa·mm1/2)and a lower wear rate(3.30×10-5 mm3N-1m-1).The layer thickness ratio Q of TiB2/Cr multilayer coating was optimized by stress analysis with the finite element method(FEM).According to the FEM model,the TiB2/Cr multilayer coatings were deposited on Ti alloy substrates.The multilayer design with metal Cr interlayer could release the residual stress in coating and lower the coating hardness.At the same time,the coating adhesion and fracture toughness were enhanced.When Q=0.5,the TiB2/Cr multilayer coating had the minimum equivalent stress concentrate area and the best fracture toughness.Therefore,it presented the optimal wear resistance,with a wear rate of only about 30%of the TiB2 monolayer coating.The high-temperature tribology behavior of TiB2 coating on Ti alloy substrate against A1 pin was evaluated by using a high-temperature pin-on-disk wear test rig.It was found that when the temperature raised to 150?,the COF reduced due to the formation of H3BO3 lubrication film.The coverage rate of the Al-adhesive transfer layer was also lower than that at room temperature.With a further increase of temperature to 300?,the H3BO3 lubrication film decomposed,the coverage rate and thickness of the Al-adhesive transfer layer increased significantly.Furthermore,the increase of sliding speed reduced the Al-adhesive coverage rate and the COF of TiB2 coating against Al pin.At last,the Al-adhesive transfer degree on the TiB2 coating was normalized with the wear length of the Al pin to obtain the adhesive-wear resistance capability coefficient Ac.It could be used to evaluate the adhesive-wear resistance of the specific friction couple.The high-speed rubbing behavior between the Ti6A14V or TiB2 deposited Ti6A14V blade and Al-hBN seal coating was evaluated on a high-speed rubbing test rig.The interface of the Al-adhesive blade tip was characterized and analyzed to establish the model of the interface reaction and the thermal stress distribution on the Al-adhesive blade tip.As for the sliding speed of 300 m/s,there was a gradient compositional Ti-Al reaction layer at the interface between the Al-adhesive transfer layer and Ti6A14V blade tip,which could release the thermal stress at this interface effectively and make the Al-adhesive transfer layer and Ti6A14V tip bonded tightly.Therefore,the adhesive transfer of Al-hBN to the Ti6A14V blade tip was more severe at higher sliding speed during rubbing.The phenomenon of adhesive-transfer of Al-hBN seal coating could be inhibited by the magnetron sputtering deposition of TiB2 coating on Ti6A14V blade tip.At a high sliding speed of 300 m/s,there was a reaction layer at the interface of Al-adhesive TiB2 deposited blade tip.This thin interface reaction layer would bring high thermal stress according to the TiB2/Al interface reaction and the thermal stress distribution model.The interface reaction layer together with the Al-adhesive transfer layer was prone to spall off from the TiB2 coating.Thus,the Al-adhesive transfer on the TiB2 deposited Ti6A14V blade would be restrained. |
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