Study On In-situ Synthesized Composite Coatings Of Aluminum Alloy And Titanium Alloy Prepared By Laser Cladding And Electrospark Deposition

The present work was a part of the localization overhaul project for a new type high performance aero-engine. With the purposes of remanufacturing and enhancing two typical light metals used in aero-engines, i.e. the titanium alloy and aluminum alloy, the in-situ synthesized composite coatings were prepared by laser cladding and electrospark deposition. The microstructures, formation processes and performances of these in-situ synthesized composite coatings were studied by SEM, XRD, EPMA, TEM, microhardness tester and magnetostrictive-induced cavitation facility. Main results are achieved as follows:(1) The failure analyses were carried out on the titanium alloy and aluminum alloy failure components of aero-engines firstly. The results showed that pressure changes caused by the afterburning and pumping components in fuel system were the main reason to lead to cavitation erosion. Phase-select and hollow out behaviors had been observed on the eroded surface. The changes of assembly positions and the poor wear properties, including the low strength, strong adhesion tendency and high coefficient of friction, led to the wear failures.(2) A system study was carried out on the reaction processes, microstructural characteristics and the formation mechanisms of the in-situ synthesized coatings prepared by laser irradiation of "titanium alloy+Cr3C2 or B4C" powder mixtures. For the Cr3C2 condition, the TiC/β-Ti composite coatings can be obtained. There were three typical in-situ synthesized TiC, i.e. the monotectic TiC, the eutectic TiC and the supersaturation separate TiC, in the TiC/β-Ti composite coatings. The composite coatings were enhanced by load transfer and Orowan mechanism. The multi-components (B and C) in-situ synthesized reaction results showed that the composite coatings enhanced with TiC, TiB and TiB2 could be obtained by laser irradiattion of TA11+B4C powder mixtures. In the in-situ synthesized reaction processes, a competitive behavior between B and C had been observed. The results were that the C diffused preferentially and the reaction between B and Ti was inhibited; (3) According to the liquid separation theory, the Cu-base in-situ composite coatings were fabricated by laser cladding. The in-situ particle reinforcements were composed of Laves phases and Co-base/Mo-base solid solutions, and the matrix of the coating was Cu-base solid solution. The studies on formation processes and growth mechanisms of the separated phases indicated that heterogeneous nucleation was the main mechanism for liquid separation. The effects of convection and the collisions-coagulations were the main reasons for growing and coarsing;(4) The study on the microstructure characteristics and the formation mechanisms of the Si/Al composite coatings formed by electrospark deposition was carried out for the first time. The Si/Al composite coatings displayed novel microstructures with the lattice-like characteristics. The lattice-like Si phases, which enveloped the soft a-Al phase in the lattices, seemed to be composed of many fine spherical Si particles with the size of～50nm. The microhardness of the Si/Al coating was also improved due to the novel composite structure;(5) The cavitatin erosion resistances of TiC/β-Ti and Si/Al composite coatings were studied by magnetostrictive-induced cavitation facility. The comparisons were carried out between the composite and non-composite coatings. The research results showed that, the 10%Cr3C2 coating possessed the best cavitation erosion resistance. The improvement could be mainly attributed to the well toughness of theβ-Ti matrix and the composite strengthening of medium size TiC dendrites. The improvement on cavitation erosion resistance for Si/Al composite coating was mainly attributed to the novel latticed composite structures;(6) The in-situ synthesized composite coating had been successfully applied to the aero-engine overhaul, and the responds were well. The in-situ synthesized composite coatings prepared by laser cladding and electrospark deposition are suitable for aero-engine overhaul application.