| Titanium alloys are used in aerospace and other fields due to their excellent properties such as low density,high specific strength and high corrosion resistance.The proportion of titanium and titanium alloys in the overall weight of aircraft used has become one of the advanced standards for measuring aircraft materials.However,the oxidation resistance of titanium alloy decreases greatly with the increasing of working temperature.Therefore,the lack of high temperature performance of titanium alloy limits its further application in high temperature service environment.Studies have shown that it is a feasible method to prepare a coating with good oxidation resistance on the substrate by surface modification.Therefore,in this paper,the Ti-Al-B coating was prepared on the surface of TC4 titanium alloy by laser cladding in situ to improve its high temperature oxidation resistance.In this paper,coatings with good oxidation resistance was fabricated on the surface of TC4 titanium alloys by laser cladding in-situ reaction between Ti,A1 and B powder.The metallurgical bonding between the cladding coating and TC4 matrix is good,and the coating has good macro morphology,no obvious cracks and pore defects.In this paper,optical microscopy(OM)was used to observe the microstructure of the coating,scanning electron microscopy(SEM)was used to observe the micro-morphology of the coating,energy dispersive spectrometer(EDS)was used to study the distribution of elements in the coating,X-ray photoelectron spectroscopy(XPS)was used to analyze the binding state of elements,and X-ray diffraction(XRD)was used to determine the phase composition of the coating.The microhardness and high temperature oxidation resistance of Ti-Al-B coating were tested by microhardness tester and tubular furnace respectively and the mechanism of the coating to improve its high temperature oxidation resistance was analyzed.From the above experiments and tests,the following conclusions were drawn:The forming effect of elemental mixed powders of elemental powders is not good,but that of pre-alloyed powders is good.The reason is that the melting point of A1 element is low and its density is low.When it exists as elemental,it is easy to volatilize and splash.Ti-Al-B coating was prepared on TC4 substrate by laser cladding.The coating was metallurgically bonded with TC4 titanium alloy substrate.The main phases in the coating include ?-Ti,Ti3Al,Al2O3 and a small amount of Ti oxides and TiB.After analysis,it can be determined that Ti is mainly existed as Ti and Ti3Al in the coating,and A1 is mainly existed as Ti3Al and Al2O3.The highest microhardness of laser in situ Ti-Al-B coating can reach 1177.5 HV0.2,which is 3.27 times of the matrix.Under the oxidation condition of 800 C×24 h x 5,the oxidation resistance of the coating can be increased by 10?15 times compared with the TC4 titanium alloy matrix.The reasons for the improvement of the laser in-situ Ti-Al-B coating are mainly reflected in the following two aspects:on the one hand,the presence of B element refines the structure of the coating,and the compactness and continuity of the coating oxide film are improved,which can effectively hinder the diffusion of oxygen in the air to the inside.On the other hand,element B can improve the adhesion between the coating and the oxide film,which makes the oxide film not easy to fall off or crack from the coating,and thus has a good protective effect on the matrix. |
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