A Study On Preparation And Properties Of The Laser Cladding Mo-Nb Alloys

Refractory metal has a good high temperature strength and corrosion resistance, plays an irreplaceable role in aerospace, energy and nuclear industry. As an excellent representative in refractory metals, Mo and its alloys have a series of advantages, with a high melting point, a low creep rate under high temperature, little coefficient of expansion, a well thermal conductivity and thermal shock resistance. Besides it also have a good abrasion and corrosion resistance. Nb can significantly refine the grain size and improve the toughness of alloys as a second phase. As a newly developed technology, laser cladding has grown rapidly in recent years and can produce coatings upon the substrate materials to display a sufficient rigidity and enhance the corrosion resistance. This technology has a wide application prospect in the field of civil and military.The Mo-Nb and Mo30NiSF-Nb series coatings are prepared on the surface of the TC4 alloys and Q235 steel with the optical coupling semiconductor laser and plasma cladding in this paper respectively. All the coatings had homogeneous structure and a good metallurgical bonding with the substrates. The microstructure and the phase composition of the laser cladding coatings are analyzed by means of SEM (Scanning Electron Microscope), EDS (Energy Disperse Spectroscopy) and XRD (X-ray Diffraction). The microhardness curves of the coatings are examined by a nanoindenter instrument. The corosion-resistance of the coatings are characterized through the H2S corrosion tests.The result shows that both of the Mo-Nb and Mo3oNiSF-Nb alloys form a dendrite and cellular grains made by laser. While the coating made by plasma cladding has a martensite structure, but the dilution of the substrate and the depth of heat affected zone arc obviouly higher than the laser coating, it still needs to be improved to reduce the dilution rate in future. The coating successfully enhances the hardness of substrate materials for 3-4 times with these two cladding methods.The substrate materials are depraved serious under the H2S circumstances,whill the 50wt.% Mo-50wt.% Nb coating only has several pitting flaws on the surface, it shows a well corrosion resistance behavior.Compared with different addition amount of Nb element into Mo3oNiSF-Nb alloy to investigate its impact on the microstructure and physical hardness to the coatings. The result shows that Nb can reduce the crack and bolwholes defects in the cladding layer effectively. It shows that with 30wt.% Nb addition can obtain a nonpore or surface defects coating, and Nb plays an important role in refining the grain size, and forms a well β-Ti solution phase.The hardness coatings increased first and then decreased with the increasing of Nb additions. To analys the best coating for Mo3oNiSF-30wt.%Nb, it advances the microhardness of original material for 4 to 5 times,and the friction coefficient is reduced by 50%, the coating shows a good physical property.