In-situ formation of laser-cladded layer on Ti-6Al-4 V titanium alloy in underwater environment

Abstract

Repairing layer on Ti-6Al-4 V alloy in underwater environment was prepared firstly by in-situ underwater laser cladding technology based on the self-designed underwater laser cladding nozzle, and effects of water environment on the formation characteristics, microstructure and performance of cladding layer and laser propagation mechanism was investigated. The appearance of the underwater layer characterized by conduction mode pool was continuous and uniform; nevertheless, cracks were observed and a small amount of oxide and spatters formed on the layer surface. The microstructures inside prior globular or columnar β-grains of the underwater and in-air layers consisted of the plate or lamellar α phase and acicular α′ phase with different size scales, and the absorption of aerosol particles on laser beam and the water cooling effect increased the amount of α′ and decreased the grain size and the thickness of α plate. The corrosion resistance of the underwater layer approached to that of the in-air layer, whereas the microhardness was slightly higher. The fracture surfaces of crack exhibiting transgranular fracture behavior in the underwater layer were characterized by tongue shaped or river pattern, indicating the fracture mode was the quasi-cleavage or cleavage fracture, and the crack formation mechanism of the cladding layer was analyzed.