Zr-4 Alloy Microsructure And Properties Of Laser Cladding Composite Ceramic Coating

In order to improve the wear resistance and corrosion resistance of the zirconium alloy tub in the application of nuclear equipment, nitride and oxide composite ceramic coating on the surface of Zr-4 alloy was prepared by laser cladding, while the powder system was preset, and the thickness of coating was optimized and the parameters laser were adjusted. Analysis of the cladding layer microstructure, phase composition, microhardness, friction and wear properties, and macro morphology of interfacial bonding state were provided. The main experimental results and conclusions are as follows:(1) When the thickness of pre-coating was 0.3 mm, overlapping cladding improved the binding strength between the coating and the substrate, which effectively improved the morphology and surface flatness of the cladding layer. By setting laser cladding process parameters P = 2.0 kw, v = 12 mm / s, laser cladding layer without pores and cracks was obtained. When the thickness of pre-coating was 0.1 mm, nano particle could refine the organization in a low laser energy density, but reduced the surface quality of the coating;However, in high-energy laser energy density, nano particle could improve the surface morphology and roughness, while had not obvious grain refinement.(2) Phase of the surface layer was mainly composed of Ti N, Zr N and t-Zr O2, m-Zr O2,and contains a small amount of Ti Zr N2. Phase of the middle coating layer was consisted of α-Zr, Zr N, Ti N; the middle of laser cladding layer prepared by adding 5% nano-Ti N contained cubic Ti Zr N2 phase.(3) The surface of single track cladding was mainly made up of dendritic, globular. The bottom of the coating was composed of needle and granular microstructure. With the increase of laser power, globular content reduced, but dendritic increased. The surface of overlapping cladding layer was mainly composed of dendritic, spherical, granules, intergranular amorphous microstructure, and the contents of nitrides and oxides decreased gradually with the distance to the surface increased, and the bottom of the coating was composed of needle-like, granular, fine dendritic microstructure. When adding 5% nano-Ti N, the number of heterogeneous nucleation is increased and the microstructure is refined.(4) Laser cladding layer microhardness was gradually reduced in depth direction, and the highest hardness was between 1130 ~ 1450 HV0.1 compared to the base(180 HV0.1), which had increased 7 times. The wear volume of laser cladding layer had decreased in dry sliding friction and wear experiment. The wear form of Zr alloy was adhesive wear. The submicron Ti N powder coating was mainly abrasive wear, along with adhesive wear. The wear of coating prepared by nitrogen-rich Ti N and adding 5% nano-Ti N was in the form of type of abrasive wear. Among them, the coating prepared by adding 5% nano-Ti N had the best wear resistance.