Research On Laser Welding Characteristics Of Zirconium Alloy In Pure Agron Atmosphere

In2007, the Nuclear Project AP1000was introduced from Westinghouse ElectricCorporation as one of the major programs. It leads directly that achieving the totallocalization of technology is becoming the chief issue. The welding of spacer gridassembly is the issue to be solved firstly.In this thesis, laser pulsed welding was adopted to join Zirconium alloy intersectjoint in box full of argon. It is required a fine shape of joint, some mechanical propertyof intersect joint and resistance to be corroded due to its roll playing on spacer gridassembly. It is critical to obtain good shape of joint in order to gain better mechanicalproperty, for the larger of depth to width the higher of mechanical property. Influence oftechnological parameters of laser pulsed welding, which includes peak power, pulsewidth, frequency and number of pulse, on shape of joint is analyzed. It shows thatgiving the same heating input, the depth-to-width ratio increase with the rise of peakpower and the number of launching. While the width of pulse and frequency have littleeffect on the depth-to-width ratio.Taking into consideration of work environment of joints, the short-term corrosionprocesses of zirconium-4were discussed and comparing to the corrosion resistance ofZirlo(Zr-1.0Nb-1.0Sn-0.1Fe) which was added Nb. It shows that the main factor whichaffects the corrosion resistance of joints was the change of element weight whichsoluted into the metal matrix. The corrosion resistance decreases with the increase ofFe/Cr ratio. Comparing to Zr-4alloy, the reason why the corrosion resistance of Zirloalloy declines is that the production of phase βZr full of Nb. The corrosion resistance ofZirlo alloy which is conducted by heat treatment is better than that of Zr-4alloy. It isbecause that the βZr phase full of Nb decomposes, with Zr+βNb emerging whichshows better corrosion resistance. Comparisons of joints which are welded in different welding environmentcontaining diverse amount of water and oxygen is done, owing to the sensibility towelding environment of zirconium alloy. Test reveals that there is no obvious oxidefilm generated on the joints welded in environment with low water and oxygen; whilewelding in environment with high water and oxygen, the thickest of oxide film is on thesurface of welding bead, subsequently HAZ, the slightest is on the surface of matrix. Inaddition, both of two joints welded in distinct atmosphere show no evidence of intakinghydrogen. There are many micro-crazes in oxide film, which supply a way to diffusefor OH-and H+, leading corrosion to be kept on. In case of the oxide film formedpreviously on the joints welded at high content of water and oxygen, the large tensilestress is aggravated during corrosion, which produce craze that is vertical to theinterface of oxide film and matrix. However, oxide film also plays a role to prevent thediffusion of H+, so that the joint appears few hydride precipitation with smalldimension.