A study on effect of heat input on mode of welding, microstructure and mechanical strength in pulsed laser welding of Zr-2.5 wt.%Nb alloy

• Published in: Journal of nuclear materials 2022-06, Vol.564, p.153685, Article 153685
• Main Authors: Bharadwaj, V., Rai, A.K., Upadhyaya, B.N., Singh, R., Rai, S.K., Bindra, K.S.
• Format: Article
• Language: English
• Subjects: Base metal; Cooling rate; Ductile fracture; Ductility; Fractography; Heat; Heat affected zone; Heat treating; Laser beam welding; Lasers; Lath martensite; Martensite; Mechanical properties; Metal plates; Microhardness; Microstructural analysis; Microstructure; Neodymium lasers; Niobium base alloys; Porosity; Process parameters; Pulsed laser welding; Pulsed lasers; Residual stress; Room temperature; Semiconductor lasers; Temperature profiles; Thickness; Welding; YAG lasers; Zirconium
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2022.153685

•A transition mode between conduction and keyhole is utilized for defect free welding of Zr-2.5 wt.% Nb alloy.•Significant change in microstructural morphology across the different weld zones is observed.•The residual stress in fusion and heat affected zones is found to be tensile in nature compared to the base metal.•The hardness is found to be changed significantly across different weld zones as result of microstructural modification.•The tensile strength of as welded Zr-2.5 wt.Nb alloy is found to higher than the base metal with poor ductility. In the present study, Zr-2.5 wt.%Nb alloy plates of thickness 4 mm have been welded using pulsed Nd:YAG laser system at different process parameters and characterized in terms of microstructural evolution, hardness, residual stress, and mechanical properties. It has been observed that heat input plays an important role on mode of welding. The full penetration up to a thickness of 4 mm of the alloy has been achieved at a minimum laser heat input of 800 J mm−1 without any crack and porosity formation. For avoiding the porosity formation in the weld zones, a transition mode between conduction and keyhole has been used by optimizing laser process parameters. The microstructural analysis revealed that the fusion (FZ) is consists of predominant lath type α′ martensitic phase with small amount of randomly distributed acicular type of α′ martensite phase. However, the heat affected zone (HAZ) have lath type α′ martensitic phase together with αZr phase. Further, in the FZ and HAZ regions, the presence of retained βZr phase is higher as compared to the base metal (BM). The change in microstructure and phase field of different weld zones has been explained by evaluating the time-temperature profiles and cooling rates using COMSOL multi-physics simulation. In addition, the FZ and HAZ zones have been found to have tensile residual stress of the order of 280 MPa and 145 MPa as compared to the BM (-70 MPa). The microhardness in the FZ region has been observed to be higher (240–260 HV0.1) as compared to the BM (∼185 HV0.1) due to the formation of martensitic phase. The tensile room temperature testing showed that the mechanical strength of as welded sample is significantly higher than the base metal with lower ductility. The fractography of the fractured surfaces confirmed ductile nature of failure in the as welded samples.