Effects of niobium addition on the microstructure and mechanical properties of laser-welded joints of NiTiNb and Ti6Al4V alloys

• Published in: Journal of alloys and compounds 2018-02, Vol.735, p.2616-2624
• Main Authors: Zhou, Xingwen, Chen, Yuhua, Huang, Yongde, Mao, Yuqing, Yu, Yangyang
• Format: Article
• Language: English
• Subjects: Base metal; Diffraction; Dilution; Dissimilar laser welding; Dissimilar material joining; Electron microscopy; Industrial applications; Intermetallic compounds; Laser beam welding; Mechanical properties; Microstructure; Nb filler metal; Niobium; Optical microscopy; Phase composition; Scanning electron microscopy; Shape memory alloy NiTiNb; Shape memory alloys; Tensile strength; Titanium alloy; Titanium alloys; Titanium base alloys; Titanium compounds; Weld metal; Welded joints
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.11.307

The dissimilar joining of shape memory alloys to Ti alloys is critically important in many industrial applications. However, joining these two alloys is a considerable challenge due to the formation of brittle intermetallics. In this paper, the dissimilar laser welding of 200-μm-thick NiTiNb and Ti6Al4V alloys was successfully achieved by the addition of a niobium filler wire with a diameter of 300 μm. The morphology, microstructure, phase composition and mechanical behavior of the obtained joints were studied by optical microscopy, scanning electron microscopy, transmission electron microscopy, micro X-ray diffraction, and tensile testing. Variations in the laser power changed the degree of Nb dilution in the weld metal, which affected the amount of intermetallic compounds (IMCs), NiTi, and Ti2Ni formed. All the welds consisted of a dendritic (Nb, Ti) solid solution and varied IMCs. The tensile strength of the joints depended on the amount of IMCs, which decreased with increasing Nb addition. All the tensile specimens fractured along the continuous IMC region in the weld. The highest tensile strength of the joint reached 82% that of the weaker base metal, Ti6Al4V, when the niobium filler was melted completely. [Display omitted] •Nb filler is an optional material for laser welding of NiTiNb to Ti6Al4V alloys.•The amount of Nb mixed into the weld metal should be controlled to achieve the available performance.•The effects of Nb addition on the microstructure and mechanical properties of joints were discussed.