Investigation of welding crack in micro laser welded NiTiNb shape memory alloy and Ti6Al4V alloy dissimilar metals joints. (1st June 2017)

• Record Type: Journal Article
• Authors: Yuhua, Chen; Yuqing, Mao; Weiwei, Lu; Peng, He
• Is Part Of: Optics & laser technology. Volume 91(2017)
• Page Start: 197
• Page End: 202
• Publication Date: 2017-06-01
• Subjects: Dissimilar metals -- Micro laser welding -- Welding cracks -- Intermetallic compounds -- Fracture morphology; Optics -- Periodicals; Lasers -- Periodicals; Electronic journals; 621.366
• DOI: 10.1016/j.optlastec.2016.12.028
• Languages: English
• ISSNs: 0030-3992

Abstract

Abstract: Dissimilar metals of NiTiNb shape memory alloy and Ti6Al4V alloy with a same thickness of 0.2 mm were joined by micro laser welding. The effect of laser power on crack sensitivity of the weld was investigated. The results show that full penetrated welds are obtained when the laser power of 7.2 W is used, many cracks are observed in the weld. With increasing the laser power to 12 W, the number of all cracks and cracking width first increase and then decrease. By XRD analysis, three different kinds of Ti2 Ni, NbNi3 and AlNbTi2 intermetallic compounds are found in the weld. According to the formation enthalpy and binary phase diagram, brittle Ti2 Ni phase with more contents is existed in the weld due to final solidification, and which is the main reason of crack formation along with large stress concentration. Moreover, the welding cracks like the weld center longitudinal solidification cracks, weld metal toe transversal liquid cracks, heat-affected-zone hot cracks and crater cracks are classified in the laser welded joints. A brittle cleavage fracture with cleavage planes and river patterns in the joints is presented from the fracture surface. Highlights: 0.2 mm thick dissimilar metals between NiTiNb and Ti6Al4V are micro laser welded. The crack sensitivity of the joints is estimated and the reason of cracking was found. Three kinds of Ti2 Ni, NbNi3 and AlNbTi2 intermetallic compounds are generated. Solidification crack, liquid crack, hot crack and crater crack are classified.