Abstract
Fiber welding of socket-joints made of nanostructured high-performance molybdenum alloy (NS Mo) was carried out to get a better understanding of the role of welding heat input. It was found that low heat input (i.e., high welding speed) resulted in significantly refined grains in the fusion zone (FZ) of fiber laser welded NS Mo joints. When welding heat input decreased from 3600 J/cm (i.e., 1.2 kW, 20 cm/min) to 250 J/cm (i.e., 2.5 kW, 600 cm/min), the tensile strength of welded joints increased from about 250 MPa to about 570 MPa. It was confirmed by energy spectrum analysis that the higher the welding heat input, the higher the oxygen contents at the grain boundary (GB) within the FZ. In addition, the most important reason for poor strength of welded joints of Mo alloys was reported as being that MoO2 was segregated on the grain boundary. Therefore, it was concluded that welding under low heat input (i.e., high welding speed) was able to reduce the segregation degree of MoO2 at the grain boundary by refining grains and increasing the total area of GBs, thus improving the strength of welded joints and reducing the proportion of the intergranular fracture zone in tensile fractures.
Highlights
Molybdenum alloy has the advantages of a high fusion point, high heat conductivity and a low neutron absorption cross-section [1,2,3]
At the beginning of this section, it is necessary to note that the welding speed for the low heat input was thirty times that for high heat input, while the laser power for the low heat input was just two times that for the high heat input
Fiber welding tests of socket joint made of powder metallurgy nanostructured high-performance molybdenum alloy (NS Mo) alloy were carried out and the welding heat inputs were taken as 250 J/cm and 3600 J/cm
Summary
Molybdenum alloy has the advantages of a high fusion point, high heat conductivity and a low neutron absorption cross-section [1,2,3]. The reliable welding technology of the NS Mo alloy is the premise of its wide application in various complex structures. The weldability of this new type of molybdenum alloy has been widely studied in recent years [5,6,7,8,9,10]. Welding methods for Mo alloys include brazing [11,12], friction stir welding [13,14], electric resistance welding (ERW) [15,16], fusion welding [17,18,19], etc
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