Effect of copper on microstructural evolution and mechanical properties of laser-welded CoCrFeNi high entropy alloy

Abstract

In this work, laser welding of CoCrFeNi and CoCrCuFeNi HEA was carried out. X-ray diffraction, electron backscattered diffraction, mechanical property and microstructural analyses were performed. In CoCrFeNi alloy, a face centred cubic (FCC) structure was observed in both base metal and laser-welded conditions. The addition of Cu in CoCrFeNi alloy is resulted in two FCC phases and has increased the tensile strength from 593 to 666 MPa. The fusion zone of both the welds shows coarser columnar grain and lower hardness compared to that of base metals. Post-welding results show 53% decrease in tensile strength in the alloy containing Cu (CoCrFeNiCu). Whereas only a marginal decrease in strength is observed in CoCrFeNi alloy.

Microstructural evolution in CoCrFeNi and CoCrCuFeNi alloys processed by autogenous fusion welding

“…However, after welding this texture is changed to <115> parallel to ND shown in Figure 7(a). Similarly, a weak fibre texture is observed in <116> parallel to ND in BM of CoCrCuFeNi [22] while post-welding fibre texture shifted to <113> parallel to ND as shown in Figure 7(b). Generally, texture has a strong influence on mechanical properties, but it is expected that the presence of weak texture in both BMs and welds will not have a significant influence on the mechanical properties.…”

“…One way of avoiding the cracks is by reducing or avoiding the Cu in the system. The other way is to employ a faster cooling rate as in the case of the laser welding process [22].

Figure 1 (a) CoCrFeNi WZ.

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“…Figure 6(a,b) shows IPF images of WZs of CoCrFeNi and CoCrCuFeNi alloys. IPF images of BM have shown equiaxed grains and twin boundaries in both the BMs [22]. CoCrFeNi BM has an average grain size of 27 μm while BM of CoCrCuFeNi has 6 μm grain size.…”

“…Figure 7 shows inverse pole figures of WZ of CoCrFeNi and CoCrFeNiCu alloys. CoCrFeNi BM shows weak fibre texture in <335> parallel to ND [22]. However, after welding this texture is changed to <115> parallel to ND shown in Figure 7(a).…”

Fiber Laser Welded Cobalt Super Alloy L605: Optimization of Weldability Characteristics

“…It is also worth stating that, the transfer of heat within the weld pool happens by convection; and therefore, the fluid dynamics predominantly determine the formation of bead shape. The major factors coming into play are surface tension, volume contraction, vapor pressure, phase transformation and gravity [ 36 ]. With the reduction in energy input, the cross-section of the weld joint transforms into almost an X-shape; whereas the V-shaped cross-section is obtained when there is partial keyhole formation [ 37 ].…”