Solidification cracking of a nickel alloy during high-power keyhole mode laser welding

Integrated modeling of cracking during deep penetration laser welding of nickel alloys

“…While the weld pool cross sections display similar sizes and shapes, there is a prominent horizontal crack that appears across the fusion zone of the Inconel 740H welds produced at laser powers of 5 kW and above. This type of cracking in the Inconel 740H alloy has been connected with solidification cracking mechanisms [10], but no similar cracks were observed in the Inconel 690 welds, indicating that the differences in composition affected the cracking susceptibility. In order to confirm these differences, the solidification pathway, which is a primary indicator of the susceptibility of the alloy to solidification cracking, was calculated for each alloy using Scheil-Gulliver methods, and these pathways are shown in Figure 4.…”

“…After examining the role of composition on the solidification behaviors of both alloys, a well-tested steady-state keyhole mode laser welding process model was then used to calculate the thermal histories experienced across the weldment [10]. This modeling approach couples a well-tested keyhole model with a three-dimensional heat transfer and fluid flow model, which solves the equations of mass, momentum, and energy in three-dimensions to calculate temperature and fluid flow fields across the weldment [20][21][22].…”

“…The thermal histories and solidification conditions can significantly vary with location, particularly with changes in weld depth [14], creating conditions which can enhance the susceptibility to defect formation in alloys which are readily weldable under traditional arc welding conditions [15,16]. During the deep penetration laser welding of a creep-resistant nickel alloy (Inconel 740H), for example, horizontal solidification cracking was consistently observed across the width of the fusion zones at depths between 70% and 80% of the overall weld depths [10]. These defects differed from the vertical centerline cracks typically attributed to solidification cracking in the relatively shallow weld pools produced under arc welding conditions [17][18][19].…”

“…Changes in the alloying elements can impact elemental segregation, which, in turn, affects the solidification temperature range and the amount of liquid remaining in the mushy zone at the terminal stages of solidification [6]. A fraction of solid (f s ) value above 0.9 is typically considered to be most representative of the conditions at these terminal solidification stages that can lead to cracking [7,10]. In order to more accurately capture the alloying element segregation leading to the formation of susceptible solidification structures during both additive manufacturing and welding processes, Scheil solidification models are commonly used [5,10].…”

“…A fraction of solid (f s ) value above 0.9 is typically considered to be most representative of the conditions at these terminal solidification stages that can lead to cracking [7,10]. In order to more accurately capture the alloying element segregation leading to the formation of susceptible solidification structures during both additive manufacturing and welding processes, Scheil solidification models are commonly used [5,10]. Through these modeling approaches, the severity of the slope between the temperature gradient (dT) and the square root of the fraction solid (f s ) 1/2 can be captured and used as a criterion for predicting solidification cracking.…”