Abstract
The purpose of this study is to evaluate the effects of pre-cold treatment on weldability of superalloys. The results of numerical calculations showed that the length of different welding regions including mushy zone (MZ), partially melted zone (PMZ) and heat affected zone (HAZ) decreased by 46, 46 and 56 percent, respectively. The experimental calculations indicated that the length of PMZ and HAZ, as well as the HAZ area, decreased by 2.1, 2.5 and 2.5 times, respectively. These results showed that significant improvement in weldability can be obtained by performing pre-cold treatment. Using pulsed Nd:YAG laser, grains boundary liquation was observed, followed by HAZ liquation cracking. The mechanism of HAZ liquation cracking is constitutional liquation of Nb-rich carbides and delta precipitates that encourage the formation of liquid films in the grain boundaries. With the accumulation of micro-pores in liquated grain boundaries, the cracks can be formed. With reducing the temperature of specimen from +200 to −30 °C, the penetration depth of laser welds decreased from 1624 to 1450 μm and the WTOP/WNECK ratio reduced from 1.45 to 1.24. The hardness profile at temperatures of -30 and + 200 °C indicates that the hardness of the weld metal increased using pre-cold conditions.
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