The Evolution of Cast Microstructures on the HAZ Liquation Cracking of Mar-M004 Weld

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Abstract:The main scope of this study investigated the occurrence of liquation cracking in the heat-affected zone (HAZ) of IN738 superalloy weld, IN738 is widely used in gas turbine blades in land-based power plants. Microstructural examinations showed considerable amounts of γ' uniformly precipitated in the γ matrix. Electron probe microanalysis (EPMA) maps showed the γ-γ' colonies were rich in Al and Ti, but lean in other alloy elements. Moreover, the metal carbides (MC), fine borides (M 3 B 2 and M 5 B 3 ), η-Ni 3 Ti, σ (Cr-Co) and lamellar Ni 7 Zr 2 intermetallic compounds could be found at the interdendritic boundaries. The fracture morphologies and the corresponding EPMA maps confirmed that the liquation cracking in the HAZ of the IN738 superalloy weld resulted from the presence of complex microconstituents at the interdendritic boundaries.

Section: Discussionmentioning

confidence: 98%

Liquation Cracking in the Heat-Affected Zone of IN738 Superalloy Weld

Chen

Shiue

et al. 2018

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“…In prior work [33], premature melting of final solidification products, such as γ-γ colonies, MC carbides, Cr-Mo borides, and Ni-Hf intermetallic compounds at the dendrite boundaries, accounted for the HAZ cracking of a Mar-M004 weldment. Pre-weld heat treatments were performed to eliminate those harmful microstructures and thereby improve the weldability of the cast superalloys [16,27,31,34].…”

Section: Pre-weld Heat Treatmentmentioning

confidence: 99%

Effects of Grain Boundary Microconstituents on Heat-Affected Zone Cracks in a Mar-M004 Weldment

Chen

Cheng

Tsay

et al. 2018

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Repair-welding of a cast Mar-M004 superalloy by gas tungsten arc welding was performed. Liquation cracks of the heat-affected zone (HAZ) in a Mar-M004 weldment were closely related to the presence of low-melting constituents along the solidified boundaries in the weld. The metal carbides (MC), M 3 B 2 and M 5 B 3 borides, Ni 7 (Hf,Zr) 2 intermetallic compounds, and γ-γ colonies were found at the interdendritic boundaries. Fine boride precipitates mixed with intermetallic compounds in lamellar form were more likely to liquate during repair-welding. The melting of borides and intermetallic compounds in 1180 • C/4 h treated samples confirmed the poor weldability of the Mar-M004 superalloy due to enhanced liquation cracking. In addition to boride formation, fractographs of liquation cracks revealed strong segregation of B element in carbides and intermetallics, which might further lower the solidus temperature of the repair weld.

“…However, severe liquation cracking can occur in the partially melted zone (PMZ), which is an area next to the outer side of the fusion zone (FZ). Liquation cracking can lead to a lower product yield rate and result in great danger while in use [6][7][8]. It also has the tendency to bring about solidification cracks, and result in serious large-scale cracking during fusion welding.…”

Section: Introductionmentioning

confidence: 99%

Liquation Cracking Tendency of Novel Al-Mg-Zn Alloys with a Zn/Mg Ratio below 1.0 during Fusion Welding

Zhang

Zhao

Pan

et al. 2020

The main obstacle for the application of high strength 7××× series aluminum alloys is that these alloys are susceptible to hot cracking during fusion welding. This study presents the liquation cracking susceptibility of the novel T-Mg32(AlZn)49 phase strengthened Al-Mg-Zn alloy with a Zn/Mg ratio below 1.0 by a circular-patch welding test, and compared the liquation cracking tendency with η-MgZn2 phase strengthened 7××× series alloys whose Zn/Mg ratios are above 1.0. It was found that all these novel Al-Mg-Zn alloys still have as low a liquation cracking susceptibility as traditional 5××× series alloys, surpassing that of traditional 7××× series alloys substantially. It was noticed that the increase of the Zn/Mg ratio will result in a larger difference between the fraction solids of the fusion zone and the partially melted zone during the terminal solidification stage, which can lead to a wider crack healing disparity between these two areas and thus result in different liquation cracking susceptibilities in different alloys.