Suppressed liquation and microcracking in linear friction welded WASPALOY

Fusion welding of nickel-base superalloys is often associated with fusion zone solidification cracking and/or liquation induced heat affected zone (HAZ) cracking. As an alternative joining technology, linear friction welding (LFW) was used in the current study to join the nickel-base superalloy, WASPALOY. Under the experimental conditions used in the present investigation, the temperature data recorded by inserting thermocouples at different locations from the weld interface indicated that the temperature in the weld area reached up to 1280 °C, which is at least 50 °C below the melting point of the bulk alloy. However, this temperature is well above the liquation temperature of the low melting point components in the alloy (1245 °C). As a result, liquation may occur in linear friction welded (LFWed) WASPALOY. The occurrence of liquation and/or microcracking was investigated using optical microscopy (OM), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) X-ray mapping. The high pressure applied during the oscillation and forge phases of the LFW process and the resulting γ grain refinement contributed in preventing liquation and microcracking in the weldments. Furthermore, according to the SEM and X-ray mapping results, LFW altered the chemical composition, morphology and size of the γ′ precipitates at a location of 2 mm from the weld interface. It was determined that γ′ coalescence at 2 mm from the weld interface played a role in decreasing the microhardness (by 30%) relative to the base metal.