Mechanical Property and Microstructure of Linear Friction Welded WASPALOY

Abstract

The mechanical properties and microstructural evolution of WASPALOY joined by linear friction welding (LFW) were investigated in this study. In-situ temperature measurements using thermocouple probes indicated exposure of the weld area to a temperature of at least 1400 K (1126°C). Based on electron backscatter diffraction (EBSD) mapping of the weldments, up to 50 pct reduction in c grain size occurred within 0.9 mm of the weld interface as a result of dynamic recrystallization (DRX). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed that progressive dissolution of c¢ precipitates took place from the base metal to the weld interface, where almost no c¢ precipitates were observed. Within 3.3 mm of the weld interface, the c¢ dissolution significantly influenced the hardness profile measured across the extended thermomechanically affected zones (TMAZs). Investigation of strain distributions during tensile testing using the optical Aramis system revealed weak bonding at the edge of the weld due to oxidation. To extrude out oxide layers into the flash, increasing the axial shortening to higher than 1.2 mm is recommended.

Microstructural Analysis of Linear Friction-Welded 718 Plus Superalloy

“…14,18 The fine grain size is a characteristic feature of the linear friction welds, which has been also observed in Inconel 718 15 and Waspaloy. 19 Microstructural characterization of the TMAZ in the linear friction welds showed features that were consistent with grain boundary liquation and constitutional liquation of second-phase particles, as was observed during fusion welding of 718 Plus alloy.…”

“…During LFW, the heating rate has been suggested to be as high as 368°C/s ± 140°C/s, 19 which could induce nonequilibrium liquation of second-phase particles. Constitutional liquation of second-phase particles during conventional fusion welding processes has been observed in 718 Plus alloy; however, its occurrence in linear friction welds has not been reported previously.…”

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“…The greatest number of publications is devoted to studying LFW of various titanium alloys [6,[17][18][19][20][21][22] that is due to LFW practical application in manufacture of welded rotors of aircraft GTE compressors («blisks»). Publication authors studied the following ranges of LFW parameters variation: 0.5-3.0 mm amplitude, 15-150 Hz frequency, 50-190 MPa pressure at heating and 320 MPa forging pressure.…”

“…In [22] the process of LFW of Waspalloy nickel alloy on 18 × 13 × 11 mm samples was studied. It is established that producing sound joints is possible at a certain, high enough value of all LFW technological parameters (amplitude, frequency, pressure).…”

Modification of creep and low cycle fatigue behaviour induced by welding

“…The residual life of the component would be increased with evident economic advantages, on condition that the reliability and the safety of the component are not reduced. Weldability of Waspaloy from a technological and metallurgical point of view has been studied in [11,12]. Generally speaking, the fusion and the following solidification determine at least grain growth and introduce defect like microcracks.…”