Residual Stresses in Linear Friction Welded IMI550

Abstract

Residual stresses in linear friction welded (LFW) IMI550 have been determined by means of high energy synchrotron X-ray diffraction. Specimens were studied in the as-welded, and three different post weld heat treated conditions. Mid-thickness-mid-width line scans were recorded across the weld line in the three principal directions of the welds. For calculating the nominal residual strain the "stress-free" lattice spacing was taken from far field measurements. The separation of a chemical induced and strain induced shift of the reflection was carried out by determining the variation of the rf-spacing across the weld line. This was done on thin slices cut from the centre region of a LFW sample using the biaxial sin^i/i-technique on a collimated laboratory X-ray source.Results show large tensile stresses close to the weld line for the as-welded sample and the sample post weld heat treated at the aging temperature typical of IMI550. Moderate residual stresses were observed after increasing the post weld heat treatment (PWHT) temperature by 100 or 150°C. All conditions displayed a significant hydrostatic tensile stress field component, which is generally difficult to relieve. This work demonstrates that residual strain measurements have to be carried out using a high spatial resolution in order to resolve the sharp strain gradients apparent in LFW Titanium alloys.

Linear and rotary friction welding review

“…The effect of each successive repeat weld was to increase in a similar fashion the number of maxima of hardness. At the same time, the maximum value was becoming lower than that of the 42 Microhardness profile across the weld interface at as-weld and PWHTed conditions obtained from the LFW'd Ti6246 weld 97 41 Effect of axial pressure on microhardness of LFW'd Ti64…”

Joining of Dissimilar Alloys Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo-0.1Si Using Linear Friction Welding

“…in the as-welded (AWed) condition [ 13 , 14 , 15 , 16 , 17 , 18 ] and after post-weld heat treatment (PWHT) [ 19 , 20 ]. Other research studies on LFW of similar titanium alloys have included near-α titanium alloys, such as Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si-0.06C (IMI 834) [ 21 ] and Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242) [ 22 ], near-β alloys such as Ti-5Al-2Sn-2Zr-4Cr-4Mo (Ti-17) [ 23 , 24 ] and Ti-5Al-5Mo-5V-3Cr (Ti-5553) [ 25 , 26 ], as well as other α-β alloys such as Ti−4Al−4Mo−2Sn−0.5Si (IMI 550) [ 27 ] and Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) [ 28 ]. Though the LFW technology is highly promising for joining two different materials together, reported research on weld joint assembly by LFW of dissimilar titanium alloys has been very limited in the open literature.…”

Fatigue Behavior of Linear Friction Welded Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo-0.1Si Dissimilar Welds

“…Previous studies on LFW of titanium alloy joints (similar and dissimilar) have also applied different microscopic techniques (e.g., optical, SEM) to link the microstructural transformation to the hardness evolution [ 10 , 11 , 15 , 22 , 26 , 27 , 40 , 48 , 49 , 50 ]. A particularly favored method for linear friction welds is the use of electron backscatter diffraction (EBSD) to map the orientation of the α-phase grains [ 13 , 18 , 23 , 26 , 27 , 28 , 51 , 52 ]; this method allows visual differentiation of the WC (with its recrystallized fine grain structure of α′ martensite) and the TMAZs (with their plastically deformed and elongated α-grain structure) from the bimodal BM microstructure. As these EBSD maps have focused on the α-phase characteristics, separating the HAZ from the BM has not been obvious microscopically due to the similarity in the α microstructural features.…”

“…Much of the research on LFW [ 12 , 13 , 14 ] has focused on characterizing the metallurgy and static tensile properties of titanium alloy welds, most particularly the alpha (α ) + beta (β) Ti–6Al–4V (Ti64) grade [ 15 , 16 , 17 , 18 ]—which is the well-known commercial workhorse of the industry, since it occupies nearly half the market share of titanium products [ 19 ]. There have been fewer studies aimed at exploring other titanium alloys [ 9 , 20 , 21 , 22 , 23 , 24 , 25 ] or dissimilar combinations of titanium alloys [ 10 , 26 , 27 ] to emulate welds tailored for the disparate service conditions on the disk (LCF) and blades (HCF and higher service temperatures). Presently, the fatigue test data in the open literature for linear friction welds also remain limited in comparison to static tensile test data; needless to say, the overall data for LFW of dissimilar titanium alloys are even less than those for similar titanium alloy welds.…”