Abstract
Dissimilar joints between Ti-6Al-4V (Ti-64) and Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242) were manufactured using linear friction welding. The weld quality, in terms of the microstructure and mechanical properties, was investigated after stress relief annealing (SRA) at 750 °C for 2 h and compared with the as-welded (AWed) results. The central weld zone (CWZ) microstructure in the AWed condition consisted of recrystallized prior-β grains with α’ martensite, which transformed into an acicular α+β structure after SRA. The hardness in the AWed condition was highest in the CWZ and decreased sharply through the thermomechanically affected zones (TMAZ) to the parent materials (PMs). After SRA, the hardness of the CWZ decreased, mainly due to tempering of the α’ martensite microstructure. Static tensile testing of the dissimilar welds in both the AWed and stress relief annealed (SRAed) conditions resulted in ductile fracture occurring exclusively in the Ti-6Al-4V side of the joint. The promising results on joining of Ti-64 to Ti-6242 provide valuable insight for tailoring performance of next-generation aero-engine products.
Highlights
Bladed integrated disks (Blisks)—manufactured by machining a single forged billet into a monolithic blade-disk assembly—were introduced in aero-engines as an advanced alternative [1]to mechanical fastening/joining of blades to disks via a fir-tree arrangement that faced service life limitations and failures due to fretting fatigue damage at the contact surfaces between the blade dovetail root and the disk slot [2]
Conclusions can be drawn based on the observations of the microstructural characteristics, microhardness evolution and tensile mechanical properties of the dissimilar titanium alloy joints in the as-welded (AWed) and stress relief annealed (SRAed) conditions: 1
The following conclusions can be drawn based on the observations of the microstructural characteristics, microhardness evolution and tensile mechanical properties of the dissimilar titanium alloy joints in the as-welded (AWed) and stress relief annealed (SRAed) conditions: 1
Summary
Bladed integrated disks (Blisks)—manufactured by machining a single forged billet into a monolithic blade-disk assembly—were introduced in aero-engines as an advanced alternative [1]to mechanical fastening/joining of blades to disks via a fir-tree arrangement that faced service life limitations and failures due to fretting fatigue damage at the contact surfaces between the blade dovetail root and the disk slot [2]. More importantly has been the impossibility of mechanical performance tailoring in the monolithic blisk design through dissimilar alloy selection and microstructural modification for the specific operational conditions on the blades (exposed to high cycle fatigue and higher temperatures) relative to the disk (exposed to low cycle fatigue) [3] This has led to avid research and development in the aerospace field over the past two decades on suitable joining technologies for titanium alloys [4,5,6,7,8,9], and in particular their solid-state assembly by linear friction welding (LFW) [10,11,12] that has been qualified for aero-engine blisk. 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
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