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

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.

Microstructure, Tensile Properties, and Fatigue Behavior of Linear Friction-Welded Ti-6Al-2Sn-4Zr-2Mo-0.1Si

“…It is noteworthy that the temperature selected for the SRA of the welds in the present research was guided by the findings of Frankel et al [30] on the effect of PWHT on residual stress levels in LFWed Ti-6242. The AWed and SRAed metallographic samples were then hot mounted using a conductive resin (Struers ConduFast), followed by automated grinding, polishing, and etching with Kroll's reagent, as described in [42]. Microstructural observations were performed using an Olympus GX71 optical microscope (OM, Richmond Hill, ON, Canada) and a Tescan Vega-II XMU scanning electron microscope (SEM, Warrendale, PA, USA) at 20 keV for both secondary electron (SE) and backscattered electron (BSE) imaging.…”

“…Microstructural observations were performed using an Olympus GX71 optical microscope (OM, Richmond Hill, ON, Canada) and a Tescan Vega-II XMU scanning electron microscope (SEM, Warrendale, PA, USA) at 20 keV for both secondary electron (SE) and backscattered electron (BSE) imaging. The volume fractions of the α and β phases were measured by thresholding image analysis according to ASTM E112-13 [43], as explained in [42].…”

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

“…Using electro-discharge machining (EDM) (Fanuc, Oakville, ON, Canada), specimens were extracted, as shown in Figure 2 b, for metallographic, tensile and fatigue testing of the dissimilar Ti6242–Ti64 linear friction welds. Metallographic preparation of the dissimilar Ti6242–Ti64 welded specimens involved hot mounting in a conductive resin followed by automated grinding and polishing to a surface finish of 0.02 µm, as described in [ 39 ]. Etching for 6–12 s with Kroll’s reagent (100 mL of distilled water, 6 mL of nitric acid (HNO 3 ) and 2 mL of hydrofluoric acid (HF)) was used to reveal the characteristics of the different microstructural features (phase constituents, morphology, grain structure, etc.)…”

“…This combination was deliberated for the higher service temperature capacity of Ti6242 (up to 510 °C) [ 36 ] relative to Ti64 (around 350 °C) [ 37 ]; Ti6242 also has (relative to Ti64) comparatively higher tensile strength, creep and fatigue resistance, as well as good toughness properties [ 38 ]. Previous research by the authors [ 39 ] has established the LFW parameters for producing integral (defect-free) joints between Ti6242 and Ti64 and has involved comprehensive characterization of the microstructural and microhardness changes across the dissimilar joint in both the AWed and SRAed states. The present work reports highlights of the microhardness evolution, microstructural characteristics and static tensile properties to provide a basis for the comprehensive results on the fatigue behavior of the dissimilar Ti6242–Ti64 joints after SRA.…”

A Novel Multiaxial Strain-Based Criterion Considering Additional Cyclic Hardening

“…In such a context, Ti-6Al-4V here examined has excellent tensile (tensile strength ≥ 895 MPa) and fatigue strength (equal to about 460MPa at a number of loading cycles of 109 under rotating bending), as well as high resistance to a wide spectrum of corrosive environments, with respect to other titanium based alloys, due to its inclination to form protective surface oxides [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. As such, it is used in life-limit components of civil aviation engines and as fractured critical components of military engines [ 36 , 37 , 38 , 39 ]. Therefore, fatigue behavior, especially under low-cycle fatigue (LCF) regimes, should be critically evaluated for the design of the above-mentioned components under service loads.…”