Abstract
Various ecological and economical concerns have spurred mankind’s quest for materials that can provide enhanced weight savings and improved fuel efficiency. As part of this pursuit, we have microstructurally tailored an exceptionally high-strength titanium alloy, Ti-6Al-2Sn-4Zr-6Mo (Ti6246) through friction stir processing (FSP). FSP has altered the as-received bimodal microstructure into a unique modulated microstructure comprised of fine acicular α″-laths with nano precipitates within the laths. The sequence of phase transformations responsible for the modulated microstructure and consequently for the strength is discussed with the help of scanning electron microscopy, transmission electron microscopy, and synchrotron X-ray diffraction studies. The specific strength attained in one of the conditions is close to 450 MPa m3/mg, which is about 22% to 85% greater than any commercially available metallic material. Therefore, our novel nano particle strengthened Ti alloy is a potential replacement for many structural alloys, enabling significant weight reduction opportunities.
Highlights
Over the past 70 years of titanium alloy research, improved and expanded utilization of these alloys have occured, largely due to their versatile properties, which include high specific strength, high temperature strength, and unparalleled corrosion resistance[1]
We report a strength of approximately 2 GPa for Ti6246 processed under friction stir processing (FSP)
The hierarchy of properties in near-β-titanium alloys is best preserved by keeping the β-grain size as fine as possible, and subsequent precipitation of α within β -grain[28]
Summary
Over the past 70 years of titanium alloy research, improved and expanded utilization of these alloys have occured, largely due to their versatile properties, which include high specific strength, high temperature strength, and unparalleled corrosion resistance[1]. It is technologically important to investigate the feasibility of a solid-state processing technique such as friction stir processing (FSP), on this alloy This investigation can expand the usage of this alloy, which possesses a strength level on par with ultra-high strength steels. Engineering stress – strain plots for the as-received (AR) and processed material at low, medium, and high heat inputs are shown in Fig. 1(a) (refer to the “Methods” section for heat input description). The most remarkable observation is UTS of 1996 MPa, with a 5% elongation obtained at low heat input This strength level is approximately 65% higher than the base material (1272 MPa). To investigate the exceptional property combinations after FSP, scanning electron microscopy (SEM) was initially performed on the AR material, as well as the specimens extracted from the transverse cross-section of the processed material, as shown in the schematic of Fig. 2(a). The contrast difference between the phases was not quite discernible, likely due to the enhanced diffusion associated with FSP
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