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Grain boundary (GB) and phase boundary (PB) are planar discontinuities in metallic crystals, which can effectively adjust the strength and toughness of polycrystalline alloys, which are usually mutually exclusive two key attributes. Therefore, GB engineering, such as adjusting the number or arrangement of GBs/PBs, is widely used to design super strong and super tough light alloys, such as titanium (Ti) alloys. However, the microstructure fineness and type that titanium alloys can achieve are limited, because once exposed to thermal load, its grains will rapidly coarsen. Therefore, the high fluidity of these crystal interfaces with relatively high GB energy limits the further improvement of GB related properties. High strength dual phase titanium alloys strengthened by densely dispersed α nano precipitation face the dilemma of strength toughness trade-off, because the strain (geometric) incompatibility of semi coherent α/β PB in the form of dislocation stacking will lead to serious fracture stress concentration, thus reducing the ductility and toughness of materials. Once moving dislocations pass through high-energy α/β PBs (forming dislocation channels), strain localization and strain softening will generally occur in titanium alloys. Therefore, how to design microstructure, especially PB, to simultaneously improve the strength and toughness of dual phase titanium alloys is a huge challenge. Scholars from Xi'an Jiaotong University, on the basis of variability engineering, have constructed layered and ordered coherent interfaces in tough titanium chromium zirconium aluminum alloys with ultra-high specific strength and ultra-high fracture toughness through densely dispersed nanoparticles to optimize strength toughness. The research reveals that these ordered coherent interfaces are both obstacles and sources of dislocations. Through layered nano diamond dislocation interaction, a sustainable self hardening deformation mechanism can be formed, thus achieving ultra-high strength and toughness of titanium alloys. The nano corundum in this study has thermal stability at a high temperature below 400 ℃. When the temperature is higher than 400 ℃, due to the decomposition of layered ordered nano corundum and the spheroidization of the previous β sheet, the transition from toughness to brittleness caused by tempering will occur. The design strategy of layered ordered coherent interface enables our cost-effective nano diamond titanium alloy to obtain an unprecedented combination of strength, ductility and toughness, which provides a new way for microstructure design of high-strength and ductile structural materials with excellent fracture resistance. Related work was published in Acta Materialia as a research article entitled "Hierarchically ordered coherent interfaces driven ultrahigh specific strength and tolerance in a nano artificial titanium alloy". Thesis link: https://doi.org/10.1016/j.actamat.2023.119540 In order to obtain super strong and super tough titanium alloys, this study, based on the "d-electron theory", adjusted the stability of β matrix according to the content of β stabilizer Cr, to create self-assembled ordered nano emery with layered coherent α '/β interface. This composition is designed to ensure that the thickness λ< can be generated after a simple water quenching process (WQ); 50 nm hard dislocation structure α 'nano sensitizer instead of soft α' 'phase. In addition to reducing the cost of alloys, Al, Cr and Zr elements are selected as alloying elements to improve the strength and corrosion resistance of Ti alloys and have good thermal stability. After careful adjustment of alloy composition, the chromium content is from 1.8 to 3.8 wt.%, and a low-cost, ductile α 'nano martensite Ti-2.8Cr-4.5Zr-5.2Al (wt.%) alloy with ultra-high specific strength and ultra-high strength toughness is obtained. Figure 1 The thermal mechanical processing scheme of Ti-2.8Cr-4.5Zr-5.2Al alloy and the schematic diagram showing the evolution of microstructure. Transmission electron microscope (TEM) images of Ti-2.8Cr-4.5Zr-2.5Al alloy showing microstructure characteristics at different stages. Figure 2 Microstructure characteristics of WQ Ti-2.8Cr-4.5Zr-5.2Al alloy. (a1) The dark field transmission electron microscope (DF-TEM) image and schematic diagram show the β - transus microstructure composed of β and α 'layers. The schematic diagram shows the microstructure of hierarchically ordered α '- martensite structure. (a2) The corresponding SAED pattern shows three martensitic variants. (a3-a4) Low magnification HAADF-STEM and corresponding IFFT micrographs show that there is no additional plane related to dislocation at α '/β PB, and IFFT micrographs using (011) β and (0110) α' diffraction points. The illustration in (a3) is the corresponding FFT mode. (a5) The high magnification HAADF-STEM micrograph shows the traditional "platform ledge" interface structure, as shown by the dotted white line. APT characterization of element distribution and composition of (b1-b2) α 'and β nano lamellae. (c) Statistical distribution of α 'and β lamellar thickness in WQ samples. (d) At present, the relationship between the yield strength and α 'thickness of Ti Cr Zr Al alloys and other reported martensitic Ti alloys includes Ti-4Mo, Ti-5Al-3Mo-1.5V, TC4 (original β grains), Ti-V - (Al, Sn) series, Ti-V-Sn series, TC4 traditional process (α+α' and all α '), TC4 SLM (α'), TC4 EBM (α ') and TC4 SLM (β+α'). Figure 3 Microstructure characteristics of 400AC Ti-2.8Cr-4.5Zr-5.2Al alloy. (a1) BF-TEM shows α p and α 'dec phases. The SAED pattern of (a2) β - transus microstructure shows three martensitic variants. (a3) HR-TEM images show β nanoparticles in the α 'martensite. (a4) Statistical distribution of β layer thickness in 400AC sample. (b1-b2) APT analysis of element distribution and composition of 400AC sample shows that β nanoparticles rich in calcium in α 'dislocation martensite, as shown by the black arrow. Figure 4 Microstructure characteristics of 500AC Ti-2.8Cr-4.5Zr-5.2Al alloy. (a) DF-TEM image shows a large number of secondary α, which is indicated by orange arrows. (b1-b2) BF-TEM and corresponding DF-TEM images show the newly formed α s and β nanoparticles in the decomposed α 'sheet. The corresponding chromium EDS (illustration) is also provided. (c1) BF-TEM image shows the microstructure of β - cross section after tempering at 500 ℃. (c2) The corresponding DF-TEM image shows the previous β - split β two-dimensional plate and nano β particles. (c3) The corresponding EDS atlas shows the distribution of Ti, Al, Cr and Zr and the depleted Cr area shown by the white arrow. (c4-c5) shows the EDS line analysis of (c1) marked lines. (c6) Statistical distribution of β particle diameter in 500AC sample. (c7) HR-TEM images show transition regions with significant lattice strain. (c8) HR-TEM images show that a new α s phase appears in the transition zone, and some mismatched dislocations appear on the interface between α s/β and BOR. Figure 5 Microstructure characteristics of 700AC Ti-2.8Cr-4.5Zr-2.5Al alloy. (a) HAADF-STEM images show β and α s nanosheets. (b) The EDS diagram shows the distribution of Cr, Al, Ti and Zr. (c) Concentration profiles of Cr, Al, Ti and Zr obtained by TEM EDS scanning along the white line in a. Statistical distribution of α s and β sheet thickness in (d-e) 700AC samples. Figure 6 The room temperature mechanical properties of Ti-2.8Cr-4.5Zr-5.2Al alloy in this study. (a) The engineering stress-strain curves of titanium alloys in different states are studied. (b) Comparison of yield strength and total elongation of this titanium alloy, and comparison of yield strength and total elongation of other martensite α 'and tempered martensite α' titanium alloys reported so far. Martensitic α 'Ti alloys: including Ti-4Mo, Ti-5Al-3Mo-1.5V, Ti-V - (Al, Sn) series, Ti-V-Sn series, Ti-4.5Al - (2.0-2.5) Fe-0.25Si, TC4 (different pre beta grain sizes) and TC4-SLM (α') series; Tempered martensitic α′ Ti alloy (including partially decomposed α′ phase or completely decomposed α′ phase): TC4-SEBM, TC4-MA, TC4 traditional process, TC4-STA, TC4-SLM (α+β), TC4-SLM (lamellar α+β), TC4-EBM (α′+β tempering) and TC4-EBM, TC4-EDE, and TC4-SLM (as HIP ′ ed). (c) Comparison of specific yield strength and raw material cost between the titanium alloy in this study and other reported strong α '/β titanium alloys. Figure 7 Fracture characteristics of Ti-2.8Cr-4.5Zr-5.2Al alloy. (a) The real stress-strain curve of WQ sample shows the calculated result of fracture work. (b) The comparison of fracture work and yield strength of titanium alloys in this study, as well as the comparison of fracture work and yield strength of moldable titanium alloys reported. (c) J-integral fracture resistance curve of current Ti Cr Zr Al alloy under different heat treatment conditions. J-R curve is measured by unilateral bending specimen. (d) The alloys in this study are compared with other typical α+β Ti alloys (including TC4 series: (TC4-ELI and TC4-F) and TC4-DT, TC4 xFe (x=0.1, 0.3, 0.5, 0.7, 0.9), TC4 (Widmanst ä tten, equiaxed and bimodal structure) and Ti Al series: (Ti-6Al-2Mo-2Cr Ti-4.5Al-3V-2Mo-2Fe, Ti-4.5Al-3V-2Mo-2Fe, Ti-7Al-4Mo, Ti-6Al-6V-2Sn, Ti-6Al-2Zr-2Sn-2Mo-1.5Cr-2Nb, Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.25Si and Ti-5Al-2.5Fe), and transferable β Ti alloys, including Ti-10V-2Fe-3Al Ti-5Al-4Zr-8Mo-7V、Ti-5Al-5Mo-5V-3Cr、Ti-15Mo-2.7Nb-3Al-0.2Si、Ti-5Al-3Mo-3V-2Zr-2Cr-1Nb-1Fe、 (Ti-6Al-2Sn-3Mo-1Cr-2Zr-2Nb, Ti-5Al-5Mo-5V-1Cr-1Fe, Ti-15V-3Cr-3Sn-3Al and Ti-3Al-5Mo-5V-2Cr) and (Ti-5Al-4Mo-4Cr-2Sn-2Zr, Ti-6Al-2Sn-4Zr-6Mo and Ti-2.5Al-12V-2Sn-6Zr) Figure 8 Fracture characteristics of Ti-2.8Cr-4.5Zr-5.2Al alloy in different states. (a1) SEM micrograph of fracture surface of WQ sample. The illustration in (a1) is a magnified image of the fracture surface with a large number of depressions. (a2) SEM images of the fracture surface show the voids at α p/β and α ′/β PB. (a3) SEM images of the fracture surface show that the crack propagates/deflects along α p/β and α '/β PB. (b1) SEM micrograph of fracture surface of 400AC sample. The illustration in (b1) is a magnified image of the fracture surface showing a large number of depressions. (b2) The SEM image of the fracture surface shows the voids at α p/β and α'dec/β PB. (b3) SEM images show the crack propagation/deformation along α p/β and α'dec/β PB. (c1) SEM micrograph of fracture surface of 500AC sample. The illustration in (c1) is a magnified image of the fracture surface, showing transgranular crack like features. (c2) SEM images show that the macro fracture surface is actually composed of discontinuous micro cavities (orange arrows) and very thin grooves (white dotted lines). (c3) The corresponding subsurface with voids at α p/β and α'dec/β PB shows that plastic deformation traces (void propagation or crack deflection) can not be distinguished even at a position quite close to the voids. Figure 9 Deformation substructure of WQ and 500AC Ti-2.8Cr-4.5Zr-5.2Al alloys. (a1-a4) WQ sample with 3.2% deformation. Two beam conditional analysis of dislocations in (a1-a2) WQ samples. Dislocations are emitted from the α '/β PB slip system along the substrate (0002) in the α' sheet, represented by a yellow dash line. A further magnified micrograph of the box area in (a1) shows the slip transport event of PB, highlighted by the pink arrow. (a3-a4) HR-TEM and corresponding IFFT images show several RIDs at α '/β PB, verifying dislocation transmission activity, and RIDs are marked with yellow symbol "∨". (b1-b3) WQ sample deformed by 6.1%. (b1) TEM images show that the dislocation density and dislocation interaction (yellow arrow) in the α 'sheet are high. In addition to the (0002) slip system, many differentials nucleate from the coherent PB, as shown by the orange arrow. The illustration in b1) is the corresponding selected area electron diffraction (SAED) diagram. (b2-b3) HR-TEM and corresponding IFFT images show more RIDs on PB. Two beam condition analysis of dislocation in 500AC sample under (c1-c2) fracture strain. Only the slip band along the (0002) plane is activated. In this study, an ultra-high specific strength and high ductility Ti-2.8Cr-4.5Zr-5.2Al alloy with high density ordered coherent α '/β PBs was successfully designed through martensitic transformation. The thinnest part of the high-density nano martensite is only ∨ 22 nm, which can be stabilized at 400 ° C. This makes the current cost-effective titanium alloy with ultra-high strength and toughness and excellent fracture toughness. The layered ordered coherent PB strategy designed by nano martensite engineering not only overcomes the shortcomings of low density of PB in micron scale in traditional titanium alloys, but also provides sufficient dislocation sources and obstacles for the sustainability and self hardening ability of alloys, thus realizing the combination of ultra-high strength and toughness. In addition, this research predicts that this design strategy will be applicable to other metabolic alloys, such as traditional steels and emerging multi-component alloys, to achieve ultra-high strength, high ductility and excellent toughness. (Article: SSC) Statement: The content of this article comes from materials science and engineering. It is only for sharing and does not represent our position. If there is infringement, please contact the editor to delete it. Thank you! 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