PDF《Amorphous martensite in β-Ti alloys》

20 a b d c Intensity (arb. unit)

30 40 β-Ti

50 2 (°)

60 111

001 [110]β

111 C C C

110 70

80 Fig.

1 Microstructure of the as-cast Ti59.1Zr37Cu2.3Fe1.6 ingot. a Next to β-Ti re?ections, a broad diffraction hump from an amorphous phase is found in the X-ray diffraction pattern. b Bright-?eld TEM micrograph revealing lenticular bright regions with their long axes preferentially oriented along β and β. The lenses are embedded in a β-Ti matrix and are usually sheared multiple times along the β directions. c Bright-?eld TEM micrograph at a higher magni?cation and a SAED pattern (as inset) from the centre of the lenticular region (see circle). The halo corroborates the presence of an amorphous phase. d HRTEM image from the region marked in c with the corresponding FFT image as inset. Both clearly imply that the lenticular regions are mainly amorphous. The scale bars are

1 μm in b,

500 nm in c, and

2 nm in d ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/s41467-018-02961-2

2 NATURE COMMUNICATIONS | (2018)9:506 |DOI: 10.1038/s41467-018-02961-2 |www.nature.com/naturecommunications cause a lattice instability, which transform the parent lattice in a diffusionless and displacive manner into a new crystal lattice36,40. Such an elastic softening and lattice shear have also been postu- lated based on theoretical consideration30 to account for poly- morphic SSA and catastrophic melting, which has later been corroborated by molecular dynamic simulations29,41,42. However, a possible link between martensitic transformation and cata- strophic (inverse) melting has escaped experimental observation so far and no related mechanism has been proposed to date. In the present work, we prepared six metastable (Ti0.615Zr0.385)100-3.9x(Cu2.3Fe1.6)x (0 ≤ x ≤ 1.5) alloys and found reversible partial SSA in certain compositions on cooling. The amorphous phase has a characteristic lenticular shape uniformly distributed inside metastable β-Ti grains along de?ned crystal- lographic directions. The amorphous phase apparently forms through a martensitic transformation in the crystalline solid as a result of local lattice shear. Simultaneously, the present SSA ful?ls the criteria of congruent inverse melting. The fact that it proceeds catastrophically via a martensitic transformation sheds light onto fundamental phenomena of martensitic transformations, solid- state amorphization (SSA) and catastrophic melting. Results Morphology of the intragranular amorphous phase. Even though the following results and discussion also hold for several other alloys, we only concentrate on Ti59.1Zr37Cu2.3Fe1.6 (x = 1) as a case study here. Figure 1a shows the X-ray diffraction (XRD) pattern of the Ti59.1Zr37Cu2.3Fe1.6 ingot. Next to the diffraction peaks of body-centred cubic (bcc) β-Ti, the broad scattering contribution of an amorphous phase is seen, which is consistent with the high-energy XRD of this sample (Supplementary Fig. 1). In the transmission electron microscope (TEM) micrograph of this sample (Fig. 1b), characteristic bright lenticular plates inside a β-Ti grain are visible. The long axis of these plates is oriented along the crystallographic........