Solid-state amorphization (SSA), i.e. the transformation from a crystalline phase to an amorphous phase, is an alternative process, besides the fast quenching of molten liquids, to obtain amorphous phases. The reported mechanisms of SSA include: inter-diffusion in multiple layers-induced SSA, mechanical alloying-induced SSA, pressure and severe deformation-induced SSA, radiation-induced SSA, and cooling of supersaturated solid solution-induced SSA, etc.
Recently, Professor ZHANG Haifeng’s group from Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences in cooperation with researchers from IFW Dresden, Germany, Xi’an Jiaotong University, Erich Schmid Institute of Materials Science, Austria and University of Science and Technology Beijing discovered a new kind of SSA—Martensitic Transformation-Induced Amorphization.
During investigating phase transformations in the as-solidified (Ti0.615Zr0.385)100-3.9x(Cu2.3Fe1.6)x (x=1) alloy, they found lenticular or lathy amorphous regions embedded in metastable β-Ti grains with the long axes along specific crystallographic directions. No obvious compositional difference can be detected between in the amorphous regions and in the β phase matrix, and many shear steps and severe lattice distortion of β phase are found at the interfacial region between the amorphous region and the β-Ti matrix. Such morphology of the current amorphous phase is clearly different with the previously reported SSA mechanisms. A mechanism of Martensitic Transformation-Induced Amorphization is proposed: Upon cooling of metastable β-type (Ti0.615Zr0.385)100-3.9x(Cu2.3Fe1.6)x alloys, the body-centered cubic (β) phase, which is the phase in equlibrium at high temperatures, becomes unstable gradually. Two phonon anomalies, T1 1/2 (1,1,0) and L 2/3 (1,1,1) occur. The former transforms β phase to α¢/α¢¢ martensite, and the latter causes the shuffle of partial {222}β planes to form ω phase. In the special case of β-Ti alloys with certain compositions, the local lattice shear and distortion during martensitic transformation make the structural-disordered amorphous phase prone to form as compared with the formation of crystalline α¢/α¢¢/ω phases, i.e. the martensitic amorphization happens. The current intragranular amorphous phase could be named as “Amorphous Martensite”.
This work was supported by projects including ones from National Natural Science Foundation of China, and was published online in Nature Communications on Feb. 6th, 2018.
Figure. Microstructure, amorphization mechanism, and metastable phase diagram of (Ti0.615Zr0.385)100-3.9x(Cu2.3Fe1.6)x alloys （Image by IMR)
