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Novel Heating-Induced Reversion during Crystallization of Al-based Glassy Alloys.

ABSTRACT: Thermal stability and crystallization of three multicomponent glassy alloys, Al₈₆Y₇Ni₅Co₁Fe_0.5Pd_0.5, Al₈₅Y₈Ni₅Co₁Fe_0.5Pd_0.5 and Al₈₄Y₉Ni₄Co_1.5Fe_0.5Pd₁, were examined to assess the ability to form the mixture of amorphous (am) and fcc-aluminum (?-Al) phases. On heating, the glass transition into the supercooled liquid is shown by the 85Al and 84Al glasses. The crystallization sequences are [am]???[am?+??-Al]???[?-Al?+?compounds] for the 86Al and 85Al alloys, and [am]???[am?+??-Al?+?cubic Al_xM_y (M?=?Y, Ni, Co, Fe, Pd)]???[am?+??-Al]???[?-Al?+?Al₃Y?+?Al₉(Co, Ni)₂?+?unknown phase] for the 84Al alloy. The glass transition appears even for the 85Al alloy where the primary phase is ?-Al. The heating-induced reversion from [am?+??-Al?+?multicomponent Al_xM_y] to [am?+??-Al] for the 84Al alloy is abnormal, not previously observed in crystallization of glassy alloys, and seems to originate from instability of the metastable Al_xM_y compound, in which significant inhomogeneous strain is caused by the mixture of solute elements. This novel reversion phenomenon is encouraging for obtaining the [am?+??-Al] mixture over a wide range of high temperature effective for the formation of Al-based high-strength nanostructured bulk alloys by warm working.

SUBMITTER: Han FF

PROVIDER: S-EPMC5390259 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Novel Heating-Induced Reversion during Crystallization of Al-based Glassy Alloys.

Han F F FF Inoue A A Han Y Y Kong F L FL Zhu S L SL Shalaan E E Al-Marzouki F F Greer A L AL

Scientific reports 20170413

Thermal stability and crystallization of three multicomponent glassy alloys, Al86Y7Ni5Co1Fe0.5Pd0.5, Al85Y8Ni5Co1Fe0.5Pd0.5 and Al84Y9Ni4Co1.5Fe0.5Pd1, were examined to assess the ability to form the mixture of amorphous (am) and fcc-aluminum (α-Al) phases. On heating, the glass transition into the su ...[more]

PMID: 28406157

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Project description:We present the enhanced properties observed in the phase change memory alloy Ge2Sb2Te5 (GST) when doped with arsenic. Although arsenic is known as a toxic element, our observations show that significant improvement can be obtained in GST systems on thermal stability, transition temperature between amorphous and crystalline phases and switching behaviors when doping with arsenic. Though both the GST and arsenic doped GST are amorphous in the as-deposited state, only GST alloy turns to crystalline NaCl-type structure after annealing at 150 °C for 1 h. Results from the resistance versus temperature study show a systematic increase in the transition temperature and resistivity in the amorphous and crystalline states when the arsenic percentage in the GST alloy increases. The crystallization temperature (Tc) of (GST)0.85As0.15 is higher than the Tc observed in GST. Optical band gap (Eopt) values of the as-deposited films show a clear increasing trend; 0.6 eV for GST to 0.76 eV for (GST)0.85As0.15. The decreases in Eopt for the samples annealed at higher temperatures shows significant optical contrast between the as-deposited and annealed samples. Though all (GST)1-xAsx alloys show memory switching behaviors, threshold switching voltages (VT) of the studied alloys show an increasing trend with arsenic doping. For (GST)0.85As0.15, VT is about 5.2 V, which is higher than GST (4.0 V). Higher transition temperature and higher threshold switching values show arsenic doping in GST can enhance the memory device properties by improving the thermal stability and data readability. Understanding the doping effect on the GST is important to understand its crystallization properties. Structure properties of amorphous GST, Ge2Sb2-0.3As0.3Te5 and (GST)0.85As0.15 models were studied using first principles molecular dynamics simulations, compared their partial radial distribution functions, and q parameter order. Arsenic doping into GST features interesting structural and electronic effects revealed by the radial distribution functions, q order parameter and band gap value, in line with the experimental findings.

Dataset Information

Novel Heating-Induced Reversion during Crystallization of Al-based Glassy Alloys.

Publications

Novel Heating-Induced Reversion during Crystallization of Al-based Glassy Alloys.

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