Papers by Keyword: Spinodal Decomposition

Abstract: In this paper, comprehensive studies on the age-hardening behavior and precipitate microstructures of severely deformed and then artificially aged aluminum alloys have been conducted to clarify whether or not concurrent strengthening by ultrafine-grained and precipitation hardenings can be achieved. From our graphically-illustrated equivalent strain dependence of both the attained hardness and increment/decrement in hardness during aging (i.e. age-hardenability), three strategies to maximize the combined processing of severe plastic deformation and age-hardening technique are proposed. (1) Lowering of aging temperature and (2) utilization of microalloying elements can improve not only the attained hardness but also the age-hardenability of high-pressure torsion (HPT) specimens of Al-Mg-Si (-Cu) alloy due to the increased volume fraction of transgranular precipitates. A further increase in hardness can be achieved by (3) taking advantage of spinodal decomposition for HPTed Al-Li-Cu alloy, in which nanoscale precipitates of δ’ phase are successfully formed within ultrafine grains, irrespective of the higher number density of grain boundaries. The attained hardness of >HV290 in the latter alloy is almost the highest among conventional wrought aluminum alloys, and therefore our proposed strategies will be useful for designing concurrently strengthened severely-deformed age-hardenable aluminum alloys.

Abstract: A Cu-20Ni-20Mn alloy was prepared and the aging characteristic of this alloy was investigated in this paper. The experimental results showed that the strength of solution treated Cu-Ni-Mn alloy was enhanced by more than 500MPa when aged for more than 20h. Much more rapid increase of tensile strength was found in the cold rolling samples during the aging process, and the strength was much higher in the range from 1200-1600MPa. The side peaks found beside (200) X-ray diffraction peaks are believed to be corresponding to the Cu-rich and Mn/Ni-rich phase regions formed by up-hill diffusion. It is also known that this fluctuation of composition is usually described by sinusoidal wave, the wave length of which is estimated to be 10-15nm.

Abstract: Solid-state reactions between Ge and Mn films are systematically examined using X-ray diffraction, photoelectron spectroscopy and magnetic measurements. The films have a nominal atomic ratio Ge:Mn = 40:60 and are investigated at temperatures from 50 to 500 °С. It is established that after annealing at ~120 °С, the ferromagnetic Mn₅Ge₃ phase is the first phase to form at the 40Ge/60Mn interface. Increasing the annealing temperature to 500 °С leads to the formation of the ferromagnetic phase with a Curie temperature T_C ~ 360 K and magnetization M_S ~ 140-200 emu/cc at room temperature. Analysis of X-ray diffraction patterns and the photoelectron spectra suggests that the increased Curie temperature and magnetization are related to the migration of C and O atoms into the Mn₅Ge₃ lattice and the formation of the Nowotny phase Mn₅Ge₃С_xO_y. The initiation temperature (~120 °С) of the Mn₅Ge₃ phase is the same both for solid-state reactions in Ge/Mn films, as well as for phase separation in Ge_xMn_1-x diluted semiconductors. We conclude that the synthesis of the Mn₅Ge₃ phase is the moving force for the spinodal decomposition of the Ge_xMn_1-x diluted semiconductors.

Abstract: Transmission electron microscopy and the cathodoluminescence method have been used to study the transition region in 3C-SiC/6H-SiC heterostructures. It is shown that this region is, as a rule, constituted by alternating 3C-SiC and 6H-SiC layers, with possible inclusion of other silicon carbide polytypes. An assumption is made that this structure of the transition region can be explained in terms of the spinodal decomposition model

Abstract: Hafnium silicate dielectric films were fabricated by radio frequency magnetron sputtering. Their microstructure and electrical properties were studied versus annealing treatment. The evolution of microstructure and the formation of alternated HfO₂-rich and SiO₂-rich layers were observed and explained by surface directed spinodal decomposition. The stable tetragonal HfO₂ phase was formed upon an annealing at 1000-1100°C. The control of annealing temperature allowed the memory window to be achieved and to be tuned as well as the dielectric constant to be enhanced.

Abstract: The temperature and amplitude dependence of internal friction fcc Mn45Cu55 alloy aged at 400 °C were studied. Two low-temperature internal friction peak observed in the quenched state. Physical mechanism of the peaks was determined by the effect of frequency and strain amplitude on the temperature dependence of internal friction. The influence of the heat treatment to the internal friction of the investigated alloy was shown.

Abstract: An investigation on behavior of the early stage of aging and its influence on theperformance of C17200 alloys is conducted in this paper. It is indicated that spinodal decomposition occured when the specimen is aged at 320 °C ,leading to the formation of G.P zones. A phase transformation from metastable precipitates to stable phase occurred with the increasing aging time, the sequence of which is believed as G..P→γ′′→γ′→γ. Spinodal decomposition and ordering of the matrix are found together in C17200 alloy.

Abstract: M2052 alloys with various aging treatments are obtained in order to investigate the relationship between aging treatment and damping capacity by the torsion pendulum, X-Ray Diffraction (XRD) and Transmission Electron Microscope (TEM) methods. The results show that M2052 can obtain high damping capacity (δ>0.2) when aged at a range from 400°C to 450°C, and the damping capacity after aged at a lower temperature is higher than that aged at a higher temperature for the maximum values. TEM and XRD results show that fcc-fct transformation occurs after aging treatment. The volumes of fct structures are one of reason to affect the damping capacity in M2052 alloy. The better understanding aging treatment could promote the applications of M2052 alloy.

Abstract: The present work is focused on a new approach for the development of Fe-Cr-Co based permanent magnets. Fe-Cr-Co alloy was prepared by using tri arc melting technique under inert atmosphere of Argon. Solution treatment was done at a temperature of 1250°C for five hours followed by water quenching and then a single step thermo-magnetic treatment (TMT) was applied at predetermined cooling rates. The influence of TMT and cooling rates on the final magnetic properties of the alloy were investigated. The results reveal that microstructure and magnetic properties were sensitive to both cooling rates & TMT and can be optimized by controlling the processing conditions. The optimum magnetic properties in the alloy with two different cooling rates of 1°C per minute and 2°C per minute were obtained as (i) 1010 Oe (H_c), 9400 G (B_r), 3.4 MGOe (BH_max) (ii) 810 Oe (H_c), 10590 G (B_r), 3.6 MGOe (BH_max) respectively. The above method provides a quick and low cost manufacturing route for the Fe-Cr-Co based permanent magnets with comparable magnetic properties to that of Alnico with added advantage of having high ductility.

Abstract: This study is focused on the development of isotropic Fe-Cr-Co based permanent magnets. Two compositions Fe-25Co-30Cr-3.5Mo-0.8Ti-0.8 and Fe-24 Co-32Cr-0.5Si-0.8V-0.8Ti were tried to optimize by adjusting heat treatment cycle. A modified single step heat treatment cycle was established which made processing easy and quick. Alloys were prepared in tri-arc melting furnace under inert atmosphere of Argon. Samples were solution treated at 1250 °C for 5 hours followed by water quenching. Then a spinodal decomposition heat treatment cycle in the temperature range 620 645 °C was applied in order to produce magnetism in this material. Samples were characterized for metallographic, chemical, structural and magnetic properties using Optical microscope, Scanning electron microscope equipped with Energy dispersive spectrometer, X-ray diffractometer and DC magnetometer. This study reveals that magnetic properties are sensitive to the spinodal decomposition temperature. Only + 5 °C change in temperature from optimum temperature can cause remarkable attenuation in magnetic properties. Magnetic properties of the alloys were achieved by controlling the spinodal decomposition temperature and subsequent cooling rate. The best magnetic properties in Mo and V containing alloys were obtained as 880 Oe (H_c), 7960 G (B_r), 2.3 MGOe (BH_max) and 700 Oe (H_c), 7750 G (B_r), 1.8 MGOe (BH_max), respectively.