Papers by Keyword: Rapid Solidification

Abstract: A small projection with a height and width of about 40 and 50 µm, respectively, was formed on a twin-roll-cast A356 aluminum alloy sheet by cold rolling at a rolling speed of 0.5 m/min. This projection was then used as a die to form a groove with a depth and width of about 40 and 50 µm, respectively, on a polyethylene terephthalate plate by pressing.

Abstract: In this study, Mg-based alloys were prepared by rapid solidification of twin roll casting (TRC), then microstructure and element distribution were investigated respectively with Scanning Electron Microscope (SEM) and Electron Probe Micro Analyzer (EPMA). What’s more, in order to analyze microstructure and crystal structure of Mg-based alloys, experiments on specimens with the usage of X-ray diffraction (XRD) and Transmission Electron Microscope (TEM) were also carried out. At last, the designed Mg-Re magnesium alloy with quasi-amorphous phase plus fine crystalline phase dual phase microstructure produced with our rapid solidification of TRC process. The rapid solidification process realized with a faster casting speed and a thinner roll gap that does not need any anther additional devices and vacuum environment. EPMA results and TEM analyses show that the quasi-amorphous phase has a high concentration in Al and RE element. There are quasi-amorphous phase in the middle of Mg-Re alloy cross section surrounded by dendrites phase and normal crystals. Acknowledgement. This work was supported by Cooperative Research and Development Center for Advanced Materials (CRDAM) funded by the Institute for Materials Research (IMR), Tohoku University (Project Number 18G0042).

Abstract: Au-20Sn (mass fraction) eutectic alloy is a key lead-free solder material for high reliability microelectronics and optoelectronics packaging. The refinement of initial solidification structure can improved the processing performance of Au-20Sn alloy. This paper reported the research progresses on refining solidification structure of Au-20Sn alloy in our research group. The results indicated that the solidification structure of alloy can be effectively refined by rapid solidification with the increasing of cooling rate. The solidification structure can also be refined by incubated nucleation treatment with Au or Sn or by proper melt temperature treatment. The refinement mechanisms of solidification structure by the three types of solidification methods were thoroughly discussed.

Abstract: The corrosion behavior and microstructure of hot extruded Mg-5 wt.%Sn-4 wt.%Al-2 wt.%Ce alloy by rapid solidification ribbon (RS-EX TAE542) are investigated. The results shows that corrosion resistance of RS-EX alloy is remarkably improved, compared with that of hot extruded TAE542 alloy by homogenized ingot (HI-EX TAE542). Relatively compact corrosion products and bedded corrosion surface of RS-EX alloy is connected with the fine grains and uniform particles caused by rapid solidification, and they can suppress the corrosion reactions.

Abstract: Glassy overspray powders of Ni₅₉Nb₃₅Sn₆ (at%) bulk metallic glass (BMG) obtained by spray forming were used in order to produce coatings on AISI 1020 mild steel substrate by laser cladding of the pre-placed powders. Different laser parameters, resulting in a variation of the power density, PD (J/mm2), were tested with a Yb fiber laser (up to 500 W). Gas atomized powders, suction cast sample trough copper mold casting and the laser clad tracks were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and coatings were subjected to measurements of Vickers microhardness. Atomized powder obtained showed no crystalline phases formation up to 425 μm, indicating good glass forming ability (GFA) of Ni₅₉Nb₃₅Sn₆ (at%) alloy. Microstructure characterization confirmed maximum glassy dimension of t_c =1mm for the Ni₅₉Nb₃₅Sn₆ (at%). Laser cladding track showed nanocrystalline phases embedded in a glassy matrix with Vickers microhardness ranging from 336 to 1184 HV.

Abstract: As a rapid solidification technology, strip casting (SC) technology is one of importance method in the production of Nd₂Fe₁₄B-based rare-earth permanent magnets. (Nd_1-2xPr_xY_x)_2.28Fe_13.58B_1.14 (x=0.05, 0.10, 0.15, 0.20) alloys prepared by arc melting method under an argon atmosphere were annealed at 1173 K for 360 hrs and then were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC). Magnetic properties of the ribbons prepared by melt-spinning method with high cooling rate were measured by Physical Property Measurement System (PPMS). The XRD and SEM results showed that the annealed (Nd_1-2xPr_xY_x)_2.28Fe_13.58B_1.14 (x=0.10, 0.15, 0.20) alloys had a single phase with tetragonal Nd2Fe14B-tpyed structure, while the annealed (Nd_0.90Pr_0.05Y_0.05)_2.28Fe_13.58B_1.14 alloy contained Nd2Fe14B phase and α-Fe secondary phase. On the other hand, the coercivities (H_cj) of (Nd_1-2xPr_xY_x)_2.28Fe_13.58B_1.14 (x=0.05, 0.10, 0.15, 0.20) melt-spun alloys were about 13.42 kOe, 13.49 kOe, 7.97 kOe and 8.36 kOe, respectively, while the remanences (B_r) of the alloys were 7.52 kGs, 7.48 kGs, 9.14 kGs and 7.48 kGs, respectively. In addition, The Curie temperature (Tc) of the annealed (Nd_1-2xPr_xY_x)_2.28Fe_13.58B_1.14 (x=0.05, 0.10, 0.15, 0.20) alloys were determined to be 573 K, 574 K, 579 K and 580 K, respectively.

Abstract: Fe-C-W-Cr-Ni alloy powder in diameter of 32-53 μm made by argon atomization was low-pressure plasma sprayed to produce high Cr-Ni cast iron base deposits with finely dispersed tungsten carbide particles. The as-sprayed deposit produced on a non-cooled substrate was composed of γFe, αFe and carbide. The fine precipitates in the as-sprayed deposit were carbide. With increasing heat treatment temperature up to 1273 K, the carbide particles coarsened. The as-sprayed deposit produced on a non-cooled substrate had higher hardness than the heat-treated deposits. The wear resistance of the as-sprayed deposit produced on a non-cooled substrate was lower than that of heat-treated deposits. The as-sprayed deposit produced on a non-cooled substrate and heat-treated deposits had higher wear resistance than commercial stainless steel.

Abstract: Liquid-liquid phase separation (LLPS) in the rapidly solidified Fe₇₁Cu₁₀P₁₀B₉ alloy under different casting conditions is investigated based on the XRD, DSC, and SEM measurements. It is found that during rapid solidification process, Cu-rich globules precipitated in the matrix which mainly consists of α-Fe and Fe₃B_0.82P_0.18 crystals. With increasing cooling rate, LLPS becomes weaker, leading to less precipitation of Cu-rich globules, while the microstructure of the matrix became finer. Magnetic measurements show that the saturation induction and the coercivity of the present samples increase first and then decrease with increasing cooling rate. The corresponding mechanisms related to magnetic performance are also discussed details.

Abstract: The microstructure of rapidly solidified melt-spun ribbon in AlCoCrFeNi_2.1 eutectic high entropy alloys (EHEAs) was investigated for clarifying the effect of rapid solidification on the constituent phases and microstructure of specimens formed through solidification. XRD analysis indicates that the melt-spun ribbons were composed of a mixture of fcc and bcc phases. The rapidly solidified melt-spun ribbon shows a fine poly-crystalline structure with fcc matrix phase and crystalline precipitates in the grain boundary, indicating that the solidification structure in the melt-spun ribbon was significantly different from that obtained by conventional casting processes.

Abstract: For decades, twin-roll casting has been applied for manufacturing aluminum alloy sheets. This conventional process contributes to make thin aluminum sheets from the molten metal directly. Recently, vertical-type high-speed twin-roll casting (HSTRC) has been developed with much higher casting speed rather than the horizontal-type. Some modifications such as feeding nozzle and water-cooling system of copper rolls contribute to increase cooling rates. This characteristic leads to many metallurgical advantages like grain refinement, super-saturation of alloying elements and fine distribution of secondary particles. The objective of this study is to investigate the constituent particles in HSTRC aluminum alloy. The commercial Al-Mn alloy strip was successfully fabricated by HSTRC. Clearly different microstructure was found in thickness direction. Many constituent particles observed along the grain boundaries/cell boundaries as well as inside of Al matrix on the surface area, while eutectic structure around globular grain boundaries was observed in mid-central area. The morphology as well as chemical compositions of the constituent particles were investigated.