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solidification behavior of Re-and Ru-containing Ni-based single-crystal superalloys with thermal and metallographic analysis

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Rare Metals 2017年第10期36卷 792-798页

作者： Gang Liu Lin Liu Zhen-Hua Han Guo-Jun Zhang Jun Zhang School of Materials Science and Engineering Xi'an University of Technology Xi'an 710048 China State Key Laboratory of solidification Processing Northwestern Polytechnical University Xi'an 710072 China

To clarify the solidification behavior of Re- and Ru-containing Ni-based single-crystal superalloys, four experimental alloys with varied contents of Re and Ru were investigated by differential scanning calorimetry （DSC） and metallographic techniques. To obtain the - solvus temperatures, the stepwise solution and aging heat treatments were used. DSC analysis shows that Re leads to the increase in freezing range and γ-solvus temperature. On the contrast, Ru only has negligible influence on the freezing range, but leads to the lower γ-solvus temperature. In comparison with Ru, Re leads to more severe segregation and higher eutectic fractions in as-cast microstructures. Furthermore, the castability and phase stability of Ni-based superalloys were analyzed by the results of DSC and metallographic analysis, such as freezing range, critical nucleation temperature, γ-solvus temperature and eutectic fractions. It shows that Re leads to the wider freezing range and lower critical nucleation temperature, indicating the worse castability of Re-con- taining Ni-based single-crystal superalloys.

关键词： Ni-based single-crystal alloys solidification behavior Metallography Thermal analysis

solidification behavior of 6061 wrought aluminum alloy during rheo-diecasting process with self-inoculation method

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Transactions of Nonferrous Metals Society of China 2018年第5期28卷 879-889页

作者： Ming LI Ynan-dong LI Hong-qiang ZHENG Xiao-feng HUANG Ti-jun CHEN Ying MA State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals Lanzhou University of Technology Lanzhou 730050 China Key Laboratory of Non-ferrous Metal Alloys Ministry of Education Lanzhou University of Technology Lanzhou 730050 China

The semisolid slurry of the 6061 wrought aluminum alloy was prepared by the self-inoculation method（SIM）. The effects of the isothermal holding parameters on microstructures of rheo-diecastings were investigated, and the solidification behavior of 6061 wrought aluminum alloy during the rheo-diecasting process was analyzed using OM, SEM, EDS and EBSD. The results indicate that the isothermal holding process during slurry preparation has great effect on primary α（Al） particles（α1）, but has little effect on the microstructure of secondary solidification in the process of thin-walled rheo-diecasting. Nucleation is expected to take place in the entire remaining liquid when the remaining liquid fills the die cavity, and the secondary solidification particles（α2） are formed after the process of stable growth, unstable growth and merging. The solute concentration of remaining liquid is higher than that of the original alloy due to the existence of α1 particles, hence the contents of Mg and Si in α2 particles are higher than those in α1 particles.

关键词： 6061 wrought aluminum alloy solidification behavior primary particle secondary particle rheo-diecasting

Influence of cooling rate on solidification behavior of sand-cast Mg-10Gd-3Y-0.4Zr alloy

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Transactions of Nonferrous Metals Society of China 2014年第11期24卷 3413-3420页

作者：庞松吴国华刘文才张亮张扬 Hans CONRAD 丁文江上海交通大学轻合金精密成型国家工程研究中心与金属基复合材料国家重点实验室 Materials Science and Engineering Department North Carolina State University Raleigh NC 27695-7907 USA

The effect of the cooling rate ranging from 1.4 °C/s to 3.5 °C/s on the solidification behavior of the sand-cast Mg?10Gd?3Y?0.4Zr alloy was studied by computer aided cooling curve analysis (CA-CCA). With the increase in cooling rate, the nucleation temperature (Tα,N) increases from 634.8 °C to 636.3 °C, the minimum temperature (Tα,Min) decreases from 631.9 °C to 630.7 °C, the nucleation undercooling (ΔTN) increases from 2.9 °C to 5.6 °C, the beginning temperature of the eutectic reaction (Teut,N) increases, the time of the eutectic reaction shortens, solidus temperature decreases from 546.0 °C to 541.4 °C, and solidification temperature range (ΔTS) increases by 6.1 °C. The increased nucleation rate (N&) is supposed to be the main reason for the increased?TN. Increased value (Teut,N?Teut,G) and shortened time of the eutectic reaction cause the change in the volume fraction and morphology of the second phase.

关键词： Mg-10Gd-3Y-0.4Zr sand-cast cooling rate thermal analysis solidification behavior

Microstructure characteristics and solidification behavior of thixomolded Mg-9%Al-1%Zn alloy

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Transactions of Nonferrous Metals Society of China 2011年第2期21卷 250-256页

作者：张友法刘勇兵曹占义东南大学材料科学与工程学院江苏省先进金属材料高技术研究重点试验室南京211189 吉林大学材料科学与工程学院汽车材料教育部重点实验室长春130022

Experimental investigation and theoretical analysis of the microstructure of thixomolded AZ91D were carried out to comprehensively understand the morphology transformation of solid particles and the solidification behavior. Typical microstructure of thixomolded AZ91D is composed of a-Mg and β-Mg17Al12, characterized with aun, aprim and eutectic. Four kinds of aun are classified according to the morphology and generation mechanism, such as spherical （al）, irregular （a2）, entrapping liquid alloy inside （a3） and entrapping pool inside （a4）. Under the effect of heating, shearing, collision, agglomeration or fragmentation, a2 and a4 can be the middle states ofal and a3. Similarly, a4 and a3 can also break into a2 and become al at the end. Controlled by undercooling, aprim nucleates and spherically grows within the remaining liquid alloy of thixomolded AZ91D until instability growth. The investigated microstructure was theoretically proved according to the analysis of Mg-Al binary phase diagram.

关键词： thixomolded AZ91D alloy solid particle solidification behavior

Effect of Pressure on the solidification behavior and Mechanical Properties of SiCp/Al-Mg Composites

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Journal of Wuhan University of Technology(Materials Science) 2013年第2期28卷 274-278页

作者：张宏伟耿林 FAN Guohua SUN Yuan School of Materials Science and Engineering Harbin Institute of Technology Institute of Metal Research Chinese Academy of Sciences

SiCp/A1-Mg metal matrix composites were manufactured by semi-solid stirring technique. The composites were remelted and then solidified under different pressures to study the solidification behavior of composites by differential thermal analysis, scanning electron microscopy, and transmission electron microscopy. The experimental results show that SiCp reinforcements can not act as heterogeneous nucleation sites for c^（A1）, and an interfacial layer composed of MgA1204 spinel and Si-rich phase existed at A1/SiCp interface. The undercooling of the matrix alloy was improved by the pressure applied, resulting in the grain of matrix alloy refining. The X-ray diffraction pattern of composites testified that the matrix alloy exhibited a certain preferred orientation during solidification. In addition, with increasing the pressure for solidification, the pored defects in the composites decreased, while the relative density, hardness and compressive strength increased. Therefore, the microstructure and mechanical properties of the composites were improved by pressure placed during the solidification of SiCp/A1-Mg composites.

关键词： MMCs nucleation solidification behavior microstructure mechanical properties

Microstructure characteristics and solidification behavior of wrought aluminum alloy 2024 rheo-diecast with self-inoculation method

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China Foundry 2012年第4期9卷 328-336页

作者： Li Yanlei Li Yuandong Li Chun Wu Huihui State Key Laboratory of Gansu Advanced Nonferrous Metal Materials Lanzhou University of TechnologyLanzhou 730050China Key Laboratory of Nonferrous Metal Alloys and Processing Ministry of EducationLanzhou University of TechnologyLanzhou 730050China

One important problem in casting wrought aluminum alloys is the high tendency to the formation of hot tears in the solidification *** using semi-solid metal(SSM) processing,the hot tearing tendency of alloys can be minimized during *** the present research,the semi-solid slurry of wrought aluminum alloy 2024 was firstly prepared with a novel self-inoculation method(SIM),and then the microstructure characteristics of the semi-solid slurry and the rheo-diecastings cast with the semi-solid slurry were *** results indicate that finer and more uniform globular primary α-Al particles can be obtained when the semi-solid slurry are isothermally held for a short period within the semi-solid temperature range,and the primary α-Al particles without entrapped liquid are uniformly fine,globular grains in the *** holding temperature and time affect the solid fraction,particle size,and shape *** the semi-solid slurry is held at 625 ℃ for 3 min and 5 min,the optimal values for the average equivalent diameter are 70.80 μm and 74.15 μm,and for the shape factor are 1.32 and 1.42,*** solidification process of the rheo-diecastings is composed of the following two distinct stages:primary solidification process and secondary solidification *** secondary solidification process consists further of the following three stages:(1) direct growth of secondary primary(α 2) phase from the surface of the primary α-Al phase particles without re-nucleation,(2) independent nucleation and growth of α 3 phase from the residual liquid,and(3) eutectic reaction at the end.

关键词： self-inoculation method wrought aluminum alloy 2024 solidification behavior secondary solidification

Structure Evolution and solidification behavior of Austenitic Stainless Steel in Pulsed Magnetic Field

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Journal of Iron and Steel Research International 2006年第5期13卷 69-72页

作者： LI Qiu-shu LI Hai-bin ZHAI Qi-jie School of Materials Science and Engineering Shanghai University Shanghai 200072 China School of Materials Science and Engineering Taiyuan University of Science and Technology Taiyuan 030024 Shanxi China

To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self-made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity.

关键词： pulsed magnetic field austenitic stainless steel solidification structure solidification behavior

Effect of Zr modification on solidification behavior and mechanical properties of Mg–Y–RE (WE54) alloy

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Journal of Magnesium and Alloys 2013年第4期1卷 346-351页

作者： Jilin Li Rongshi Chen Yuequn Ma Wei Ke State Key Laboratory for Corrosion and Protection Institute of Metal ResearchChinese Academy of Sciences62 Wencui RoadShenyang 110016China

Magnesium alloys containing rare earth elements (RE) have received considerable attention in recent years due to their high mechanical strength and good heat-resisting performance. Among them, Mg–5%Y–4%RE (WE54) magnesium alloy is a high strength sand casting magnesium alloy for use at temperatures up to 300 ℃, which is of great interest to engineers in the aerospace industry. In the present work, the solidification behavior of Zr-containing WE54 alloy and Zr-free alloy was investigated by computer-aided cooling curve analysis (CA-CCA) technique. And the solidification microstructure and mechanical properties of them were also investigated comparatively. It is found from the cooling curves and as-cast microstructure of WE54 alloy that the nucleation temperature of α-Mg in WE54 alloy increases after Zr addition, and the as-cast microstructure of the alloy is significantly refined by Zr. While the phase constitution of WE54 alloy is not changed after Zr addition. These phenomena indicate that Zr acts as heterogeneous nuclei during the solidification of WE54 alloy. Due to refined microstructure, the mechanical properties of Zr-containing WE54 alloy is much higher than Zr-free WE54 alloy.

关键词： WE54 alloy Zr modification solidification behavior Mechanical properties

Effect of Cooling Rate on the solidification behavior and Microstructure of SiC_w/Al-18Si Composites

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Journal of Wuhan University of Technology(Materials Science) 2009年第S1期24卷 1-4页

作者：耿林魏红梅 School of Materials Science & Engineering Harbin Institute of Technology

Al-18Si alloy reinforced with 15%,20% and 25%(volume fraction) SiC whiskers were prepared by squeeze casting technique and the solidification behavior and microstructure of as-prepared composites at different cooling rates were studied by DSC,optical microscope,SEM and *** results show that silicon phase is nucleated on SiC *** the increase of cooling rate,the degree of undercooling increases in the composites as well as in the *** increase of cooling rate leads to a reduction in the size of eutectic Al-Si and also changes its morphology from short stick to ***,the change of primary Si is *** primary Si size is refined,and then coarsened with increasing cooling *** primary Si morphology of composites changes from agglomerate to stick.

关键词： SiCw/Al-Si composites cooling rate solidification behavior microstructure