Space Materials Science in China: II. Ground-based Researches and Academic Activities*

PAN Mingxiang WANG Weihua FAN Shuqian ZHANG Qi PAN Xiuhong DENG Weijie HU Liang WEI Bingbo WANG Haipeng YIN Zhigang FANG Jinghong2, YU Jianding2, ZHANG Xingwang YUAN Zhangfu JIANG Hongxiang ZHAO Jiuzhou WANG Gong

Space Materials Science in China: II. Ground-based Researches and Academic Activities*

PAN Mingxiang1,2,3WANG Weihua1,2,3FAN Shuqian4ZHANG Qi4PAN Xiuhong5DENG Weijie5HU Liang6WEI Bingbo6WANG Haipeng6YIN Zhigang2,7FANG Jinghong2,5YU Jianding2,5ZHANG Xingwang2,7YUAN Zhangfu8,9JIANG Hongxiang10ZHAO Jiuzhou10WANG Gong2,11

1 (100191) 2 (100049) 3 (523808) 4 (400714) 5 (201899) 6 (710072) 7 (100083) 8 (100083) 9 (100871) 10 (110016) 11 (100094)

Activities of space materials science research in China have been continuously supported by two main national programs. One is the China Space Station (CSS) program since 1992, and the other is the Strategic Priority Program (SPP) on Space Science since 2011. In CSS plan in 2019, eleven space materials science experimental projects were officially approved for execution during the construction of the space station. In the SPP Phase II launched in 2018, seven pre-research projects are deployed as the first batch in 2018, and one concept study project in 2019. These pre-research projects will be cultivated as candidates for future selection as space experiment projects on the recovery of scientific experimental satellites in the future. A new apparatus of electrostatic levitation system for ground-based research of space materials science and rapid solidification research has been developed under the support of the National Natural Science Foundation of China. In order to promote domestic academic activities and to enhance the advancement of space materials science in China, the Space Materials Science and Technology Division belong to the Chinese Materials Research Society was established in 2019. We also organized scientists to write five review papers on space materials science as a special topic published in the journalto provide valuable scientific and technical references for Chinese researchers.

Additive manufacturing, Aerogel preparation, Electrostatic levitation system, Crystal growth, Solidification, Academic activities of space materials science

1 Introduction

Chinese planned space materials science experiments began in 1992 with the launch of China’s manned spaceflight program. Space materials science as a branch of space science in China has been continuously supported by two main national programs: one is the China Space Station (CSS) program that star-ted in 1992, and the other is the Strategic Priority Program (SPP) on Space Science since 2011. Most of the space materials science experiments conducted in the past, including those performed on board the Tiangong-2 space laboratory and the SJ-10 recovery satellite in China, are mainly exploratory, due to the limitation on space resource conditions and experimental opportunities and the considerations of developing the space technologies first. In the era of China’s own space station, space materials science will focus on systemic and quantitative research. In the CSS plan in 2019, 11 space materials science experimental projects were finally reviewed and officially approved for implementation during the construction of the space station. By launching scientific experiment satellites the SPP will primarily support those space materials science experiments that are not suitable for the space station, such as with the requirement of high microgravity level or long-time microgravity environment with small gra-vity disturbances, or safety considerations for as-tronauts. In the SPP phase II launched in 2018, the Qingyang program (alias for space materials science in SPP) deployed 7 pre-research projects on the gro-und as the first batch in 2018, and 1 concept study project for the necessity of integrating a materials science experiment satellite in 2019. These pre-rese-arch projects will be cultivated as candidates for fu-ture selection as space experiment projects on reco-very scientific experimental satellites in the future.

In recent years the National Natural Science Foundation of China (NSFC) has also increased fun-ding for related researches including space materials science, and a new apparatus of electrostatic levitation system for ground-based research of space materials science and rapid solidification research has been developed under the support of the NSFC[1-3].

In order to promote domestic academic exch-ange activities and to enhance the advancement of space materials science in China, the Space Materials Science and Technology Division belonging to the Chinese Materials Research Society (CMRS) was established in 2019. We also organized scientists to write review papers on space materials science as special topic published in the journal) to provide va-lu-able scientific and technical references for Chinese researchers or scholars who are interested in joining the team of space materials science research in the future in the planning and design of materials science experiments in related directions[4-8].

2 Ground-based Researches

2.1 Fundamental Science Problems during the Rapid Solidification of Metallic Materials in Microgravity

There may be significant differences in the material manufacturing process between space and ground, due to the special environment in space such as micro-gravity, high vacuum, and ultra-low temperature. To study the special phenomenon and the mechanism for additive manufacturing in space, including the microstructure, the mechanical properties, and the correlation among them, the Chongqing Institute of Green and Intelligent Technology of CAS has started an advanced research program titled “Fundamental science problems during the rapid solidification of metallic materials in microgravity”, and following preliminary results have been achieved.

(1) Design of prototype machine for space experiments (suitable for both the space environments and the resource constraints), and the verification of key components.

(2) Finite element simulation of the rapid solidification process for metallic materials under microgravity, including the heat and mass transportation, the phase transition, and the instability of li-quid bridge caused by the environmental disturbance such as equipment vibration and gravity fluctuation.

(3) Design and early-stage verification of space experiments, including on ground experiments and the optimization of manufacturing parameters.

(4) Suggestions for an experiment payload and accompanying program that will be run in the recovery experiment satellite.

(5) Progress of circular multi-laser melting wire additive manufacturing experiment in parabolic fli-ght test to simulate microgravity environment.

The achievements above would be very helpful for the science experiments in space, especially for the discovering of new phenomena, effects, and new rules in the additive manufacturing process in space.

2.2 Facility for Aerogel Preparation in Space

A prototype of the facility to be served under microgravity for aerogels preparation was developed. This facility has the functions of both the sol-gel process and the sample drying process. It consists of three main parts: one synthesis part for the sol-gel process, one heating part for sample drying, and a controller. The core of synthesis part is three cylindrical chambers made of stainless steel. The inner diameter of each chamber is 25 mm and the height is 80 mm. The sol-gel process is performed by injecting the solvent and the catalytic agent into one synthesis chamber simultaneously from two individual smaller tubes through plastic pipes by a motor. In order to avoid the backflow under microgravity, one-way ele-c-tro-magnetic valves are used. The chamber is sealed by one cover, on which a vacuum pump adapter is designed besides two plastic pipe connectors. Thus, the gas pressure in the chamber can be adjusted according to experimental requirements. The mixture of solvent and catalysis agent in the synthesis chamber can be stirred by the rotation of one magnetic rotor near the inside wall of the chamber, which is driven by a rotating magnet outside.

Totally three types of gelatum can be achieved by this facility in space. The synthesis chamber can be heated up to 400oC by the heating unit which is a tubular heating furnace. By this way, the gel can be dried and xerogel is obtained. The heating furnace is composed of helical resistance coils which are enclosed by some inorganic ceramic fibers. One S-type thermocouple is used for temperature control.

All the operations such as solvent injection, magnet rotation, furnace heating are controlled by the controller. The present prototype is designed aiming to prepare inorganic aerogels in space, especially for the preparation of heat insulating materials. Some synthesis experiments have been done on the ground for the preparation of SiO2aerogel as well as SiO2-Al2O3aerogel.

3 Electrostatic levitation System for Rapid Solidification of Metallic Materials

A large scale new apparatus for rapid solidification research and space materials science has been developed under the support of NSFC National Special Fund for Major Research Instruments. It was designed and manufactured by a research team directed by Prof. Wei from the Laboratory of Space Materials Science and Technology in Northwestern Polytechnical University.

The extraordinary solidification of metallic materials and the ground simulation of microgravity environment are essential subjects for both materials science and space science. According to the national strategy for medium and long-term scientific deve- lopment, China is about to embrace a space station era in the year of 2020–2030. This experimental sys-tem has been developed on the basis of electrostatic levitation technique, which can simulate outer-space environments like microgravity, containerless state, and ultrahigh vacuum, to accomplish the extraordinary solidification of metallic materials. A series of scientific and technological problems such as intrinsic physicochemical properties and rapid solidification mechanisms of liquid alloys are effectively solved by utilizing these extraordinary conditions[1-3].

This system occupies an area of 110 m2and exceeds 2 m in height. The original design ideas, blue prints, and kernel control programs are all fulfilled by the research team independently. Several progresses have been made at least in three key techniques and important scientific issues, which are levitation capability, containerless rapid solidification, and ther-mophysical properties. Firstly, the electrostatic levi-tation ability has been improved to set a new record of 15 mm diameter metallic sample, which almost triples the previously published international record. Secondly, the liquid supercooling and containerless solidification of tungsten, which is the most refractory metal in nature with a melting point up to 3695 K, have been achieved under electrostatic lev-i-tation conditions. And the in-situ observation and measurement on its solidification rate have been accomplished for the first time to reveal the dendritic growth mechanism within liquid tungsten. Thirdly, the ultrafast solidification of metallic materials has been realized, where liquid titanium displays a dendritic growth velocity as high as 122 m·s–1on account of the ultrahigh vacuum condition (about 10–8Pa) and precisely active control performance in the system. Moreover, it integrates the five experimental functions including electrostatic levitation, thermophysical property measurement, rapid solidification, material preparation, and real-time data processing. The relevant investigations are being conducted on thermophysical properties, rapid solidification me-ch-a-nism, and novel material synthesis of refractory alloys, titanium alloys, and nickel-based superalloys.

On the basis of this innovative instrument, the research on solidification science and space science in China will be facilitated to a desirable extent. It helps to update the preparation technique of traditional materials and push forward the research and development on new materials. Meanwhile, it may also promote the research on fluid science under stimulated space environments[9]. Besides, this system is even capable of evolving into a platform mo-unted on China’s space station after a miniaturiza-tion design.

4 Establishment of a Space Materials Science and Technology Division

The Space Materials Science and Technology Divi-sion, affiliated with the CMRS, was established in Beijing in 2019.

The scope of academic activities of the space materials science and technology division covers: (i) The physical characteristics of outer space environment and its ground simulation; (ii) materials pre-paration, research, and development for manufac-turing rockets and outer spacecraft; (iii) preparation and processing of metals and non-metallic materials in space environment (including ground-based sim-u-lation, the same below); (iv) the physical and che-mical properties, application performance, and service behavior of the materials in space environment; (v) the solidification, heat treatment, plastic processing, and jointing,of various spacecraft materials; (vi) the mathematical modeling and computational simulation relating to space materials science and technology.

As part of the CMRS’s annual conference, the division has hosted three symposia. The 2018’s sym-posium was held in Xiamen, Fujian Province, and the 2019’s one was held in Chengdu, Sichuan Province. This year will be held in Qingdao, Shandong Province, China.

5 Publications of Special Topic: Space Material Science

5.1 Study on Crystal Growth of InxGa1–xSb under Mic-ro-gravity[4,10]

InGa1–xSb is a ternary alloy that has tunable pro-perties. The wavelength of InGa1–xSb can be varied in the range 1.7~6.8 μm, which is in the Infrared (IR) region and makes that InGa1–xSb can be used as a substrate for IR detector and Thermophotovoltaic (TPV). The phase diagram reveals that there is a large temperature gap between liquidus and solidus lines, which leads to constitutional supercooling and the formation of crystal defects during the solidification process of InGaSb crystal. Moreover, convection caused by gravity will increase the inhomogeneity of transport in the liquid region near the crystal growth interface, making it difficult to grow InGa1–xSb crystal. The convection will be restrained in microgravity environment, and thus, it is very beneficial for crystal growth. This article introduces the effect of microgravity on the growth of InGa1–xSb crystal and the results of the space growth experiment of InGa1–xSb ternary crystal with a high In concentration in SJ-10 Recoverable scientific experiment satellite.

5.2 Growth of III-V Semiconductor Crystals under Microgravity

The low-gravity environment aboard the space pro-vides a unique platform for both understanding the crystal-growth-related phenomena that are masked by gravity on the Earth and exploring new crystal growth techniques. III~V semiconductor crystal gro-wths were carried out under microgravity and the main results include: (i) device-grade semi-insulating GaAs single crystal with improved stoichiometry was grown under microgravity condition, and low noise field-effect transistors and analog switch integrated circuits were fabricated and the performances were better than their terrestrial counterparts; (ii) detached Bridgman growth was realized in two model systems of GaSb and InSb by suppressing the hydrostatic pressure of melt, and largely reduced dislocation densities in the materials were observed; (iii) the contributions of buoyancy-driven convection, Marangoni convection, and rotation magnetic field forced convection on the microscopic segregation were carefully studied; (iv) the vertical gradient freezing method was employed to grow semiconductor alloys and chemically homogeneous GaInSb crystal was obtained. In this review, the main progress in these aspects are summarized and future challenges are discussed[5].

5.3 Wettability of High-temperature Melts under Microgravity and Ground Gravity Conditions

The physical characteristics of the material could not be accurately observed due to the effect of gravity which hides some experimental phenomena of the material surface and interface. So, it is greatly significant to study the influence mechanism of microgravity on the melt wetting behavior and solid/liquid interface reaction. In this paper, the wetting behavior of high-temperature melts, especially of Sn-based alloys, and the reaction properties on the melt/sub-strate interface were summarized. Comparing with related research and experimental results under no-rmal gravity and microgravity conditions, the high- temperature melt wetting characteristics in both satellite microgravity environment and ground en-vironment are summarized. This paper provides a theoretical reference for future space microgravity experiments and analysis[6].

5.4 Progress in the Solidification ofMonotectic Alloys under the MicrogravityCondition of Space

Monotectic alloys or alloys with a miscibility gap in the liquid state are a broad kind of materials. They are especially suitable for the manufacturing of either the in-situ particle composite materials or the com-posite materials with a core/shell structure and, thus, have a strong industry application background. Th-ese alloys, however, have an essential drawback that just the miscibility gap poses problems during so-lidification. When a single-phase melt of these alloys is cooled into the miscibility gap, it decomposes into two liquids enriched with different components. Ge-n-erally, the convection flow caused by the gravity and the liquid-liquid phase transformation causes the formation of a phase segregated microstructure when these alloys are solidified under the normal gravitational conditions. Under microgravity condition, the convection flow caused by the gravity and the sediment or floating of the second phase due to the density difference between the components are obviously weakened, it is beneficial for the study of solidification theory of monotectic alloy and the preparation of monotectic alloys composited with a well dispersed microstructure. In recent decades, plenty of efforts have been made to investigate the solidification of monotectic alloys under microgravity conditions, this article will review the research work in this field during the last few decades[7,11,12].

5.5 Review of Space Manufacturing Technique and Development

Since the first additive manufacturing equipment was sent to the international space station in 2014, space manufacturing technology has become one of the most active scientific and application frontiers of the world’s major space powers. Space manufacturing technology is a key strategic technology to enhance the capability of human space activities and deep space exploration. By investigating the development status of space manufacturing technology and combining the development status of advanced manufacturing technology at home and abroad. We introduce the space manufacturing materials (including polymer, composite, biological materials, metals, and ceramics) and the development trend of space manufacturing in the future, which provides a the-oretical reference for the deployment of space man-ufacturing technology in China[8].

[1] ZOU P F, WANG H P, YANG S J,. Density measurement and atomic structure simulation of metastable liquid Ti-Ni alloys [J]., 2018, 49A:5488- 5496

[2] LU P, WANG H P, ZOU P F,. Local atomic structure correlating to phase selection in undercooled liquid Ni-Zr peritectic alloy [J].., 2018, 124:025103

[3] ZOU P F, WANG H P, YANG S J, HU L, WEI B. Anomalous temperature dependence of liquid state density for Ni50Ti50alloy investigated under electrostatic levitation state [J].., 2017, 681:101-104

[4] FANG Jinghon, XIA Zhaoyang, WANG Hui,. Study on crystal growth of InGa1-xSb under microgravity [J]., 2020, 50:047002

[5] YIN Zhigang, ZHANG Xingwang, WU Jinliang. Growth of III-V semiconductor crystals under microgravity [J]., 2020, 50:047003

[6] YUAN Zhangfu, WANG Rongyue, XIE Shanshan,. Wettability of high-temperature melts under microgravity and ground gravity conditions [J]., 2020, 50:047004

[7] JIANG Hongxiang, LI Wang, ZHANG Lili,. Progress in the solidification of monotectic alloys under the microgravity condition of space [J]., 2020, 50:047005

[8] WANG Gong, ZHAO Wei, CHENG Tianjin, LIU Yifei. Review of space manufacturing technique and developments [J]., 2020, 50:047006

[9] WANG H P, LI M X, ZOU P F,. Experimental modulation and theoretical simulation of zonal oscillation for electrostatically levitated metallic droplets at high temperatures [J]., 2018, 98:063106

[10] YU J, INATOMI Y, KUMAR V N,. Homogeneous InGaSb crystal grown under microgravity using Chinese recovery satellite SJ-10 [J], 2019, 5(1):8

[11] LI Wang, JIANG Hongxiang, ZHANG Lili,. Solidification of Al-Bi-Sn immiscible alloy under microgravity conditions of space [J].., 2019, 162:426-431

[12] JIANG Hongxiang, LI Shixin, ZHANG Lili,. Effect of microgravity on the solidification of aluminum–bismuth–tin immiscible alloys [J], 2019, 5:26

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PAN Mingxiang, WANG Weihua, FAN Shuqian, ZHANG Qi, PAN Xiuhong, DENG Weijie, HU Liang, WEI Bingbo, WANG Haipeng, YIN Zhigang, FANG Jinghong, YU Jianding, ZHANG Xingwang, YUAN Zhangfu, JIANG Hongxiang, ZHAO Jiuzhou, WANG Gong. Space Materials Science in China: II. Ground-based Researches and Academic Activities., 2020, 40(5): 950-955. DOI:10.11728/cjss2020.05.950

* Supports by the Strategic Priority Research Program on Space Science, the Chinese Academy of Sciences (XDA15013200, XDA15013700, XDA15013800, XDA15051200), the China’s Manned Space Station Project (TGJZ800-2-RW024), and the National Natural Science Foundation of China (51327901)

March 26, 2020

E-mail: panmx@iphy.ac.cn