Under normal conditions, when the ratio of an object' s acceleration to gravitational acceleration is less than one or even equal to zero, the object is considered to be in a microgravity or weightless state. Under such conditions, the solidification characteristics of metals differ significantly from those under normal gravity, which in turn affects the resulting microstructure and properties after solidification. With the deepening of space research, the unique features of metal solidification under microgravity (or weightless) conditions have opened up new areas for the development of solidification theory and technology.
Achieving a Microgravity Environment
Creating localized microgravity environments through free-fall systems is of great significance for studying material solidification under microgravity conditions. Methods for achieving microgravity environments mainly include: drop towers, drop tubes, aircraft, rockets, and orbital spaceflight (e.g., satellites, space stations, space shuttles, etc.).
Characteristics of Alloy Solidification Under Microgravity
In a microgravity field, liquid metals exhibit the following characteristics:
1. Convection caused by gravity in the liquid metal is almost eliminated.
2. Phenomena such as sedimentation, flotation, and compositional segregation caused by density differences among different substances in the liquid metal nearly disappear.
3. The effects of surface tension and wettability become more prominent.
4. Solidification can occur under high vacuum conditions. On spacecraft orbiting 500 km above Earth’s surface, the vacuum can reach as high as 133.32×10⁻⁸ Pa. Under such high vacuum, gases within the metal materials can be eliminated, allowing the production of high-purity materials.
5. Solidification can occur under conditions of rapid cooling in the liquid state.
6. On Earth, melting active metals and high-melting-point metals often faces challenges due to crucible materials and ambient air. However, in a microgravity field, the melt can float without the need for a crucible, eliminating concerns over crucible contamination or impurities introduced from the container. In the microgravity field of space, the high vacuum eliminates the influence of air, making it easier to melt even the most reactive or high-melting-point metals.
Generally speaking, microgravity solidification is costly to achieve and is therefore mainly applied in the development of high-tech materials. Traditional processes such as investment casting typically do not employ microgravity solidification.
Post time: Jun-09-2025