Up to now, it is a very important research topic to improve the strength and damping performance of the alloy at the same time, but it still faces huge challenges. This is because these two qualities are mutually restrictive, and they are mutually reinforcing. The researchers of the Institute of Metals and the staff of Lawrence Berkeley National Laboratory in the United States have proposed a new multi-path design strategy to break this dilemma, and developed a Mg-NiTi composite material that can achieve high strength and high damping And high energy absorption. The manufacturing method is to inject Mg melt into a three-dimensionally printed NiTi stent. Multiphase materials exhibit unique mechanical properties. At room temperature and high temperature, the mechanical properties are improved and the damage tolerance is also improved. At the same time, it has high strength and high damping characteristics, and also has excellent energy absorption characteristics, which is not available in traditional metals or alloys. The deformed shape and strength can be recovered after heat treatment. This research has opened up new directions for engineering and biological applications of magnesium alloys.
Lightweight Mg and magnesium alloys are the lightest of all engineering structural metals, and their specific strength is relatively high. However, its bearing capacity at low and high temperatures is relatively poor, and its toughness and shape are also poor compared to steel and aluminum. But the only opposite is that the damping performance of magnesium alloys is better. It can be said that Mg and its alloys are the materials with the best damping performance among all engineering structural metals. This is because magnesium and its alloys are prone to twinning, dislocation movement, and the dislocation pinning effect is weak when there are defects or impurities. This feature allows magnesium alloys to be used in applications where mechanical energy is dissipated and vibration is reduced. However, strength and damping performance are often mutually exclusive and trade-off performance. Commonly used strengthening methods of magnesium alloys will reduce the damping performance of magnesium alloys during strengthening. This contradiction is also true for magnesium alloy composites. Magnesium alloy composites generally add a second phase to the magnesium alloy matrix, which often results in a decrease in the toughness of the magnesium alloy. This is because the discontinuity of the strengthening phase causes stress concentration in the matrix. In addition, most engineering materials, magnesium alloys and their composite materials rarely recover their original shape and strength after damage or inelastic deformation. If the same durability or self-recovery performance as the shape memory alloy can be achieved in the magnesium alloy, it will open up new wireless possibilities for the time engineering application of the magnesium alloy and the application of the biological magnesium alloy.
To solve this problem, researchers from the Shenyang Institute of Metal Research, Chinese Academy of Sciences and Lawrence Berkeley National Laboratory in the United States collaborated to propose a multi-path design strategy to prepare multiphase Mg-NiTi materials on the basis of 3D printing. First, select the strengthening phase to strengthen magnesium, this strengthening phase is NiTi shape memory alloy. NiTi is a material with good damping properties among all metals. This alloy undergoes in-situ deformation due to the transformation of martensite to austenite at high temperatures, thereby returning to its original shape. At this time, the creep of magnesium has just begun, and only a very small stress level occurs. This internal stress due to the phase transition can provide the driving force for the deformation of the composite (complex phase) material. The second step is to design a three-dimensional interpenetrating phase structure, so that the individual phase cycles are continuous and connected to each other. At this time, the integrity and continuity of the NiTi alloy structure produce high strength and sufficient recovery effect so that it can effectively improve the load-bearing capacity. This structure can improve the damping performance and increase the damage tolerance. In the third step, a two-step additive manufacturing method is used to manufacture the NiTi stent, and then the magnesium melt is extruded into the structure of the manufactured Mg-NiTi composite material by pressure infiltration. Additive manufacturing technology provides a variable solution to control the structure of NiTi reinforced composites. For example, the melt penetration effect is realized by the huge melting point difference between NiTti and Mg (NiTi melting point is 1310K, Mg melting point is 648K) and the interaction and dissolution of the two may be very small, at this time not too high temperature The melting of Mg can be achieved under the following conditions.
This research provides a new idea for the preparation and characterization of Mg-NiTi composite materials that simultaneously achieve high strength, excellent damping performance, good energy absorption characteristics, and significant self-recovery capabilities. The results show that an unprecedented Mg total performance is obtained, with high strength, high damping performance and high energy absorption characteristics. This design idea and the obtained research results have opened up new directions and provided new design ideas for the application of magnesium alloy engineering structure and the application of biomagnesium alloy.