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Mechanical alloying (abbreviated as MA) is a powder technology for preparing alloy powders or composite powders having a balanced or non-equilibrium phase composition from elemental powders. It is in a high-energy ball mill, where very intense grinding occurs between the powder particles and between the powder particles and the grinding balls. The powder is crushed and torn, and the newly formed surfaces are cold-welded to each other and gradually alloyed. Repeatedly, eventually achieving the purpose of mechanical alloying.
Mechanical alloying was developed by Benjamin et al. of the United States in late 1960s when it was mainly used to prepare nickel-based and iron-based superalloys with both precipitation hardening and oxide dispersion hardening effects. In the early 1980s, American scientist Koch and his colleagues succeeded in obtaining Ni60Nb40 amorphous powder by means of mechanical alloying. Since then, the method has developed rapidly. After extensive experiments by W. Schlum and H. Grewe, it was proposed in 1988 that the mechanical alloying method could produce nanocrystals. Later, Fecht successfully fabricated nano-scale ultrafine-grained alloys using mechanical alloying methods, creating a new field of mechanical alloying technology. Nowadays, mechanical alloying methods have been successfully applied to the preparation of nano-scale ultra-fine grain dispersion strengthening materials, magnetic materials, superconducting materials, amorphous materials, nanocrystalline materials, light metal high-strength materials, and supersaturated dispersion solid solutions. Developed countries such as the United States, Germany, and Japan have invested a great deal of manpower, material resources, and financial resources. They have done a great deal of research work and achieved remarkable results, and have already achieved industrialized production. US INCO has built a mechanical alloying line of iron, nickel and aluminum oxide dispersion-strengthened alloys with a production capacity of 350t/year. The research work on mechanical alloying in China began in 1988 and has made remarkable progress in more than a decade.
Mechanical alloying
1 Basic principles
In 1988, Japan's Shinmiya Hideo proposed a rolling and refolding model. When the reduction rate is 1/a, after n times of rolling, the thickness is changed from the original d0 to d, and d=d0(1/a). If the powders of the two elements are mixed and calendered 10 times and set to 1/a≈31 6296 by the mechanical alloy method, the particle size of the powder can be reduced to one hundred thousandth of its original thickness, resulting in a very slight double layer overlap. The powder can be nanometer-sized fine structure after more calendering. Therefore, the mechanical alloying method may cause alloying of the powder in the solid state. In 1990, Atzmon proposed another principle of mechanical alloying. The mechanism of mechanically induced self-propagating reaction is that intermetallic compounds are not a process of nucleation and growth, but suddenly formed. Because the ignition temperature of the combustion self-propagating reaction is related to the size of the powder particles and the grain size, the ignition temperature decreases as the size of the powder particles or grains decreases. As the powder particles or grains decrease to a certain extent, the local high temperatures created by mechanical collisions during ball milling can "ignite" the powder, manifesting itself as a sudden burst of alloy formation.
At present, it is generally believed that most mechanical alloying processes in ball milling are controlled by diffusion. The basic process of mechanical alloying is repeated mixing, crushing and cold welding of powder particles. A mixture of several metal elements or non-metallic element powders will form high-density dislocations during ball milling, and the grains will gradually refine to the nanometer level. This provides a fast channel for the interdiffusion of atoms and, under certain conditions, the nuclei of the alloy phase are formed. In the further milling process, all the elemental powders form an alloy phase and gradually grow.
Mechanical alloying was developed by Benjamin et al. of the United States in late 1960s when it was mainly used to prepare nickel-based and iron-based superalloys with both precipitation hardening and oxide dispersion hardening effects. In the early 1980s, American scientist Koch and his colleagues succeeded in obtaining Ni60Nb40 amorphous powder by means of mechanical alloying. Since then, the method has developed rapidly. After extensive experiments by W. Schlum and H. Grewe, it was proposed in 1988 that the mechanical alloying method could produce nanocrystals. Later, Fecht successfully fabricated nano-scale ultrafine-grained alloys using mechanical alloying methods, creating a new field of mechanical alloying technology. Nowadays, mechanical alloying methods have been successfully applied to the preparation of nano-scale ultra-fine grain dispersion strengthening materials, magnetic materials, superconducting materials, amorphous materials, nanocrystalline materials, light metal high-strength materials, and supersaturated dispersion solid solutions. Developed countries such as the United States, Germany, and Japan have invested a great deal of manpower, material resources, and financial resources. They have done a great deal of research work and achieved remarkable results, and have already achieved industrialized production. US INCO has built a mechanical alloying line of iron, nickel and aluminum oxide dispersion-strengthened alloys with a production capacity of 350t/year. The research work on mechanical alloying in China began in 1988 and has made remarkable progress in more than a decade.
Mechanical alloying
1 Basic principles
In 1988, Japan's Shinmiya Hideo proposed a rolling and refolding model. When the reduction rate is 1/a, after n times of rolling, the thickness is changed from the original d0 to d, and d=d0(1/a). If the powders of the two elements are mixed and calendered 10 times and set to 1/a≈31 6296 by the mechanical alloy method, the particle size of the powder can be reduced to one hundred thousandth of its original thickness, resulting in a very slight double layer overlap. The powder can be nanometer-sized fine structure after more calendering. Therefore, the mechanical alloying method may cause alloying of the powder in the solid state. In 1990, Atzmon proposed another principle of mechanical alloying. The mechanism of mechanically induced self-propagating reaction is that intermetallic compounds are not a process of nucleation and growth, but suddenly formed. Because the ignition temperature of the combustion self-propagating reaction is related to the size of the powder particles and the grain size, the ignition temperature decreases as the size of the powder particles or grains decreases. As the powder particles or grains decrease to a certain extent, the local high temperatures created by mechanical collisions during ball milling can "ignite" the powder, manifesting itself as a sudden burst of alloy formation.
At present, it is generally believed that most mechanical alloying processes in ball milling are controlled by diffusion. The basic process of mechanical alloying is repeated mixing, crushing and cold welding of powder particles. A mixture of several metal elements or non-metallic element powders will form high-density dislocations during ball milling, and the grains will gradually refine to the nanometer level. This provides a fast channel for the interdiffusion of atoms and, under certain conditions, the nuclei of the alloy phase are formed. In the further milling process, all the elemental powders form an alloy phase and gradually grow.
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