Analysis of the Application Prospects of Mechanical Alloying Preparation Powder Materials

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Mechanical Alloying(abbreviation MA), is a kind of pulverizing technology used for making the either balanced or unbalanced powdered alloy or composite powder from elements of powder. It makes use of the long and fierce grinding between powder particles and powder particles, and between powder particles and grinding balls in the high energy ball mills to crush and tear the metal powders. A new surface will be formed after cold welding with each other and gradual alloying, and after repetition, the goal of mechanical alloying can be achieved finally.

Mechanical alloying was put forward in the late 1960s by Benjamin et al from American International Nickel Company. At that time, it was mainly used to produce the nickel-based and iron-based superalloy with the precipitation hardening and oxide dispersion hardening effects. In the early 1980s, American scientist Koch and his colleagues successfully obtained the Ni60Nb40 amorphous powder via the mechanical alloying techniques. After that, this method developed fast. After a lot of researches and tests, W.Schlum and H.Grewe put forward the idea that the mechanical alloying method can be used to make nanocrystals. Later, Fecht et al successfully made nano-crystalline ultrafine grain materials by mechanical alloying, proposing a new way in the field of mechanical alloying technology. Now, mechanical alloying method has been successfully applied to the preparation and manufacturing of Nanocrystalline dispersion strengthened materials, magnetic materials, superconducting materials, amorphous materials , nanocrystalline materials, light metal with high specific strength materials and dispersed solid solution. The United States, Germany, Japan and other developed countries have invested a lot of manpower, material and financial resources to carry out a lot of research work and have achieved remarkable results of industrial production. The INCO Ltd has built iron, nickel and aluminum oxide dispersion strengthened alloys mechanical alloying production lines, with production capacity of 350t/years. In 1988, China mechanical alloying research work began, and very significant progress has been made in more than ten years.

The Basic Principle of the Mechanical Alloying

In 1988, Japan’s Ninomiya Hideo put forward the calendering and repeated folding model. When reduction rate is 1/a, after n times calendering, the thickness changes from the original d0 to d, and d = d0 (1/a). If using the mechanical alloying method to mix calender these 2 elements 10 times and set 1/a ≈ 316296, then, the particle size can be thinned to a thickness of one hundred thousandth of its original. Very tiny double overlap powder will be formed. If calendering more times, it can reach the fine organizational structure of nanoscale. Thus, the mechanical alloying methods make the powder alloying possible in the solid state. In 1990, Atzmon proposed another alternative mechanical alloying principle—mechanical sensor self-propagating reaction mechanism, namely, the intermetallic compound is not a nucleation and growth process, but suddenly broke formation. Because the self-propagating combustion reaction ignition temperature and grain size of the powder particles and related ignition temperature decreases with the powder particles or grain size decreases.

When the powder particles or grains is reduced to a certain extent , the local high temperature mechanical milling process collisions can “ignite” powder alloy showed a sudden eruption.

Now, it is generally considered that the most mechanical alloying milling process is controlled by diffusion. The basic mechanical alloying process is repeated mixing of the powder particles, crushing and cold welding, a mixture of several metal elements or nonmetal elements in the powder milling process will form a high density of dislocations, while gradually refined grains to nanometer, which provides fast access for mutual diffusion of atoms. Under certain conditions, the core alloy phase is formed. Further milling process is necessary until all the elements powder formed into alloy phase and gradually grow bigger.