Plastic processing of niobium alloy

Plastic processing technology is divided into two kinds: volume forming and sheet forming. Volume forming process refers to the mass transfer of metal materials to obtain various profiles, such as forging, extrusion, rolling and other processes. Bulk forming process is characterized by large plastic deformation of metal materials, so most of it is carried out under hot state. Sheet metal forming technology refers to the use of related abrasive plastic processing of sheet metal, such as stamping, spinning and other processes. Sheet metal forming plastic deformation is not necessarily large, but relative to the abrasive movement more, usually at room temperature.

Forging and extrusion in the plastic processing process of niobium alloys are generally hot processed at the recrystallization temperature of the niobium alloy or slightly higher than the recrystallization temperature. For different energy alloys, the recrystallization temperature is different, and there are usually several typical ones. The hot working temperature of energy alloy is 1000~1350℃. The niobium alloy is extremely easy to react with oxygen during the processing at such a high temperature, so measures such as metal cladding, coating or inert gas protection and heating must be adopted during the hot processing. Since the niobium alloy ingot has as-cast structure, the grains should be broken as much as possible to obtain a better machinability structure. Compared with other materials like steel or titanium alloys, niobium alloys have greater flow stress at hot working temperature, which puts a very large pressure on the processing tools of niobium alloy materials.

The plastic processing of niobium alloy is also called pressure processing. It is the processing process of the plastic deformation of niobium alloy material so as to achieve the shape of products needed by people. Through plastic deformation, saw alloy material grain size can be fine, grain structure uniformity, texture, so as to improve the structure and properties of niobium alloy material, improve the flexibility and machinability of niobium alloy material later processing, further improve the final product yield and mechanical properties. According to the different temperature of plastic processing technology, it can be divided into hot processing and cold processing. Hot processing is characterized by large deformation processing of niobium alloy materials at high temperature, suitable for large size or weight of niobium alloy materials, mostly used for product opening or semi-finished products processing. The main deformation modes of hot working are staggered-slip, climbing, cross-slip and multi-slip system. Taylor polycrystalline constraint relaxation, grain rotation and rotation, the slip system to the direction of external force; Grain boundary weakening and sliding deformation; Strain transfer is very short and diffusion creep occurs. From the microscopic structure, the ingot dendrites and inclusions are elongated along the deformation direction into strip, line or lamellar processing streamline structure. Cold processing is mainly applied to niobium alloy material surface and dimensional precision requirements of the product processing. The main degeneration mode of cold working is there is cross-slip and a small amount of cross-slip. The deformation texture is similar to that of hot-working, but the boundary strength is higher than that of in-grain. When the dislocation slips to the grain boundary, it stops sliding and forms a dislocation heap. The stress concentration generated by the dislocation heap together with the external force starts the dislocation source of adjacent grains, and so on, the deformation to the whole sheet alloy material. In microstructure, the cold processing elongates the grains along the deformation direction of the niobium alloy, and the elongation increases with the increase of deformation amount, forming fibrous or lamellar structure under a large amount of deformation.

Niobium alloys usually use processing techniques such as extrusion, forging, drawing, stamping and spinning to produce niobium bar, niobium sheet, niobium tube, niobium wire and special-shaped parts.