Properties of Nb521 niobium-tungsten alloy

Tungsten is an effective strengthening element for niobium, but with the increase of tungsten addition, the plasticity and brittle transition temperature of the alloy will increase, and the grain will grow significantly. Therefore, to obtain high-strength niobium-tungsten alloy, must be appropriate to control the addition of tungsten, but also must be appropriate to join the grain refinement, reduce the plasticity of a brittle transition temperature of elements such as zirconium and hafnium, etc. 1961, the United States developed a successful Nb-10W-2.5Zr alloy used for the space shuttle skin, and later developed into a Nb-10W-1Zr-0.1C alloy. the early 70's, China also NbWl0Zr2.5 and NbWl0Zr1C0.1 alloys were successfully developed in China in the early 1970s.

Niobium-tungsten alloys can be divided into solid solution strengthened alloys and alloys combined with solid solution strengthening and diffusion strengthening according to the strengthening method.

Since 1999, domestic aerospace units have been seeking a new type of niobium-based alloy that can be used at a temperature of more than 1600℃. Ningxia Oriental Tantalum Industry Co., Ltd. and Northwest Nonferrous Metals Research Institute have successively developed two alloys, Nb521 (Nb-5W-2Mo-1Zr- 0.01C) and Nb522 (Nb-5W-2Mo-2Zr), which are collectively referred to as niobium-tungsten alloys.

These alloys are alloyed with W, Mo, and Zr as alloying elements, and the main strengthening mechanism is solid solution strengthening, with recrystallization temperatures ranging from 1350℃ to 1500℃. Among them, Nb521 also uses 600-1000ppm C elements to form NbC, ZrC second phase, solid solution + precipitation strengthening method to comprehensively enhance the alloy's strength and machinability.

Niobium-tungsten alloy has similar density (8.6-9.0g-cm-3) and better high-temperature strength compared with C103 alloy. However, due to the addition of a large number of W, Mo and other reinforcing elements, the ingot of the room temperature strength is higher, the plasticity is poorer, in the ingot processing of high-temperature extrusion is used to refine the ingot grain. The plasticity of the alloy ingot is greatly improved after extrusion, and the required specifications of rods, plates and forgings, spinning parts can be obtained through forging, rolling, spinning and other processing methods.
Chemical composition of NB521 niobium-tungsten alloy:

Zr: 0.75-0.98

Mo: 1.60-2.10

W: 4.5-5.1