Effect of Stress on Properties of Tungsten Alloys

Tungsten Alloy is an alloy material made by powder metallurgy process or injection molding technology with refractory metal tungsten as the hard phase and nickel, iron, copper, cobalt or molybdenum as the bonding phase. It has excellent thermal, mechanical, chemical and electrical properties and is widely used in high-tech industries. However, the properties of tungsten alloys are not static, and are affected by many factors such as processing stress.

Tungsten alloy processing stress refers to the forces that interact with each other in the alloy, mainly caused by machining. Mechanical processing will change the disorderly oriented polycrystalline material into a material with preferred orientation, and will elongate the grains, which will deform the second phase of insoluble impurities or porosity and other defects in the material, thus generating large processing stress on the material surface.

Due to the existence of stress, tungsten alloys are more likely to appear cracking, warping and deformation after being subjected to external actions, thus affecting the mechanical properties. Generally, the greater the processing stress is, the worse the mechanical properties (such as impact toughness and tensile properties) of tungsten alloys are; On the contrary, the mechanical properties are better.

The processing stress of tungsten nickel iron alloy can be eliminated by vacuum heat treatment. The research shows that in the process of high temperature vacuum heat treatment, tungsten, nickel and iron elements on the tungsten based interface will mutually diffuse, resulting in the increase of nickel and iron content on the side of tungsten particles at the tungsten based interface, and the decrease of nickel and iron content on the side of bonding phase, thus enhancing the bonding force of tungsten based interface. In addition, vacuum heat treatment can also make the brittle inclusions gathered between the tungsten particle phase and the bonding phase dissolve, reduce the segregation of the brittle inclusions at the interface, and thus enhance the interface bonding force.