Mechanical Properties’ Impacts on Processing Tungsten and Molybdenum Materials
The mechanical properties of tungsten and molybdenum include elastic and inelastic reactions under the action of external forces. In the stamping process of metal materials, the performance relationship is an important index.
The main characteristics reflecting material properties are yield limit, strength limit, a ratio of yield to strength, hardness, elongation, section shrinkage, work hardening index, anisotropy coefficient, and elastic modulus.
These characteristics involve the following types of parameters:
1. Plastic parameters include elongation and section shrinkage.
2. Deformation resistance parameter is the ability of a material to restrain plastic deformation under the action of external force. The main parameters include tensile strength, compressive strength, and shear strength.
3. The yield strength parameter represents the stress required for plastic deformation of the material.
4. The elastic modulus parameter represents the index of material rigidity. The greater the rigidity, the smaller the elastic deformation of the tensile part.
5. Hardness parameter is the mechanical property index to measure the hardness and softness of solid materials. Hardness parameters can represent the elasticity, plasticity, deformation strengthening, strength, and toughness of materials. Under certain conditions, the hardness value can roughly infer the strength value of the material.
Besides, it should be noted that tungsten and molybdenum have high strength, high hardness, poor ductility at low temperature, and poor turning performance at room temperature. In the cutting process, the tungsten molybdenum material is easy to embrittle, and the turning tool is easy to wear.
Physical Properties’ Impacts on Processing Tungsten and Molybdenum Materials
The processing of tungsten includes stamping forming, surface coating, and connection. Because metal tungsten is a material difficult to be melted, tungsten has remarkable physical properties. The processing of tungsten materials is affected by the physical properties of tungsten materials. Take stamping forming as an example, stamping forming is to exert pressure on a tungsten sheet under the action of external force. Press machines or other equipment provide stamping pressure. Tungsten materials become section bar and required parts after separation or plastic deformation under pressure. Tungsten material has a body-centered cubic crystal form, so tungsten should be easy to process and form in theory because tungsten material has good plasticity and deformation properties. However, since the DBTT of tungsten is as high as 350 to 500 ℃, the processing temperature must be kept between the recrystallization temperature of tungsten and DBTT when stamping tungsten materials. Otherwise, the processing of tungsten material will fail due to fragmentation. The characteristics of tungsten materials determine the high DBTT of tungsten. In an active slip system, the ratio of bulk elastic modulus K of tungsten to shear modulus µ is low. Therefore, tungsten material has high brittleness and high DBTT. In addition, the interstitial impurities in grains have a significant effect on the brittleness of tungsten and aluminum. Oxygen in tungsten material is also a harmful element. A small amount of oxygen can make the DBTT of tungsten rise linearly.
The electroplating technology of tungsten materials has strict requirements for the structural design of electro-deposited coatings. Electroplating processing involves matching the expansion properties of the electroplating layer and substrate. During electroplating processing, the expansion coefficient of coating and substrate shall be matched as much as possible. The material’s melting point and its wettability to matrix must be considered in welding technology. Many kinds of solders can be used for brazing tungsten materials. The melting point of solder is from 618 ° C to 2995 ° C. Solder can be made of pure metal or alloy. Therefore, according to the usage, selecting the appropriate material with a good melting point and good wettability (That is to say, the infiltration angle is as slight as possible).