Physical Basis of Molybdenum and TZM Alloy Plastic Working

Before molybdenum and TZM alloy plastic should a certain understanding of its brittleness, toughness, fracture behavior and other physical properties, to understand the physical basis of the material, in order to better carry out plastic working. The plasticity of material refers to the deformation degree before breaking. The strength refers to a kind of ability to resist deformation and fracture. And toughness is the ability to absorb energy from plastic deformation to fracture of the whole process. Molybdenum and TZM alloy has high strength, but the plastic deformation is poor, namely poor toughness, having obvious brittleness.

The brittleness and toughness of material will changes as the temperature changes, namely, plastic-brittle transition temperature (DBTT). In the above DBTT temperature range, under high stress the plastic deformation is more smoothly, and the resulting products showed good toughness. Conversely, at temperatures below the DBTT to process deformation is prone to produce brittle fracture with different forms. Different metal materials, the plastic-brittle transition temperature is different, tungsten plastic-brittle transition temperature is generally about 400 ℃ and molybdenum DBTT is near the room temperature. High plastic-brittle transition temperature, the brittle of material is high which is not conducive to material processing. In order to reduce the plastic-brittle transition temperature of the material the measure is to overcome the brittleness and increase the toughness. The effect factors of material’s plastic-brittle transition temperature include purity, grain size, deformation degree, stress and alloying element material.

Molybdenum and its alloys low (or room) recrystallization brittleness is unlike copper, aluminum. After recrystallization annealed, copper and aluminum will form equiaxial recrystallization grain structure has excellent room temperature plastic processing, which can easily be processed at room temperature. However, molybdenum and TZM alloy after recrystallization has high brittleness at room temperature, so during the processing and using is prone to brittle fracture.

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