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Electron Beam Welding Molybdenum and TZM Alloy

Using electron beam welding molybdenum and TZM alloy study the microstructure and fracture behavior of them, to understand the nature of intergranular brittleness, improving weldability. Electron beam welding molybdenum and TZM alloy the specific process parameters are as follows: working distance: 175mm; acceleration voltage: 50kV; focus point: surface; beam current: 50mA ; degree of vacuum: <6.7 * 10^-2Pa; welding speed: 3mm/s.

As below are some research results:
1. Molybdenum and TZM alloy welded joints brittle behavior began in the realm of fracture at 300K, then it expands by intergranular or transgranular mode;
2. Molybdenum and TZM alloy welded joints showed plastic failure when temperature is higher than 573K. TZM alloy has better high-temperature performance than molybdenum, so the welded joints of TZM shows better tensile properties than molybdenum welded joints;
3. In the state of welding, on the molybdenum grains boundaries nitrogen segregation will make it embrittlement, and it also make stress distribution not so uniform.
4. Molybdenum after welding will cause carbonization which will increase in yield stress and leads to plasticity have significant improvement at 300K;
5. After the welding, carbonization TZM alloy also showing plasticized effect, particularly at the 300K has about 50% elongation of the weld metal;
6. Carbon increases cohesion of grain boundary and the segregation and precipitation on the surface of the grain boundary can be effectively improved ductility.

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