Ultrasonic NDT Used in Tungsten Copper Contacts

We introduce how to measure the porosity of powder metallurgy products by ultrasonic NDT based on the principle of pulse reflection, and through metallographic observation of fracture morphology and to further analyze the relationship between the test results and powder metallurgy product defects and related performance. In general, we use ultrasonic detector and supporting direct probe to determine defects burial depth according to the position of the defect wave, and estimate the equivalent defect size according to defect wave amplitude.

For instance, there is an experiment that uses NaCl as a pore-forming agent is mixed with tungsten powder and copper powder, obtained by the method of powder metallurgy tungsten copper contacts with different porosity. By microstructure photograph can be seen that with the increasing amount of pore former, the pore volume occupied by proportionately decrease, lower porosity means relatively dense structure and the loose structure has higher porosity. And then analyze based on the width of the peak intensity of different porosity defects resulting waves and waves of difference.

The sample with pores small and few, due to the pore size is smaller than the wavelength of ultrasound, which can not form scattering. At this time only by the noise signal itself affected by the material of matrix, and the ultrasonic scattering is weak, the waveform is smoother; on the contrary, the coarser pores and higher porosity will form the intensive scattering signal and the waveform will be sharper. Furthermore, with the increase of open porosity, defect wave peak will be significantly reduced. This is due to the absorption will increase with the increasing open porosity rate, sound waves encounter defects reflected sound waves to reduce the intensity of the inevitable, the peak value decreases correspondly. And there is a certain relationship between the speed of sound and the opening rate and hardness of the sample. With the sound velocity decreases, the opening rate increases, the density decreases, the hardness decreases. As a result of increasing amount of pores, the absorption of ultrasonic enhanced, thus the speed of sound decreased. The severe plastic deformation will be affected by increasing porosity. However, materials of different elastic module are different, need to draw the curve separately.

In a word, Ultrasonic nondestructive testing the scattering wave waveform can reflect the tungsten copper contacts, and other powder metallurgy products and the number of pores in the state to some extent. Scattered wave is smoother, no obvious ups and downs, which indicate that the porosity of the material is lower, and may be less than the ultrasonic wavelength; or scattered wave signal messy and there is significant ups and downs, it indicates the porosity defects is more. In addition, nondestructive has certain linear relationship between the detected speed of sound and material porosity. Reducing the speed of sound material represents the increase in porosity, at the same time can objectively reflect the overall performance of other materials.

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