シンクロトロン光X線CTによるガスアトマイズ粉末に含まれる気孔量評価およびガス種の影響調査

抄録

The presence of pores in gas-atomized alloy powders induces a significant deterioration in the properties of the final product. However, there is no established technique to quantitatively analyze the porosity of gas-atomized powders. In this study, the pores in gas-atomized amorphous Fe₇₆Si₉B₁₀P₅ powder particles prepared under different atomization conditions were analyzed in detail using synchrotron radiation X-ray computed tomography. This technique allowed the detection of small pores with diameters below 10 µm. It also enabled the quantification of the porosity; thus, the pore diameter and volume ratio under different atomization conditions were determined. The volume ratio of the pores with the use of low-pressure Ar as the atomization gas was lower than that with the use of high-pressure Ar. The use of a low-pressure gas during spraying induced an increase in the diameter of the powder particles, thereby resulting in the presence of numerous irregular-shaped particles. The results of X-ray diffraction confirmed the partial precipitation of a crystalline phase with a decrease in the cooling rate. The use of 3 or 7% Ar–H₂ mixtures as the atomization gas induced a decrease in the number and volume of pores, without affecting the particle size and cooling rate. The presence of H₂ as a reducing gas suppressed the surface oxidation of the droplet during the atomization of the molten-metal stream, which allowed trapped gas bubbles to be efficiently removed before solidification.