Preparation And Properties Of Fe-based Bulk Amorphous Alloys

Fe-base bulk amorphous alloys have potential application for their high strength, high thermal stability, good soft magnetic and corrosion resistant properties. For obtaining larger amorphous samples, high purity raw materials or flux treatment methods were applied during the preparation process. This is unfavorable for practical application. In order to lower the cost and simplify the production process, we prepared Fe-base bulk amorphous alloys using copper mould casting the raw materials in industry grade. The thermal, magnetic, mechanical and corrosion resistant properties of the samples were investigated by means of X-ray diffractometry (XRD), differential scanning calorimetry(DSC), compression test, scanning electron microscopy(SEM) and corrosion resistant test. The work included the following:(1) Prepared Fe-Cr-Mo-Er-C-B bulk metallic glass successfully with good forming ability in diameter of 8mm. The supercooled liquid region was 50K or so, reduced glass transition temperature was 0.584, and the composition was nearly eutectic. Based on the relationship between glass forming ability with Al content, we got Turnbull's rule was fit for the judging of the glass forming ability in this system. Then the compression test performed on the Φ2 rod, found the fracture strength improved from 3.4GPa to 3.7GPa. With regard to the fracture morphology, a novel striation was found in the mirror zone. The size of striation was related to the rupture toughness, the fracture of brittle metallic glass was a soft mechanism on nm scale. The birth of the striation was a kind of mutual effect of fracture elastic wave and dynamic expansion of fracture. Because the strength of fracture elastic wave and fracture strength were direct ratio, for the lower toughness (smaller plastic deformation zone), it is easier birth of striation on fracture. With regard to the corrosion resistant properties in 3.5wt% NaCl solution, Fe-based metallic glass was an ideal corrosion resistat material in Cl^-1 solution instead of stainless steel. It had a broad blunt section near 1000mV, low current density, and was a kind of coat for 304stainless steel.(2) To analysis the judgments of glass forming ability, we added Al, Co in Fe-Cr-Mo-(Y, Gd)-C-B system. It was found in Fe-Cr-Mo-Y-C-B system the glass forming ability was improved with Al addition, but the tendency was not described by the Turnbull's rule. It may be the Al, Co addition deleterious for the high density of interface in the alloys, therefore, the low content of Al, Co was not enough for the negative effect but high content would. For the corrosion resistant properties, in Fe(Al)-Cr-Mo-Y-C-B system, when Al is 3at%, the corrosion current density and blunt current density were nm/cm² grade, which demonstrated the good corrosion resistant properties of amorphous alloys.(3) Explored the process of the coat manufacture, since the thickness was only few μm now.