Laser processing of Fe based bulk amorphous alloy coatings

Himanshu Sahasrabudhe

In this study, Laser Engineered Net Shaping (LENSTM), a solid freeform fabrication technique, was employed for the processing of Fe–based glass forming alloy powder on different metallic substrates whilst retaining the partial amorphous character of the feedstock powder. T hic was done in two ways. First, Fe-based bulk amorphous alloy (BAA) was coated on titanium. Multiple layers were deposited. These coatings were also laser remelted. In the second part, the Fe-based BAA powder with smaller size and with the addition of niobium was processed on zirconium. Hard, wear and corrosion resistant bulk amorphous alloys are of immense engineering interest. Controlling the evolving microstructure thus becomes difficult with traditional processing techniques and hence the properties are not fully achieved. LENSTM technology allows us to overcome these issues by partially retaining the amorphous character of the feedstock powder. Amorphous alloy powder of the composition (atomic %) of Cr<25 Mo<15 W<10 C<3 Mn<5 Si<2 B<5 Febalance was coated on commercially pure Ti. The coatings evolved as amorphous-crystalline composites. The coatings were further enriched in the amorphous phase by laser remelting. Microhardness numbers show a magnitude of increase in the hardness of the coating as compared to the Ti substrate. The wear volume in saline environment for one layer of Fe BAA coating was 3.23 x 10-5 mm3 /Nm as compared to 96.06 x 10-5 mm3 /Nm in the Ti substrate. These properties were enhanced after the laser remelting process. The coatings showed extremely low and localized fretting corrosion as compared to the heavy inter granular corrosion in titanium in saline environment. The second part focuses on the effect of smaller feed size powder and the addition Nb in the glass forming alloy besides the processing on Zr substrates. Microhardness, wear aspect of these Fe BAA coatings are studied with respect to the Zr substrate. Hardness of 1450±40 HV0.1 was recorded for the coating as compared to 165±8 HV0.1 for the Zr substrate. The wear volume of the Fe BAA coating was measured to be 0.77 x 10-5 mm3 /Nm, which was 41 times less than the Zr substrate of 31.70 x 10-5 mm3 /Nm.

Laser processing of Fe based bulk amorphous alloy coatings

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