Laser processing of Fe-based bulk amorphous alloy

Abstract

Laser processing of Fe–Cr–Mo–W–C–Mn–Si–B glass forming alloy components without losing feedstock's partial amorphous structure is successfully demonstrated using Laser Engineered Net Shaping (LENS(tm)) — a solid freeform fabrication technique. In spite of known decreasing quenching effect with increasing deposit thickness in this process, no significant microstructural differences were found from the first layer to the last layer of the part with 10mm diameter and 15mm height. SEM, XRD and DSC analysis of a laser processed alloy indicated retention of feedstock's partial amorphous structure. This has been achieved by maintaining lower prior deposit temperatures via a short time delay between successive laser scans, which also aided the glass stability during deposition of subsequent laser passes/layers. Estimated cooling rates indicated that under present experimental conditions every freshly deposited layer experienced a cooling rate much higher than it was required to achieve full amorphization in this alloy. However, incomplete melting of the coarse fraction of the powder during deposition restricted the formation of fully amorphous structure in the final parts. Current experimental results demonstrate that bulk amorphous components, for structural applications, can potentially be fabricated via process optimization of laser based direct manufacturing techniques.