Investigating Laser Additive Manufacturing of Functionally Graded Ni-Cr-B-Si and SS 316L
6 Pages Posted: 12 Feb 2018
Date Written: December 21, 2017
Laser additive manufacturing (LAM) is a laser based solid freeform fabrication method used for “feature based design and manufacturing”. One of the interesting applications of LAM is the fabrication of functionally graded materials (FGM) for joining materials with different thermophysical properties. In the present work, a 2 kW fiber based LAM system is deployed for the fabrication of functionally graded Ni-Cr-B-Si alloy on SS 316L. Functional grading is achieved by varying the composition of NiCr-B-Si alloy and SS 316L. Trial experiments are performed to optimize the process parameters for LAM of Ni-Cr-B-Si layers on preheated substrate of SS 316L with qualification criteria of uniform regular crack free deposit. The microstructure and the mechanical properties are investigated using optical microscopy, microhardness and ball indentation testing. The optical microscopic examination revealed that a uniform regular crack free deposition could be made at optimum process parameters. The microstructural examination revealed the presence of dendritic microstructure at the top most layers. Subsequently, a gradual transition from dendritic to cellular microstructure is observed in lower layers. Vickers microhardness testing showed a gradual decline in the hardness of the sample from Ni-Cr-B-Si to SS 316L. The average hardness of 430.63 HV0.2 of 100% Ni-Cr-BSi is reduced to 185.5 HV0.2 at the substrate. Variation of hardness and energy stored by the material can be clearly observed from Ni-Cr-B-Si to other graded composition through ball indentation studies.
Keywords: Functionally Graded Materials, Laser Additive Manufacturing, Mechanical Property, Microstructure
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