Abstract
In this study, pulse-width modulation of laser power was identified as a feasible means for varying the chemical gradient in copper–nickel-graded materials. Graded material deposits of 70 wt. %. copper-30 wt. %. nickel on 100 wt. %. nickel and vice versa were deposited and characterized. The 70/30 copper–nickel weight ratio in the feedstock powder was achieved through blending elemental copper and 96 wt. %. Ni–Delero-22 alloy. At the dissimilar material interface over the course of four layers, the duty cycle of power was ramped down from a high value to optimized deposition conditions. This change was theorized to influence the remelting and deposition height, and by extension, vary the chemistry gradient. X-ray Energy Dispersive Spectroscopy (EDS) analysis showed significant differences in the span and nature of chemistry gradient with varying duty cycles. These observations were also supported by the variation in microhardness values across the interface. The influence of different chemistry gradients on the tensile performance was observed through mini-tensile testing, coupled with Digital Image Correlation (DIC). The strain fields from the DIC analysis showed variations in strain for different chemistry gradients. The strength measurements from these specimens were also different for different chemistry gradients. The site of failure was observed to always occur within the copper-rich region.
Highlights
Graded materials (FGM), are monolithic inhomogeneous materials whose anisotropy is tailored per the designer’s definition
A custom built 3-axis Computer Numerical Control (CNC) system was used for facilitating motion during deposition
The width was expected to be the same, since the power/beam intensity was the same for all of the duty cycles [28]. This variation in melt pool dimensions was theorized to vary the remelting between successive layers and the volume of the material deposited in every layer
Summary
Graded materials (FGM), are monolithic inhomogeneous materials whose anisotropy is tailored per the designer’s definition. [2,3,4,5,6] Techniques such as plasma spraying [4], die compaction [7], powder metallurgy [8], slip casting [9], and additive manufacturing [10,11,12,13,14,15] have been shown to be successful in fabricating FGMs. While successful, all of the above processes, excluding additive manufacturing, possess limited scope for attaining fine resolutions in grading material composition. All of the above processes, excluding additive manufacturing, possess limited scope for attaining fine resolutions in grading material composition The influence of varying chemistry on hardness and tensile performance was investigated
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