Effect of copper addition on solidification behavior, microstructure and hardness of modified low-Ni ductile Ni-resist alloy

M. Aminuddin; Mohd Rashidi Maarof

doi:10.15282/ijame.23.3.2026.13.1049

Authors

M. Aminuddin Faculty of Mechanical and Automotive Engineering Technology, Universiti Malaysia Pahang Al-Sultan Abdullah, 26600 Pekan, Pahang, Malaysia , Universiti Malaysia Pahang Al-Sultan Abdullah
Mohd Rashidi Maarof Faculty of Mechanical and Automotive Engineering Technology, Universiti Malaysia Pahang Al-Sultan Abdullah, 26600 Pekan, Pahang, Malaysia , Universiti Malaysia Pahang Al-Sultan Abdullah https://orcid.org/0000-0001-5106-6104

DOI:

https://doi.org/10.15282/ijame.23.3.2026.13.1049

Keywords:

Ductile Ni-resist, Copper addition, Nickel substitution, Solidification, Microsegregation, Graphite nodularity, Dendritic arm spacing, Hardness

Abstract

Because of their excellent thermal properties and stable austenitic matrix, ductile Ni-resist alloys are widely used in corrosion-resistant and high-temperature applications. However, the high nickel content required to produce traditional Ni-resistant alloys considerably increases production costs. To assess the impact of Cu substitution on the solidification behavior, microstructural evolution, segregation characteristics, and hardness response, modified ductile Ni-resist alloys with a reduced Ni content (18 wt.% Ni) and varying Cu additions (6–10 wt.% Cu) were prepared. Induction melting, in-mold nodularization, and inoculation were used to create the alloy specimens. X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM–EDS), and dendritic arm spacing analysis were used to characterize the microstructure. The dendritic arm spacing (DAS) increased from approximately 240 to 250 µm, and the secondary dendritic arm spacing increased from 20 to 24 µm, indicating that the increased Cu content promoted interdendritic segregation and coarsening of dendrites. With increasing Cu addition, graphite nodularity gradually dropped from 75.1 ± 0.3% to 71.3 ± 0.1%, and nodule count dropped from 213.0 ± 1.0 to 201.7 ± 0.6 nodules/mm². Cu enrichment in the interdendritic and grain boundary regions was confirmed by SEM-EDS analysis, whereas Ni remained comparatively evenly distributed within the γ-austenitic matrix. With a γ-Fe content of approximately 94.61%, XRD analysis confirmed that the FCC austenitic phase was stable in all compositions. Owing to solid-solution strengthening and solute segregation, the macro-hardness in the Cu-rich interdendritic regions increased from 160.0 ± 8.7 HB to 194.3 ± 5.1 HB, whereas the micro-hardness increased from approximately 215.7 ± 7.4 HV to 298.3 ± 1.5 HV. The results show that partial substitution of Cu for Ni can preserve a stable austenitic structure while altering the morphology and hardness behavior of graphite, offering valuable information for the creation of less expensive ductile Ni-resist alloys with regulated microstructural performance.

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