Early-stage local melting during solid-state sintering of a Cu-Ni-Ti-Zr-Hf alloy: A combined thermodynamic and kinetic analysis
Abstract
Complex concentrated alloys (CCAs) combining elements from 3d transition and refractory groups, specifically Cu-Ni-Ti-Zr-Hf-based shape memory systems, exhibit excellent functional properties but present significant manufacturing challenges via powder metallurgy. In this study, a non-equimolar Cu15Ni35Ti25Zr12.5Hf12.5 (at. %) alloy was successfully produced by induction melting, followed by atomization and subsequent consolidation via Spark Plasma Sintering (SPS) at temperatures ranging from 850 to 1100 C. Although global equilibrium phase diagrams predict solid-state stability up to 1260 C, localized melting unexpectedly occurred during SPS at 1100 C. By combining retrospective Scheil-Gulliver solidification simulations with 2D local equilibrium heat maps, we demonstrate that this early-stage melting is not driven by macroscopic thermal gradients, but by microsegregation inherited from atomization. During solid-state heating, thermally activated short-range diffusion, accelerated by high defect densities at particle interfaces, partitions Ti towards the interparticle network, leaving Cu-enriched regions (up to ~41 at. %) within the particle interiors. Owing to the strongly negative mixing enthalpy of Cu with Hf (-19.2 kJ/mol for ΔHmixl−l) and, to a lesser extent, with Ti, the local solidus of these Cu-rich regions is dramatically depressed. Upon heating to 1100 C, these regions cross their local solidus and form a liquid phase, whose solidification produces the Cu-Hf co-segregation. This framework accounts for localized melting phenomena in rapidly solidified CCA powders containing low-melting constituents with strong negative mixing enthalpies.
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BibTeX
@misc{skolakova2026earlystage,
title = {{Early-stage local melting during solid-state sintering of a Cu-Ni-Ti-Zr-Hf alloy: A combined thermodynamic and kinetic analysis}},
author = {Andrea Skolakova and Hana Lesakova and Frantisek Lukac and Marketa Jarosova and Jan Pinc},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.27825},
eprint = {2610.27825},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.27825},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Early-stage local melting during solid-state sintering of a Cu-Ni-Ti-Zr-Hf alloy: A combined thermodynamic and kinetic analysis
AU - Andrea Skolakova
AU - Hana Lesakova
AU - Frantisek Lukac
AU - Marketa Jarosova
AU - Jan Pinc
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.27825
UR - https://arxiv.org/abs/2610.27825
AB - Complex concentrated alloys (CCAs) combining elements from 3d transition and refractory groups, specifically Cu-Ni-Ti-Zr-Hf-based shape memory systems, exhibit excellent functional properties but present significant manufacturing challenges via powder metallurgy. In this study, a non-equimolar Cu15Ni35Ti25Zr12.5Hf12.5 (at. %) alloy was successfully produced by induction melting, followed by atomization and subsequent consolidation via Spark Plasma Sintering (SPS) at temperatures ranging from 850 to 1100 C. Although global equilibrium phase diagrams predict solid-state stability up to 1260 C, localized melting unexpectedly occurred during SPS at 1100 C. By combining retrospective Scheil-Gulliver solidification simulations with 2D local equilibrium heat maps, we demonstrate that this early-stage melting is not driven by macroscopic thermal gradients, but by microsegregation inherited from atomization. During solid-state heating, thermally activated short-range diffusion, accelerated by high defect densities at particle interfaces, partitions Ti towards the interparticle network, leaving Cu-enriched regions (up to ~41 at. %) within the particle interiors. Owing to the strongly negative mixing enthalpy of Cu with Hf (-19.2 kJ/mol for ΔH_mix^l−l) and, to a lesser extent, with Ti, the local solidus of these Cu-rich regions is dramatically depressed. Upon heating to 1100 C, these regions cross their local solidus and form a liquid phase, whose solidification produces the Cu-Hf co-segregation. This framework accounts for localized melting phenomena in rapidly solidified CCA powders containing low-melting constituents with strong negative mixing enthalpies.
ER -