11th April 2025

Effects of differential plasticity on thermally enhanced machining of calcium fluoride

J. Zhan, Y.J. Lee, H. Wang
Ceramics International 51 (2025) 12587–12599

Field-assisted augmentations are well-recognized for improving the machinability of brittle materials by enhancing their plasticity. However, the extent of such plasticity remains unclear to be optimally applied in manufacturing. This study explores the use of thermal addition to plasticize calcium fluoride (CaF2) single crystals and employs a novel approach by implementing a thermal gradient during deformation to better understand the dynamics of thermally activated differential plasticity. Scratch testing under high thermal gradient conditions displayed gradients in mechanical properties and crack formation, which were attributed to differences in plastic flow across regions with varying temperatures. Atomic simulations revealed the fundamental impact of thermal addition on enhancing the plasticity and deformability of CaF2, which affirmed the preferential propagation of dislocations and stress states among the differently heated regions of the work material. Further analysis determined that subsurface-graded heating not only facilitated favorable plastic flow along high-temperature regions but also induced compressive effects akin to physical constraints caused by strain mismatches. This study successfully demonstrates the potential of controlling the differential plasticity of brittle materials for beneficial enhancements to precision machining.

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Supported by Singapore Ministry of Education Academic Research Funds (Grant Nos.: MOE-T2EP50120–0010, MOE-T2EP50220–0010, and A-8001225-00-00). The computational work for this article was partially performed on resources of the National Supercomputing Center, Singapore
30th March 2025

Graphene nanosheets networking: A novel material design strategy to enhance ultra-precision machining of titanium alloys and composites

Y. Guo, Q. Yan, D. Ma, D. Yan, H. Wang
Journal of Materials Processing Technology 339 (2025) 118816

Positive efforts (e.g., cryogenic machining, vibration assistance, and laser assistance) have been proposed to address the challenges of low thermal conductivity and the heterogeneous structure in titanium alloys and titanium metal matrix composites (Ti-MMCs) during ultra-precision machining. However, these techniques often require complex auxiliary equipment with high costs and stringent precision control precision control, posing a major challenge to the sustainable production of titanium alloys and Ti-MMCs. Unlike other existing methods relying on external assistance, this study introduces a novel material design strategy to intrinsically improve the machinability of titanium alloys and Ti-MMCs by incorporating networked graphene nanosheets (GNSs) as internal reinforcement. To systematically evaluate this approach, three Ti-6Al-4V (Ti64) alloy-based materials: the matrix alloy, a composite reinforced with randomly dispersed GNSs (GNSs/Ti64 composite), and a composite reinforced with a networked GNSs structure (networked GNSs/Ti64 composite), were respectively designed and employed as workpiece in ultra-precision micro-cutting tests. The results reveal that the networked GNSs/Ti64 composite exhibits significantly reduced machining vibration induced by machining force, enhanced surface integrity, and more uniform chip formation compared to both the Ti64 alloy and GNSs/Ti64 composite. In-depth material characterization and mechanistic analysis attribute this improvement to the networked GNSs structure that optimizes the occurrence of shear fracture in the primary shear zone, leading to more uniform serrated chips for chip formation. This research effectively improves the ultra-precision machinability of titanium alloys and Ti-MMCs, which lays the foundation for the subsequent fabrication of advanced products from titanium alloys and composites.
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Supported by Singapore Ministry of Education Academic Research Funds (Grant No.:A-8001225-00-00).
10th March 2025

Dynamic response in high strain rate deformation of stainless steel 316L fabricated by selective laser melting

Y. Yang, Z. Zheng, Y. Bai, W.F. Lu, H. Wang
Materials Science and Engineering: A 929 (2025) 148105

This paper investigates the dynamic mechanical response of stainless steel 316L fabricated via selective laser melting under high strain rate deformation. The analysis focuses on the compressive deformation behaviour with respect to different printing strategies with scanning rotation angles of 0°, 90°, and 67°, under three heat treatment conditions. The study focuses on microstructural evolution and compressive deformation mechanisms at high strain rates. Selective laser melted SS316L exhibits sensitivity to both high strain rate and elevated temperature, comparable to that of wrought SS316L in high strain rate deformation. At a fixed strain, the observed rise in stress with an increasing strain rate suggests the strain hardening phenomena in high-strain rate deformation. The flow stress decreases significantly with rise in temperature due to the thermal-softening effect. With the increase in temperature, more recrystallized grains are formed and the viscosity of the material decreases. The samples with a 0° rotation display deformation in the direction of the laser scanning due to the presence of a pronounced local texture morphology on the top surface, leading to anisotropic deformation in the samples with uni-directional scanning, and the elliptical shape of samples are formed after high strain rate compression. Systematic experiments yielded a complete set of material constants for the Johnson-Cook material constitutive model, which describes the connection between flow stress and plastic strain in the presence of severe deformation, large strain rates and high temperatures.

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Supported by Singapore Ministry of Education Academic Research Funds (Grant Nos.: MOE-T2EP50120–0010, MOE-T2EP50220–0010, and A-8001225-00-00).