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<p>This study investigates the microstructural evolution, mechanical performance, and fracture behavior of 18% Ni maraging steel deposited via wire arc additive manufacturing (WAAM) and subjected to various heat treatments: as-built (AB), direct aged (DA), solution treated (ST), and solution treated + aged (STA). A comprehensive analysis was conducted, including microstructural characterization using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD), phase analysis through x-ray diffraction (XRD), and evaluation of mechanical properties such as microhardness and tensile strength followed by fractography. The as-built condition exhibited a martensitic structure with grain size variations across regions due to thermal gradients, with the finest grains (~1.61&#xa0;µm) at the bottom, intermediate (~1.79&#xa0;µm) in the middle, and coarsest (~2.34&#xa0;µm) at the top. Heat treatments significantly refined the microstructure and reduced regional variations. The STA condition achieved the most uniform grain structure and distribution of intermetallic phases such as Ni<sub>3</sub>Ti, Ni<sub>4</sub>Ti<sub>3</sub>, and FeMo. Tensile strength and hardness varied significantly across conditions: AB achieved 1131.6&#xa0;MPa and 400 HV, DA reached 1432.1&#xa0;MPa and 470 HV, ST recorded 945.2&#xa0;MPa and 420 HV, and STA attained the highest values at 1492.2&#xa0;MPa and 489 HV, attributed to matrix refinement, precipitation hardening, and solid solution strengthening. Fractographic analysis (Figure 11) revealed a transition from mixed brittle–ductile fracture in the as-built (AB) condition to more ductile features in the solution treated (ST) and solution treated + aged (STA) conditions. In contrast, the direct aged (DA) condition, despite showing fine dimples, exhibited a low elongation to failure (~1.8%), indicating a strength-dominated fracture with limited ductility. The highest ductility was observed in ST (~3.2%), whereas STA achieved the best balance of strength and moderate ductility due to matrix homogenization and precipitation hardening demonstrated the best combination of strength, hardness, and fracture resistance, making it suitable for high-performance applications in aerospace, defense, and tooling industries.</p>

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Microstructural Characterization and Mechanical Properties of Wire and Arc Additively Manufactured 18% Ni Maraging Steel 250

  • 期刊论文

  • 发表日期：

    2025年10月8日

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  • Ratan Kumar,
  • P. Mastanaiah,
  • Guttikonda Manohar,
  • Adepu Kumar

摘要

This study investigates the microstructural evolution, mechanical performance, and fracture behavior of 18% Ni maraging steel deposited via wire arc additive manufacturing (WAAM) and subjected to various heat treatments: as-built (AB), direct aged (DA), solution treated (ST), and solution treated + aged (STA). A comprehensive analysis was conducted, including microstructural characterization using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD), phase analysis through x-ray diffraction (XRD), and evaluation of mechanical properties such as microhardness and tensile strength followed by fractography. The as-built condition exhibited a martensitic structure with grain size variations across regions due to thermal gradients, with the finest grains (~1.61 µm) at the bottom, intermediate (~1.79 µm) in the middle, and coarsest (~2.34 µm) at the top. Heat treatments significantly refined the microstructure and reduced regional variations. The STA condition achieved the most uniform grain structure and distribution of intermetallic phases such as Ni3Ti, Ni4Ti3, and FeMo. Tensile strength and hardness varied significantly across conditions: AB achieved 1131.6 MPa and 400 HV, DA reached 1432.1 MPa and 470 HV, ST recorded 945.2 MPa and 420 HV, and STA attained the highest values at 1492.2 MPa and 489 HV, attributed to matrix refinement, precipitation hardening, and solid solution strengthening. Fractographic analysis (Figure 11) revealed a transition from mixed brittle–ductile fracture in the as-built (AB) condition to more ductile features in the solution treated (ST) and solution treated + aged (STA) conditions. In contrast, the direct aged (DA) condition, despite showing fine dimples, exhibited a low elongation to failure (~1.8%), indicating a strength-dominated fracture with limited ductility. The highest ductility was observed in ST (~3.2%), whereas STA achieved the best balance of strength and moderate ductility due to matrix homogenization and precipitation hardening demonstrated the best combination of strength, hardness, and fracture resistance, making it suitable for high-performance applications in aerospace, defense, and tooling industries.