Microstructure Evolution and Mechanical Properties of a Wire-Arc Additive Manufactured Austenitic Stainless Steel: Effect of Processing Parameter

Area of Science:

• Materials Science
• Metallurgy
• Additive Manufacturing

Background:

• Wire Arc Additive Manufacturing (WAAM) is a growing field for metal component fabrication.
• Understanding the relationship between processing parameters and material properties is crucial for WAAM applications.
• The microstructure and mechanical behavior of WAAM steels are significantly influenced by thermal history.

Purpose of the Study:

• To investigate the effect of linear energy input (LEI) and cooling rate (CR) on the microstructure, mechanical properties, and fracture mechanisms of steel deposited via WAAM.
• To analyze the formation of phases like sigma (σ) phase and their impact on material performance.
• To correlate processing parameters with microstructural features and resulting tensile properties.

Main Methods:

• Deposition of multi-layer walls using a cold metal transfer-based WAAM system with varying LEIs (219 and 590 J/mm).
• Microstructural analysis using X-ray diffraction and scanning electron microscopy.
• Evaluation of mechanical properties through uniaxial tensile testing.

Main Results:

• The steel microstructure primarily consists of δ-ferrite and austenite dendrites.
• Sigma (σ) phase formation occurs at the δ-ferrite-austenite interface under low cooling rates.
• Decreasing LEI or increasing CR reduces primary dendrite spacing.
• Elongation to fracture generally decreases with lower LEI or higher CR, while ultimate tensile strength and yield stress increase.
• Fracture mechanisms shift from pore coalescence (low LEI) to dislocation pile-up around δ-ferrite (high LEI).

Conclusions:

• LEI and CR are critical parameters controlling microstructure evolution and mechanical properties in WAAM steels.
• Optimizing LEI and CR can tailor the steel's tensile properties and fracture behavior.
• The study provides insights into phase formation and damage mechanisms relevant to WAAM process control.