MIG Arc Additive Manufacturing of 316L Stainless Steel and Inconel 625 Gradient Materials

Literature Overview

This 2024 publication by Wen Chunjie et al. in Precision Forming Engineering (Vol. 16, No. 10, pp. 208-216) presents a systematic investigation into the arc additive manufacturing (AAM) of functionally graded materials using 316L stainless steel and Inconel 625 nickel-based alloy wire feedstocks. The work is supported by the National Natural Science Foundation of China and Guangdong Provincial Education Department, reflecting the growing academic and industrial interest in hybrid material deposition technologies.

Core Technical Findings

The researchers employed a dual-pulse arc mode to deposit 50 layers of material in a reciprocating pattern, creating two gradient samples with 25% and 5% transition ratios between 316L and Inconel 625. The study evaluated deposition morphology, deposition efficiency, microstructure, hardness, and tensile properties, using a multi-index evaluation system for comprehensive quality assessment.

Process and Materials Analysis

The dual-pulse arc mode is a critical process innovation that enables stable arc characteristics during the transition between dissimilar wire feedstocks. This mode provides controlled energy input that accommodates the differing melting behaviors of austenitic stainless steel and nickel-based superalloy wires, which have significantly different thermal conductivities and liquidus temperatures.

The 5% gradient sample demonstrated superior performance across all evaluated metrics. The higher deposition efficiency is attributed to the more uniform thermal history, as the smaller proportion of nickel alloy minimizes thermal disruption during each layer transition. Hardness increased monotonically with increasing Inconel 625 content, reflecting the strengthening effects of γ' precipitates and solid solution hardening from the nickel-based alloy.

The critical finding is that the 25% gradient sample developed cracks in the 75% 316L + 25% Inconel 625 region, accompanied by reduced hardness and tensile properties. This crack formation is likely attributed to the significant mismatch in thermal expansion coefficients between the two alloys, combined with the residual stress accumulation in the transition zone where microstructural discontinuities are most pronounced.

Microstructural Considerations

The transition between 316L austenitic stainless steel and Inconel 625 nickel-based alloy involves a complex metallurgical interface. The 316L contains approximately 17% chromium and 12% nickel, while Inconel 625 contains approximately 21% chromium, 9% nickel, and significant amounts of molybdenum and niobium. This compositional gradient creates zones of varying solid solubility, precipitate formation tendencies, and phase stability.

The absence of cracks in the 5% gradient sample suggests that the narrow transition zone minimizes the volume of material experiencing severe thermal mismatch stresses. The gradual compositional change over a smaller proportion of the deposit allows for more uniform thermal behavior during the multi-layer deposition process.

Engineering Practice Integration

For engineers considering arc additive manufacturing for gradient material applications, this research provides several critical guidelines:

1. The 5% transition ratio represents a practical and reliable design choice for 316L/Inconel 625 gradient components, offering superior mechanical properties without crack formation.
2. Deposition efficiency should be a key selection criterion, as the 5% gradient process achieves higher productivity while maintaining quality.
3. The multi-index evaluation system employed in this study is recommended for quality assurance in additive manufacturing operations, providing a comprehensive framework for process optimization.
4. Engineers should be aware that larger gradient ratios, while potentially offering more gradual property transitions, may introduce crack susceptibility due to thermal mismatch effects.

Key Questions and Reflections

The crack formation in the 25% gradient sample raises important questions about the fundamental limits of gradient material design in arc additive manufacturing. Is the issue primarily thermal in nature, or does it involve metallurgical incompatibilities that cannot be overcome by process optimization alone? Further investigation into the residual stress distribution and phase transformations in the transition zones would provide valuable insights for future process development.

Additionally, the study does not address the corrosion resistance of the gradient materials, which is a primary motivation for using Inconel 625 in combination with stainless steel. The localized composition variations in the gradient zones may create galvanic coupling effects that could compromise corrosion performance in aggressive environments.

Study Insights and Implications

This research demonstrates that arc additive manufacturing can successfully produce functionally graded materials with tailored mechanical properties, provided that the gradient ratio is carefully selected to avoid thermal mismatch cracking. The 5% transition ratio emerges as a robust design parameter that balances the benefits of gradient material functionality with the practical requirements of defect-free production. These findings have direct implications for the manufacturing of components requiring localized property enhancement, such as turbine blades, chemical processing equipment, and wear-resistant overlays.