316L stainless steel is a common biomedical material. Currently, biomedical parts are produced through powder injection molding (PIM). Carbon control is the most critical in PIM. Improper debinding can significantly change the properties of the final product. In this work, thermal debinding and sintering were performed in two different furnaces (i.e. laboratory and commercially available furnaces) to study the mechanical properties and corrosion resistance. Debounded samples were sintered in different atmospheres. The samples sintered in inert gas showed enhanced mechanical properties compared with wrought 316L stainless steel and higher corrosion rate than those sintered in the vacuum furnace. The densification and tensile strength of the hydrogen sintered samples increased up to 3% and 51%, respectively, compared with those of the vacuum-sintered samples. However, the samples sintered in inert gas also exhibited reduced ductility and corrosion resistance. This finding is attributed to the presence of residual carbon in debonded samples during debinding.

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Four feedstock formulations namely, F1, F2, F3 and F4, were prepared with solid loading of 60, 65, 67 and 69 vol%, respectively. Binder system consists of 70 vol% Paraffin wax, 25 vol% polypropylene and 5 vol% stearic acid. The stainless steel powder and wax-based binder were mixed using a Z-blade mixer with blade speed of 60 rpm at 180+5°C for 90 min. The paste was dried and converted into granules after mixing. The test specimens were molded using a 100 KSA vertical injection molding machine according to MPIF standard 50. All formulations were molded at 180+5°C and the molding dwell time was varied from 18-30 s, depending on the solid loading employed. Physical defects (i.e. cracks and trapped air) on the surface of the test samples were not observed.

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Advancement of PIM Technology:The research contributes to the advancement of PIM by exploring various binder systems, debinding parameters, and sintering atmospheres. This enhances understanding of how these factors affect the final properties of PIM-produced parts.

Material Science and Engineering:The article provides valuable insights into the effects of residual carbon and different sintering atmospheres on the densification, mechanical properties, and corrosion resistance of 316L SS parts. This knowledge is crucial for optimizing PIM processes and improving material performance.

Cost-Effective Manufacturing:PIM is a low-cost technique for producing high volumes of complex parts with dimensional accuracy. This research supports the development of cost-effective manufacturing processes, making high-quality 316L SS parts more accessible.

Enhanced Material Properties:The study identifies conditions that maximize densification and tensile strength while optimizing corrosion resistance. This leads to better-performing materials for various applications, especially in the medical field.

Improved Corrosion Resistance:Findings suggest that vacuum sintering enhances corrosion resistance and minimizes metal ion release, which is critical for the longevity and safety of medical implants. This can improve patient outcomes and extend the lifespan of implants.

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The release of ions are higher in the test sample sintered in gas atmosphere that those in the vacuumsintered samples. This finding can be attributed to the formation of carbides by residual carbon produced during debinding. In addition, the presence of H2 hindered the formation of an oxide layer (Davis 1994), thereby resulting in increased corrosion rate. The same behavior was observed for the samples sintered in the mixed-gas atmosphere.The behavior of N2 is still not clearly understood. N2 atoms clearly diffused within the matrix and formed nitrides, which may help dissolve the carbide and form nitride. N2 may have terminated the release of metal ions in a chloride environment. The N2 -sintered samples released higher amounts of metal ions than the samples sintered in H2

Versatility and Application in Various Industries:PIM is used to produce high-quality medical implants from metals like Ti, Ti alloys, Co-Cr alloys, and stainless steel, especially 316L SS. The demand for medical implants is increasing due to an aging population and advancements in medical technology.

Technological Advancements and Research:Continuous research into improving the PIM process, such as optimizing binder compositions, debinding processes, and sintering conditions, enhances the quality and performance of the final products. This can lead to wider adoption and higher demand for PIM-produced parts.

Cost-Effectiveness:PIM is described as a low-cost technique for mass production, making it attractive for industries that require large volumes of parts with complex geometries. The cost advantages can drive market growth as companies seek to reduce manufacturing costs.

Material Properties and Performance:316L stainless steel produced by PIM shows excellent mechanical properties and corrosion resistance, making it suitable for demanding applications. The development of formulations with varying solid loadings and the investigation of different sintering atmospheres can further enhance these properties.

Corrosion Resistance and Safety:Improving corrosion resistance and reducing the release of toxic metal ions (Fe, Ni, Cr) from 316L SS implants can address safety concerns and regulatory requirements in the medical industry. This can increase the acceptance and usage of PIM-produced implants.