Effect of Multi-axial Forging on Microstructure and Functional Properties of Bioresorbable Fe–30Mn–5Si (Wt Pct) Alloy
摘要
In this study, thermomechanical treatment via multi-axial forging (MAF) was employed to produce bar semi-products of an advanced Fe–30Mn–5Si alloy (wt pct) intended for bioresorbable implant applications. The effects of MAF on microstructure, phase composition, mechanical properties (ultimate tensile strength UTS, apparent yield stress σ0.2, elongation to failure δ, Young's modulus E), electrochemical behavior, and functional corrosion-fatigue life were investigated and compared to those of a reference heat treatment (RHT). MAF induced the formation of a homogeneous, mixed, statically recrystallized microstructure with an average grain size of 1 to 5 µm, alongside a dynamically polygonized substructure characterized by subgrain sizes of 200–400 nm in both peripheral and central regions. The treatment resulted in a predominantly single-phase γ-austenite state, with a minor fraction of HCP cooling-induced ε-martensite. Tensile testing to failure demonstrated that MAF significantly enhanced UTS up to 890 MPa, σ0.2 up to 300 MPa, and δ up to 26 pct, compared to RHT values (460 MPa, 210 MPa, and 11 pct, respectively) while maintaining a relatively low Young’s modulus (143 GPa for MAF vs. 140 GPa for RHT). Furthermore, the microstructure developed by MAF substantially improved the functional corrosion-fatigue life in Hanks’ solution, compared to RHT, with 8069 cycles to failure for MAF vs. 2326 cycles for RHT. It was determined that the predominantly single-phase γ-austenite state formed after MAF exhibits a reduced biodegradation rate (0.19 mm/year) compared to the two-phase γ-austenite + ε-martensite structure formed after RHT (0.6 mm/year). Subsequent cooling of MAF specimens to –125 °C induces the formation of two-phase γ-austenite and cooling-induced ε-martensite state resulting in a significant increase in the biodegradation rate to 0.68 mm/year.