Development of biodegradable Fe-Mn-Mg alloys by mechanical alloying and spark plasma sintering

The development of an Fe-Mn-Mg alloy by mechanical alloying (MA) and spark plasma sintering (SPS) is reported for the first time with the aim of improving the slow corrosion rate of Fe-based alloys to expand their application in biodegradable materials. Fe-21Mn-xMg (x = 0, 10, 20, and 30 at%: named 0Mg, 10Mg, 20Mg, and 30Mg, respectively) was subjected to a maximum of 60 h of MA. The 0Mg and 10Mg mechanically alloyed powders exhibited the single alpha(bcc)-Fe phase, however, a single alpha-Fe phase alloy powder could not be obtained for 20Mg and 30Mg, even after 60 h of MA. The sintered specimens of 0-30Mg were fabricated by SPS from the 60 h mechanically alloyed powders. The phase transformation from alpha-Fe to gamma(fcc)-Fe+ epsilon(hcp)-Fe was confirmed in all specimens. In addition, phase separation of Mg and alloying of Mn occurred during SPS in 20Mg. The Vickers hardness of the sintered specimens decreased with increasing Mg amount, while 10Mg showed the highest compressive strength because of its low porosity. The immersion test results showed that the corrosion rate of the 10Mg sintered specimen was lower than that of 0Mg. This was because, in the 0Mg sintered specimen, local corrosion, such as pitting corrosion, occurred from the pores and promoted specimen elution. Furthermore, corrosion products were observed on the surface of the 10Mg sintered specimen after one week of immersion testing, which may have inhibited the elution of the specimen. On the other hand, its corrosion rate calculated from the corrosion current density obtained from the polarization test was higher than that of 0Mg, suggesting that the 10Mg sintered specimen may have a faster corrosion rate in the absence of corrosion products. The 10Mg alloy exhibited excellent mechanical strength and moderate corrosion rate and, thus, is a suitable candidate for Fe-based high-performance biodegradable alloys; it can also be used as a biodegradable implant.