Degradation behavior of as cast and powder metallurgy processed Mg-Ca alloys


Biodegradability and mechanical properties similar to natural bone have made Mg alloys potential competitors for metal implant applications. Mg-Ca alloys are of interest as Ca is an essential element in the human body. However, an increased Mg2Ca secondary phase with increasing Ca addition results in pitting corrosion in these alloys. Reports suggest that Mg alloys with ≤ 1wt % Ca additions possess good degradation resistance. Hence, Mg-xCa alloys (x= 0.3, 0.6, 0.9 wt %) were fabricated by gravity die chill casting and powder metallurgy (PM) techniques. Their ‘mean degradation depth, h (µm)’ values were measured by immersion test. Physiological cell-culture medium DMEM+ Glutamax with proteins (10% FBS) and an incubator were adopted for conducting the test. The volume fraction of Mg2Ca was calculated with Image J image analysis software. Results show that degradation behavior is influenced by the amount of secondary phase and its distribution in the Mg matrix. PM alloys showed homogenous degradation compared to the as cast alloys. The highest degradation resistance was exhibited by PM processed Mg-0.3Ca alloy with lowest h value of 0.39 µm. A long term immersion test revealed the ‘mean degradation rate, ḣ∞ (µm/day)’ as 0.51 µm/day.
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