Mechanical and in vitro degradation behavior of ultrafine calcium polyphosphate reinforced magnesium-alloy composites

Magnesium alloy (ZK60A) matrix composites reinforced with 2.5, 5, 7.5 and 10 wt.% calcium polyphosphate particles, which were sphere-like in shape with average size of about 750 nm, were fabricated by powder metallurgy. The microstructure, mechanical properties and degradation behavior in physiological saline of the composites were investigated. The obtained results show that ultrafine calcium polyphosphate particles uniformly distribute in the ZK60A matrices without voids for the composites containing 2.5 and 5 wt.% calcium polyphosphate. For the composites containing 7.5 and 10 wt.% calcium polyphosphate, however, calcium polyphosphate particles agglomerate in the ZK60A matrices, and some obvious voids appear. The ultimate tensile strengths, yield strengths and elastic moduli of the composites tend to increase when the calcium polyphosphate contents increase from 0 to 5 wt.%, however, appear to decrease with the further increase of calcium polyphosphate from 5 to 10 wt.%. The weight losses of the composites, pH values and Mg ion concentrations of the solutions immersing the composites gradually decrease with increase of calcium polyphosphate content, which indicates that the addition of more calcium polyphosphate into ZK60A alloy results in significant degradation slow-up of the composites. This can be attributed to the formation of dense corrosion product layers on the composites. The composites have good mechanical properties and controllable degradation rates and thereby have potential to be used as load-bearing bone implants.

Research highlights
► We synthesize the magnesium matrix composites by powder metallurgy.
► CPP uniformly distribute in matrices for composites containing 2.5 and 5 wt% CPP.
► Yield strengths of samples increase with the increasing of CPP from 0 to 5 wt%.
► The corrosion rates decrease gradually with the increase of CPP contents.