Bioactivity and mechanical properties of plasma-sprayed coatings of bioglass powders

Abstract

Bioactive glass powders were prepared from four different types of oxides (SiO2, P2O5, CaO and MgO). These oxides were mixed, melted and milled to produce two compositions of a 31SiO2–11P2O5–(58−x)CaO–xMgO system, where the values x=0 and x=2 describe powders P1 and P2, respectively. The powders were sieved to obtain a particle size distribution of 1.8–40μm for P1 and 13–59μm for P2. The thermal stability of the powders was determined by differential thermal analysis (DTA). The powders were plasma sprayed on AISI 316L stainless steel substrates using a F4MB Sulzer Metco gun. The plasma-forming gas was a mixture of Ar/H2 (47/8L/min), and the current intensity used was 650A. The microstructure of the powders and the obtained coatings was examined by SEM. X-ray diffraction (XRD) was used to identify the crystalline phases in the powders and coatings. The hardness of the coatings, their adhesion to the substrates and the residual stresses in them were determined by a Vickers micro-indentation test, tensile test (according to ASTM C633) and curvature method, respectively. The microhardness of the coatings was between 4.7 and 5.2GPa, their strength of adhesion to the substrate was between 2.73 and 4.42MPa and the compression residual stress generated during the thermal spraying process was between −11.9 and −27.3MPa. The bioactivity was determined by the dissolution and subsequent formation of a hydroxyapatite layer by contacting the coatings with simulated body fluid for 1 and 15days.