“…Recently, the surface modification of the conventional substrates has become more popular, for example, to coat a fine-porous ceramic surface layer on the substrate, which aims at reducing surface pore-size, repairing surface defects and decreasing surface roughness [10,27,28]. So far, many approaches have been developed to coat a fine-porous ceramic surface layer, including solgel [14][15][16][17], chemical vapour deposition [18], wet powder spray [19], thermal spray [20,21], and magnetron sputtering [22]. Unfortunately, the high cost of these processes often offsets or even exceeds the cost that is saved through the application of less expensive substrate materials.…”