A Review of Additive Mixed-Electric Discharge Machining: Current Status and Future Perspectives for Surface Modification of Biomedical Implants

Table 5

Benefits and limitations of CaP-based coating methods.

Coating methods	Thickness	Benefits	Drawbacks	Refs.
Sol-gel	<1 μm	Coat complex shapes, low cost (thin), low processing temperature, high purity	Controlled atmosphere required, costly raw materials	[34, 68, 69]
Sputter processes	0.5–3 μm	Thickness uniformity on Coat flat substrate, good adhesion, dense coating	High cost, time consuming, produces amorphous coatings	[67]
Plasma spray	<20 μm	High deposition efficiency, low cost, reduced risk of coat degradation	High temperature led to grain growth, Amorphous coatings, poor adhesion	[70–72]
PLD	0.05–5 μm	Crystalline and amorphous coating, dense and porous coating	High cost, time, no uniformity in thickness consuming, surface need to be pretreated	[73–76]
ESD	1–10 μm	Low cost, uniformity in coating flat substrate	Coats only visible area, it is fragile	[77–79]
Electrophoretic coating	0.1–2.0 mm	Uniformity in coating thickness, coat complex substrate, rapid deposition rate	Produces cracks coated surface, high sintering temperature required	[80–82]
Hot (isostatic) pressing	0.2–2.0 mm	Dense coating is achieved, coat any dimension	Requires high temperature, complex shapes cannot be coat, high cost, mismatch thermal expansion, differences in elastic property	[83, 84]
Dip coating		Complex 3D and porous substrate can be coat, low cost, faster application	Requires high temperature for sintering, fragile due to thickness, amorphous due to thermal expansion	[85]