**2.1.1 Powder flame spray coatings**

200 Ceramic Coatings – Applications in Engineering

 Thermal spray coating: Plasma spray, wire flame spray and powder flame spray, electrical arc spray, detonation gun technique and high speed oxy fuel system Chemical ceramic coating: Sole-gel, slurry, chemical vapour sedimentation, physical

Material conglomerations can be avoided by reducing erosion-corrosion, friction-wear, using ceramics as well as improving heat insulation. Non the less, these methods are proper for very thin coatings except thermal spray coatings. Thin layer coatings are successfully used in gas turbine industry, coating turbine and stator blades and combustion rooms. For thick layer coatings like diesel engines, plasma spray and flame spray coatings are generally

Oxy-hydrogen and oxy-acetylene systems are preferred in flame spray coatings and usually refractory oxides which have lower melting point than 2760 0C are used in coating with these systems. Before ceramic coatings, a binding layer resistant to high temperature like nickel-chromium should be applied to material surface for preventing oxidation as can be seen in Fig. 3. Otherwise, ceramic coating can't adhere to the surface properly. Coating speed in flame spray method is relatively slow and it changes between 4.4x10-5 and 1.13x10-3 m/s. There are two flame spray method which are wire flame spray method and powder

Fig. 3. Ceramic coated material surface, binding layer and coating layer

vapour sedimentation, hard coating

Ion enrichment method (Yaşar, 1997; Kamo et. al., 1989)

 Laser coating Arc spark alloying

utilized (Kamo et. al., 1989).

**2.1 Flame spray coatings** 

flame spray method (Geçkinli, 1992).

In this method, micro-pulverized powder alloys are sprayed to target surface in oxyacetylene flame by oxygen vacuum. It is called cold coating because flame temperature is about 3300 0C and target surface is about 200 0C during coating process. Adherence is mechanical. Coating layer thickness is changed 0,5 to 2,5 mm according to shape of work piece. Using highly alloyed and self lubricant NiCrBSi materials as coating powder and making materials which are not produced in rod or wire shapes possible for coating are the main advantages of this method. Powder flame spray systems are proper for spraying primarily ceramics and metals and cermets (metals and ceramic oxide alloys) as coating materials. Bearing supports, axle and shaft pivots, compressor pistons, cam shafts, bushes, rings and sleeves, hydraulic cylinders and pistons can be coated by this very method (Yaşar, 1997; Anonymous, 2004).
