The concept, development background and the present applications of functionally gradient materials (FGMs) are introduced. Some spraying methods to fabricate FGM coatings, such as plasma spraying, flame spraying, high velocity oxy-fuel (HVOF) spraying and detonation flame spraying are reviewed. The research emphases and prospects of the technologies are put forward.

In this paper, copper coatings were deposited on a metallic substrate by means of multi-function micro-plasma spraying under different processing parameters. The microstructure and phase structure of copper coatings were investigated using a scanning electron microscope and X-ray diffraction, bonding strength were tested by an electron tensile tester, droplet impinging and flattening on a flat substrate surface and the residual stress after solidification were studied numerically. The experimental results show that the density of copper coatings was improved with increasing plasma power and operating gas flow, and this copper coating possessed high adhesion strength and low residual stress, still without obvious oxidation. This spraying system extends the application field of tradition plasma spray. Through changing the processing parameters, materials with different melting points, even as low as copper can be produced.

The adhesive strength between substrate and sprayed coatings seems to be mainly due to the mechanical interlocking effect. The physical bonding of spray particles to the substrate is the second factor. In this paper, the bonding mechanisms of sprayed coatings were studied on basis of experiments with the substrate at different surface roughness. The substrate surface roughness was quantitatively evaluated using a surface roughness tester. The tensile adhesion strength test method was used to evaluate the adhesive properties. The relationship between surface roughness and adhesive strength was investigated. The adhesive strength of plasma sprayed coating decreased with an increase in substrate surface roughness, as the size of the grit particles for roughening increased. On the contrary, the adhesive strength of arc sprayed coating increased.

Thick Nanostructured PSZ- NiCoCrAlY graded TBCs were got by air plasma spraying. The results reveal the morphology and phase transformation of TBCs by means of SEM and XRD. The plasma spray process results in a characteristic layered structure consisting of lamellae, unmelted nano-particles and an inter-lamellar porosity. The test results of thermal shock show that the graded coatings have different failure behavior, which caused by thermal stress, radial cracks penetrating and substrate oxidation. The failure mode was the spallation of top coat due to thermal stress. The improved strain tolerance of the top coat was benefited from the high coating porosity, the segmentation cracking, the fine-splat size and the unmelted nanoparticles. It has been found that the lamella consists of nanoscale columnar grains parallel to the spraying direction.