This paper explores the effect of bond coat processes and surface characteristics on the failure mechanism of thermal barrier coatings (TBC's). TBC's consist of a 300µm thick air plasma sprayed (APS) top coating of ZrO 2 -8Y 2 O 3 w% and CoNiCrAlY bond coats which were deposited using low pressure plasma spray (LPPS), shrouded air plasma spray (SPAS) and high velocity oxy-fuel (HVOF) combustion spray and different size powder. Bond coat surface profiles were measured by profilometric techniques and surface roughness was calculated according to the measured results. TBC performance and failure mechanisms were evaluated by adhesive bond strength testing, image analysis measurements of porosity, thermal cycling testing. X-ray diffraction and microstructural analyses. Research results show that bond coat deposition processes and surface characteristics had significant effects on the thermal cycling lifetime and failure mechanism.

The objective of this study was to investigate the effects of thermal spray process selection and corresponding bondcoat surface roughness on thermal barrier coating (TBC) performance. TBC's consisting of a 300 µm (12 mil) thick air plasma sprayed (APS) top coating of ZrO 2 -8 Wt.% Y 2 O 3 and CoNiCrAlY bondcoats deposited by three different thermal spray processes were produced and their surface roughness characterized. The bondcoats were deposited using low pressure plasma spray (LPPS), shrouded air plasma spray (SPS) and high velocity oxy-fuel (HVOF) combustion spray. Bondcoat surface profiles were measured by profilometric and interferometric techniques and surface roughness values calculated. TBC performance was evaluated by adhesive bond strength testing, thermal shock and thermal cycling testing, and microstructural analysis. Results showed that the bondcoat deposition process used and corresponding surface roughness had significant effects on the adhesive strength, thermal shock and thermal cycling lifetime, and failure mechanisms.

The results of low stress, pin-on-disc and high stress grinding abrasive wear tests on coatings produced by plasma and oxy-acetylene flame spraywelding are presented. FNil5A and FNiWC35 Ni-based self-fluxing alloys were selected as typical spraywelding materials for abrasive wear resistance. The abrasive wear resistance mechanisms of welded overlays produced by various materials and processes were also characterized by hardness tests, microstructural and compositional analyses, and through analysis of the effect of different kinds of abrasive on the wear resistant of Ni-base self-fluxing spraywelding overlays. Results showed that FNiWC35 overlays exhibited improved resistance under low stress abrasion, but the relative wear resistances of FNiWC35 and FNil5A still depended primarily on the type and hardness of the abrasive medium used. For the same material, the abrasive wear resistance of oxyacetylene flame sprayed overlays was higher than that produced by plasma spraywelding. The wear resistance of the plasma spraywelding overlays depended not only on the material, but also strongly on the spraywelding process parameters.

Ceramic/polymer nanocomposites promise to be a new class of materials that will have wide application either for surface protection, providing low friction and inert corrosion barriers, or where tailored electrical and magnetic properties with increased abrasion and wear resistance are required. The high velocity oxy-fuel (HVOF) combustion spray process has been used to successfully process polymer-ceramic nanocomposites at 5 - 20 volume % of reinforcement. The latest results of process-structure- property relationship studies in silica and carbon black reinforced nylon 11 coatings are presented. It was found that the improvement in mechanical properties depends on the distribution and surface chemistry of the particulates and on the increase in matrix crystallinity due to the particulates.

Functionally gradient composites were spray formed via vacuum plasma spray deposition using tungsten cylindrical substrates. Materials deposited included tungsten-hafnium alloys and M-2 tool steel. Some deposits included micro-laminate layering with hafiiium alloys sprayed within the tungsten-hafnium matrix. Vacuum plasma deposition was shown to provide a viable means of producing functionally gradient composites from tungsten base materials. This was determined both by microstructural characterization of deposit structures and by measuring the compressive properties of the materials. Compression testing of the W-Hf matrix composites demonstrated compression strength of 1,552 MPa (225 ksi). Compression strengths of the tungsten/steel composite averaged 1,068 MPa (155 ksi). Failure of the W-Hf samples occurred via fracture of the tungsten/hafnium matrix whereas the tungsten/steel composites failed within the wrought tungsten core.