Air plasma sprayed thermal barrier coatings on titanium alloy substrates

Abstract

Titanium alloys as lightweight structure materials have been shown more interest in the use at moderately elevated temperatures. However, their poor oxidation resistance at temperature above 600°C limits a wide application. Consequently, thermal protection becomes a concern. 8 wt. % yttria partially stabilized zirconia thermal barrier coatings (TBCs) were air plasma sprayed on titanium alloy substrates (Ti-6.6Al-3.61Mo-1.69Zr-0.28Si in wt.%). The microstructures and mechanical properties of the coating system were studied by using SEM, XRD, MIP, tensile test and Vickers microhardness. The results show that the as-sprayed ceramic coating consists of the non-transformable tetragonal t′ phase of zirconia. The microstructure of the internal substrate keeps unchanged, no reaction and interdiffusion happen obviously at the bond coat/substrate interface during plasma spraying. However, there exists a thin layer of plastic deformation zone in the substrate beneath the bond coat/substrate interface. The surface connected porosity of the as-sprayed ceramic coating shows a typical bimodal pore size distribution. The adhesive strength of the TBCs decreases with increasing the thickness of the as-sprayed ceramic coatings, which is attributed to the residual stresses induced during thermal spraying. The anisotropy in the mechanical properties between the cross section and the top surface of the ceramic coatings is examined.

Effect of Thermal Exposure on Mechanical Properties of a Plasma-Sprayed Nanostructured Thermal Barrier Coating

“…This theory is based on an exponential law of a decreasing defect size distribution. And the two-parameter Weibull distribution function is described as: p = 1 À exp[À(x/x 0 ) m ], where x 0 is known as the scale parameter where the probability of occurrence is 63.2% and m is the Weibull modulus (Ref [16][17][18]. The magnitude of m increases with decreasing scatter.…”

Recent advances in laser surface treatment of titanium alloys

“…Atmospheric plasma spraying ͑APS͒ remains one of the most used techniques for increasing the maximum service temperature, while thermal barrier coating ͑TBC͒ is an alternative approach. 20 Meng et al worked with laser cladding coatings of NiCoCrAlY on Ti6Al4V and confirmed that it is possible to produce layers with a good metallurgical bond with the substrate and without cracks or pores. Moreover, the substrate becomes twice as hard and more resistant to erosion.…”

Properties of TiN-matrix coating deposited by reactive HVOF spraying

“…Weibull distribution, which is fit for the broad and dispersive distribution of microhardness for brittle ceramic material, was used to analyze microhardness values of TiN-matrix coating. The Weibull distribution of two parameters is given as follows 17 :…”