A high electromagnetic field (0.3 T-Teslas) was applied during the solidification of Ni-based alloyed splats. Ni, NiCr, NiCrAl, NiCrBSiFe powders were deposited over steel polished substrates using a flame spray and a plasma spray torch. A strong electromagnet was used to produce sufficient magnetic field to induce effects over the splats during solidification. A remarkable change in splat morphology and chemical segregation was identified specially in NiCrBSiFe and the other alloys. Optical microscopy, surface profilometry, and SEM images revealed changes in the regular cracking trends, splashing, and thickness of the splats. This experimental study discusses the possible explanations for this phenomena. The adherence of the coating is the main property to be analyzed with the goal of improving the mechanical interlocking, and therefore, adhesion by engineering the applied electromagnetic field.

Pores and cracks have significant influence on the structural rigidity and mechanical behavior of the thermally sprayed materials. For some applications dense coatings are needed, while for others (e.g. thermal barriers) some level of porosity is desirable. Recent development in thermal spraying focuses on the tailored design of pores and cracks for specific applications. In this project, ceramic coatings with different level and morphology of pores and cracks were plasma and HVOF sprayed on titanium alloy substrates. Coating microstructures were observed using scanning electron microscopy. Mechanical behavior of the prepared coatings was evaluated using four-point bending test in terms of changing coating stiffness with increasing mechanical load both in compression and tension. Significant level of coating non-linearity and hysteresis were observed. Tests carried out for coatings with the same chemical composition but different microstructure proved strong dependency of coatings mechanical properties on pores and cracks morphology. Microstructure features relevant for the applied loading are discussed.

The coating stresses induced by thermal spray using a High Velocity Gas Fuel (HVOF) and Liquid Fuel (HVLF) gun and a High Velocity Plasma (HVP) gun with the high velocity nozzle are compared using a curvature based in-situ coating stress analysis approach that measures the deflection of a beam while a coating is applied to it. This novel diagnostic tool provides new insights into the internal stresses generated in a coating system during the actual application of the coating. Coatings were sprayed with three process guns and the same material feed stock that result in similar coating structures and properties. HVOF, HVLF and HVP processes induce similar particle energy states at high velocity regimes as measured with particle diagnostic tools during spraying but due to the differences in particle history are expected to result in different coating stresses. In some cases the actual measured stress conditions using the in-situ coating stress method were dramatically different. Analysis is presented to explain the reason for these surprising results. The understanding of these differences will lead to an improved methodology for mapping coating processes from one another along with a more in depth understanding of coating stresses buildup.

The concept of ‘process maps’ has been utilized to study the fundamentals of process–structure–property relationships in high velocity oxygen fuel (HVOF) sprayed coatings. Ni- 20%Cr was chosen as a representing material of metallic alloys. In this paper, concurrent experiments including diagnostic studies, splat collection, and deposition of coatings were carried out to investigate the effects of fuel gas chemistry (fuel gas/oxygen ratio), total gas flow, and energy input on particle temperature (T) and velocity (V), and coating microstructure formation and properties. Coatings were deposited on an ‘in situ’ curvature monitoring sensor to study residual stress evolution. A strong influence of particle velocity on induced compressive stresses through peening effect is discussed. The complete tracking of the coating buildup history including residual stress evolution and temperature deposition, in addition to single splat analysis allows the interpretation of resultant coating microstructures and properties, and enables coating design with desired properties.

The general method of process maps to understand and control thermal spray processes has been applied to monitor the deposition of WC-Co by high velocity oxygen fuel (HVOF). A selected number of particle state conditions (velocity and temperature) has been performed to produce a variety of coatings. Microstructure, mechanical properties, and wear resistance were evaluated and compared. A second order process map for sliding wear, impacting particle erosion and abrasive wear control can be constructed from the process map to provide the limits within which the particle state can be changed to achieve a predefined coating specification. The mechanisms behind the wear resistance are discussed within the framework of wear maps –third order process map-in the context of analysis of inter splat de-bonding, mechanical properties of the coating, and delamination failure.