Feng Cai

Solid Particle Erosion Behaviors of Carbon-Fiber Epoxy Composite and Pure Titanium

Abstract Rotor blades of Bell CH-146 Griffon helicopter experience excessive solid particle erosion at low altitudes in desert environment. The rotor blade is made of an advanced light-weight composite which, however, has a low resistance to solid particle erosion. Coatings have been developed and applied to protect the composite blade. However, due to the influence of coating process on composite material, the compatibility between coating and composite base, and the challenges of repairing damaged coatings as well as the inconsistency between the old and new coatings, replaceable thin metal shielding is an alternative approach; and titanium, due to its high-specific strength and better formability, is an ideal candidate. This work investigates solid particle erosion behaviors of carbon-fiber epoxy composite and titanium in order to assess the feasibility of titanium as a viable candidate for erosion shielding. Experiment results showed that carbon-fiber epoxy composite showed a brittle erosion behavior, whereas titanium showed a ductile erosion mode. The erosion rate on composite was 1.5 times of that on titanium at impingement angle 15° and increased to 5 times at impact angle 90°.

Tribological Behaviors of Titanium Nitride- and Chromium-Nitride-Based Physical Vapor Deposition Coating Systems

This study investigates the effects of the deposition process and coating composition on microstructural and tribological properties of TiN- and CrN-based coating systems. Coatings were produced using various PVD-based processes—electron beam (EB), cathodic arc (CA), and plasma enhanced magnetron sputtering (PEMS). All coated samples were evaluated for their composition, microstructure, and surface morphology. Coating mechanical properties such as hardness, Young’s modulus, and coefficient of friction were also studied and related to their microstructures, wear, and erosion resistances. It was found that hardness (H), Young’s modulus (E), and coefficient of friction had impact on both wear and erosion rates. In particular, the H3 /E2 ratio was inversely proportional to the specific wear rate. For erosion behavior, higher H3 /E2 ratios relate to lower erosion rates at low impingement angles, whereas higher H3 /E2 ratios relate to higher erosion rates at high impingement angles.

Effect of Microstructure on the Solid Particle Erosion Properties of Ni Plating

The effect of microstructure on erosion resistance of nickel plating was investigated in this study. Two electrode nickel plating processes, one with conventional nickel sulfamate electrolyte and the other with carbon nanotubes (CNTs) dispersed in the electrolyte, at various pulse frequencies were used to generate surface depositions of different microstructures. The samples were subjected to microstructural evaluations and mechanical property testing for microhardness and elastic modulus. Subsequently, erosion tests were conducted to evaluate the material’s erosion resistance under various plating conditions. It was found that both changes in pulse frequency and the addition of CNTs resulted in grain size refinement and surface morphology modification. Microhardness of the plating was observed to increase with the pulse frequency in the absence of CNTs. Erosion resistance increased with grain refinement initially due to the surface hardness increase but this effect subsided as the thickness of the deposition approached that of the plastic deformation layer caused by the erodent.

Microstructure, bioactivity and wear resistance of sintered composite Co-Cr-Mo/Bioglass® for medical implant applications

A sintered Co-Cr-Mo/Bioglass® composite coating, developed for medical implant application, is examined and compared to plasma-sprayed and sintered monolithic Co-Cr-Mo coatings. In addition to microstructure and wear resistance analysis, the bioactivities and corrosion behaviours of various coatings are assessed using simulated body fluid (SBF) immersion. The sintered Co-Cr-Mo/Bioglass® composite and monolithic Co-Cr-Mo coatings have more porous structure than the plasma sprayed Co-Cr-Mo coating. Although the Co-Cr-Mo/Bioglass® composite coating has adequate bonding between Co-Cr-Mo powder and glass particles, the wear resistance is lower than the plasma sprayed Co-Cr-Mo and Stellite 21 substrate. After SBF immersion, calcium is present on the Co-Cr-Mo/Bioglass composite coating, but not on the Co-Cr-Mo coating. It indicates the formation of an apatite layer on the Co-Cr- Mo/Bioglass composite coating and potentially better bioactivity than the monolithic coatings.

Electrochemical Behaviours of Titanium Nitride (TiN) and Chromium Nitride (CrN) Based PVD Coating Systems

Hard coatings applied to steel components prevent corrosion attacks while at the same time mitigate erosion attack. However, the presence of process related through-coating defects such as pin holes, voids and growth defects, provides accesses for corrosive media to metal substrates, initializing pitting corrosion and eventually resulting in coating failure. This research studies the corrosion behavior of PVD TiN and CrN (CrSiCN) coated steels in 3.5 wt. % NaCl aqueous solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results revealed that in a coating-substrate system, effective diffusion coefficient and diffusion layer thickness control the corrosion resistance; both factors are found to be related to coating microstructure. A denser and thicker coating structure are shown to have lower effective diffusion coefficients and greater effective diffusion layer thicknesses and consequently provided a high resistance to electrochemical corrosion.Copyright

Tribological Behaviours of Titanium Nitride and Chromium Nitride Based PVD Coating Systems

This study investigates the effects of the deposition process and coating composition on microstructural and tribological properties of TiN and CrN based coating systems. Coatings were produced using various PVD based processes — electron beam (EB), cathodic arc (CA) and plasma enhanced magnetron sputtering (PEMS). All coated samples were evaluated for their composition, microstructure and surface morphology. Coating mechanical properties such as hardness, Young’s modulus and coefficient of friction were also studied and related to their microstructures, wear and erosion resistances. It was found that hardness (H), Young’s modulus (E) and coefficient of friction had impact on both wear and erosion rates. In particular, the H3/E2 ratio was inversely proportional to the specific wear rate. For erosion behaviour, higher H3/E2 ratios relate to lower erosion rates at low impingement angles; whereas higher H3/E2 ratios relate to higher erosion rates at high impingement angles.Copyright