Influence of adhesion strength on cavitation erosion resistance of diamond-like carbon coating

Purpose The disbonding of DLC coating is a main failure mode in the high-speed cavitation condition, which shortens the service life of the bearing. This study aims to investigate influence of adhesion strength on cavitation erosion resistance of DLC coating. Design/methodology/approach Three DLC coatings with different adhesion strengths were grown on the 304 steel surfaces by using a cathodic arc plasma deposition method. Cavitation tests were performed by using a vibratory test rig to investigate the influence of adhesion strength on cavitation erosion resistance of a DLC coating. The cavitation mechanism of the substrate-coating systems was further discussed by means of surface analyses. Findings The results indicated that, the residual stress decreased and then increased with the increasing DLC coating thickness from 1 µm to 2.9 µm, and the lower residual stress can improve the adhesion strength of the DLC coating to the substrate. It was also concluded that, the plastic deformation as well as the fracture occurred on the DLC coating surface at the same time, owing to higher residual stress and poorer adhesion strength. However, lower residual stress and better adhesion strength could help resist the occurrence of the coating fracture. Originality/value Cavitation tests were performed by using a vibratory test rig to investigate the influence of adhesion strength on cavitation erosion resistance of the DLC coating. The plastic deformation and the fracture occurred on the DLC coating surface at the same time, owing to higher residual stress and poorer adhesion of coating. Lower residual stress and better adhesion of coating could resist the occurrence of the DLC coating fracture.

Features of Creating Nanostructured Intermetallic Ti-Al-Si-Cr Coatings for the Hot Section Part of Gas Turbine Engines

The paper deals with the results of a research study into Ti-Al-Si-Cr-based thin heat resistant ion-plasma coatings for titan alloy-based parts of a gas turbine engine (GTE). The research involved the use of three Ti-Al-Si-Cr-based alloys – intermetallic, with different Cr-Ti priority. The analysis of surface oxidation process in the range of 600-850°C with the help of scanning electron microscopy was performed, and the key features of coating fracture process under high-temperature oxidation conditions were identified.

Investigation on the Stress Behaviour of Coating-Substrate Interface under Contact Loading

This study is intended to predict the stress behavior of thick hard coating at the interface with the changes of coating stiffness and thickness to the substrate of Ti-6Al-4V and SCMV. The elastic mismatch between the coating and the substrate is presented in the value of Dundurs parameter α. The prediction is done using simple geometry of a cylinder-on-flat model in 2D analysis subjected to normal and tangential loading. Tangential stress distribution along the coating-substrate interface is then obtained from the FE modelling after a finite sliding of the cylinder. It is predicted that the maximum tangential stress value predicted at the interface which relates to coating fracture failure is increasing as stiffer coating is used on compliant substrate (i.e. increasing α values). The location of the maximum tangential stress predicted also changes from the trailing edge to the center of contact with increasing α values. Effect of changes of coating thickness on the predicted maximum tangential stress value is more significant for high positive α values. Risk of coating fracture at the interface is therefore predicted to increase with the increase of coating thickness and stiffness.

Evaluation of Influence of Cracks on DVC Coating Using Finite Element Analysis

TBCs (Thermal Barrier Coatings) are one technique for assuring appropriate endurance in extreme environments. DVC coating is a type of TBC that is applied by the insertion of artificial vertical cracks in a TBC to reduce the possibility of coating fracture. This study evaluates the influence crack depth and the distance between cracks, which are the main parameters of DVC coating, by FEM (Finite Element Method).

Galvanneal Coating of Galvannealed Steel Sheet Fracture Research by Dynamic Tensility

Dynamic tensility experiment has been done to research Galvanneal coating fracture of Galvannealed steel sheet with in-situ SEM observation and Galvanneal coating Fracture has been analysed. It is been thongt that desquamation takes place at the interface of substrate /Γ phase. The Fracture of Γ phase is serrated and its thickness is hundreds of nano-metres. The Fracture shape of Γ phase is different from other phases of of the galvanneal coating.

Critical Fracture Processes in Army Cannons: A Review

Fast fracture in cannons can be well described using elastic-plastic fracture toughness, in combination with comparisons of cannon section size relative to the size required to maintain plane strain fracture. Fatigue fracture of cannon tubes is modeled from results of full-size fatigue tests that simulate cannon firing. These tests are also the basis of fatigue-intensity-factor modeling of fatigue life, which incorporates material strength, initial crack size and Bauschinger-modified autofrettage residual stress into life predictions. Environment-assisted fracture in the thermally damaged near-bore region of fired cannons is shown to be controlled by hydrogen. High strength cannon steels are susceptible to hydrogen; cannon propellant gases provide the hydrogen; and the source of sustained tensile stress is the near-bore thermal damage and compressive yielding. A thermo-mechanical model predicts tensile residual stress of similar depth to that of observed hydrogen cracks. Coating fracture in the thermal-damage region of fired cannons is characterized and modeled. The Evans/Hutchinson slip zone concept is extended to calculate in-situ coating fracture strength from observed crack spacing and hardness in the damaged region.