Ghosh, Gourhari

The maritime sector, vital for global economic growth, encounters challenges due to the corrosive aquatic environment, particularly concerning cavitation erosion (CE). CE is a leading cause of turbo-machinery failure, causing critical damage to essential components like propellers and naval hulls. Recent research focuses on materials with improved CE resistance, emphasizing advanced coatings. Tungsten carbide (WC) cermet coatings, often containing cobalt (Co) and chromium (Cr), show promise in enhancing wear resistance and reducing cavitation erosion. With an aim to increase CE resistance, this paper investigates the application of a WC-10Co-4Cr + graphene nanoplatelet (GNPs) coating on an IS-2062 steel substrate using the High-Velocity Oxygen Fuel (HVOF) technique in conjunction with laser surface texturing as a pre-coating preparation technique. Also, Response Surface Methodology (RSM) is utilized to study and optimize the coating's erosion behaviour, offering valuable insights for practical applications in challenging maritime environments. The analysis revealed that WC-10Co-4Cr + 2% GNPs has the highest cavitation resistance, when compared to other coating configurations. Further, the HVOF-coated specimens exhibited significantly improved corrosion resistance, as evident from lower corrosion current densities (ICorr) ranging from 9.36 × 10−6 to 19.31 × 10−6 A/cm2 compared to the pristine substrate (ICorr = 66.32 × 10−6 A/cm2). Effect of GNPs was envisioned to be investigated, and the results reveled that the WC-10Co-4Cr + 2% GNPs coated surface demonstrated the most notable reduction in corrosion rate (9.36 mm/y), highlighting its superior performance, attributed to GNPs reinforcement and a Cr binder that minimized porosity and mitigated micro-cavities and pitting corrosion.

Metal matrix composites (MMC) possess an excellent combination of mechanical and metallurgical properties but are difficult to process. Laser-directed energy deposition (DED) technique can be effectively employed to fabricate MMC coatings, producing dense coatings with sound metallurgical bonding. In this investigation, Inconel 718/ alumina (Al2O3) MMC coating is manufactured using powder-fed laser DED process. At first, different wt. % of alumina particles (i.e., 1, 3, 5, and 7 wt%) were mixed with Inconel 718 powder, and after that, four different types of MMC coatings were fabricated. By analyzing the mechanical properties and microstructure of those MMC coatings, the optimum amount of Al2O3 in MMC coating is determined. It is observed that IN718 −5 wt% Al2O3 composite coating exhibits better mechanical properties (i.e., hardness = 625 ± 6 HV), so further experiments were conducted with this coating. In the second phase of this investigation, the effect of laser power, scanning speed, and powder feed rate on porosity is analyzed. Beyond a laser power of 1700 W, porosity increases significantly due to the formation of gas porosity. On the other hand, beyond a scanning speed of 500 mm/min, the energy input is insufficient to melt the powder, which leads to the enhancement of lack-of-fusion porosity. With an increase in the powder feed rate, the lack of fusion porosity grows due to a higher laser power attenuation. The mid-range of laser power and scanning speed and lower range of powder feed rate are suitable for creating MMC coatings with better mechanical properties.

Thermally sprayed tungsten carbide coating is extensively engaged in wear resistance applications due to its good tribological properties. For some applications in aerospace, automotive, printing and forming industries, these coated components require a nanolevel surface finish. In the current investigation, magnetorheological fluid based finishing (MRF) process is carried out on the pre-polished tungsten carbide coating using standard magnetorheological (MR) fluid which contains diamond powder as the abrasive particles. In this case, the lower gripping strength of non-magnetic abrasives into the chain structures of carbonyl iron particles (CIPs) is responsible for inadequate material removal rate (MRR) and irregular polishing. To overcome these problems, MRF is conducted with a chemical etchant and that leads to a higher finishing rate due to the integrated effect of etching and polishing. However, it is perceived that the ability of normal MRF technique and MRF with chemical etchant is somehow restricted at a higher wheel velocity. To address these challenges of MRF process, CIP-diamond and CIP-diamond-graphene composite abrasives are introduced in this investigation. Due to the resilient attraction force among the composite abrasives, a much higher yield stress is observed and that leads to higher MRR and less spilling of MR fluid even at an elevated wheel speed. Composite magnetic abrasives are characterized using nanohardness tester, magnetometer and rheometer to assess its mechanical and magnetic behaviours. The lowest surface roughness (Sa) of 55 nm and highest MRR are attained using MRF with CIP-diamond-graphene abrasives.

Modeling multitrack laser-directed energy deposition (LDED) is different from single-track deposition. There is a temporal variation in the deposition geometry and integrity in a multitrack deposition, which is not well understood. This article employs an analytical model for power attenuation and powder catchment in the melt pool in conjunction with a robust fully coupled metallurgical-thermomechanical finite element (FE) model iteratively to simulate the multitrack deposition. The novel hybrid analytical–numerical approach incorporates the effect of preexisting tracks on melt pool formation, powder catchment, geometry evolution, dilution, residual stress, and defect generation. CPM 9V steel powder was deposited on the H13 tool steel substrate for validating the model. The deposition height is found to be a function of the track sequence but reaches a steady-state height after a finite number of tracks. The height variation determines the waviness of the deposited surface and, therefore, the effective layer height. The inter-track spacing (I) plays a vital role in steady-state height evolution. A larger value of I facilitates faster convergence to the steady-state height but increases the surface waviness. The FE model incorporates the effects of differential thermal contraction, volume dilation, and transformation-induced plasticity. It predicts the deposition geometry and integrity as a function of inter-track spacing and powder feed rate. The insufficient remelting of the substrate or the preceding track can induce defects. A method to predict and mitigate these defects has also been presented in this article.