Increasing Resistance to Ultrasonic Cavitation Erosion of Metallic Parts by Means of Surface Modification

Comparison of the corrosion and cavitation erosion behaviors of the cast and surface-modified manganese-aluminum bronzes in sodium chloride solution

Laser surface melting (LSM) of Manganese Nickel Aluminium Bronze (Cu-Mn-Al-Ni-Fe) to improve cavitation erosion and corrosion resistance was performed using a 2-kW continuous wave (CW) Nd-YAG laser. A modified layer with a single β-phase structure and with highly refined and homogenized grains was obtained. Under favorable laser processing conditions (Power = 1 kW; Scanning velocity = 35 mm/s; Spot diameter = 2 mm) the microhardness was increased by 2 times and the cavitation erosion resistance in 3.5 wt% NaCl solution was increased by 5.8 times. This was even higher than that of Nickel Aluminium Bronze (NAB). For as-received MAB, the SEM micrographs of the surface taken at an early stage of the cavitation erosion and general corrosion tests revealed that the iron/manganese-rich κI phase and the α/κI interface were initiation sites of damage. On the other hand, attack was much milder in the laser melted samples and started at the triple junctions of the grain boundaries. The corrosion current density in 3.5 wt% NaCl was also improved after laser surface melting, with a reduction from 9.54 µA/cm2 to 4.26 µA/cm2. The corrosion potential also shifted in the noble direction by about 80 mV. It could be concluded that the improvement in both cavitation erosion and corrosion resistance was in particular attributable to homogenization and refinement of the microstructure.Laser surface melting (LSM) of Manganese Nickel Aluminium Bronze (Cu-Mn-Al-Ni-Fe) to improve cavitation erosion and corrosion resistance was performed using a 2-kW continuous wave (CW) Nd-YAG laser. A modified layer with a single β-phase structure and with highly refined and homogenized grains was obtained. Under favorable laser processing conditions (Power = 1 kW; Scanning velocity = 35 mm/s; Spot diameter = 2 mm) the microhardness was increased by 2 times and the cavitation erosion resistance in 3.5 wt% NaCl solution was increased by 5.8 times. This was even higher than that of Nickel Aluminium Bronze (NAB). For as-received MAB, the SEM micrographs of the surface taken at an early stage of the cavitation erosion and general corrosion tests revealed that the iron/manganese-rich κI phase and the α/κI interface were initiation sites of damage. On the other hand, attack was much milder in the laser melted samples and started at the triple junctions of the grain boundaries. The corrosion current density in 3...

Laser surface alloying of a marine propeller bronze using aluminium powder: Part I: Microstructural analysis and cavitation erosion study

An enormous amount of research has been conducted on aluminium alloys in friction stir processing (FSP), despite magnesium alloys reporting severe weight reduction when compared to aluminium alloys; a very slight amount of research has testified for FSP of magnesium alloys. Magnesium is highly reactive and susceptible to corrosion in the presence of an aggressive environment. This highly corrosive nature of magnesium limits its applications. Surface properties like crystal structure, composition, and microstructure influence the corrosion and wear properties of the material. Coating techniques and alloying techniques like laser surface modifications are performed to passivate the magnesium surface from corrosion. Coating techniques, however, have been found to be insufficient in corrosion protection due to coating defects like pores, cracks, etc, adhesion problems due to poor surface preparation of the substrate, and impurities present in the coating which provide microgalvanic cells for corrosion. The current study gives a detailed overview of different types of surface modification methods, such as physical vapour deposition, chemical vapour deposition, chemical conversion coating, and ion implantation coating techniques, and also focuses on a few alloying or surface processing methods, such as laser surface modification – namely laser surface melting, laser surface cladding, laser shot peening, laser surface alloying and FSP. FSP is a novel surface modification method derived from friction stir welding, which modifies the microstructure and composition of surface layer without changing the bulk properties to enhance corrosion resistance. FSP enhances and homogenizes the microstructure but also eliminates the breakup of the brittle-network phases and cast microstructure imperfections. Indeed, FSP can produce particle and fibre-reinforced magnesium-based surface composites. FSP empowers the manufacturing of magnesium by adding additives. The different methods of coating and surface modification are compared with FSP.

Developments in laser-based surface engineering processes: with particular reference to protection against cavitation erosion

In this investigation, the friction stir processing (FSP) method was utilized to improve the properties of the surface of the as-cast nickel aluminum bronze (NAB) alloy in two different processing parameters. The microstructure, element distribution and mechanical properties of the alloys before and after FSP were observed and estimated. The cavitation erosion behaviors of the original NAB and FSP NAB in different test solutions were also discussed. The results indicated that the microstructure became finer and more homogeneous and the element distribution became more uniform after FSP. The FSP NAB alloys also possessed better mechanical properties. The lower cumulative cavitation erosion mass loss of FSP NAB in all test solutions indicated the fact that the cavitation erosion resistance of the as-cast NAB could also be improved by the FSP method. Compared to the as-cast NAB, the corrosion effect on the cavitation erosion was more significant for the FSP NAB alloys owing to their better pure cavitation erosion resistance.

Improvement in cavitation erosion resistance of AISI 316L stainless steel by friction stir processing

A cast manganese-aluminum bronze (MAB) is subjected to friction stir processing (FSP), and the corrosion and cavitation erosion behaviors are studied. Results indicate that FSP breaks the large-sized κ phases into small particles and remarkably homogenizes and refines the α and β phases in the cast substrate. Therefore, the hardness is raised after FSP. A finer microstructure is obtained by the double-pass FSP. The FSP MABs exhibit higher electrochemical activity than the cast in 3.5 wt% NaCl solution, probably due to the residual stress induced by severe plastic deformation during FSP. However, after long-term immersion, severe localized corrosion occurs and results in the formation of large-size corrosion pits on the cast MAB. By contrast, the FSPed MABs undergoes relatively uniform corrosion and no noticeable pits are found on the double-pass FSPed MAB because of the homogenized microstructure and formation of homogeneous and protective corrosion product films. Under cavitation erosion in 3.5 wt% NaCl solution, the mass loss rate of the FSPed MABs is only half that of the cast. For the cast and FSPed MABs, cavitation transforms the corrosion potential towards a positive direction and raises the corrosion current density by nearly an order of magnitude, and the mechanical impact contributes largely to the cavitation erosion damage. For the cast MAB, severe cleavage fracture occurs at the coarse β phases and large cavities form on the eroded surface. However, the FSPed MABs are evenly and slightly eroded because of the homogeneous microstructure and increased hardness.

Slurry and cavitation erosion often limits the durability of many fluid machines such as hydroturbines, pumps, and propellers. Despite good resistance against slurry erosion, thermal spray coatings generally exhibit poor resistance against cavitation erosion. The performance of thermal spray coatings under cavitation erosion is limited by the presence of defects such as pores, splat boundaries, and limited adhesion with the substrate. In the present work, we performed post-processing of the WC-10Co-4Cr and Ni coatings deposited using the detonation gun process. For post-processing, microwave technique was used owing to its capability for atomic-level heating. The microstructural characterization of the as-sprayed and post-processed coatings showed significant homogenization for the latter. Compared to the typical lamellar structure of as-sprayed, the processed samples exhibited a columnar structure with metallurgical bonding with the substrate. The mechanical properties of the coatings were significantly improved after post-processing owing to the elimination of splat boundaries and pores which significantly enhanced the cavitation and slurry erosion resistance. Post-processed coatings showed at least ten times higher resistance to cavitation erosion. The slurry erosion resistance of the coatings also improved up to three times depending upon the impingement angle. A significant difference in the erosion mechanism was also observed after post-processing.

Improvement of cavitation erosion resistance of AISI 316 stainless steel by laser surface alloying using fine WC powder

Enhancement of cavitation erosion and corrosion resistance of brass by laser surface alloying with Ni–Cr–Si–B

Friction stir processing of dual certified 304/304L austenitic stainless steel for improved cavitation erosion resistance

As-cast Ni-Al bronze (NAB) was subjected to friction stir processing (FSP). Different processing parameters including rotating rate, traverse speed, and processing passes were selected to investigate their effect on the corrosion and cavitation erosion properties. Polarization curve and electrochemical impedance spectroscopy (EIS) were used to reveal the corrosion behavior. Cavitation erosion tests were conducted with an ultrasonic vibration device, and the eroded surfaces were observed using scanning electron microscopy (SEM). Results showed that cavitation erosion resistance was improved for all the processed NAB compared to the as-cast, and a two-pass processed NAB possessed the best corrosion resistance since it had further homogenized microstructure compared to the single-pass processed ones. Corrosion and cavitation erosion tests were also conducted on samples (Surface, Subsurface, Middle, and Bottom) obtained by machining from different positions of the stirred zone (SZ) in a constant-parameter processed NAB along the plate thickness. The Middle was more corrosion resistant since its equiaxed microstructure contributed to a homogeneous oxide film on the surface. The grains in the Bottom were the finest, so the Bottom was the most cavitation erosion resistant.

Laser surface alloying of FeCoCrAlNi high-entropy alloy on 304 stainless steel to enhance corrosion and cavitation erosion resistance

Microstructure evolution of the laser surface melted WC-Ni coatings exposed to cavitation erosion