Afsaneh Edrisy

Wear mechanisms in thermal spray steel coatings

Abstract Low carbon steel coatings (0.2% C) deposited on 319 Al alloy substrates by a plasma transfer wire arc (PTWA) process, were subjected to dry sliding tests over a range of loads (5–75 N) and sliding speed (0.2–2.5 m/s). A wear map was constructed to summarize the measured wear rates and mechanisms that control the wear rates. Four regimes were identified for sliding wear under dry atmospheric conditions: at low loads (

Evaluation of Local Anisotropy of Magnetic Response From Non-Oriented Electrical Steel by Magnetic Barkhausen Noise

Non-oriented electrical steels are indispensable materials for use in electric motors as magnetic cores. It is desired that the magnetic properties of the steel sheets be optimal and uniform in all the directions in the sheet plane. Thus, knowing the magnetic properties of the steel sheets in all the directions is crucial for the design of the electric motors. However, the magnetic properties of non-oriented electrical steels are usually measured by standard Epstein frame method, which normally only gives the overall magnetic properties in the rolling and transverse directions, and the magnetic properties in other directions are usually not known. In this research, magnetic Barkhausen noise (MBN) technique is utilized to characterize the local magnetic response of the processed non-oriented electrical steel. By rotating the MBN sensor to all the directions in the sheet plane, the local magnetic responses are obtained. The measured MBN is then directly compared to the crystallographic texture (texture factor) measured in the same direction. In this way, the local magnetic response of the steel sheet can be correlated to the crystallographic texture. It was found that magnetic Barkhausen noise technique was able to detect the difference in magnetic response induced by magnetocrystalline anisotropy if the effect of the residual stress can be eliminated. This would provide a potential technique for the characterization of magnetic properties of non-oriented electrical steel.

Effect of Annealing Time on the Texture of a 2.8% Si Non-Oriented Electrical Steel After Inclined and Skew Rolling

Non-oriented electrical steels are widely used in electric motors and generators as core materials to amplify magnetic flux and thus enhancing the conversion of energy. The efficiency of the motors and generators is closely related to the magnetic properties of the lamination core. In order to produce the magnetically favourable //ND texture (θ-fibre) and suppress the unfavourable //ND (γ-fiber) components in non-oriented electrical steels, two unconventional cold rolling schemes (inclined and skew rolling) were employed to process the steel. These rolling schemes have shown great potential in altering the texture of non-oriented electrical steel, especially for the 60° (inclined rolling) and 22.5° (skew rolling) angles. In this paper the effect of annealing time on the texture evolution of a 2.8 wt% Si steel was investigated using EBSD techniques. It was found that, all the unconventional rolling schemes were able to produce a strong θ-fiber texture, but the annealing time to achieve this texture was different.

Fluoropolymer Coated Condensing Heat Exchangers for Low-Grade Waste Heat Recovery

Low-grade waste heat from industrial processes usually has temperatures lower than ~232 °C, and thus has low thermal and economic values. However, low-grade waste heat is abundant and its total work potential is huge. To effectively recover low-temperature waste heat, i.e. recover both the sensible and latent heats, the exhaust streams usually need to be cooled to temperatures below the water and acid dew points, which causes severe corrosion problems in the heat exchangers. In this research, a fluoropolymer-based composite coating was applied to heat exchangers made of inexpensive metals (e.g. stainless steel, aluminum, carbon steel, etc.) to protect the surfaces contacting the waste streams. Corrosion tests were conducted in 80% sulphuric acid at ambient and elevated temperatures for more than 1500 h, and no corrosion was detected. The composite material has much higher thermal conductivity than virgin fluoropolymer, and can be applied to both bare and finned heat exchangers. The composite coating can be continuously utilized at temperatures up to ~260 °C. The coating also shows excellent adhesion strength to the substrate.

Design factors for reducing ice adhesion

Abstract The purpose of this study was to investigate the relationships between a type of engineering material and the ice adhesion strength while in direct application in icing conditions. Ice adhesion tests were conducted on various materials with different surface conditions. There is an identified need for systematic studies on the effects of varying surface conditions with well-characterized roughness and accurate adhesion measurement. This information is key in understanding the adhering behaviour of ice which is a necessary prerequisite for modelling the behaviour of ice adhesion to other surfaces and for icing prevention. Results show that the type of material will determine, in large, the strength of the ice adhesion between surfaces with similar roughness characteristics and the receding contact angle of water can be used as a predictor of relative ice adhesion. The adhesive strength of ice can be increased or decreased dramatically by means of adjusting the surface roughness with a uniform process. Each material tested exhibits a similar linear relationship. There was a stark contrast in the ice adhesion between the varying materials despite very similar polished surface conditions and static water contact angles. Ice bonded to the glass surface with an adhesion of 1562 ± 113 kPa, and to aluminum at 1039 ± 117 kPa, and stainless steel at 1022 ± 115 kPa, and finally Teflon at only 33 ± 52 kPa and during 80% of trials the ice/substrate interface was broken with no measured adhesion. The information gathered can be used to improve designs for a number of devices needed in cold weather climates.