Al-hamdani, Kamaal
(2019)
Deposition of satellited Al-TiC powders for coating applications.
PhD thesis, University of Nottingham.
Abstract
Metal matrix composite (MMC) coatings have good wear resistance, given the combined ductility of the metal matrix and high hardness and strength of the ceramic
reinforcements. Surface modification by coating deposition is an important approach for improving the functional surface region of materials without replacing the entire component, which is also a cost-effective approach for extension the component working life.
Cold spray (CS) is an important technique used to deposit different types of materials without the need for heating or melting. Because of the dependence of cold spray on
deformation of the sprayed and substrate materials, hard particles tend to rebound, while less-ductile materials experience limited deformation during impact. Laser
cladding (LC) has some advantages in terms of surface processing over other techniques, including narrow wavelength, low divergence, and a highly coherent beam. However, the use of blended feedstocks within powder-injection LC can lead to the separation of the blended phases that may cause stream.
Satelliting is a simple powder-mixing process recently used to produce composite feedstocks consisting of fine ceramic particles attached to the surfaces of relatively
large (parent) metal particles. This is based on adding a small amount of liquid binder to the powder mixture during the mixing process without the need for high energy or heat. The main point of investigation of this research is the use of satellited Al-TiC feedstocks for cold spray and laser cladding processes, along with blended feedstocks with the same compositions for comparison. This is a trails for improving the
behaviour of the composite coating by increasing the reinforcement fraction through elimination particles rebounding.
In the first stage of this work, preliminary satelliting processes were performed using TiC as a reinforcing phase, adjusting the fraction of Al powder and the binder to produce a satellited powder. The prepared satellited powder then was used in the CS process to evaluate its cold-sprayability, this was along with pure Al and blended Al/TiC feedstocks for comparison purposes. A seven-fold increase in TiC area fraction was measured in the satellited coating compared to that in the blended coating.
In the second stage, the effects of using the satelliting technique on the deposition and characteristics of composite coatings of a less-ductile Al alloy (A6061) and TiC, fabricated by cold-spray were investigated. The use of satellited feedstock has resulted in increasing the TiC catchment and deposition efficiency by 66% and 78%,
respectively, compared to the blended feedstock. The satellited coating presented a reduction of 67% in the interlamellar porosity compared with the blended 6061/TiC
coating, while the heat-treated coating exhibited a 70% reduction in interlamellar porosity.
Finally, the behaviour of Al/TiC satellited feedstock under laser cladding was investigated along with a blended feedstock. The blended and satellited and have
presented several differences regarding: clad geometry, clad area, TiC fraction and other characteristics. These differences indicated a different interaction of the
satellited feedstock with the lase radiations; thus, two interaction mechanisms between the laser radiation and the feedstocks were suggested and demonstrated depending on their morphologies.
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