Nanostructured WC-Co coating was deposited by cold spraying using a nanostructured WC-12Co powder. The critical velocity for the particle to deposit was measured. The coating microstructure was characterized by X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy. The coating hardness was tested using a Vickers hardness tester. The deposition behavior of single WC-Co particle was examined. WC particle size was measured for comparison of deposit properties to that of sintered bulk. The result shows that the nanostructured WC-Co coating can be successfully deposited by cold spraying using nanostructured powders. The coating exhibited a dense microstructure with full retention of the original nanostructure in the powder to the coating. The test of microhardness of the coating yielded a value of over 1820 Hv 0.3 , which is comparable to that of sintered nanostructured WC-Co. The deposition behavior of WC-Co powders as superhard cermet materials in cold spraying and powder structure effects is discussed.
The
photoresponse of the coumarin derivative based on reversible
photodimerization and photocleavage has been studied for a long time.
This paper reports a novel approach of preparing photoresponsive polymer
materials containing coumarin structure by photopolymerization based
on the wavelength selectivity. A photopolymerizable and photoresponsive
monomer, 7-(hydroxyethoxy)-4-methyl-coumarin (AECM), was synthesized,
and photopolymerization was performed on it using UV light irradiation
(λ = 405 nm). After polymerization the polymer with coumarin
pendant groups can achieve reversible photo-induced [2 + 2] dimerization
under UV light (λ > 300 nm) and photocleavage of the cross-link
to recovery back to the original structure through further irradiation
with UV light (λ = 254 nm). What’s more, this monomer
could be used to produce a high-resolution pattern and photo-responsive
pressure sensitive adhesive through photopolymerization. The demonstrated
approach opens new perspectives for the design of photoresponse materials.
The limited deformation of hard cermet particles and impacted coating makes it difficult for conventional thermal spray powders to continuously build up on impact in cold spraying. In this study, three nanostructured WC-12Co powders with different porous structure and apparent hardness were employed to deposit WC-Co coatings on stainless steel substrate by cold spraying. The deposition characteristics of three powders of porosity from 44 to 5% were investigated. It was found that WC-Co coating is easily built-up using porous powders with WC particles bonded loosely and a low hardness. The microhardness of WC-12Co coatings varied from 400 to 1790 Hv with powders and spray conditions, which depends on the densification effects by impacting particles. With porous WC-Co powders, the fracture of particles on impact may occur and low deposition efficiency during cold spraying. The successful building up of coating at high deposition efficiency depends on the design of powder porous structure.
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