A new method which allows the development of Low Pressure Cold Sprayed copper coatings on PEEK (Poly-Ether-Ether-Ketone) based composites reinforced by carbon fibers is investigated. Due to the solid ...state and high velocities of impacting particles, cold spraying involves a high erosion on composite materials, leading to an absence of coatings and sometimes damaged carbon fibers. As a result, few dozen micrometers of pure PEEK matrix have been added on the surface of the composite to act as an interfacial layer between composite and coating. Optimization of the LPCS parameters has been carried out, using a careful choice of powder size distribution in order to avoid substrate damage, erosion and coating delamination.
Dense copper coatings exceeding 100 μm thick have been obtained. SEM observations have been carried out to evaluate the microstructure of coatings, and the minimal required matrix thickness regarding the size distribution of the powder.
•Low Pressure Cold Sprayed (LPCS) copper coatings on PEEK (Poly-Ether-Ether-Ketone) based composites reinforced by carbon fibers.•Optimization of the LPCS parameters using specific powder size distribution.•Optimization of PEEK matrix thickness on top surface.•Evaluation of coating behaviors (porosity, electrical resistivity).
Additive manufacturing processes and especially the family of laser powder bed fusion technologies have a great industrial potential since it enables, from metal powder beds, to produce full density ...complex monolithic parts. The high-temperature gradient resulting from the locally concentrated energy input leads to strong temperature fields driving non-negligible residual stress gradients, part deformations and crack formation. Resulting stress and texture gradients arise from the interdependent physical phenomena (metallurgical, thermal, mechanical and fluid mechanics) occurring during the process. Present work focuses on the residual stress being built in an austenitic stainless steel cubical shaped part of 1 cm side, prepared by a laser powder bed fusion process from a gas-atomized metallic powder (from martensitic X40CrMoVN16-2 stainless steel), through a full residual stress tensor mapping achieved thanks to neutron diffraction. Stress analyses incorporate morphological and crystallographic textures, as well as elastic anisotropy. Components of the principal stress tensor display compressive values close to the baseplate that develop into low compression, and a tensile stress state at the subsurface (surrounding thermal history effects). Results also underline the strong impact of matter environment (and thus thermal environment) onto stress gradient magnitude and the complex loading origins of the residual stress.
alpha-Fe(Cr)-h-BN and alpha-Fe(Cr)-Fe2B-FeB coatings on X30Cr13 stainless steel are synthesized by laser melting with incorporation of hexagonal boron nitride, or by alloying of boron. The additive ...powders are deposited on steel before pulsed irradiation by Nd-YAG laser beam. The solidification structures of the obtained coatings are investigated by optical microscopy and X-ray diffractometry. The mechanical properties are investigated by nanoindentation and the tribological behaviour is characterized on pin-on-disc tribometer, under dry-sliding conditions with different loads and a temperature range 25-500 deg C. h-13N-alpha-Fe(Cr) and Fe2B-alpha-Fe(Cr) coatings have average hardnesses 10.0 and 14.5 GPa, respectively, while hardness of untreated stainless steel is 4.2 GPa. In comparison with this untreated steel, the sliding contact on ceramic (ruby) of such coating shows a lower coefficient friction and a definitively better wear resistance.
This experimental study was performed with intent to improve the surface properties of titanium and to minimize the friction on ceramic. Its main object was to strengthen the resistance against wear ...resulting from dry-sliding contact. Titanium-covered or not, graphite powder was irradiated and superficially melted by means of a pulsed Nd–YAG laser beam. Different irradiations were carried out, changing the distance between irradiated surface and laser beam focal plane. The variations in the dry-sliding friction coefficient were recorded using a pin-on-disc tribometer. An optimum irradiation of graphite-covered titanium generated hard granular titanium carbide and lubricating graphite inclusions which drastically reduced dry friction and wear of the Laser-Melted Zone. In this way, a self-lubricating composite coating has been successfully synthesized on titanium from the laser melting process.
Experimental results of surface melting by pulsed Nd-YAG laser irradiation of titanium covered with graphite powder were analyzed in comparison with the results of numerical simulations. The ...simulations of the thermal events, such as the maximum of temperature gradient at the surface and the duration of the liquid state after irradiation, were found due to a semi-analytic model of the space-time temperature distributions which were induced by the irradiation treatments. These simulations were required in order to calculate a series of integrals by Simpson's numerical method. They allowed us to explain the experimental results, such as the incorporation of carbon in melted zone, which produces titanium carbide and possible graphite inclusions, as a function of the irradiation parameters. The perpetual absence in the thickness and the exceptional presence at the surface of the solidification structure resulting from the plane-front growth of titanium carbide were justified. (Author)
Titanium foils coated with graphite films 20
μm thick were irradiated by means of a pulsed Nd-YAG in order to harden this metal by surface melting and alloying. The relationships between irradiation ...parameters, microstructure and hardness of the synthesized composite coatings were determined. Four relevant parameters were defined as governing the irradiation processes. The parametric working field of the laser source was investigated next to its periphery. The influences of the relevant irradiation parameters on the microstructure and hardness of the melted zone were deduced from the metallographic analyses and Vickers micro-indentation tests of the cross sections of this composite zone. Such a zone was constituted always with hard titanium carbide and ductile metallic titanium, some times with the presence of lubricating graphite inclusions. The main advantage of such a surface treatment of titanium is to synthesize, under clearly defined irradiation conditions, a self-lubricating composite coating that resists abrasive or adhesive wear.
α-Fe(Cr)-h-BN and α-Fe(Cr)-Fe
2B-FeB coatings on X30Cr13 stainless steel are synthesized by laser melting with incorporation of hexagonal boron nitride, or by alloying of boron. The additive powders ...are deposited on steel before pulsed irradiation by Nd-YAG laser beam. The solidification structures of the obtained coatings are investigated by optical microscopy and X-ray diffractometry. The mechanical properties are investigated by nanoindentation and the tribological behaviour is characterized on pin-on-disc tribometer, under dry-sliding conditions with different loads and a temperature range 25–500
°C. h-BN-α-Fe(Cr) and Fe
2B-α-Fe(Cr) coatings have average hardnesses 10.0 and 14.5
GPa, respectively, while hardness of untreated stainless steel is 4.2
GPa. In comparison with this untreated steel, the sliding contact on ceramic (ruby) of such coating shows a lower coefficient friction and a definitively better wear resistance.
In 2005, after the State Elections Enforcement Commission concluded she had committed absentee ballot fraud the year before, Holloway signed an agreement to pay a $10,000 fine and not to distribute ...absentee ballots or assist voters with ballots for two years.
PDF
