51 research outputs found
Wear resistant solid lubricating coatings via compression molding and thermal spraying technologies
This work combines two industrially friendly processing methods in order to create wear resistant and solid-lubricating composite coatings potentially suitable for high load applications. Layered composite coatings were fabricated over wrought stainless steel 444 (SS444) by compression molding a mixture of solid lubricant polymer, polytetrafluoroethylene (PTFE, 80 wt%), and wear resistant polymer, polyimide (PI, 20 wt%), onto iron aluminide (Fe3Al) thermal spray coatings without the need of either primers or adhesives. The fabrication process consisted of three main steps: deposition of the Fe3Al thermal spray coating onto a SS444 substrate and transfer into a metal mold; transfer, compress, and sinter mixed polymeric powder onto the thermal spray coating; and finally, sample cooling to room temperature. This method takes advantage of the high surface roughness of thermal spray coatings, which increases mechanical adhesion of slippery PTFE to the underlying metallic material. Coatings were produced with and without a small amount of graphite (5 wt%) to analyze its impact on sliding and wear properties. Unlike current coating technologies, the thickness of the coatings presented herein can be easily and quickly tailored by varying the amount of polymer powder added to the mold prior to compression or by grinding after fabrication. We produced and analyzed coatings ~1.3 mm in total thickness that portray coefficient of frictions ~0.1, similar to pure PTFE. The calculated wear rates for both coatings with and without graphite are an order of magnitude lower than what has been previously reported for coatings of similar composition. The influence of graphite on wear properties was found to be minimal due to the high content of self-lubricating PTFE yet can act as a way to lower material costs and increase the coatings load capacity
Controls on Subglacial Rock Friction: Experiments With Debris in Temperate Ice
Glacier sliding has major environmental consequences, but friction caused by debris in the basal ice of glaciers is seldom considered in sliding models. To include such friction, divergent hypotheses for clastâbed contact forces require testing. In experiments we rotate an ice ring (outside diameter = 0.9 m), with and without isolated till clasts, over a smooth rock bed. Ice is kept at its pressureâmelting temperature, and meltwater drains along a film at the bed to atmospheric pressure at its edges. The ice pressure or bedânormal component of ice velocity is controlled, while bed shear stress is measured. Results with debrisâfree ice indicate friction coefficients \u3c 0.01. Shear stresses caused by clasts in ice are independent of ice pressure. This independence indicates that with increases in ice pressure the water pressure in cavities observed beneath clasts increases commensurately to allow drainage of cavities into the melt film, leaving clastâbed contact forces unaffected. Shear stresses, instead, are proportional to bedânormal ice velocity. Cavities and the absence of regelation ice indicate that, unlike model formulations, regelation past clasts does not control contact forces. Alternatively, heat from the bed melts ice above clasts, creating pressure gradients in adjacent meltwater films that cause contact forces to depend on bedânormal ice velocity. This model can account for observations if rock friction predicated on Hertzian clastâbed contacts is assumed. Including debrisâbed friction in glacier sliding models will require coupling the ice velocity field near the bed to contact forces rather than imposing a pressureâbased friction rule
Control of cultured human cells with femtosecond laser ablated patterns on steel and plastic surfaces
Fabrication of superhydrophilic surface on metallic nickel by sub-nanosecond laser-induced ablation
Injection-molded plastic plate with hydrophobic surface by nanoperiodic structure applied in uniaxial direction
Wettability modification of laser-fabricated hierarchical surface structures in Ti-6Al-4V titanium alloy
Femtosecond laser irradiation of metallic surfaces: effects of laser parameters on superhydrophobicity
Controlling the stainless steel surface wettability by nanosecond direct laser texturing at high fluences
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