Laser clad and HVOF sprayed Stellite 6 coating in chlorine rich environment with KCI at 700 °C

Laser clads and HVOF coatings from a stellite 6 alloy (Co–Cr–W–C alloy) on 304 stainless steel substrates were exposed both bare and with KCl deposits in 500 ppm HCl with 5% O2 for 250 h at 700 C. SEM/EDX and PXRD analyses with Rietveld refinement were used for assessment of the attack and for analysis of the scales. The bare samples suffered from scale spallation and the scale was mostly composed of Cr2O3, CoCr2O4 and CoO, although due to dilution haematite (Fe2O3) was detected in the scale formed on the laser clad sample. A small amount of hydrated HCl was detected in bare samples. While the corrosion of the bare surfaces was limited to comparatively shallow depths and manifested by g and M7C3 carbide formation, the presence of KCl on the surface led to severe Cr depletion from the HVOF coating (to 1 wt%). Both inward and outward diffusion of elements occurred in the HVOF coating resulting in Kirdendall voids at the coating–steel interface. The laser clad sample performed significantly better in conditions of the KCl deposit-induced corrosion. In addition to the oxides, CoCl2 was detected in the HVOF sample and K3CrO4 was detected in the laser clad sample. Thermodynamic calculations and kinetic simulations were carried out to interpret the oxidation and diffusion behaviours of coatings

Tribological properties of hard metal coatings sprayed by high velocity air fuel process

Lowering the thermal energy and increasing the kinetic energy of sprayed particles by newly developed HVAF systems can significantly reduce material decarburization, and increases sliding wear and corrosion resistance of hard metal coatings, making HVAF coatings attractive both economically and environmentally over its HVOFs predecessors. Two agglomerated and sintered feedstock powder chemistries, respectively WC-Co (88/12) and WC-CoCr (86/10/4), with increasing primary carbides grain size from 0.2 to 4.0 microns, have been deposited by the latest HVAF-M3 process onto carbon steel substrates. Respective dry sliding wear behaviours and friction coefficients were evaluated at room temperature via Ball-on-disk (ASTM G99-90) wear tests against A1203 counterparts, and via Pin-on-disk (ASTM G77-05) wear tests against modified martensitic steel counterparts in both dry and lubricated conditions. Sliding wear mechanisms, with formation of wavy surface morphology and brittle cracking, are discussed regarding the distribution and size of primary carbides. Corrosion behaviours were evaluated via standard Neutral Salt Spray (NSS), Acetic Acid Salt Spray (AASS), accelerated corrosion test and electrochemical polarization test at room temperature. Optimization of coating tribological properties are discussed regarding the suitable selection of primary carbide size for different working load applications

Band bending at heterovalent interfaces Hard X ray photoelectron spectroscopy of GaP Si 001 heterostructures

GaP is a preferred candidate for the transition between Si and heterogeneous III V epilayers as it is nearly lattice matched to Si. Here, we scrutinize the atomic structure and electronic properties of GaP Si 0 0 1 heterointerfaces utilizing hard X ray photoelectron spectroscopy HAXPES . GaP 0 0 1 epitaxial films with thicknesses between 4 and 50 nm are prepared by metalorganic vapor phase epitaxy on either predominantly single domain SD or two domain TD Si 0 0 1 surfaces. The antiphase domain content in the GaP films is in situ controlled, employing reflection anisotropy spectroscopy. Via the analysis of core level photoelectron intensities, we reveal core level shifts of the P 2p and Si 2p peaks near the interface as well as core level shifts in the Ga 3d peaks near the surface. We suggest an Inter Diffused Layer IDL model of the GaP Si 0 0 1 interfacial structure with Sisingle bondP bonds at the heterointerface and residual P atoms in the Si substrate. Using a newly developed Parametrized Polynomial Function PPF approach, we derive a non monotonic band bending profile in the heterostructures, correct experimental valence band offsets implying interfacial electronic barriers, and determine valence band discontinuities of amp; 9651;EV 1.1 0.2 eV SD samples and amp; 9651;EV 0.8 0.2 eV TD samples at GaP Si 0 0 1 interface

Stříbrem dopovaný hydroxidapatitový povlak nanášený pomocí suspenzního plazmatického nástřiku

Čistá suspenze hydroxidapatatu byla vyrobena pomocí chemické sysntézy. S použitím WSP hořáku byl vytvořen HA povlak na substrátu z SS304 a Ti6Al4V. Vlastnosti povlaku byly hodnoceny pomocí SEM, XRD a EDX. PO dopozici bylo dosaženo 4-10% podílu amorfní fáze a 75-82% krystalické HA fáze v tloušťcě cca 145 um. Tribologické chování bylo hodnoceno pomocí testu pin-on-disc. Přídavek AgNO3 do suspenze vedl k vzniku Ag disperze mezi splaty v 8% podílu Ag. Úspěšné přidání antibakteriálního Ag je pokrokem v oblasti výzkumu materiálů kloubních náhrad.Pure hydroxyapatite suspension was produced by wet chemical synthesis. Using a hybrid water-stabilized torch, a series of HA coatings were produced on SS304 and Ti6Al4V substrates and their properties were characterized by SEM, EDX and XRD techniques. After deposition, the amorphous phase content reached 6-10% and the coatings retained 75-82% of crystalline HA phase. Their thickness reached 145 lm. To understand the wear behavior of the coatings, pin-on-disc tribology evaluation was performed. Additionally, a set of HA coatings was prepared with pure metallic Ag content. This formed by in situ chemical decomposition of AgNO3 added into the HA suspension. The Ag was dispersed evenly within the coatings in the form of submicron-sized particles situated predominantly along the HA splats boundaries with a total Ag content of 8 wt.%. Given the antibacterial properties of Ag, such result presents a promising step forward in the hard tissue replacement research