Janette Brezinová

A study of the effect of surface pre-treatment on the adhesion of coatings

This paper deals with the study of effects of mechanical surface preparation on the adhesion of coating with high content of zinc dust. Five kinds of mechanically blasted surfaces were studied. The following were used as abrasives: steel shot, steel grit, brown corundum oxide and zirblast. The last surface type was modified by MBX Blaster technology (mechanical bristle blasting). The surfaces topography was quantified by a roughness profilometer. The shape and size of the incurred inequalities on the modified surfaces were studied using 3D microscope images of the surface. The purity of the surfaces after pre-treatment was evaluated by impurity glued on the tape and measuring the reflection of light from the surface. Fractal analysis was used to evaluate the diversity of inequalities on the prepared surfaces. Cross-sections were also taken of the prepared surfaces. The prepared surfaces were coated with zinc-filled coating. The adhesion of the coating to the substrate was evaluated by a pull-off test after curing the coating (as sprayed), as well as after exposure to severe corrosive environments. The best adhesion of the coating was found for the coating applied to the substrate which had been pre-treated with brown corundum and steel grit.

Effect of Long Term Operation on Degradation of Material of Main Gas Pipelines

The mechanisms of metal damage in the pipe of the main pipeline are investigated, the main reasons for their appearance are found and analysed. The main results are obtained by joint use of metallography, indentation, method for processing and analysis of digital images.

Friction Conditions during the Wear of Injection Mold Functional Parts in Contact with Polymer Composites

This article deals with the evaluation of material wear of injection molds made of aluminium alloy Alumec 89 and copper alloy Moldmax HH in friction couples with polymer materials with various filler contents. The friction relations in injection molding were simulated in an adhesion dry wear test using an Amsler machine, with an area contact of the friction couple materials. The wear intensity was evaluated by determination of friction coefficient and relative wearing by the mass loss. Surface morphology changes of evaluated alloys after wear and the thermal conditions in particular friction couples were analyzed simultaneously.

Tribological properties of selected ceramic coatings

The paper presents the characteristics of some ceramic coatings obtained by a plasma spray method. The ceramic coatings Al2O3, Cr2O3 and Cr2O3 + 5% TiO2 were evaluated. Also the influence of the NiCr interlayer on the functional properties of sprayed coatings was studied. Other parameters studied included: thickness; microhardness; adhesion of the coatings; resistance to abrasive wear and thermal cyclic loading. The addition of TiO2 to the Cr2O3 material increased the coating density, but did not substantially reduce the hardness. On the other hand, the lowest loss of material thickness was seen for Cr2O3; while the Al2O3 and the Cr2O3 + 5 wt.% TiO2 material showed a higher loss. The loss in the case of the latter two was about the same. Relatively, higher values of abrasive wear resistance were observed in the Cr2O3 coatings, as compared to the reference material (Al2O3 coating), and the highest microhardness values were measured in the Cr2O3 coating. Finally, the metal interlayers in all coatings increased their resistance to thermal shock. All the coatings, using the interlayer to reduce differences in coefficients of thermal expansion, were suitable for the purpose of the thermal loading up to 1000 °C.

The Study of Parameters of Surface Roughness by the Correlation Analysis

The paper deals with evaluation of relation between individual parameters of roughness of the blasted surfaces by the correlation analysis. Based on the measured values on the surfaces which were blasted by various types of blasting devices, the correlation matrix was set and the standard of statistic importance of correlation between the monitored parameters was determined from it. The correlation coefficient was also set.

DEFORMATION AND ENERGY PARAMETERS OF FRACTURE OF STEEL OF THE MAIN GAS PIPELINE

By example of steel 17G1S, the regularities in the impact fracture of Charpy specimens at normal and low temperatures are described. The relationship between the energy parameters of fracture (impact toughness) and the deformation response of the material (the height of shear lips) of the specimens from the pipe steel is established. The micromechanisms of impact fracture of the material are described. At 20 °C and –30 °C, focal splitting of the material was observed on the fracture surface of specimens; at –60 °C, the material failed in a brittle manner by the mechanism of cleavage.

Quality Evaluation of HVOF Coatings on the Basis of WC-Co in Tribocorrosive Conditions

Article deals with analysis of production and characteristics of ceramic coatings applied using HVOF technology. It presents the results of research focused on quality evaluation of HVOF coatings on the basis of WC-Co and impact of Boron Nitride protective layer. HVOF coatings were exposed to hard tribocorrosive conditions. For determining of corrosive resistance of coatings 1M solution of NaCl, potentiodynamic tests and accelerated salt spray test were used. Experiment confirmed that using of Boron Nitride protective coating clearly improves corrosive resistance of the coating on the basis of WC-Co even in hard combined tribocorrosive conditions. Protective layer seals the pores in the structure of coating and thus prevents the formation of corrosion and subsequent depreciation of coating in various corrosive environments. Using of protective layer thus improves lifetime and reliability of spraying and the part itself. Improved lifetime positively influences also the economics of the operation of energetic equipment in which these coating are used.

Degradation of renovation layers deposited on continuous steel casting rollers by submerged arc welding

The factors that affect the life of continuous steel casting rollers were investigated. Rollers that were removed from a manufacturing line because they had failed were renovated by submerged arc welding and subjected to working conditions until they again failed. The welding parameters (welding current, welding voltage, welding speed, current polarity, preheating temperature, interpass, postheating, and cooling conditions of clad) and chemical reactions and compositions had important effects on roller lifetime. Chromium has a dominant influence on the abrasion resistance of hard martensitic structures of the roller. Cr produces several types of precipitates (M3C, M23C6, M7C3, and M3C2). Alloying elements Mo and V in welding wire form fine carbides Mo2C and VC in weld layers. In low-carbon welding wires, precipitation hardening by N2 is used, by formation of chromium nitrides CrN and Cr2N. This article analyzes the process of failure of the functional surfaces of the repaired roller, in order to identify the origin and propagation of the cracks and share of corrosive environment on the tribo-degradation processes.

Investigation of Statically Deformed Aluminum Alloy Surface

The peculiarities of the accumulation of structural and mechanical defects on the surface of the D16chT aluminum alloy under significant plastic strains are analyzed. The peculiarities of the surface strain hardening are found, and the geometrical parameters of the relief formations are described. The relationship between multiple cracking and specimen deformation is established. It is proved that the deformation relief parameters can be used to assess damage of the D16chT alloy under static deformation.

Study of Selected Properties of Thermally Sprayed Coatings Containing WC and WB Hard Particles

Abstract The paper presents results of research of the essential characteristics of two kinds of advanced coatings applied by HVOF technology. One studied coating: WB-WC-Co (60-30-10%) contains two types of hard particles (WC and WB), the second coating is eco-friendly alternative to the previously used WC-based coatings, called “green carbides” with the composition WC-FeCrAl (85-15%). In green carbides coating the heavy metals (Co, Ni, NiCr) forming the binding matrix in conventional wear-resistant coatings are replaced by more environmentally friendly matrix based on FeCrAl alloy. On the coatings was carried out: metallographic analysis, measurement of thickness, micro-hardness, adhesion, resistance to thermal cyclic loading and adhesive wear resistance (pin-on-disk test). One thermal cycle consisted of heating the coatings to 600°C, dwell for 10 minutes, and subsequently cooling on the still air. The number of thermal cycles: 10. The base material was stainless steel AISI 316L, pretreatment prior to application of the coating: blasting with white corundum, application device JP-5000.