Dagmar Draganovská

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.

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.

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.

Influence of the CAM Parameters and Selection of End-Mill Cutter when Assessing the Resultant Surface Quality in 3D Milling

The paper deals with the effects of CAM data needed to produce desired quality of shaped surfaces in forming dies making. In general, the input CAM data have strong influence to the final surface quality. The shaped surfaces 3D milling has been modeled as end ball milling of the surfaces with defined inclination. The end ball milling is the most common way to finish shaped surfaces. Directions of the milling tools motion and applied cutting conditions have been used to simulate data when setting milling strategies. The resultant machined surface quality has been identified in terms of the surface roughness. The paper introduces recommendations applicable to the programming of the different types of milling strategy when producing form surfaces.

Sampling Based Assessment of the Free-Form Milling Strategies

In this paper, author introduce common needs of increasing surface quality in tool making, a sort of products manufactured by free form milling technology. Principles of the free-form surface decomposition into measurable samples are presented and that is a method of combining CAD modeling with design of sampling objects. Sampling objects are classed both according to their measurability and applied milling strategy. Authors verify experimentally their sampling approach for three milling strategies applied in surface finishing operations while free-form surfaces are investigated in terms of their signed radii. Verification of proposed approach is based on statistical distribution of the measured surface roughness data.

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.

Tribological Properties of Coatings for Sheet Metal Stamping Dies

The conventional and innovative surface technologies are applied to sheet metal stamping dies in order to produce a composite material with properties unattainable in either the base or surface material. To select proper materials for forming dies the systematic evaluation of dies materials, their heat treatment and coatings are required. This paper deals with evaluation of plasma sprayed coatings Cr2O3, Al2O3 and WC12Co by pressure plate-ring test (tester T 05) and deep drawing process. Friction coefficients and seizure of these coatings were studied under dry and wet friction conditions. For different types of die rings (with and without ceramic coatings) the punching forces were measured during deep-drawing process. The results show that the main advantage of application of plasma sprayed coatings on the die contact surfaces under wet friction conditions compare to dies made of the tool steel may be the increase of seizure resistance of stamped part surface. The more significant difference in the friction coefficient values was not observed.

ASSESSMENT TRIBOLOGICAL PROPERTIES OF COATINGS APPLIED BY HVOF TECHNOLOGY

Abstract In this article, the attention is paid to the HVOF (High Velocity Oxygen Fuel) thermal spraying method by which the progressive coatings are applied on basic material C15E (STN 412020). These coatings are based on C-17CO, WC-CO-Cr and Cr3C2-25NiCr. There was made determination of the chemical composition of the coatings and assessment of coatings quality - adhesion, microhardness, porosity and wear resistance at room temperature (21°C) and also at operational elevated temperature (900°C). Results of adhesive wear showed high quality of all evaluated coatings and their suitability to extreme tribological conditions.

Modification of surface morphology of Ti6Al4V alloy manufactured by Laser Sintering

Abstract The paper deals with the evaluation of relation between roughness parameters of Ti6Al4V alloy produced by DMLS and modified by abrasive blasting. There were two types of blasting abrasives that were used – white corundum and Zirblast at three levels of air pressure. The effect of pressure on the value of individual roughness parameters and an influence of blasting media on the parameters for samples blasted by white corundum and Zirblast were evaluated by ANOVA. Based on the measured values, the correlation matrix was set and the standard of correlation statistic importance between the monitored parameters was determined from it. The correlation coefficient was also set.

Electrochemical Characteristics of Mechanically Treated Metallic Surfaces

The paper presents the results of research aimed at determining the corrosive properties of steel surfaces after mechanical treatment by grinding and blasting. The aim of the study was to determine the changes in the electrochemical characteristics of the material during exposure in the 1 M NaCl solution in distilled water, and establish the optimal time of application the coatings on pre-treated surface without reducing the adhesion. With help of potentiodynamic tests and electrochemical impedance spectroscopy there were determined polarization resistance (Rp), the anodic and cathodic Tafel plots, corrosion current (Icorr), corrosion rate (rcorr) and corrosion potential (Ecorr). The results pointed to the fact that after the mechanical treatment by grinding and blasting with aluminum oxide and steel shot the highest surface activity was found within 1 hour since the pretreatment. After this time, the activity decreases and corrosion products appear causing a reduction in adhesion of subsequently applied coatings. After blasting with cut wire the reduction of the adhesion appear not before 8 hours after blasting because of the different shape of the resulting surface. Potentiodynamic test proved that the highest corrosion rate showed a ground surface. Lower corrosion rate reached blasted surfaces depending on the type of abrasive used, which is closely related to the kinetic energy of the impacting grains and the actual surface area.