Pavel Doležal

Characterization of Ni-P coating prepared via electroless deposition on AZ31 magnesium alloy

Abstract This work deals with the characterization of Ni–P coating prepared via electroless deposition on wrought AZ31magnesium alloy. For the application of electroless deposition was proposed and optimized a suitable pretreatment process of magnesium alloy surface followed by Ni–P coating in the nickel bath. The chemical composition of Ni–P based coating was characterized using the scanning electron microscope with chemical composition analysis. Next, physico-chemical properties and mechanical characteristics of Ni–P coating were evaluated. The mechanism of corrosion degradation of the coating and the substrate was also studied in this work.

Improvement of bio-compatible AZ61 magnesium alloy corrosion resistance by fluoride conversion coating

Abstract Magnesium and its alloys are perspective bio-degradable materials used mainly due to their mechanical properties similar to those of mammal bones. Potential problems in utilization of magnesium alloys as bio-materials may relate to their rapid degradation which is associated with resorption problems and intensive hydrogen evolution. These problems can be eliminated by magnesium alloys surface treatment. Therefore, this work aims with analysis of the influence of fluoride conversion coating on corrosion characteristics of magnesium alloy. Unconventional technique by insertion of wrought magnesium alloy AZ61 into molten Na[BF4] salt at temperature of 450 °C at different treatment times was used for fluoride conversion coating preparation. The consequent effect of the coating on magnesium alloy corrosion was analyzed by means of linear polarization in simulated body fluid solution at 37 ± 2 °C. The obtained results prove that this method radically improve corrosion resistance of wrought AZ61magnesium alloy even in the case of short time of coating preparation.

Unconventional fluoride conversion coating preparation and characterization

Purpose n n n n nThe purpose of this paper is to compare electrochemical corrosion characteristics of conventional and unconventional fluoride conversion coating prepared on magnesium alloy. n n n n nDesign/methodology/approach n n n n nThe chemical reaction of AZ61 with 38 wt.% hydrofluoric acid (HF) for 24 h was used as a conventional way of fluoride conversion coating preparation. The unconventionally prepared coating was created in Na[BF4] salt melt at 450°C for 2 h. Morphology and chemical composition of prepared fluoride conversion coatings were studied with scanning electron microscopy and energy-dispersive X-ray spectroscopy. Electrochemical corrosion characteristics of the coatings were analyzed in Hank’s solution using potentiodynamic tests. n n n n nFindings n n n n nBoth the coating preparation ways resulted in the creation of uniform conversion coatings with the same thickness (1.3 ± 0.1 μm). Some defects were observed on the coatings surface; however, the defects did not reach the AZ61 surface. Electrochemical tests performed in Hank’s solution at 37°C showed an improvement of corrosion resistance of AZ61 treated with fluoride conversion coatings when compared to the untreated material. Unconventionally prepared coating reached better electrochemical corrosion characteristics when compared to the conventionally prepared coating. n n n n nOriginality/value n n n n nElectrochemical corrosion characteristics of AZ61 magnesium alloy can be improved with fluoride conversion coatings. Two methods are used in the literature for the coatings preparation. The conventional method is based on dipping of the coated material to the HF, and the unconventional method lies in dipping of the sample to the Na[BF4] salt melt. The main purpose of the present study is to analyze the conventionally and unconventionally prepared coatings in terms of chemical analysis, morphology and material corrosion protection (electrochemical corrosion characteristics), while the data are not provided in the literature, according to the authors’ knowledge. Very similar coatings were prepared using both the methods from the morphological and chemical composition point of view. However, unconventionally prepared coating created in Na[BF4] salt melt reached better electrochemical corrosion characteristics compared to the coating prepared in HF.

Corrosion behavior of wrought magnesium alloys AZ31 and AZ61 in Hank’s solution

Abstract Corrosion behavior of wrought magnesium alloys AZ31 and AZ61 was studied in Hank’s solution. Potentiodynamic curves measured after short-term of exposure showed higher corrosion resistance of AZ31 magnesium alloy in comparison with AZ61 magnesium alloy. On the contrary, long-term tests measured by electrochemical impedance spectroscopy showed higher corrosion resistance of AZ61 magnesium alloy in comparison with AZ31 magnesium alloy.

The Effect of Arc Current on Microstructure and Mechanical Properties of Hybrid LasTIG Welds of High-Strength Low-Alloy Steels

A hybrid laser-tungsten inert gas (LasTIG) welding system was applied for 3-mm-thick S460MC and S700MC high-strength low-alloy steel sheet butt welding with the aim to reduce the cooling rate compared with laser welding. The effect of the electric current was evaluated. Increasing arc current led to the increase of fused metal and heat-affected-zone (HAZ) dimensions. Fused metal grains were larger whereas the microhardness increase toward the base metal was lower at higher currents in this region. Microhardness peaks corresponding to the coarse-grained HAZ were reduced at higher currents for S460MC but were almost not affected in S700MC. The tensile strength of both the laser weld and LasTIG welds was comparable to the base metal for both alloys.

Methodology for In Situ Microstructural Characterisation of AZ31 Magnesium Alloy Corrosion Degradation in Hanks' Solution

Due to their specific properties magnesium and magnesium alloys find huge application possibilities mainly in automotive, engineering, transport and space industry. Important properties of magnesium alloys for engineering applications are high specific strength and high internal dumping values, while biocompatibility, biotoxicity and biodegradability open them the possibility to be used for biomedical applications. Development of new biodegradable magnesium alloys, investigation of new production and processing technologies on their properties and evaluation of corrosion degradation in simulated body fluids solutions are the main topics of the last decades.The paper offers a method simulating in-vivo tests for description of the corrosion process of potential biomedical materials in time using atomic force microscopy (AFM). To prove the proposed methodology detailed analysis of the corrosion degradation of AZ31 cast magnesium alloy in flowing Hanks’ balanced salt solution (HBSS) was performed. Corrosion degradation process of the examined alloy was influenced by different microstructural features and their interfaces. Results of the created corrosion galvanic cells and the corrosion attack evolution on the interface of the present intermetallic phases and the matrix led to profile changes detected by AFM.

Evolution of microstructure and electrochemical corrosion characteristics of cold compacted magnesium

Abstract The main advantage of magnesium and its alloys is high specific strength and biocompatibility. A modern approach to magnesium-based materials preparation is powder metallurgy. This technique allows preparation of new materials with a unique structure, chemical composition, and controlled porosity. In this study, cold compaction of magnesium powder was studied. Magnesium powder of average particle size of 30 μm was compacted applying pressures of 100 MPa, 200 MPa, 300 MPa, 400 MPa and 500 MPa at laboratory temperature. Influence of compacting pressure was studied with microstructural and electrochemical corrosion characteristics analysis. The resulting microstructure was studied in terms of light and electron microscopy. Obtained electrochemical characteristics were compared with those of wrought magnesium. Compacting pressure had a significant influence on microstructure and electrochemical characteristics of prepared bulk magnesium. With the increase in compaction pressure, the porosity decreased. Compacting pressures of 300 MPa, 400 MPa and 500 MPa led to the similar microstructure of the prepared material. Polarization resistance of compacted magnesium was much lower and samples degraded faster when compared to wrought magnesium. Also, the corrosion degradation mechanism changed due to the microstructural differences between the material states.

Chain Segment Analysis

The work is aimed at a detailed analysis of impaired chain segments manufactured by welding and determining the cause of chain segment failure. The main interest was focused on the base material structure, the quality of weld joint, the heat treatment of the weldment, and the overall condition of the component after operating workload. The chain segments were investigated in terms of the microstructure by means of the light microscope, scanning electron microscope equipped with an energy dispersive microanalyser, and hardness measurement.

Failure Analysis of Spherical Roller Bearing

The failure of a spherical-roller bearing consisting of spherical rollers, outer and inner rings made of 100CrMn6 steel was studied. After a trial test, in which several spherical rollers were completely destroyed and a long continuous radial crack appeared in the outer ring, pitting degradation was observed on all bearing parts. The bearing components were studied (separately) by means of light and electron microscopy. The chemical composition was estimated by means of glow discharge optical emission spectroscopy. X-ray diffraction was utilized for qualitative and quantitative phase analyses. As a representative of mechanical properties, the hardness was also measured.