Jakub Horník

The Effect of PVD Tungsten-Based Coatings on Improvement of Hardness and Wear Resistance

This article deals with the analysis and evaluation of coatings applications made by Physical vapour deposition on ceramics substrates. Main focus is on the application of tungsten and tungsten nitride coatings for functionally graded materials (FGM). The article focuses on analysis and evaluation of tungsten and tungsten nitride coatings with ceramics substrates. Firstly suitable deposition parameters of W and WN coatings, prepared by magnetron sputtering, were tested. Test coatings on tool steel substrate exhibited high adhesion and good mechanical and technological properties. Both tungsten and tungsten nitride coatings on selected ceramics substrates exhibited good mechanical a technological properties. Properties such as hardness, reduced elastic modulus and wear are discussed for each coating/substrate combination. Both coatings seem to be good candidates for application in field of FGM. The results of the presented experiment shows that the adhesion and the final quality of the coating depends on the type of chemical bond in the coating and in the substrate, and on the ability of the coating to deform plastically.

Determination of BGA solder joint detachment cause - warpage effect

Many aspects such as different materials used during the electronic assembly, increasingly finer dimensions of components, different processes and their settings have an influence on reliability of electronics products. This article deals with BGA assembly, specifically the determination of BGA solder joint detachment cause - with a warpage effect. Samples for diagnostic were obtained from manufacturer, who already pointed to the probable problematic location (BGA component) by electric in-circuit test. Cross-section of BGA assembly was made and an open joint - thin longitudinal gap between BGA component and solder joints connection was observed. The task was to identify a cause that produced axial detachment of BGA solder ball from component pads. The use of Scanning Electron Microscopy (SEM) determined that detachment was caused by a warpage effect.

Failures of Engineering Structures Caused by Weld Imperfections

The problematic of welding in terms of weld quality in dependence on service life of mechanical structures is discussed. Some examples of inadequate quality weld joints causing failure under load are described. Materials of the evaluated welds were following: S355 steel and Inconel 635 super alloy. Service conditions of homogeneous welds were different for both materials and weld quality was covered by Welding Procedure Specification. Using metallographic evaluation, the main problems were detected in a form of geometrical imperfections or insufficient penetration. These existing imperfections combined with static and dynamic load initiate the partial malfunction or failure of parts or constructions.

Analysis of Corrosion Attack on Kaplan Turbine Blades

The problematic of pitting corrosion on blades of Kaplan turbine is discussed. Corrosion behaviour was observed during the first year of service. Material of the water turbine blades is martensitic stainless steel GX4CrNi13-4. Chemical composition and hardness of blades was measured, EDS analysis of corrosion products and microstructural evaluation on replicas were carried out. The main problem was found in heterogeneities in the cast microstructure and local disproportions in chemical composition. Influence of microbiologically induced corrosion and surface roughness is considered.

Structural Changes of Hot Work Tool Steel due to Heat load

The paper deals with the influence of thermal load on functionality of the Toolox 33 hot work tool steel equivalent to the materials of W.Nr. 1.2311, 1.2312, 1.2738 and P20 in order to assess its suitability as a material for glass manufacture preform. Using light and electron microscopy it was shown that the steel was highly unfitting for this application where the steel comes into contact with the hot glass. Regarding the evaluation of the microstructure, it was shown that intense decarburization reflecting on the fracture behaviour of the surface layer during the thermal load has occurred. This fact was confirmed by a static tensile test and hardness measurements. Moreover, the thick layer of flakes has formed on the surface.

The Influence of Microstructure on the Fracture Development in Engineering Parts

Examples of failure of mechanical parts on account of the microstructural defects or heterogeneity are described. The evaluation of defect problematic was carried out using light and scanning electron microscopy. The root detected cause of problems was in a form of coarse particles in the microstructure, intensive line spacing or banding in the material. The influence of combination of intensive stress and inappropriate orientation of parts towards the direction of forming of semi-products was often observed. A rigorous approach to the material selection and the appropriate quality control of semi-products has to be considered to prevent the risk of a failure of engineering parts.

Evaluation of Changes of Mechanical Properties of Selected Cr-Ni-Mo Steels for Heavy Forgings during Long Time Annealing

The effect of long dwell time at elevated temperatures on two types of steels used for production of heavy forgings was evaluated. Microstructural changes and mechanical properties were monitored in temperature interval of 200 - 700 °C in order to avoid the possibility of grain boundary embrittlement during long dwell time at the processing temperature. Samples of the evaluated steels 26NiCrMoV14-5 and 22CrNiMoWV8-8 were being austenitized for 2 hours at temperature of 1200 °C and oil quenched. Subsequently the annealing at selected temperatures for 100 hours was applied. Tensile test, hardness and impact energy measurements were used for the evaluation. The results of mechanical testing, structural and fracture surface analyses indicate that for steels 26NiCrMoV145 and 22CrMoNiWV8-8 there exist a temperature interval of 300 - 400 °C and 500 600 °C respectively showing the toughness decrease.

Influence of Annealing Temperature and Time on the Mechanical Properties of Selected Steels for Heavy Forgings

Two types of steels used for production of heavy forgings were selected for the experimental evaluation of the effect of long time dwell at elevated temperatures and cooling during heat treatment on their mechanical properties in order avoid the possibility of grain boundary embrittlement. Samples from evaluated steels 26NiCrMoV14-5 and 22CrNiMoWV8-8 were austenitized for 2 hours at temperature of 1200°C and oil quenched. Subsequently the annealing at temperatures (200 - 700)°C for 1 hour and 100 hours was applied. Selected mechanical properties, especially hardness and impact energy, were monitored. It was found that for steels 26NiCrMoV14‑5 and 22CrMoNiWV8-8 exist the temperature intervals (300 - 400)°C and (500 ‑ 600)°C respectively with the possible potential for toughness decreasing.

MULTILAYER COATINGS Ti/TiN, Cr/CrN AND W/WN DEPOSITED BY MAGNETRON SPUTTERING FOR IMPROVEMENT OF ADHESION TO BASE MATERIALS

The paper deals with evaluation of single and multilayer layer PVD coatings based on Cr and Ti widely used in tool application. Additionally, W and WN based coating which are not so widespread were designed and deposited as functionally graded material. The coatings properties were evaluated from the point of view of hardness and adhesion. The hardness measuring was carried out using nanoindentation method. The scratch test was performed to test adhesion. Moreover, the presence of metallic interlayer in functionally graded materials further increases the coating adhesion by gradually approaching its composition to the substrate. Coatings consisting of W and WN have showed very good adhesion. With regard to the results of the scratch test, the multilayer coatings of CrN, TiN and WN have increased adhesion and can be assumed to have their protective function improved. Results will be appliedin development of functionally graded layers for functionally graded materials.

Kinetics of Austenite Recrystallization of Selected Steels Used for Heavy Forgings

The kinetics of austenite recrystallization was evaluated in range of typical forging temperatures (850 - 1250) °C. The steels SA-508 and 3.5Ni-1.5Cr were compared. The laboratory one step deformation was applied. The effect of selected chemical elements in evaluated steels on grain growth and recrystallization kinetics of austenite and precipitation was monitored using metallographic methods. The retarding of static recrystallization was proved and no abnormal grain coarsening at defined condition was observed.