Jiří Švejcar

Diffusion in Al-Ni and Al-NiCr Interfaces at Moderate Temperatures

The diffusion couples for experimental study were prepared by HVOF spraying of nickel and nickel with 20 wt.% of chromium powders onto an aluminium sheet surface. The interfaces with sharp gradients of chemical concentration of these elements were prepared. Annealing at temperatures of 600°C and 630°C, close to the Al + Al3Ni eutectic melting point (639.9°C), with different dwell times were used. During annealing, the reactants diffuse and form layers of Al3Ni2 and Al3Ni intermediate phase compositions. Moreover, nickel without the assistance of chromium diffuses preferably along the grain boundaries into aluminium substrate and produces the strengthening of the substrate by stable Al3Ni and metastable Al9Ni2 particles. The microstructures were obtained by scanning electron microscopy. Layer thickness measurements were realized by means of image analyses. Chemical composition was estimated by energy dispersive microanalysis measurements. According to the results of the analyses performed the average chemical interdiffusion coefficients and Wagner’s integral interdiffusion coefficients were calculated.

Use of the Powder Liquid Method for Aluminide Diffusion Coatings Formation on Inconel 713LC Nickel-Based Superalloy

Powder liquid method was used for aluminides diffusion coatings formation on the Inconel 713LC nickel-based superalloy. Two different powder mixtures (Al and Al + Si) in organic binder solution were prepared. Coatings deposition onto the substrate surface was realized by spraying. Two-stage heat treatment under the argon-flow atmosphere was designed. First stage at 200°C was used to decompose organic binder. In the second stage at 1000°C the elements from the coating interact with the substrate. Protective intermetallic layer and an interaction zone between the layer and substrate start to form. Elements interaction and phase transformations during annealing at 1000°C up to 600 min were studied. For this study the light microscopy, scanning electron microscopy, energy dispersive microanalysis, x-ray diffraction phase analysis, microhardness measurement, and image analysis methods were used.

Microstructure and Mechanical Properties of Electrodeposited Nickel and its Particle-Reinforced Nanocomposite

There are two types of experimental material used – pure nickel and its nano-composite reinforced with nano-sized SiO2. These materials were produced by TU Clausthal, Germany. The results have shown that the creep resistance of the nickel nano-composite reinforced with nanosized SiO2 particles is higher in comparison with non-reinforced nickel. The mechanism responsible for creep behaviour is the dislocation creep at 293 K and at elevated temperatures the dislocation creep is controlled by grain boundary sliding.

Critical Weak Points of Atmospheric Plasma Sprayed Thermal Barrier Coatings

The 8 wt. % yttria stabilized zirconia top coat (TC) and the CoNiCrAlY bond coat (BC) were sprayed onto the surface of newly developed fine-grained cast polycrystalline nickel-based superalloy Inconel 713LC by means of atmospheric plasma spraying (APS). As-prepared samples were isothermally exposed at the temperature of 1050 °C for 200 hours in an ambient atmosphere. Structural changes in the thermal barrier coatings (TBC) system after thermal exposure were studied by means of scanning electron microscope equipped with an energy dispersive microanalyzer. Critical weak points were identified on both the substrate-bond coat and bond coat-top coat interfaces.

Comparative Analysis of Hard Anodized Layer on Aluminium Alloy

Hard anodized layers were produced by two different manufacturers on the same type of aluminium alloy on a vacuum pump part of complex shape. The sulphuric acid/water solution was used to produce alumina layers, which were subsequently sealed in demineralized water. A comparative analysis based on metallographic methodology, with the aim to control the stability of alumina formation process and to identify its defects, was performed by means of light and scanning electron microscopy, surface profilometry and microhardness measurements. To determine the thickness of alumina layers, the image analysis was also used.

Application of sacrificial coatings and effect of composition on Al-Al3Ni ultrafine eutectic formation

This paper introduces an unconventional method designed for forming hypereutectic alloys via coating deposition onto the substrate surface and subsequent heat treatment of such systems. The coating was produced from 99.7 wt% nickel powder by means of high velocity oxyfuel (HVOF) spraying onto the surface of 99.999 wt% aluminium sheet. The specimens were manufactured immediately after the spraying. Specimens were heat-treated using a differential thermal analysis (DTA) apparatus up to a temperature of 900°C and then cooled down to the room temperature in an argon atmosphere with constant heating and cooling rates, under which the NiAl3 intermetallic phase formed within the initial substrate. Two different alloy microstructures consisting of a coarse eutectic and an ultrafine well-dispersed eutectic were produced. The formation processes and resultant microstructures were studied by means of differential thermal analysis, metallography, scanning electron microscopy, energy dispersive microanalysis, and image analysis techniques.

Bending Fatigue Behaviour of Diffusion and Thermal Barrier Coating Systems

Room temperature fatigue behaviour of two variants of diffusion aluminide coatings and conventional air plasma sprayed CoNiCrAlY + ZrO2-Y2O3 thermal barrier system, which were deposited on a cast nickel-based supperalloy substrate, was studied under symmetrical bending loading regime. The study elucidates the differences in a fatigue crack initiation micromechanism with respect to applied stress level and its impact on the fatigue performance of studied coating systems.

Analysis of Causes of Fractures of Terminal Board Bolts

The paper sums up the results of a complex analysis, using metallographic, microfractograpic and other methods, with the aim of establishing the cause of fractures appearing in bolts of a terminal board. The analysis has shown unambiguously that the bolt failure was a synergic effect of inadequately performed heat treatment and hydrogenation that occurred in course of surface treatment via pickling and subsequent zinc plating.

Analysis of Damage of Solder Joint of Heat Exchanger

The paper focus on the metallographic analysis of damaged heat exchanger made of high‑alloy austenitic steel by soldering. The object in question is a soldered joint of main mounting plate of the heat exchanger and first heat exchanging plate of it. In this part of the heat exchanger after the vibration and pressure test crack appeared. The subject of the analysis is the evaluation of the microstructure of the solder joint (high-alloy austenitic steel and copper), and evaluation of the appeared crack. The problematic is solved with aid of metallographic analysis of the microstructure of the material, using light microscopy and scanning electron microscopy and the EDS microanalysis of chemical composition.

Failure Analysis of Corrugated Hoses

Stainless steel corrugated hoses are widely used in many areas of industry. They are used in application such as distribution of drinking and supply water, gas and also various working fluids, for example in cooling systems. During the assembly of AISI 316L corrugated hoses for cooling systems defects form due to deformation of the hoses during assembly. The absolute tightness of such systems is required and any defects of the hoses are therefore undesirable. This study deals with evaluation of most common defects of corrugated hoses via light and scanning electron microscopy and proposes measures to minimize such defects. It was revealed, that defects form due to deformation of the hoses during assembly or, in case of unfavorable microstructure, during the service life. In later case, failure of the hose was caused by higher content of deformation-induced martensite in microstructure as a result of intense cold forming. Component with such microstructure exhibited less favorable mechanical properties and hoses were more prone to the failure.