Martin Juliš

Effect of Thermal Barrier Coating on Low Cycle Fatigue Behavior of Cast Inconel 713LC at 900 °C

The effect of thermal barrier coating (TBC) on low cycle fatigue behavior of cast superalloy Inconel 713 LC has been studied at 900 °C. The TBC consisting of a CoNiCrAlY bond coat and a zirconia (ZrO2) top coat stabilized by 8% yttria (Y2O3) was deposited on the gauge section of cylindrical specimens using the atmospheric plasma spray technique. Cylindrical specimens of Inconel 713LC in as-received condition and with surface treatment were cyclically strained under strain control with constant total strain amplitude in symmetrical cycle at 900 °C in air. Hardening/softening curves, cyclic stress-strain curve and fatigue life data of coated and uncoated material were obtained. The stress response of the TBC coated specimens is lower in comparison with the uncoated specimens. Detrimental effect of surface treatment on the Basquin curve is documented. Specimen sectioning and fracture surface observations revealed fatigue damage mechanisms and help to discuss differences in fatigue behavior of the coated and uncoated superalloy.

Degradation of TBC Coating during Low-Cycle Fatigue Tests at High Temperature

The work is focused on the study of degradation of ZrO2 stabilized by Y2O3 (YSZ) thermal barrier-coating system with CoNiCrAlY bond coat applied on cast polycrystalline nickel-based superalloy Inconel 713LC. Cylindrical specimens in as-coated conditions were cyclically strained under strain control with constant total strain amplitude in symmetrical cycle at high temperature (900 °C) in air. Coating system YSZ with CoNiCrAlY bond coat were prepared by APS method on blasted surface. The microstructure of TBC was characterized with scanning electron microscopy and energy dispersion X-ray analysis. The coating thickness and hardness profile was measured. Fracture surface, surface relief and polished sections parallel to the specimen axis were examined to study damage mechanisms in coatings under cyclic loading at high temperature. It was find that initiation of the fatigue crack usually occurs on interface YSZ-CoNiCrAlY and the trajectory of the further crack propagation was documented.

Influence of Al-Si Diffusion Coating on Low Cycle Fatigue Properties of Cast Superalloy Inconel 738LC at 800 °C

High temperature low cycle fatigue behaviour of cast nickel-based superalloy Inconel 738LC in as-received condition and coated with an Al-Si diffusion layer was studied. The Al-Si protective layer was deposited on the gauge section of cylindrical specimens using the slurry technique. Fatigue tests were performed on cylindrical specimens under total strain control in symmetrical cycle at 800 °C in air. The coating has a beneficial effect on fatigue life in the low amplitude domain. The stress response of the coated material is higher for high amplitudes in comparison with the uncoated one. Fracture surfaces and sections parallel to the specimen axis have been examined to study fatigue damage mechanisms.

Low Cycle Fatigue Behavior of Cast Superalloy Inconel 713LC with Al Coating at 800 °C

Cylindrical specimens of Inconel 713LC in as-cast condition and with Al diffusion coating by the CVD technique were cyclically strained under total strain control at 800 °C. Hardening/softening curves, cyclic stress-strain curves, and fatigue life curves are obtained. The coating has a beneficial effect on the Manson-Coffin curve while the fatigue life is reduced in the Basquin representation. The stress response of the coated material is lower in comparison with the uncoated one. Sections parallel to the specimen axis have been examined to study fatigue damage mechanisms.

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.

The Study of Microstructure and Properties of Al Diffusion Coating on Inconel 713LC

Protective layers are used to improve high temperature performance of structural materials. However, the effect of coatings on mechanical and fatigue properties is not sufficiently known because it is a combination of many factors as high-temperature exposure time, thermal cycle and coating deposition technique. Interactions between the coating and the substrate under high-temperature conditions influence the life time of coated blades. This paper is focused on the study of microstructure and properties of aluminide protective layers deposited on cast polycrystalline nickel base superalloy Inconel713LC. The light microscopy with image analyses and scanning electron microscopy with energy dispersion spectroscopy were used. The surface treated specimens exposed at 800 °C in air and cylindrical specimens with protective layer cyclically loaded under strain control at 800 °C in air were studied. Experimental data on thickness, uniformity and chemical analysis of individual phases are obtained for as-coated specimens, for specimens exposed to 800 °C for 500 hours in air and for specimens fatigued to fracture at 800 °C in air.

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.