R. Sitek

Structure and Properties of Nickel Aluminide Layers on INCONEL 100

The paper presents the results of investigations into the structure and properties of Ni-Al diffusion layers produced on INCONEL 100 by Chemical Vapour Deposition (CVD). The process was carried out in aluminium chloride (AlCl3) mixed with hydrogen atmosphere. The as-deposited layers were subjected to thermal treatment in vacuum to optimize their adhesion, hardness and temperature-resistance. Microstructural characterization of the coatings was carried out by scanning electron microscopy (SEM) The chemical composition was measured via EDS and the phase content was investigated by X-ray diffraction XRD. The resistance to high temperature of the coatings at atmospheric pressure was tested by applying 24-hours cycles at 950 °C. Scratch-tests provided data on the microhardness and adhesion of the coatings. The results indicate that the layers produced on the INCONEL 100 exhibit a very good adhesion combined with exceptional corrosion resistance at high temperatures.

Corrosion Resistance of Titanium Aluminide Layers on Two Phase (α+β) Ti6Al4V Titanium Alloy

The paper presents results of investigations into the structure and corrosion resistance of Ti-Al diffusion layers produced on two phase (a+b) Ti6Al4V alloy by Chemical Vapour Deposition (CVD). The process was carried out in aluminium chloride (AlCl3) mixed with argon atmosphere. Surface topography and microstructure characterization of the coatings were examined by scanning electron microscopy (SEM). The local chemical composition witch 1 μm lateral resolution was measured via EDS. The phase content was investigated by X-ray diffraction and analysis of the chemical composition of the surface by XPS. Corrosion resistance was tested using the potentiodynamic method in 0.1M Na2SO4 and 0.1M H2SO4 solutions at the room temperature. Their resistance to high temperature at atmospheric pressure was tested by 24-hours cycling to 700°C. The results indicate that the layers produced on the Ti6Al4V titanium alloy exhibit a very good adhesion combined with exceptional corrosion resistance, especially high at high temperatures.

Influence of Aluminide Layer on the Dynamics of the Development of Fatigue Damage in Ni-Cr-Co Alloy

Thermomechanical conditions in which the elements of modern aircraft engines work, require the use of protective coatings. The coatings increase the creep strength and also the local thermal stress in the near-surface areas due to the differing thermal expansion of particular material layers. For this reason it is necessary to develop a method for evaluating the operating properties of nickel superalloys with the aluminide layer, taking into consideration the surface processes related to the thermo-mechanical fatigue, taking place during the operation. In the presented work the assessment of the influence of the aluminium-coated layer, deposited on the nickel alloy specimens in the chemical deposition process (CVD) on the changes of the damage parameter in cyclic load conditions was carried out. The damage parameter was defined as a total strain in consecutive load cycles. The dynamics of damage development was analysed for two specimen lots (4 with the layer and 4 without it) displaying axial symmetry with a narrowing in the measured section. The results obtained were correlated with the results of fractography studies using SEM. The results obtained were used for the determination of the relationship between the damage parameter being the sum of the average strain and the strain amplitude, and the number of cycles, until the specimen is destroyed.

Hydrostatic Extrusion and Nano-Hardness of Nanocrystalline Grade 2 Titanium.

The structure and corrosion resistance of Grade 2 titanium subjected to the hydroextrusion processes were examined. The microstructure was characterized using optical microscopy and transmission electron microscopy. The corrosion resistance was determined using the impedance and potentiodynamic methods, in 0.1 M H2SO4 solutions and an acidified 0.1 M NaCl solution with a pH of 4.2, at ambient temperature. Nanohardness tests were performed under a load of 100 mN. It has been demonstrated that the hydroextrusion method makes it possible to obtain relatively homogeneous nanocrystalline titanium Grade 2 with an increased hardness, the elastic modulus almost unchanged with respect to that of the initial structure and a lower corrosion resistance.

Microstructure and properties of ultrafine grain nickel 200 after hydrostatic extrusion processes

This paper presents the results of the studies of the structure and properties of ultrafine grained nickel 200 obtained by hydrostatic extrusion processes. Microstructure was characterized by means of optical microscopy and electron transmission microscopy. Corrosion resistance was studied by impedance and potentiodynamic methods using an AutoLab PGSTAT 100 potentiostat in 0.1 M Na2SO4 solution and in acidified (by addition of H2SO4) 0.1 M NaCl solution at pH = 4.2 at room temperature. Microhardness tests were also performed. The results showed that hydrostatic extrusion produces a heterogeneous, ultrafine-grained microstructure in nickel 200. The corrosive resistance tests showed that the grain refinement by hydrostatic extrusion is accompanied by a decreased corrosive resistance of nickel 200.