Refine
Year of publication
Document Type
Way of publication
- Open Access (4)
Language
- English (91) (remove)
Keywords
- mechanical properties (6)
- X-ray diffraction (5)
- Biomedical applications (4)
- Mechanical properties (4)
- Nanobiomaterials (4)
- Sintering (4)
- Wear (4)
- tribology (4)
- XPS (3)
- hydrogenation (3)
Institute
BTU
- an der BTU erstellt / created at BTU (91) (remove)
(Cr1-x Al x)N as a candidate for corrosion protection in high temperature segments of CCS plants
(2013)
Three (Cr1−x Al x )N (x = 0.33, 0.5, 0.66) coatings were deposited on Ni-super alloy IN718 using reactive magnetron sputtering. The oxidation behavior of all coatings at 900 °C up to 500 h in air was studied. Furthermore, the corrosion behavior of the (Cr0.33,Al0.66)N coating at 900 °C (corrosion type I) by spraying a uniform salt scale of Na2SO4 on the sample surface (1 mg/cm2) was investigated. It was found that the coated samples indicate significantly higher oxidation and corrosion resistance compared to uncoated Ni super alloy. This is mainly due to the formation of protective Cr2O3 and Al2O3 layers on the coating surface. With the increase of Al content, the coatings exhibited improved oxidation resistance. The formation of thin and adherent Al2O3 scale on the surface of Al rich coating is the reason for its better oxidation behavior. The detailed structures of the oxide scales and the interdiffusion between coating and substrate were studied using energy dispersive X-ray spectroscopy-analysis.
Coronary heart disease is still one of the most common sources for death in western industrial countries. Since 1986, a metal vessel scaffold (stent) has been inserted to prevent the vessel wall from collapsing. Most of these coronary stents are made from CrNiMosteel (316L). Due to its austenitic structure, the material shows a good combination of strength, ductility, corrosion resistance, and biocompatibility. However, this material has some disadvantages like its non-MRI compatibility and its poor fluoroscopic visibility. Other typically used materials are the CoBase alloys L-605 and F-562 which are MRI compatible as well as radiopaque. Another interesting fact is their excellent radial strength and therefore the ability to produce extra thin struts with increased strength. However, because of a strut diameter much less than 100 μm, the cross section consists of about 5 to 10 crystal grains (oligocrystalline). Thus, very few or even just one grain can be responsible for the success or failure of the whole stent. To investigate the relation between microstructure, mechanical factors and stent design, commercially available Cobalt-Chromium stents were investigated with focus on distinct inhomogeneous plastic deformation due to crimping and dilation. A characteristic, material related deformation behavior with predominantly primary slip was identified to be responsible for the special properties of CoCr stents.
In the cast condition g titanium aluminide alloys that solidify completely through the b phase are
characterized by fine and homogeneous microstructures, weak textures and low segregation. For these reasons such alloys have a relatively good workability and can be closed-die forged without preceding ingot breakdown even if the alloys contain no large fractions of the b phase at the working temperature. The present work was devoted to a combined study of the constitution and microstructural morphologies that develop in various two-step heat treatments of a single-step forged b solidifying alloy. The
study included high-energy X-ray diffraction for in situ investigations of the constitution at the heat treatment temperature. It was observed that the phase ransformations are quite sluggish in the material which results in fine microstructures and some conditions that significantly deviate from thermodynamic equilibrium. Further, tensile and creep testing was carried out on the different material conditions in order to identify the range in which the properties can be varied. It is found that this easily forgeable material exhibits comparable strength, ductility and creep strength as more conventional peritectically solidifying alloys.
The literature review reveals that the honeycomb-structured thin sheet metals are not adequately investigated with regard to their fatigue strength. A question that remains almost completely ignored in the process is the direct comparability of structured thin sheet metals with flat reference specimens. A thin sheet is not a classic specimen to determine the fatigue strength because of the known problem of the fracture mechanics. Structured thin sheet metals of deep-drawing steel DC04 with a thickness of 0.5 mm were examined. Flat specimens were used as reference material. The frequency analysis was used for comparison.
Fundamental differences in the mechanical behavior between flat and structured sheets under cyclic load were observed. Whereas an extremely flat S-N curve in the low-cycle region with a high slope coefficient was observed for the smooth thin sheets, the structured specimens show a curve typical for notched specimens. Moreover, the smooth sheets have a specific cyclic hardening and/or softening behavior. The state of plane stress of a fine sheet in contrast to a multi-axial one for the structured sheet complicates the direct comparison. For this reason, such a comparison with respect to their fatigue strength in the Wohler diagram should only be considered with caution.
Investigation of the wear resistance properties of Cr/CrN multilayer coatings against sand erosion
(2015)
The wear of metallic components used in gas and steam turbines due to erosive sand particles lead to a tremendous decrease in their lifetime. This wear can be reduced by the use of suitable erosion resistant coatings resulting in lower maintenance costs. In this context, multilayer Cr/CrN PVD coatings using an industrial coater was designed and applied on Inconel 718, a material which finds its application in gas turbines. A variation in the bimodal period has been induced in order to achieve an optimal coating architecture providing optimum properties needed for the erosion resistant coatings. The coating was deposited using a single Cr- target with an induction of N2 during the nitriding phase at a temperature of 480-500 °C and the coating thickness of 24-26 µm was kept constant throughout. The erosion tests were conducted at angles of 30°, 60° and 90°. The sand used for the test is an irregular shaped SiO2. The erosion tests were followed by a detailed microscopic examination of the eroded coating structure in combination with nanoindentation and scratch tests.
This research work provides information about the influence of Ti2AlC MAX phase coatings on the
erosion resistance of Ti624 2alloy.Flat specimens were coated witha20 µm Ti2AlC film using an industrial siz emagnetron sputtering coater and annealed at 800 °C for 1h in vacuum for the formation of the MAX phase.The erosion resistance of the specimens was tested using high velocity particles at room
temperature.The results indicate that the erosion resistance of Ti6242 has been significantly enhanced
by the employment of MAX-phase coatings. This demonstrates the capability of using MAX phase
coatings as erosion protective medium for engine components exposed to similar damage conditions.
Additionally,the results show that uncoated Ti6242 samples with duplex microstructure have a better
durability against erosion attack compared to uncoated samples with globular microstructure.
Carbon fibre reinforced thermoplastics (CFRP) are intensively used in lightweight
applications due to their high strength to weight ratio. In addition they offer good crash,
damping and recycling properties. On the basis of their morphology they are suitable for large
scale manufacturing processes. A major disadvantage consists of its poor hardness properties,
which is again an important requirement to realize a good erosion and wear behaviour.
Design/methodology/approach: In this work the application of orthotropic carbon
fibre reinforced polymers (PA6), with protective TiAlN coatings, produced by physical
vapor deposition (PVD), is investigated. The characterization of the coating is performed
by nanoindentation tests, roughness measurements and scanning electron microscopy.
Furthermore micro hardness tests on selected well prepared cross sections are conducted,
to compare the coating quality with established coating systems.
Findings: By applying TiAlN coating, the hardness of the CFRP samples can be increased
substantially up to 15 GPa, in comparison to the basic substrate. In addition the quality of
the coating surface can be improved significantly by plasma etching pre-treatment.
Research limitations/implications: The presented findings are preliminary results to
prove the application of a standard processed ceramic coating on new composite types
for mass production. The PVD coating process as well as the utilized testing methods are
suitable to realize hard coatings on thermoplastic CFRP. This effect can be exploited for
several lightweight applications to increase the erosion and wear resistance of composite
materials.
Originality/value: The presented results show, that ceramic coatings can be deposited
on standard thermoplastic CFRP with polyamide 6 matrix. Therewith it can be expected,
that the PVD coating process can make a essential contribution to increase the range of
applications.