ICMCTF2017 Session GP: Symposium G Poster Session

Bipolar plate is a key component of solid oxide electrolysis cells, which increases the power density and decreases the costs of the stacks. In general, high operating temperature cause a severe oxidation to decline electrical conductivity. Although Crofer 22 APU (ferritic stainless steel) was developed specifically for SOFC interconnect applications, the oxidation rate is not sufficiently low to enable uncoated Crofer22 APU interconnects to meet the current 40,000 h SOFC lifetime requirement. Therefore, Crofer 22 APU also requires a protective coating both to retard the oxidation rate and to prevent the volatile chromium species.

The Superduplex stainless steel (SDSS) are biphasic materials compound portion of ferrite and austenite with equal parts approximately as well as high levels of chromium and nickel in its chemical composition. This materials are usually employed as pipeline for offshore oil and gas industry. During the cutting process this material presents the follow combination: (i) It shows a tendency to work hardening the surface reflecting in microstructural modifications and residual stress on surface machined; and (ii) It presents high temperatures in the cutting region, resulting in a reduction of tool life. The goal of this work is to evaluate the surface integrity (work hardening and stress corrosion behavior) of the SDSS obtained after machining process (finish turning) with cemented carbide tools coated with three different PVD coatings. The cemented carbide inserts were coated by Physical Vapor Deposition (PVD) with Al₅₀Cr₅₀N/Ti₉₅Si₅N, Al₅₀Cr₅₀N and Al₆₇Ti₃₃N. The responses analyzed were tool wear, microstructural characterization, machined surface and stress corrosion analysis. The results indicate that aluminum-rich (Al₆₇Ti₃₃N) coatings improve the wear resistance of inserts in this type of machining as well as reduce the surface hardening levels of machined part, reflecting in a better stress corrosion resistance.

Mg alloy, being lightest among the engineering materials, has limited use in automotive, biomedical and structural industries due to poor surface mechanical properties. Protection against wear and corrosion may increase the use of Mg-alloys in various engineering applications. Wear and corrosion being the surface related phenomenon, surface modification by various techniques can be sought for improved performance. This paper investigates the deposition and estimation of surface and interface properties of thermally sprayed alumina based coatings. Effect of CeO₂ doping into Al₂O₃ based coatings is also explored. The elastic modulus and hardness at surface and interface both were measured using nanoindentation. In order to investigate the role of substrate microstructure on coating characteristics, the solution treated and peak aged samples of AZ91 Mg alloy have been used as a substrate material. The coatings were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD). The results indicate that peak aged substrate microstructure results in coating with better interfacial properties as compared to solution treated case. The role of ceria doping in manipulating the microstructure is discussed in detail.

The cubic-structured nitrides of Mo and Ta exhibit excellent tribo-mechanical and electrical properties and are often used as alloying components for improving e.g. materials resistance against wear and oxidation. The outstanding properties both materials owe to their inherent driving force to form vacancies, which are commonly disregarded for any material.

Fusing Mo–N^1,2 with Ta–N² – experimentally and theoretically – we have investigated a novel quasi-binary materials system Mo–N–Ta–N. Its natural preference for point defects inherited from relative binaries can furthermore be significantly influenced e.g. by altering the chemical potentials. When dealing with the point defects, the ab initio studies are of a great significance: particularly to distinguish between the structures developing “without” point defects and with Schottky defects is anything but trivial experimental issue. Varying the type and volume density of vacancies we present the evolution of structure and mechanical properties of “MoNTaN” coatings. The insights into the origin of the observed phenomena allow us to tune the hardness–toughness relationship and hence design materials for applications requiring tailor-made properties.

References:

1 Klimashin, F., Koutná, N., Euchner, H., Holec, D. & Mayrhofer, P. The impact of nitrogen content and vacancies on structure and mechanical properties of Mo–N thin films. Journal of Applied Physics 120, 185301 (2016).

Aluminum and its alloys have been a successful metal materials used for many applications like commodity roles, automotive and vital structural components in aircrafts. A substantial portion of Al-Fe-Si alloy is also used for manufacturing the packaging foils and sheets for common heat exchanger applications. The present research was aimed at studying the morphology and distribution of the iron-containing intermetallics in the Al-Fe-Si alloy. These Fe-intermetallic compounds influence the material properties during rapid cooling by laser alloying technique and play a crucial role for the material quality. Thus, it is of considerable technological interest to control the morphology and distribution of these phases in order to eliminate the negative effects on microstructure. A 3 kW continuous wave ytterbium laser system (YLS) attached to a KUKA robot which controls the movement of the alloying process was utilized for the fabrication of the coatings at optimum laser parameters. The fabricated coatings were investigated for its hardness and corrosion properties. The corrosion performance was investigated in 0.5M H₂SO₄ and 0.5M NaCl solutions at 30^oC via Open Circuit Potential (OCP) and Linear Polarization techniques. The field emission scanning electron microscope equipped with energy dispersive spectroscopy (SEM/EDS) were used to study the morphology of the fabricated coatings and X-ray diffractometer (XRD) for the identification of the phases present in the coatings . The coatings were free of cracks and pores with homogeneous and refined microstructures. The enhanced hardness and anti-corrosion performances were attributed to metastable intermetallic compounds αAlFeMnSi, Fe₂Si₂Al₂, Fe₃SiAl₁₂, Al₅Fe₂, Fe₅Si₃, Al₄Fe₅Si₆ formed. Computational model used in this research authenticates reasonably with the experimental results.