Materials Science Forum Vol. 879

Abstract: The scope of this paper is to examine the improvement from laser welding by an innovative beam wobbling head towards the welding of tailored blanks parts, widely used in automotive to develop different stiffness aluminum components. For this purpose, butt joints and overlapping joints were produced from sheets made out of two industrial grades, i.e. AA-6082 T6 and AA-5754 H111 of different thickness. The technique was evaluated both with and without the use of a filler wire (AA-5556). The qualification of the welding process encompassed Non Destructive Testing (NDT) and mechanical testing. The results indicate that butt joints tend to fail within the base material (BM) of sheet with smaller thickness. On the contrary, the shear tests on lap joints highlighted a rupture mode occurring in the heat affected zone (HAZ) of the thin sheet. Remarkably, the wobbling process generally allows avoiding porosity when combined with an optimized set of welding parameters. Yet, a residual porosity was always detected in lap joints, varying with the size of the fused zone.

Abstract: Soft chemistry (chimie douce) processes allow the design of multifunctional composite coatings tailoring the interfaces between phases. Instrumented indentation has become routinely used to characterize thin systems and allows for getting insight into interface mechanics. The paper illustrates both experimental approaches allowing for the fabrication PMMA based nanocomposites and their characterization employing nanoindentation.

Abstract: High-pressure torsion (HPT) is one of the major severe plastic deformation (SPD) procedures where disk metals generally achieve exceptional grain refinement at ambient temperatures. HPT has been applied for the consolidation of metallic powders and bonding of machining chips whereas very limited reports examined the application of HPT for the fabrication of nanocomposites. An investigation was initiated to evaluate the potential for the formation of a metal matrix nanocomposite (MMNC) by processing two commercial metal disks of Al-1050 and ZK60 magnesium alloy through HPT at room temperature. Evolutions in microstructure and mechanical properties including hardness and plasticity were examined in the processed disks with increasing numbers of HPT turns up to 5. This study demonstrates the promising possibility for using HPT to fabricate a wide range of hybrid MMNCs from simple metals.

Abstract: Plasma nitriding was performed on the 2205 duplex stainless steel samples at 400 V with a gas mixture of H₂ and N₂ for 15 hrs with changing N₂ percent, temperature and adding various amounts of CH₄. After treatment the behavior of the surface layer was investigated by optical microscopy, X-ray diffraction, GDOES analysis and micro-hardness testing. Potentiodynamic polarization test was also used to evaluate the corrosion resistance of the samples. With increasing both N₂ percentage from 10% to 25% and nitriding temperature from 370°C to 430°C, the thickness of nitrogen expanded austenite (S-phase) layer and surface hardness increase up to 16 μm and 1200 HV_0.1 at the treatment temperature of 430°C with 25% N₂, but decreases the corrosion resistance due to the formation of Cr₂N and γ`(Fe, Cr)₄N. Thus in order to further increase the thickness of S-phase layer and the corrosion resistance, the influence of adding various amount of CH₄ (1% to 5%) in the nitriding atmosphere was investigated. Adding CH₄ in the nitriding atmosphere increases the layer thickness compared with that of nitrided sample. The highest thickness can be obtained at 1 % CH₄, but addition of CH₄ beyond 1 % slightly decreases the layer thickness. Moreover, when nitrided at 400°C with 10% N₂ and 5% CH₄ content, best corrosion behavior is obtained which also have around 10 μm layer thickness and about 870 HV_0.1 surface hardness.

Abstract: Zirconia (ZrO₂) has excellent properties such as high toughness, high strength, thermal stability and high corrosion resistance. Thus, recent zirconia has been spotlighted as a dental material. Most of pure zirconia has been separated from zircon sand (ZrSiO₄) by wet refining process which is very complex and not an environmental. The arc plasma fusion method has the advantages as a sustainable process that can easily and quickly get very good fine and high pure powders from the original materials compared with traditional wet method. In this study, zircon sand is separated into zirconia and silica by using the Ar-H₂(hydrogen) arc plasma refining. And then silica is removed from it by the microwave leaching method to produce a high pure zirconia. Argon gas, hydrogen gas, copper anode and tungsten cathode are used for the plasma arc generation. To facilitate zirconia and silica separation, carbon of 1-3molar ratios are added with zircon sand. Plasma melting were sequentially conducted two processes. After a reduction process using Ar gas only, it was refined using a mixed gas of Ar-H₂. After melting and water cooling in chamber, the solid phases composed with zirconia and silica were obtained at 240 ̊C, and 20% sulfuric acid solution was used as the leaching materials to obtain a high purity zirconia (more than 99%).

Abstract: This paper reviews the use of Atomic Layer Deposition (ALD) in protective coatings. Because of the growth principle ALD allows the deposition of dense conformal films on substrates of different size and shape. Recently, ALD has received increasingly interest in deposition of protective coatings. In protective coatings oxides are the most common materials and especially Al, Ti, and Ta oxides have been applied. The use of nanolaminates enables improving the protection properties. Since ALD films are pinhole-free and often thin they are used to protect against moisture, radiation, out-gassing but not often against corrosion of metals. Very good moisture barriers are obtained with thin ALD oxide layers on polymers and cardboard. This property is also very attractive in encapsulation of OLEDs. In studies of energy technology materials protection of electrodes in Li-ion batteries, fuel cells and supercapacitors by ALD has been reported and significant improvement in the stability has been achieved. Yet another area is protection of silver jewelry from tarnishing by a thin oxide layer. In traditional corrosion protection of metals ALD films have proven to be useful in tailoring of interfaces and sealing of defects in coatings made by other techniques.

Abstract: In recent years was developed a number of new methods of processing of metals by pressure aimed at obtaining metal with sub-ultrafine-grained structure, the basic principle of which is the realization in the process of deformation of simple shear scheme. One of those ways is pressing blanks in matrices of different designs, in particular in equal-channel step die. However, this method has a significant disadvantage - it can’t be used for deforming of lengthy billets. Another disadvantage of this method of deformation is that it does not provide the continuity of the pressing process. For removing these shortcomings at the Department "Metal Forming" of Karaganda state industrial University was developed a combined process "Rolling-pressing" using equal channel step matrix with calibrated and smooth rolls. This work investigates the impact of the proposed combined process "rolling-pressing", and also preliminary and final heat treatment during the implementation of this combined process on the evolution of microstructure and mechanical properties of copper alloy. Obtained in the course of these studies, the results indicate that the proposed technology can be recommended for implementation in production to produce blanks of ferrous and non-ferrous metals and alloys with ultrafine-grained structure and high level of mechanical properties.

Abstract: One of the ways to improve the quality of steel production by rolling is the creation of additional streams of the metal flow, i.e. intensification of shear deformation not only in longitudinal but also in transverse direction. From the review of scientific-technical and patent literature it is known that to improve the quality of products when rolling usually use a system of alternating projections and depressions, which is created on the surface of the wide faces of slab or on work rolls. In this case, along with deformation in altitudinal and longitudinal directions, the conditions for deformation of the metal in the transverse direction, which has a positive effect on reducing the anisotropy of properties. Knowing the advantages of rolling with additional shear deformations, we have developed energy-saving technology of plate billets rolling of non-ferrous metals and alloys, allowing to obtain a uniform fine-grained structure throughout the volume of the workpiece, and designed two new constructions of the pair of work rolls with embossed surface as an annular groove, forming a trapezoidal protrusions and depressions alternating each other along the entire length of the barrel (the first pair to unequal treatment of the ledge to the depression and the second pair with equal respect to the ledge to the depression) to implement this technology in practice. In this paper were described results of investigations of microstructure evolution of copper alloys by rolling on the proposed technology in the relief rolls and according to the current technology in smooth rolls.

Abstract: A composite surface layer was fabricated on a high-vanadium alloy steel (HVAS) plate by means of a surface gas nitriding at 550°C for 70h. The microstructural charaterization and phase analysis of resultant nitride layers were performed using optical, scanning electron microscopy, electron probe microanalyzer, X-ray diffraction methods and hardness measurements. The results of the investigation showed that a composite layer consisting of ε-Fe_2–3N and γ'-Fe₄N phases is feasible on the surface of HVAS. Vickers hardness test indicate that the hardness value of the nitrided sample is about 1100 HV at the top surface, and decreases gradually to about 700 HV in the matrix. The depth of hardened layer after surface gas nitriding was about 200 μm.

Abstract: The effects of grain boundary characters on the morphology evolution of grain boundary carbides in Inconel Alloy 600 with high proportional low Σ coincidence site lattice (CSL) boundaries aged at 715 ^oC for 1-100 h were investigated by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). During the aging process, the carbides precipitated at coherent twin (Σ3) boundaries are very few and finest within all the aging time. Bar like carbides precipitated near both sides of the incoherent twin (Σ3) boundaries, and bigger carbides than that of coherent Σ3 boundaries had been found on the incoherent Σ3 boundaries. Bar like carbides precipitated near only one side of Σ9 boundaries, and much bigger carbides than that of Σ3 boundaries have been found on the Σ9 boundaries. The morphology of carbides precipitated at Σ27 and random grain boundaries are similar, and is bigger than that of precipitated at other grain boundaries. The carbides precipitated at grain boundaries with all types grow bigger with the aging time prolonging, but their growth rates are different.