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Reobservations of Recrystallization and its Effect on Mechanical and Magnetic Properties in a Severely Cold-Rolled Ni-Based Soft Magnetic Alloy

Mahdavi Azizeh, Mashreghi Ali Reza, Hasani Saeed, Kamali Mohammad Reza

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 2

703--717

EN

Despite of extensive researches for decades, there are many unclear aspects for recrystallization phenomenon in the cold rolled Ni-based alloys. Hence, different thermal cycles were conducted in order to determine microstructural evolutions and its effect on the magnetic and mechanical properties of a 90% cold-rolled thin sheet of a Ni-Fe-Cu-Mo alloy (~80 μm). The obtained results revealed that the recrystallization was started at a temperature of 550°C and was completed after 4 hours. An increase in the number of annealing twins was observed with an increase in annealing temperature, which was due to a bulging and long-range migration of grain boundaries during the discontinuous recrystallization. Ordering transformation occurred in the temperature range of 400-600°C and as a result, hardness, yield strength, and UTS were increased, while with an increase in the annealing temperature these mechanical properties were decreased. Maximum toughness was obtained by annealing at 550°C for 4 hours, while the highest elongation was obtained after annealing at 1050°C, where other mechanical properties including toughness, hardness, yield strength, and UTS were decreased due to the grain growth and secondary recrystallization. Moreover, coercivity and remanence magnetization were decreased from 4.5 Oe and 3.8 emu/g for the cold rolled sample to below 0.5 Oe and 0.15 emu/g for the sample annealed at 950°C, respectively.

2

Dispersion mechanism-induced variations in microstructural and mechanical behavior of CNT-reinforced aluminum nanocomposites

Doğan Kemal, Özgün Muhammed Ihsan, Sübütay Halit, Salur Emin, Eker Yasin, Kuntoğlu Mustafa, Aslan Abdullah, Gupta Munish Kumar, Acarer Mustafa

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e55, 2022

EN

The combination of powder metallurgy and ball milling method has been widely regarded as the most beneficial route for producing multi-walled carbon nanotubes (MWCNTs)-reinforced aluminum matrix composites. In this study, the effects of different milling times (1, 2, 4, and 8 h) on the structural, morphological, and crystallographic properties of MWCNTs-reinforced Al7075 composite powders were characterized by particle size analyzer, Raman spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). After the morphological and structural characterization of the milled powders, the microstructural and mechanical properties of the hot-pressed composites were evaluated using an optical microscope, SEM, density, and Brinell hardness measurements. Considering milled powder characterization, the MWCNTs were gradually distributed and embedded within the matrix as the milling time increased. Milling for 8 h resulted in a minimum level of particle size (11 µm) with shortened and uniformly dispersed CNTs. Brinell hardness of the composite increased from 91 to 237 HB -a ⁓%160 after 8 h of milling. Such a remarkable increment in hardness could be attributed to several concurrent strengthening effects related to dispersion, solution, grain refinement, and Orowan looping mechanisms. However, relative density results revealed that the composite produced by 2 h milled powders exhibited the highest density (%99.96). The observed differences between hardness and density results were ascribed to powders’ deteriorated packing and sintering behavior due to an increment in the hardness of particles and variation in particle size range and morphology, which resulted from following different milling protocols.

3

Wytwarzanie i mikrostruktura osadzanych elektrolitycznie stopów Ni-Co i kompozytów TiO2 / Ni-Co

Ledwig Piotr, Dubiel Beata, Kopia Agnieszka

Hutnik, Wiadomości Hutnicze

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2020

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Vol. 87, nr 4

107--113

PL

Stopy Ni-Co oraz kompozyty TiO2/Ni-Co osadzono elektrolitycznie z kąpieli siarczanowo-cytrynianowych o względnej zawartości jonów Co:Ni równej 1:49, 1:24 i 1:9 stosując gęstości prądu 2,5, 5 i 7,5 A/dm2. Wpływ parametrów osadzania na morfologię powierzchni, mikrostrukturę, skład chemiczny i skład fazowy zbadano za pomocą skaningowej i transmisyjnej mikroskopii elektronowej, spektroskopii dyspersji energii charakterystycznego promieniowania rentgenowskiego oraz dyfrakcji promieniowania rentgenowskiego. Wytworzone kompozyty charakteryzowały się globularną morfologią i nanokrystaliczną mikrostrukturą. Wykazano, że w osnowie kompozytów występują pojedyncze nanocząstki oraz aglomeraty TiO2. Zawartość TiO2 w kompozytach wynosiła około 4% mas. Stwierdzono, że wielkość ziarna kompozytów TiO2/Ni-Co zależy od obecności fazy umacniającej, warunków prądowych podczas osadzania oraz stężenia Co w osnowie Ni-Co.

EN

TiO2/Ni-Co composites were electrodeposited from citrate-sulfate bath with varying Ni:Co ratios. Effect of deposition conditions on chemical composition, surface morphology, microstructure and phase composition were investigated using scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Manufactured composites were characterized by typical cauliflower surface morphology and nanocrystalline structure. Nanocrystalline TiO2 particles were embedded in the Ni-Co matrix both in the form of dispersive nanoparticles and clusters. The concentration of nc-TiO2 in composites was about 4 wt. %. Grain size of TiO2/Ni-Co composites depended on the content of strengthening phase, deposition current conditions and Co concentration in the Ni-Co matrix.

4

Effects of multi-pass FSP on the β phase (Mg17Al12) distribution and mechanical properties of AZ91C magnesium alloy

Rouhi S., Dadashpour M., Mostafapour A., Doniavi A.

Journal of Achievements in Materials and Manufacturing Engineering

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2017

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Vol. 82, nr 2

77--85

EN

Purpose: The principle and advantages of friction stir processing (FSP) for the production of a highly formable Mg alloy, and some convincing experimental results are reported in this paper. The aim is to understand the relationship between the microstructure characteristics and the mechanical properties behaviour of the number of FSP passes AZ91C alloy. Design/methodology/approach: FSP is a solid state processing technique which involves plunging and traversing a square pin profiles FSP tool through the material. In this study, a fine-grained multi-phase AZ91C magnesium alloy was produced by applying FSP on as-cast AZ91C alloy. Findings: FSP achieved grain refinement and homogenization of the as-cast microstructure in Mg alloy AZ91C. FSP produced a fine homogeneous microstructure having a grain size of 6 μm throughout the plate. Also tensile properties of the specimen produced in one, two and three passes were investigated by standard tensile test. Results show that FSP improved the tensile characteristics of the as cast AZ91C alloy significantly. As the number of passes increased, higher UTS and TE were achieved due to finer grains and more dissolution of β phase (Mg17Al12). Originality/value: The present study shows that FSP is an efficient production method for a large-scale plate of a highly formable Mg alloy.

5

Characterization of thermally oxidized titanium based coating

Cetiner D., Paksoy A. H., Tazegul O., Atar E., Cimenoglu H.

Journal of Achievements in Materials and Manufacturing Engineering

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2016

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Vol. 75, nr 2

49--54

EN

Purpose: Aim of the study is to improve the bioactivity of CoCr alloy upon covering the surface with titanium based coating. Design/methodology/approach: CoCr alloy was coated by cold spraying of powder mixture having a composition of 92 wt.%Ti + 8 wt.%Al. Coated samples were thermally oxidized at 600°C for 60 hours. Characterization of the coating was made by X-Ray diffraction analyses, microstructural surveys, cross-section and surface SEM elemental mapping analyses, roughness and hardness measurements. Findings: Results showed that sequential application of cold spray and thermal oxidation processes provided the multi-layered coating consisting of an inner titanium based layer and an outer oxide layer consisted of TiO2 and Al2O3. Thermal oxidation also caused the remarkable increasing in the surface hardness as compared to the as-cold sprayed state. Practical implications: Modifying the surface of CoCr metallic implants for long term success. Originality/value: Producing a multilayer coating on the surface of the CoCr alloy for biomedical application by sequential application of cold spray and thermal oxidation processes is the orginality of the study.

6

A comparative study of Ti-Al and Ti-Nb alloys for advanced technological applications

Peter I., Rosso M., Castella C.

Journal of Achievements in Materials and Manufacturing Engineering

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2015

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Vol. 73, nr 2

199--205

EN

Purpose: of this paper is to compare some properties of Ti-Al and Ti-Nb alloys to investigate on the possibility to jointly employed them industrially. Ti-Al alloys have been proposed because they present challenging characteristics for high temperature purposes and β type Ti-Nb alloy has specific mechanical properties at room temperature. Ti-Al alloys are very attractive materials and represent one of the most important materials employed for aero jet engines. The most promising alloy belonging to the above mentioned classes are predominantly based on simultaneously presence of two phases, namely γ-TiAl (gamma titanium aluminides) and α2-Ti3Al both with a fully lamellar microstructure and could replace Ni-based superalloys in some high temperature applications in aerospace and automotive industries. The most important advantages of such alloys compared to some superalloys consist in their low density correlated to their superior efficiency in service and reduced gas emission. Design/methodology/approach: The Ti-Al alloy have been produced by gravity casting, using a vibrating furnace, while the Ti-Nb alloy samples have been realized by the cold crucible levitation melting (CCLM) casting technology. Microstructural and mechanical characterization have been performed. Findings: The microstructural analysis for the Ti-Al alloy reveals a fully-lamellar microstructure with alternate plates of α2-(Ti3Al) and γ-(TiAl) plates. The grains have an average size of about 200 μm. For the Ti-Nb based alloy only a β mono-phase has been detected. This alloy has a equiaxed microstructure with an average grain dimension of about 170 μm. The Ti-Nb alloy presents a high mechanical strength while on the contrary that of the Ti-Al has been deleteriously affected by the presence of large gas porosities. Superior hardness values have been reached with Ti-Al alloy, due to the presence of hard γ-TiAl. Practical implications: The most important implication is related to the transfer toward the proper choice of the correct parameters during manufacturing. Originality/value: Investigation on the influence of the elemental composition enriched by other elements and casting processes on the defect development, the microstructural characteristics and on the mechanical behaviour of the alloys.