High-resolution EBSD characterisation of friction stir welded nickel-copper alloy:Effect of the initial microstructure on microstructural evolution and mechanical properties

The effect of the initial structure on the microstructure and texture of the friction stir welded Monel 400 alloy joints was investigated. For this aim, Monel 400 alloy of two initially treated conditions, annealed and rolled, was studied. Orientation imaging microscopy with a step size of 70nm was used to characterise the microstructures of the joints. The mechanical properties were evaluated using Vickers hardness and nanoindentation tests. In the joint of the initial annealed alloy, continuous dynamic recrystallisation governed the grain structure formation. However, in the case of the initial rolled base material, discontinuous dynamic recrystallisation also occurred to cause more random texture, smaller grains, much more high-angle grain boundaries and higher dislocation densities. In the stir zone, the hardness and yielding strength increased respectively from 177 HV to 192 HV and 215.9 to 238.8MPa by changing the base metal from the initial annealed to rolled condition. In addition, the microstructural features of the different zones containing the texture components and grain boundaries were scrutinised thoroughly

Strengthening mechanisms of graphene sheets in aluminium matrix nanocomposites

Uniform dispersion of SiC nanoparticles with a high propensity to agglomerate within a thixoformed aluminium matrix was attained using a graphene encapsulating approach. The analytical model devised in this study has demonstrated the significant role of shear lag and thermally activated dislocation mechanisms in strengthening aluminium metal matrix composites due to the exceptional negative thermal expansion coefficient of graphene sheets. This, in turn, triggers the pinning capacity of nano-sized rod-liked aluminium carbide, prompting strong interface bonding for SiC nanoparticles with the matrix, thereby enhancing tensile elongation

A novel method for incorporation of micron-sized SiC particles into molten pure aluminum utilizing a Co coating

Ceramic particles typically do not have sufficiently high wettability by molten metal for effective bonding during metal matrix composite fabrication. In this study, a novel method has been used to overcome this drawback. Micron-sized SiC particles were coated by a cobalt metallic layer using an electroless deposition method. A layer of cobalt on the SiC particles was produced prior to incorporation in molten pure aluminum in order to improve the injected particle bonding with the matrix. For comparison, magnesium was added to the melt in separate experiments as a wetting agent to assess which method was more effective for particle incorporation. It was found that both of these methods were more effective as regard ceramic particulate incorporation compared with samples produced with as-received SiC particles injected into the pure aluminum matrix. SEM images indicated that cobalt coating of the particles was more effective than magnesium for incorporation of fine SiC particles (below 30 lm), while totally the incorporation percentage of the particles was higher for a sample in which Mg was added as a wetting agent. In addition, microhardness tests revealed that the cobalt coating leads to the fabrication of a harder composite due to increased amount of ceramic incorporation, ceramic-matrix bonding, and possibly also to formation of Al-Co intermetallic phases

Fabrication of aluminum matrix composites reinforced with nano- to micrometer-sized SiC particles

In this study, the hot extrusion process was applied to stir cast aluminum matrix–SiC composites in order to improve their microstructure and reduce cast part defects. SiC particles were ball milled with Cr, Cu, and Ti as three forms of carrier agents to improve SiC incorporation. Large brittle ceramic particles (average particle size: 80 μm) were fragmented during ball-milling to form nanoparticles in order to reduce the cost of composite manufacturing. The experimental results indicate that full conversion of coarse micron sized to nanoparticles, even after 36 h of ball milling, was not possible. Multi modal SiC particle size distributions which included SiC nanoparticles were produced after the milling process, leading to the incorporation of a size range of SiC particle sizes from about 50 nm to larger than 10 μm, into the molten A356 aluminum alloy. The particle size of the milled powders and the amount of released heat from the reaction between the carrier agent and molten aluminum are inferred as two crucial factors that affect the resultant part tensile properties and microhardness

Effect of interfacial-active elements addition on the incorporation of micron-sized SiC particles in molten pure aluminum

Ceramic particles generally have poor wettability by liquid metal, leading to a major drawback in fabrication of cast metal matrix composites (MMCs). In this work, the effect of 1 wt. % of Ca, Mg, Si, Ti, Zn and Zr interfacial-active alloying elements was studied on the incorporation of micron-sized SiC particles into the molten pure aluminum using the vortex casting method at 680 1C. The results indicated that Ti, Zr, Zn and Si were not positively effective in improving particulate incorporation, while Ca and especially Mg were very efficient at increasing the incorporation of ceramic particles into the molten Al. Also, it was revealed that Al3Ti, and Al3Zr intermetallic phases were formed for samples containing Ti and Zr, making hybrid MMCs with a higher amount of hardness. Finally, it was found that a reaction layer between Al and SiC particles was formed at the Al/SiC interface for all of the samples, expect for the ones containing Si and Ti, indicating that for most of the samples at 680 1C an exothermic reaction took place between the Al and SiC particles

Effect of electroless coating parameters and ceramic particle size on fabrication of a uniform Ni–P coating on SiC particles

The formation of a uniform nickel phosphorous (Ni–P) electroless (EL) coating on micronsized SiC particles was investigated in this study. Metal coated ceramic particles could be used in applications including as the fabrication of cast metal matrix composites.Such ceramic particles have a better wettability in molten metal. In this work, the effects of EL coating parameters, SiC particle size and morphology on the coating uniformity and mechanical bonding at the SiC/Ni–P interface were studied. The results indicated that etching treatment was very effective (especially for coarse powders) on the mechanical bonding at the interface. Theoptimum values of bath temperature and pH were determined to be 50+_2 0C and 8+_0.2, respectively. The best uniformity and mechanical bonding were obtained for SiC particles with average particle size of 80 μm (considered relatively as coarse powders in this study). The ball milling of SiC particles (with the average particle size of 80 μm) for 1 h led to the formation of a multi-modal particle size distribution which resulted in a non-uniform quality of particulate coating. The larger SiC particles after ball milling were more completely covered by the Ni–P coating compared to the smaller more fragmented particles. The smaller ceramic particles processed via Ni–P EL coating lead to formation of segregated clusters of Ni–P and therefore such ceramic particles contained many uncoated parts

Determination of atomic-scale structure and compressive behavior of solidified AlxCrCoFeCuNi high entropy alloys

The atomic configurations play a key role in predicting the solidification process of high-entropy alloys (HEAs). The atomic scale structures of AlxCrCoFeCuNi (x = 0.5, 1.5, 3.0) HEAs that emerge during solidification with a cooling rate of 12 × 109 (K/s) are evaluated using molecular dynamics (MD) simulation. While BCC (body-centered cubic) structure is obtained for Al0.5CrCoFeCuNi and Al1.5CrCoFeCuNi where lattice distortion increases with increasing aluminum fraction from x = 0.5 to x = 1.5, for Al3.0CrCoFeCuNi, an amorphous structure is formed under the same cooling rate. The diffusion coefficient of all the elements at 2200 K and the super-heating temperature of each alloy are evaluated to explain the disordering mechanism due to aluminum addition, which affects both the aluminum mobility and diffusion of the constituent atoms in the HEA. Finally, the compression behavior of all the three HEAs was studied to show the effect of crystalline structure on the stress fluctuation. It was found that phase transformation induced plasticity occurred which led to a secondary hardening of crystalline alloys after ultimate compressive strength (UCS)

Nano-scale simulation of directional solidification in TWIP stainless steels: a focus on plastic deformation mechanisms

In this study, in order to understand the nanostructure of FeCrNi steels in the laser powder bed fusion (LPBF) process, directional solidification was simulated using largescale molecular dynamics simulation (LSMDS). For this purpose, an atomic box with a dimension of including random dispersion of Fe, Cr and Ni was created. Then, two different fixed temperatures were considered for the left and right side of the box during cooling from the liquid molten state. For evaluation of the uniformity in mechanical properties, uniaxial tensile tests were performed in the parallel and perpendicular directions. Extensive twinning induced plasticity (TWIP) occurred alongside Shockley partial dislocations (DLs) evolution in both directions, while different ultimate tensile strengths (UTS) were obtained as a sign of nonuniform tensile behavior. Different plastic deformation mechanisms at the nano-scale including stacking faults (SFs) interaction with each other/grain boundaries (GBs)/twin boundaries (TBs), formation of defective coherent twins (DCTs), dynamic Hall-Petch, shear stress gradient (back stress), and a new mechanism for dynamic recrystallization at room temperature are discussed in detail

Study of LDL receptor gene mutations in patients with familial hypercholesterolemia in Chaharmahal va Bakhtiari province.

چکیده: زمینه و هدف: هایپرکلسترولمی فامیلی (FH) بیماری غالب اتوزومال است که عمدتاً بدلیل جهش در ژن گیرنده لیپوپروتئین با دانسیته کم (LDLR) ایجاد می شود. این مطالعه با هدف بررسی تغییرات ژن LDLR بیماران مبتلا به کلسترول بالای خانوادگی در استان چهارمحال و بختیاری انجام شد. روش بررسی: در این مطالعه توصیفی- آزمایشگاهی، 57 بیمار مشکوک به FH غربالگری و با استفاده از روش PCR-SSCP جهش در پروموتر و اگزون های 1، 3، 5، 11، 13، 15، 16، 17 و 18 ژن LDLR بررسی شد. یافته ها: در این مطالعه دو تغییر در ژن LDLR شناسایی شد، جهش هتروزیگوت 283T>A و پلی مورفیسم 1959T>C که به ترتیب در 1 و 9 فرد مبتلا به FH شناسایی گردید. نتیجه گیری: نتایج این تحقیق نشان داد نقش ژن LDLR در ایجاد FH در جمعیت مورد مطالعه ضعیف است و احتمالا ژن یا لوکوس های دیگری در ایجاد FH در این منطقه نقش دارن

Advanced production routes for metal matrix composites

The use of metal matrix composites (MMCs) in a variety of products is significantly increasing with time due to the fact that their properties can be tailored and designed to suit specific applications. However, the future usage of MMC products is very much dependent on their beneficial aspects and hence it is critical to ensure in a robust repeatable manner the superior physical property advantages compared to conventional unreinforced monolithic metal counterparts. Although numerous routes are available for production of MMC products, each of them has their own advantages and disadvantages. This article provides an overview of advanced production routes for MMCs. The discussion also highlights challenges and presents a future prospectus for MMCs. Powder metallurgy and casting routes are still extensively used for production of MMCs. Aluminum alloys are today the most commonly used matrix materials in MMC products. Carbides (eg, SiC, TiC, and B4C), carbon allotropes (eg, CNTs and graphene), and alumina (Al2O3) are currently the most used reinforcement materials. Nevertheless, the use of nano and of hybrid reinforcements are seeing increased usage in niche applications. Additive manufacturing (AM) is discussed as a novel production route for MMC products. This process represents a promising method for the production of MMC products