Microstructural Features and Properties of Al-Cu-Mg Alloy Containing Silver and Cerium

The article presents the results of an investigation of microstructural features and mechanical characteristics of Al-5.0Cu-0.5Mg alloy containing up to 0.4 wt. % Ag and up to 0.1 wt. % Ce. The experiment was conducted using optical microscopy, Scanning Electron Microscopy as well as an electron probe micro-analyzer and Differential Scanning Calorimetry. Samples in cast condition and after heat treatment were examined. The melting temperatures of non-equilibrium eutectics (non-equilibrium solidus), equilibrium solidus and liquidus were determined. The optimal temperature of the homogenizing heat treatment was determined, which was 500°C. Using this heat treatment mode resulted in the elimination of dendritic segregation and complete dissolution of silver in aluminum. Injection of cerium into the Al-Cu-Mg-Ag system during crystallization of the melt is accompanied by the formation of a coarse four-component phase, which has the morphology of polyhedrons, is on the grain boundaries. The estimation of the relation between microstructure characteristics and mechanical properties of the alloy has been made.

The cooling rate effect during a continuously cast billet solidification on the dendritic structure features of carbon steel

The analysis of the formation process of the cast structure of carbon steel grade ОС (ДСТУ ГОСТ 4728:2014) after the completion of its crystallization with a change in a wide range of metal cooling rate during solidification of a continuously cast billet (ССB) with a diameter of 450 mm has been carried out. The effect of the cooling rate during the solidification of ССB Ø 450 mm on the parameters of the chemical heterogeneity of the distribution of silicon and manganese in the microstructure of carbon steel has been shown. It has been determined that the effect of the metal cooling rate during the solidification of the investigated CCB on the size of dendritic crystals is described by the inversely proportional relationship: у = 423.75 х-0,161. With a change in the cooling rate of the metal during solidification from 106 до 1 °C/min, the size of the dendrites in the direction from the surface to the central layers of the CCB Ø 450 mm increased by ~ 8 times, and the density of the dendritic structure of carbon steel ОС decreases by 65 times. In this case, the nature of its dependence on the intensity of heat removal is the opposite nature of the change in the size of dendrites. It has been established that by varying the cooling rate in the range 1 – 106 °C/min, one can achieve a significant change in the average size and density of dendritic crystals while maintaining the constancy of the volume fraction of segregation areas of silicon and manganese ~ 24% in carbon steel (0.42 – 0.50 % wt. C). It has been determined that in the entire investigated range of cooling rates 1 – 106 °C/min, the coefficients of dendritic segregation КдI and КдII of silicon and manganese change insignificantly and amount to 1.8-1.9 and 1.5 for КдI and КдII, respectively. In this case, the values of the coefficients КдI and КдII for both elements are practically constant in both pearlite and ferrite. It has been proven that both silicon and manganese have high diffusion mobility only at sufficiently high temperatures, when steel is in a solid-liquid state. Based on the results of X-ray microanalysis, it has been established that the heterogeneity of the distribution of chemical elements, which is formed as a result of dendritic segregation of silicon and manganese, is the primary and constant component of the microstructure of carbon steel. Keywords: carbon steel, continuously cast billet, solidification, cooling rate, dendritic structure.

Efficient Spike-Driven Learning With Dendritic Event-Based Processing

A critical challenge in neuromorphic computing is to present computationally efficient algorithms of learning. When implementing gradient-based learning, error information must be routed through the network, such that each neuron knows its contribution to output, and thus how to adjust its weight. This is known as the credit assignment problem. Exactly implementing a solution like backpropagation involves weight sharing, which requires additional bandwidth and computations in a neuromorphic system. Instead, models of learning from neuroscience can provide inspiration for how to communicate error information efficiently, without weight sharing. Here we present a novel dendritic event-based processing (DEP) algorithm, using a two-compartment leaky integrate-and-fire neuron with partially segregated dendrites that effectively solves the credit assignment problem. In order to optimize the proposed algorithm, a dynamic fixed-point representation method and piecewise linear approximation approach are presented, while the synaptic events are binarized during learning. The presented optimization makes the proposed DEP algorithm very suitable for implementation in digital or mixed-signal neuromorphic hardware. The experimental results show that spiking representations can rapidly learn, achieving high performance by using the proposed DEP algorithm. We find the learning capability is affected by the degree of dendritic segregation, and the form of synaptic feedback connections. This study provides a bridge between the biological learning and neuromorphic learning, and is meaningful for the real-time applications in the field of artificial intelligence.

The Microstructure and Properties of Low Carbon PM 625 Alloy for Marine-Based Application

The low carbon content powder metallurgy (PM) 625 alloy were manufactured by vacuum induction gas atomization (VIGA) and hot isostatically pressing (HIP) for marine-based application such as parts in the subsea Xmas tree. Corrosion experiment was performed in simulated deep seawater and subsea oil & gas service environment. The microstructures and properties of low carbon 625 alloy were comparably investigated with that of the as-cast alloy. The results indicated that the dendritic arm spacing (DAS) of the as-cast 625 alloy is 2 orders of magnitude higher than that of the powders, whereas the HIPed alloys possess a fine equiaxed grain structures without dendritic segregation and an average grain size of 14.5μm. No minor phase has been found beside the γ matrix in the original powders with different particle size. The tensile strength of low carbon PM 625 alloy is 26% higher than that of as-cast 625 alloy. PM 625 alloy possesses an excellent corrosion resistant in simulated deep seawater and oil & gas service environment for 30 days.

Reasons for banding formation in steels of K60 strength category

Active development of pipeline transport of gas and oil with increasing working pressure to 120 atm. increases the need for pipes with large wall thickness that correspond the requirements of the DNV OS-F101 standard. Quality of continuously cast billets is decisive for improving quality of sheet metal for main pipelines. Inheritance of cast structure imperfections by a hot-rolled sheet leads to structural heterogeneity of the strip and the layered nature of the fracture surface and adversely affects the mechanical properties and corrosion resistance. Structural heterogeneity of rolled products is appeared in the form of axial ferrite-martensitic metal banding and metal banding in the main section of the sheet consisting of a mixture of ferritic and pearlitic grains — pearlitic metal banding. The flatness in the axial zone of the rolled products is due to axial chemical heterogeneity which is objectively formed during crystallization of the continuously cast billet and further phase transformations. The axial chemical inhomogeneity does not resolve despite the recrystallization of the structure and deformation and the high content of alloying elements contributes to the formation of the martensite phase and large carbonitride precipitates. The cause of pearlite bands is considered usually to be the presence of dendritic segregation. According to us the reason of this metal banding is the shift of the temperature front of γ → α transformation parallel to the sheet surface in depth as a result of which before the next volume of formed ferrite the concentration of carbon dissolved in austenite increases with the subsequent formation of pearlite. The enrichment of austenite proceeds along the boundaries preserved from the δ → γ transformation during cooling the slab and the formed pearlite structure repeats the shape of the boundaries of these grains in the section parallel to the sheet plane.

Microstructure of 7N01 Aluminum Alloy Microalloyed with Er and Zr in the Homogenization Process

The microstructure and segregation of 7N01 aluminum alloy microalloyed with Er and Zr before and after homogenization process at 470 °C for 24 h have been investigated using transmission electron microscope (TEM), and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscope (EDS) and transmission electron detecter (STEM). SEM images and EDS line scan results showed that there were dendritic segregation of Mg and Zn and micron-sized primary phases along dendrites in the as-cast alloy. The primary phases were mainly Al2Mg3Zn3 containing Al, Zn, Mg and Mn. And a small amount of primary phases were the particles containing Al, Zn, Mg, Mn, Cr and Er and the particles containing Al, Zn, Mg, Er, Mn, Fe and Cr. After homogenization at 470°C for 24 h, dendritic segregation of Mg and Zn was eliminated, Al2Mg3Zn3 and the particles containing Al, Zn, Mg and Mn were basically dissolved. The particles containing Al, Zn, Mg, Mn, Cr and Er and the particles containing Al, Zn, Mg, Er, Mn, Fe and Cr remained. Meanwhile, TEM and STEM images showed that a large number of secondary phases appeared after the homogenization, which were mainly distributed in the inter-dendrite area. EDS results showed that the block-shaped and rod-shaped phases with the width of 10-70 nm and length of 100-500 nm were the particles containing Al, Cr and Mn or Al, Mg, Cr and Mn, and the ellipsoid secondary phase with the size of 50-100 nm was MgZn2.

Research of the effect of the cooling rate during solidification of a continuously cast billet on the features of the dendritic structure of carbon steel

The analysis of the formation process of the cast structure of carbon steel grade EA1N (EN 13261: 2009 + A1: 2010 (Е)) after the completion of its crystallization with a change in a wide range of metal cooling rate during solidification of a continuously cast billet (ССB) with a diameter of 470 mm has been carried out. The effect of the cooling rate during the solidification of ССB Ø 470 mm on the parameters of the chemical heterogeneity of the distribution of silicon and manganese in the microstructure of carbon steel has been shown. It has been determined that the effect of the metal cooling rate during the solidification of the investigated CCB on the size of dendritic crystals is described by the inversely proportional relationship: у = 510,85 х-0,156. With a change in the cooling rate of the metal during solidification from 106 до 1 ℃ / min, the size of the dendrites in the direction from the surface to the central layers of the CCB Ø 470 mm increased by ~ 8 times, and the density of the dendritic structure of carbon steel EA1N decreases by 64 times. In this case, the nature of its dependence on the intensity of heat removal is the opposite nature of the change in the size of dendrites. It has been established that by varying the cooling rate in the range 1 – 106 ℃ / min, one can achieve a significant change in the average size and density of dendritic crystals while maintaining the constancy of the volume fraction of segregation areas of silicon and manganese ~ 23% in carbon steel (~ 0.4 % wt. C). The results of X-ray spectral analysis of samples of ССB Ø 470 mm made of carbon steel grade EA1N showed that the maximum content of silicon and manganese is characteristic of the former spaces between the first-order dendritic branches, their minimum content is for the former dendritic branches. At the same time, the amount of these elements in steel microvolumes, which are the former spaces between the second-order dendritic branches, is on average 50 % more than in the former dendritic branches. It has been determined that in the entire investigated range of cooling rates 1 – 106 ℃ / min, the coefficients of dendritic segregation КдI and КдII of silicon and manganese change insignificantly and amount to 1.8-1.9 and 1.5 for КдI and КдII, respectively. In this case, the values of the coefficients КдI and КдII for both elements are practically constant in both pearlite and ferrite. It has been proven that both silicon and manganese have high diffusion mobility only at sufficiently high temperatures, when steel is in a solid-liquid state. Based on the results of X-ray microanalysis, it has been established that the heterogeneity of the distribution of chemical elements, which is formed as a result of dendritic segregation of silicon and manganese, is the primary and constant component of the microstructure of carbon steel.