STRUCTURAL-PHASE STATE OF SILUMIN OF HYPEREUTECTIC COMPOSITION IRRADIATED BY A PULSED ELECTRON BEAM

Силумин (сплав алюминия с кремнием) является дешевым промышленным сплавом, обладающим хорошей коррозионной стойкостью, высокими удельными механическими свойствами и хорошими литейными свойствами, вследствие чего нашел широкое применение в современной промышленности (авиа- и машиностроение, приборостроение, судостроение и т.д.). Целью настоящей работы является анализ закономерностей преобразования структуры и фазового состава поверхностного слоя силумина заэвтектического состава (Al - 22 вес. % Si ), подвергнутого облучению интенсивным импульсным электронным пучком. Установлено, что облучение силумина импульсным электронным пучком (18 кэВ, 25 Дж/см, 200 мкс, 3 имп., 0,3 с) приводит к плавлению поверхностного слоя толщиной до 60 мкм, высокоскоростная кристаллизация которого сопровождается формированием субмикро- нанокристаллической многофазной структуры. Показано, что алюминий (твердый раствор на основе ГЦК кристаллической решетки) формирует ячейки высокоскоростной кристаллизации; на границах ячеек расположены наноразмерные частицы вторых фаз. Выполнен анализ трехкомпонентных диаграмм состояния системы Al - Si - Fe - Cu (основные элементы исследуемого силумина) и продемонстрирована возможность формирования в сплаве в равновесных условиях большого количества двух- и трехэлементных соединений. Методами дифракционной электронной микроскопии показано, что наряду с трехэлементными фазами в силумине образуются и фазы на основе четырех и, возможно, большего количества элементов. Silumin (an alloy of aluminum with silicon) is a cheap industrial alloy with good corrosion resistance, high specific mechanical properties and good casting properties. As a result it has found wide applications in modern industry (aircraft and mechanical engineering, instrument making, shipbuilding, etc.). The aim of this work is to analyze the regularities of transformation of the structure and phase composition of the surface layer of a hypereutectic silumin (Al - 22 wt % Si), subjected to irradiation with an intense pulsed electron beam. It was found that irradiation of silumin with a pulsed electron beam (18 keV, 25 J / cm, 200 μs, 3 pulses, 0,3 s) leads to melting of the surface layer up to 60 pm thick, the high-speed crystallization of which is accompanied by the formation of a submicro-nanocrystalline multiphase structure. It is shown that aluminum (a solid solution based on fcc crystal lattice) forms cells of high-speed crystallization; nanoscale particles of the second phases are located at the cell boundaries. Analysis of three-component state diagrams of the Al - Si - Fe - Cu system (the main elements of the studied silumin) demonstrated the possibility of forming a large number of two- and three-element compounds in the alloy under equilibrium conditions. It has been shown by diffraction electron microscopy that, along with three-element phases, phases based on four and, possibly, more elements are formed in silumin.

Microstructure, mechanical and corrosion properties of TIG welded Hastelloy C-276

Hastelloy C-276 is a corrosion resistant nickel based solid solution hardened industrial alloy which has superior mechanical and corrosion properties. In this study, Hastelloy C-276 alloy was welded via the GTAW (Gas tungsten arc welding) method using ERNiCrMo-4 filler metal. Tensile, bending and notch impact tests were performed to determine the mechanical properties. The microstructure of the weld metal was investigated by light microscopy (LM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The impact toughness values of the heat affected zone (HAZ) showed a better performance than those of the weld metal. In addition, the corrosion properties of the weld metal and the base material were investigated by potentiodynamic polarization tests. Electrochemical potentiodynamic polarization parameters were determined according to corrosion behavior and microstructure properties. In particular, the corrosion rate of the weld metal increased because of the Mo-rich phases deposited in the weld metal microstructure.

Investigation of the corrosion process and destruction of metals by using acoustodamage method

The paper presents the results of investigation of acoustic anisotropy in industrial alloy made of steel 14HGNDC after hydrogen-induced cracking (HIC) tests according to the standard NACE TM0284-2003. It was found that location and parameters of corrosion cracks with size about 20 microns can be determined by distribution and value of acoustic anisotropy. A quantitative relationship between value of acoustic anisotropy and size of corrosion cracks in the range from 60 to 6600 microns was established. The obtained results have a great importance for improving methods of hydrogen-induced cracking tests and for non-destructive testing of brittle destruction of structures in oil and gas industry by using the acoustodamage method.