STUDY OF THE STRUCTURE AND PROPERTIES OF LEAD-FREE RAPIDLY SOLIDIFIED ZINC-BASED ALLOYS DURING A HEAT TREATMENT

Представлены результаты исследований влияния сверхвысоких скоростей охлаждения расплава, равных не менее 10К/с, на свойства быстрозатвердевших сплавов системы Zn - Sn. Верхняя область фольги, контактирующая с кристаллизатором в процессе затвердевания, имела дисперсные частицы второй фазы, и по мере удаления от верхних слоёв размеры частиц укрупнялись. При комнатной температуре протекает распад пересыщенного твёрдого раствора с выделением дисперсных частиц. Дополнительная термическая обработка приводит к укрупнению частиц второй фазы, и способствует снижению микротвёрдости. Быстрозатвердевшие фольги с максимальной концентрацией цинка характеризуются наличием текстуры (0001), которая по мере увеличения содержания олова в цинке ослабляется, и при легировании выше 20 мас. % Sn происходит перестройка на текстуру (101̅0). Термическая обработка до 160 °С не приводит к изменению текстуры. The results of studies of the effect of ultrahigh melt cooling rates, equal to at least 10 K/s, on the properties of rapidly solidified alloys of the Zn - Sn system are presented. The upper region of the foil, in contact with the crystallizer during solidification, had more dispersed particles of the second phase, and as the distance from the upper layers increased, the particle sizes increased. At room temperature, the decomposition of a supersaturated solid solution proceeds with the release of dispersed particles. Additional heat treatment leads to the coarsening of the particles of the second phase, and helps to reduce the microhardness. Rapidly solidified foils with a maximum zinc concentration are characterized by the presence of a (0001) texture, which weakens as the tin content in zinc increases, and upon alloying up to 30 wt. % Sn is rearranged to (101̅0) texture. Heat treatment up to 160 °C does not change the texture.

High quality polymer sulfur production techniques: patent review

Основным способом предотвращения выцветания серы в резине является применение ее нерастворимой µ-формы (полимерная сера). Нерастворимая сера используется для увеличения прочности, термостойкости и износостойкости изделий. Она нашла применение также в производстве серных и сероасфальтобетонов для формирования дорожного покрытия в различных отраслях строительства. Термические методы получения полимерной серы (газификация и метод охлаждения расплава) наиболее распространены в мировом промышленном производстве. Но имеется множество до конца нерешенных проблем, таких как низкое содержание целевого продукта, использование высокотоксичных реагентов в производстве, получение плохо диспергируемого в каучуке продукта, возвращение полимерной формы в более устойчивую циклическую восьмичленную в процессе производства и хранения. Таким образом, основные тенденции в развитии методов производства полимерной серы направлены на достижение «трех максимумов» показателей нерастворимой серы, а именно: высокое содержание, высокая диспергируемость и высокая термостойкость. Целью данной статьи является обзор текущих технических достижений в области производства высококачественной полимерной серы на основе анализа мировой патентной литературы последних лет. В объем обзора входит обсуждение путей увеличения стабильности полимерной формы, количественного выхода, снижения электростатического эффекта и улучшения диспергируемости при производстве резины. Рассмотрено применение различных индивидуальных веществ и композиций для получения максимального выхода нерастворимой формы серы с прочно связанными обрывами цепочечной структуры. Представлены условия их применения, концентрации, влияние на термическую стойкость. Показано, что химическая природа стабилизатора и метод его добавления непосредственно влияют на термостойкость продукта и стабильность при хранении. Для улучшения этого комплекса свойств полимерной серы идут по пути усложнения состава добавок и многоступенчатого их ведения. Рассмотрены различные варианты традиционных и новых антистатических и диспергирующих добавок, возникающие технические и технологические проблемы при их применении. The main method of preventing sulfur from fading out of rubber is the use of its insoluble µ-form (polymeric sulfur). Insoluble sulfur is used to increase the strength, heat resistance and wear resistance of articles. It also found application in the production of sulfur concrete for the formation of pavement in various sectors of construction. Thermal methods for producing insoluble sulfur (gasification and melt cooling method) are most common in world industrial production. But there are many unresolved problems: the low content of the target product, the use of highly toxic reagents in production, the production of a product that is poorly dispersible in rubber, the return of the polymer form to a more stable cyclic eight-membered in the process of production and storage. The main trends in the development of insoluble sulfur production methods are aimed at achieving "three maxima" of insoluble sulfur indicators: high content, high dispersibility and high heat resistance. The purpose of this article is to review the current technical achievements in the production of high-quality insoluble sulfur based on the analysis of the world patent literature of recent years. The scope of the review includes discussion of ways to increase polymer form stability, quantitative yield, reduce electrostatic effect and improve dispersibility in rubber production. The use of various individual substances and compositions for maximizing the yield of insoluble form of sulfur with firmly bound cuts of chain structure is considered. The conditions of their application, concentration, influence on thermal resistance are shown. It has been shown that the chemical nature of the stabilizer and the method of its addition directly affect the heat resistance of the product and storage stability. To improve this complex of properties of polymer sulfur, the composition of additives and their multistage management are complicated. Various versions of traditional and new antistatic and dispersing additives, arising technical and technological problems in their application are considered.

Influence of chemical composition and the processing conditions on structure, thermal stability and mechanical properties of rapidly cooled Al-TM-RE-based alloys

The results of t studies are directed to development of new competitive amorphous and nanocrystalline alloys as well as to improvement of technology of their manufacturing. The physical and technological aspects of interrelations between the conditions for production of rapidly quenched alloys, formation of different structural and phase states, and their properties are discussed. The influence of the chemical composition of alloys and the conditions of their quenching on the glass-forming ability, phase composition, and the structure of the rapidly cooled specimens is investigated; the regularities of the effect of alloying elements concentration on the structural features of the Al75–87(Ni,Co,B/Ga)8–20Gd1Y4 alloys obtained by superfast quenching from the liquid state are established. The thermal stability of the rapidly quenched ribbons with an amorphous structure is investigated and the temperature ranges of phase transformations at continuous heating and under isothermal conditions are found. The strength characteristics of the ribbons as a function of the content and nature of alloying elements as well as the melt cooling rate are determined. The methods of obtaining both Al-based bulk nanocrystalline composites with the shapes of rods and plates with thickness of 0.5–3.5 mm and metal matrix hardening coatings are worked out.

Shape Memory Behavior of Rapidly Quenched High-copper TiNiCu Alloys

Rapidly quenched quasibinary TiNi–TiCu system alloys with high copper contents (above 20 at.%) exhibit excellent shape memory effect and have considerably narrower hysteresis as compared with the TiNi binary alloy, this advantage being of special importance for cyclic load applications, e.g. for microelectromechanics (MEMS). The aim of this work is to study the effect of annealing parameters and copper content on the shape memory effect in TiNiCu alloys. Thin amorphous ribbons of TiNi-TiCu alloys with copper contents of 25 to 40 at.% were produced by planar flow casting at a melt cooling rate of about 106 K/s. The alloys were crystallized by isothermal annealing with variable duration and by exposing specimens to a short (10 ms) electric pulse. Increasing the copper content to above 30 at.% considerably reduces the plasticity and shape memory effect of the alloys. However, significant reduction of annealing duration greatly improves the shape memory performance due to prevention of the formation of brittle Ti-Cu phases in the alloys structure.

Selective Laser Melting of Aluminum and Its Alloys

The laser-based powder bed fusion (LBPF) process or commonly known as selective laser melting (SLM) has made significant progress since its inception. Initially, conventional materials like 316L, Ti6Al4V, and IN-718 were fabricated using the SLM process. However, it was inevitable to explore the possible fabrication of the second most popular structural material after Fe-based alloys/steel, the Al-based alloys by SLM. Al-based alloys exhibit some inherent difficulties due to the following factors: the presence of surface oxide layer, solidification cracking during melt cooling, high reflectivity from the surface, high thermal conductivity of the metal, poor flowability of the powder, low melting temperature, etc. Researchers have overcome these difficulties to successfully fabricate the different Al-based alloys by SLM. However, there exists no review dealing with the fabrication of different Al-based alloys by SLM, their fabrication issues, microstructure, and their correlation with properties in detail. Hence, the present review attempts to introduce the SLM process followed by a detailed discussion about the processing parameters that form the core of the alloy development process. This is followed by the current research status on the processing of Al-based alloys and microstructure evaluation (including defects, internal stresses, etc.), which are dealt with on the basis of individual Al-based series. The mechanical properties of these alloys are discussed in detail followed by the other important properties like tribological properties, fatigue properties, etc. Lastly, an outlook is given at the end of this review.

Crystal transition and thermal behavior of Nylon 12

The polyamide 12 (PA12) with different crystal forms is prepared with three crystallization paths. The crystal structures and corresponding thermal properties are systematically investigated. The results reveal that an α-form and a mixed (α + γ)-form of PA12 can be obtained by casting at 30°C and (40–80°C), respectively. Meanwhile, the γ-form of PA12 can be obtained by both casting at 90°C and slow melt cooling. However, the γ′-form is obtained only by melt quenching. Both the γ and γ′ forms of PA12 exhibit a single melting peak, whereas the α-form exhibits two melting peaks. The higher peak is attributed to the melting of γ-PA12, which originates from the melting–recrystallization of the α-PA12. It is found that the tensile properties of PA12 depend on the crystal forms. Both the γ and γ′-PA12 are strong and tough polymer materials, while α-PA12 is a strong but brittle polymer material.