The physical and mechanical characteristics of cast steel 20ГЛ after electric spark alloing and ultrasonic impact treatment

Досліджено мікротвердість, структуру, фазовий склад і корозійну стійкість низьколегованої ливарної сталі 20ГЛ у вихідному стані після стандартної термообробки, а також після електроіскрового легування(ЕІЛ) різними елементами (Ni, Cr, Mo) і ультразвукової ударної обробки (УЗУО). Великий розмір феритної і перлітної складових обумовлює суттєву різницю між значеннями мікротвердості сталі як у вихідному, так і деформованому станах. Застосування ЕІЛ призводить до суттєвішого зміцнення, ніж УЗУО, особливо у випадку легування хромом та молібденом. Це зумовлено складними фазовими та структурними перетвореннями, які протікають при комбінованій обробці ЕІЛ+УЗУО: формування ОЦК твердих розчинів Fe-Cr і Fe-Mo, зміцнених інтерметалідними та карбідними фазами. Шорсткість поверхонь зразків при цьому значно знижувалась. Усі сформовані поверхневі шари на сталі 20ГЛ, леговані нікелем, хромом та молібденом, характеризуються більшим потенціалом корозії та меншим струмом корозії в порівнянні зі стальними зразками у вихідному стані, що свідчить про їх вищу стійкість до електрохімічної корозії. Згідно з аналізом морфології кородованих поверхонь найефективнішим виявилось ЕІЛ поверхневого шару нікелем, яке призводить до формування в ньому ГЦК твердого розчину залізо-нікель.Microhardness, structure, phase composition and corrosion resistance of low alloyed cast 20GL steel are studied in initial state after standard heat treatment, and after the electro-sparking alloying (ESA) by different elements (Ni, Cr, Mo) and ultrasonic impact treatment (UIT). Relatively large size of ferritic and pearlitic constituents determines a substantial difference between the microhardness values of the steel both in initial and in deformed states. The UIT process leads to slight increase in microhardness, and for the specimen after the UIT processing for 60 s the microhardness becomes 4 GPa, which is 1.45 times higher than that for initial state. Application of the ESA+UIT results in more substantial hardening than UIT, especially in the case of alloying with chromium (5.81 GPa) and molybdenum (7.47 GPa), which are 2.0 – 3.5 times and 2.7 – 4.3 times higher than initial specimen, respectively. It is due to complex phase and structural transformations, which occur at the combined ESA+UIT treatment. The ESA processes with chromium and molybdenum leads to formation of BCC Fe-Cr and Fe-Mo solid solutions strengthened by intermetallic phases and/or chromium-iron carbides. Using the nickel electrode at the ESA process promotes formation the FCC Fe-Ni solid solution. In all the cases, the UIT process decreases the surface roughness of specimens considerably. All the formed superficial layers on the 20GL steel, alloyed with nickel, chromium and molybdenum are characterized by higher corrosion potential and lower corrosion current in comparison with the initial steel specimens that testifies to their higher resistances to electrochemical corrosion. According to the analysis of morphology of corroded surfaces the ESA process of superficial layer with nickel electrode is the most effective one, which leads to formation the iron-nickel FCC solid solution. The superficial layers alloyed with chromium and molybdenum underwent more severe corrosion attack due to their heterogenic phase structure. Considerable misfit between lattices of BCC solid solutions (Fe-Cr or Fe-Mo) and intermetallic or carbide phases with crystalline lattices of low symmetry results in formation of defects and stresses can also promote higher corrosion rate

Microstructure of Co–Cr Dental Alloys Manufactured by Casting and 3D Selective Laser Melting

The review analyses the microstructure of the commercial Co–Cr–(Mo, W) dental alloys fabricated by 3D digital selective laser melting (SLM), which is the most promising technique among the emerging additive fabrication technologies used for metal products manufacturing in dentistry. In this regard, the main goal is to compare the microstructures of the metal dental products produced by two currently used technologies, namely, conventional casting and SLM. We consider the latest research published from 2013 to 2022. The microstructures are evaluated using optical microscopy (OM), scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM–EDS), x-ray diffractometry (XRD), electron backscatter diffraction (EBSD) pattern analysis, and atomic force microscopy (AFM). The microstructure analysis allows concluding whether the SLM fabrication process is suitable for dental applications. As shown, the microstructure of the Co–Cr dental alloys depends on both the chemical composition of the samples and the parameters of the manufacturing technique used. Experimental results have proven that, in contrast to the conventional casting, the SLM-fabricated specimens display superior microstructure due to complete local melting and rapid solidification. Additionally, the SLM process minimizes residual flaws and porosity. As a result, SLM allows producing the dense material comprising homogeneous fine-grain microstructure

Effect of ultrasonic vibrations on interface strength in composites of shape memory alloy with metallic matrix

The main problem in developing the composite materials containing Shape Memory Alloy (SMA) actuators is to provide the strength of interface between matrix and SMA. The other important problem is to provide the martensitic transformation with needed parameters and resistance to thermal cycling in the composite material. Application of ultrasonic (US) technologies for obtaining composite materials helps to some extent to solve the above-mentioned problems. The ultrasonic technologies available are the composite materials crystallization in ultrasonic field, simultaneous deformations of composite components by using ultrasound and sintering of powdered/fractured composite mix with high-intensity ultrasound apply to different stages of the process. All these are aimed at obtaining the composites with good functional properties. In the present paper, main attention is paid to the composite materials consisting of the CuAlNi, CuAlMn, CuAlZn and Ni-Ti shape memory alloys and various second component (aluminum, copper and Cu-alloys), Two main achievements have been reached by application of the US vibrations: modification and refinement of the shape memory alloy microstructure; improvement in adhesion of the superelastic/shape memory materials to the metal substrate surface subjected to ultrasonic metallisation