Vol 22, No 2 (2020)

Introduction. Ultrasonic impact-frictional treatment (UIFT) is a new method of surface strain hardening that improves the properties and refines the microstructure of the surface layer of metallic material. Unlike traditional ultrasonic impact treatment (UIT), the UIFT applies impacts with ultrasonic frequency at an acute angle α to the metal surface in order to activate the shear deformation mode. Oxygen-free atmosphere of argon enhances friction and prevents embrittlement of the diffusion-active deformed layer. A decrease of the angle α during the UIFT leads to a shift of the metal displaced by the tool towards the impact. Therefore, the tool position, oscillating with an ultrasonic frequency, with respect to the tool trajectory may have a profound effect on the surface microrelief. Objective is studying the influence of the impact direction on the roughness and hardening degree of the 09Mn2Si structural steel surface regarding the tool cross-feed during UIFT at an angle α = 50º in the argon medium. Research Methods are following: microhardness measurements, atomic force microscopy (AFM), optical profilometry, optical microscopy and scanning electron microscopy with EBSD analysis. Results and discussion. After grinding, the steel surface microhardness is 200 HV0.1 and the arithmetic mean deviation of the surface profile is Ra= 0.6 μm. UIT at an angle α = 90º in an industrial oil medium results in the surface hardening up to 260 HV0.1, while the Ra parameter increases to 1.6 μm. UIFT with the impact vertical deviation towards the specimen cross-feed (forehand) provides a relatively uniform microrelief with Ra= 0.4 μm and the deformed layer microhardness of up to 500 HV0.1. The tool deviation in the contrary direction towards the specimen cross-feed (backhand) increases the surface hardening degree (620 HV0.1), but leads to the formation of an advanced microrelief consisting of shifted metal displaced by the tool, as well as to the Ra parameter increase up to 3.5 μm. At the same time, the submicrorelief roughness remains approximately at the same level (Ra= 0.03–0.04 μm) for all three hardening treatment methods. Thus, the angle and impact direction during ultrasonic hardening treatment are important technological parameters that allow long-range controlling of the surface microrelief with the UIFT applied as a finishing hardening treatment. UIFT is an effective method of surface hardening, intended to form a surface even with a lower roughness of the microprofile compared to that of a traditional grease-applied UIT.

Introduction. Current trends in the development of composite materials based on aluminum alloys discretely hardened by SiC are aimed at structural applications, including at high temperatures. The manufacture of parts using metal forming processes allows to minimize the finishing of workpieces, in which there is a rapid wear of the cutting tool. However, it is necessary to increase the ductility of aluminium matrix composite materials by preliminary deformation-heat treatment. After such treatment, under certain thermomechanical conditions, the composites may exhibit signs of superplasticity. It is also important to be able to predict how external influences (high temperature and pressure) will affect the deformation behavior of composites during operation. Therefore, an integral part of the assessment of the deformation properties of composite materials intended for continuous service is creep testing. At the same time, a joint review of the results of uniaxial tensile tests under creep and superplasticity conditions broadens the picture of the deformation behavior of composite materials in a wide range of temperature-velocity effects. Objective: to conduct a comparative analysis of the results of published studies on the deformation behavior of aluminium matrix composite materials discretely reinforced with silicon carbide during the manifestation of superplasticity and under conditions of high temperature creep. The paper presents the results of published studies of composite materials with matrices based on the following grades of aluminum alloys: Al2009, Al2014, Al2024, Al2124, Al6013, Al6061, Al6063, Al6090, Al8009, Al8090, IN9021. The deformation of aluminium matrix composite materials in the state of superplasticity and under conditions of high temperature creep is considered. Results and discussion. A literature review shows that superplastic deformation mainly manifests itself at strain rates of more than 10–2 s–1. Moreover, the maximum elongation reaches the limits of 200 to 450%. The highest elongation of 685% is obtained at a rate of 5 • 10-4 s-1 for Al2024 / 10SiCp material. In a number of works, it is found that in order to achieve superplastic deformation, the process temperature should be equal to or slightly higher than the temperature of partial melting of the matrix at the grain boundaries of the matrix and the boundaries of the matrix with reinforcing particles. Composite materials with matrices based on the following alloying systems are best studied: Al-Mg-Cu (Al2124), Al-Mg-Si (Al6061), Al-Fe-V-Si (Al8009). Among the factors that most significantly affect the deformation behavior of aluminium matrix composites during creep, it can be noted: the technology of primary production of a composite material, preliminary deformation-heat treatment, the chemical composition of the matrix alloy, and the type and size of the hardening phase. Studies are noted to study the effect of temperature fluctuations on deformation behavior during operation under unsteady creep conditions with a change in pressure. The data collected show that, under certain thermal cycling conditions and low applied pressures, composite materials tend to have high degrees of deformation, which can be promising for developing manufacturing techniques for workpieces and products.

Introduction. In modern industrial and scientific-technical sphere the problem of details formation from various metals and alloys by additive methods is one of the most critical and demanding timely decision. This is primarily due to the need to produce large, complex shaped parts with high productivity and as little waste as possible. One of the most applicable methods for the formation of products by additive method is electron beam wire-feed technology. With use of wire filament and an electron beam for melting in a printing zone it is possible to obtain details with high productivity and acceptable indicators of final structure and mechanical properties. However, interrelation of received structure and mechanical properties depending on parameters of electron beam additive manufacturing process nowadays insufficiently presented in the literature.  In this regard, the purpose of this work is to analyze the influence of additive electron-beam production process parameters on the formation of products from SS 321. Results and discussion. Electron beam current, linear printing speed, and wire feeding ratio are used as variable parameters, and the ultimate tensile strength is taken as the optimization parameter. Optimal parameters of the electron beam current (40 mA), printing speed (180 mm/min) and wire feeding ratio (1.3) at constant accelerating voltage (30 kV) are established. These parameters allow forming the product without defects and without melting the previously formed layers with the ultimate tensile strength of 583 MPa. It is shown that the use of the highest values of printing speed (320 mm/min) and wire feeding ratio (1.3) at varying the electron beam current does not allow to perform the sample formation process. It is established that at the parameters of the electron beam additive manufacturing process, which provide the complete formation of the product, the structures obtained in materials achieve ultimate tensile strength within 558-595 MPa.

Introduction. The formation of protective layers on working surfaces of machine parts comprised of chromium-nickel austenitic steels is an effective way to increase its reliability and durability. Ni-base self-fluxing alloys are widely used in order to create wear resistant coatings. The possibility of increasing the set of properties of Ni-Cr-Si-B alloys by adding reinforcing compounds to its matrix or by synthesizing reinforcing phases directly in the process of forming a protective layer is a significant interest of domestic and foreign scientists. The literature does not provide the information on the formation of protective layers on the surface of austenitic steels using cladding by relativistic electron beams of a Ni-Cr-Si-B alloy in combination with hardening additives. Aim of the current work is to increase the tribotechnical properties of the surface layers of steel workpieces via air-revealed electron beam cladding of a Ni-Cr-Si-B alloy in combination with amorphous boron taken in different weight ratios. The proportion of amorphous boron in the powder mixture is 5, 10, and 15 wt. % respectively. The structural features of the cladded layers are investigated by using the following research methods: optical metallography (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron microprobe analysis (EMPA). The properties of the surface hardened materials are determined by microhardness investigations and wear resistance during friction against fixed abrasive particles and under conditions of hydroabrasive treatment. Results and discussion. The material produced during cladding of a Ni-Cr-Si-B alloy in combination with 15 wt. % boron is characterized by the maximum microhardness (1000 HV) and wear resistance under various wear conditions. The main structural factor providing an effective increase in the operational characteristics is the formation Fe2B, (Cr, Fe)B borides. It is shown that during Ni-Cr-Si-B alloy +15 wt. % boron cladding precipitation compounds are characterized by phase heterogeneity. The inner part of the two-phase complex particles is CrB2 around which (Fe, Cr)2B is released.

Introduction. The development of additive manufacturing technologies expands the possibilities of manufacturing (printing) products using a variety of materials. The printing process is carried out by local high-energy heating of the filament and substrate, due to which a molten bath is formed. Under such conditions, the formation of the structure of the material occurs under conditions of rapid crystallization and repeated cyclic heating. An important problem in printing bulk products from most structural alloys is the formation of a dendritic structure. The shape and size of dendrites, as well as the formation of secondary phases associated with it, can affect the strength and performance of products. The purpose of the work is to study the structure and mechanical properties of aluminum bronze obtained by the method of electron beam additive production. In this work, the features of the formation of the structure of aluminum bronze depending on the area of the sample are studied. Mechanical tests are carried out under static tension and compression of samples cut in longitudinal and cross sections relative to the direction of printing. The methods of investigation are mechanical tests for compression and tension, optical metallography, scanning electron microscopy. Results and discussion. Based on the analysis of metallographic images, four characteristic types of microstructures are formed at different heights from the substrate in the printed material. The first type is small dendritic grains with intermetallic particles. The second is small dendritic grains. The third is large columnar dendritic grains. Fourth are wide dendritic grains with small inclusions of the secondary phase. The formation of these types of microstructures is due, firstly, to the use of a steel substrate, and secondly, to a change in heat removal conditions as the height of the sample increases during printing. Based on the tests, a significant anisotropy of the mechanical properties was revealed, which is due to the directed nature of the growth of columnar dendritic grains, as well as a change in grain size along the height of the printed material. The obtained results expand the fundamental ideas about the processes of structure formation of alloys in the conditions of electron-beam additive production and can be used in developing technologies for printing products made of copper alloys.