Thermal stability of a laser-clad NiCrBSi coating hardened by frictional finishing

Frictional treatment decreases surface roughness of a NiCrBSi laser coating and increases its microhardness and abrasive wear resistance. Even after softening annealing at 900 °C, the coating subjected to frictional treatment preserves its advantage in hardness and wear resistance over the original clad coating. Annealing at 1000 °C after frictional treatment ensures less effective growth of the hardness and wear resistance of the coating as compared to annealing of the undeformed coating due to the limited precipitation of large Cr23C6 carbides on the deformed surface, which form a wear-resistant framework. © 2017 Author(s).Russian Foundation for Basic Research, RFBR: 16-38-00452-mol-a01201375904108692015Federal Agency for Scientific Organizations: 01201463331Federal Agency for Scientific OrganizationsUral Branch, Russian Academy of Sciences, UB RAS: 15-9-12-45The study was financially supported by the Russian Foundation for Basic Research (RFBR), grant No. 16-38-00452-mol-a, by the Foundation for Assistance to Small Innovative Enterprises (FASIE), project UMNIK No. 108692015; the work was done within the Complex Program of UB RAS, project No. 15-9-12-45, within the state order for IES UB RAS, No. 01201375904 and within the state order of The Federal Agency for Scientific Organizations (FASO Russia) on the subject “Structure”, No. 01201463331. The experimental research was done on the equipment installed at the Plastometriya Collective Use Center of IES UB RAS

Increasing the resistance of a NiCrBSi coating to heat wear by means of combined laser heat treatment

Testing of NiCrBSi coatings formed by gas-powder laser cladding and combined laser heat treatment, including laser cladding and high-temperature annealing, were conducted under conditions of sliding friction on the Kh12M steel according to the pin-on-disk scheme. The combined processing resulting in the formation of large carbides and chromium borides in the coatings is shown to increase their wear resistance by a factor of 1.8 at sliding velocities of 6.1 and 9.3 m/s, when there is significant frictional heating of the friction surfaces. © 2018 Author(s)

Nanostructuring and surface hardening of structural steels by ultrasonic impact-frictional treatment

With two structural steels (the steels 50 and 09G2S) as examples, the paper studies the effectiveness of a new method of ultrasonic impact-frictional treatment (UIFT) for the hardening and nanostructuring of the surface layer with the variation of the tilt angle of the vibrating indenter and the treatment environment. It is demonstrated that treatment with tool tilt angles different from 90° and with the absence of a contact liquid results in the formation of a nanostructured surface layer with increased microhardness. © 2018 Author(s)

Properties of arc-sprayed coatings from Fe-based cored wires for high-temperature applications

Equipment of a thermal power plant is subjected to high temperature oxidation and wear. This raises operating costs through frequent repair of worn parts and high metal consumption. The paper proposes a possible solution to this problem through arc spraying of protective coatings. Cored wires of the Fe-Cr-C basic alloying system are used as a feedstock. Additional alloying by Al, B, Si, Ti and Y allows one to create wear- and heat-resistant coatings, which are an attractive substitute of more expensive Co- and Ni-based materials. © 2017 Author(s)

The influence of a combined strain-heat treatment on the features of electromagnetic testing of fatigue degradation of quenched constructional steel

The possibilities of the magnetic and eddy-current methods for testing fatigue degradation during low-cycle loading of quenched steel 50 (0.51% C) that was subjected to a combined strain-heat treatment according to an optimal regime that included friction treatment with subsequent tempering at T = 350 C, were investigated. It is shown that for steel that was subjected to a combined nanostructuring treatment, the accumulation of a plastic strain under "hard" cyclic loading can be tested using the coercimetric method and values of the residual magnetic induction on the major and minor magnetic-hysteresis loops, values of the maximum and initial magnetic permeabilities, and readings of an eddy-current instrument at a low excitation frequency of the eddy-current transducer. The appearance of surface fatigue cracks can be tested via eddy-current measurements at high frequencies, when the contribution of the crack formation in the hardened layer to the eddy-current characteristics is considerable. © 2013 Pleiades Publishing, Ltd

Wear-resistant nickel-based laser clad coatings for high-temperature applications

The effect of high-temperature processing on laser clad Ni-based coatings is studied. Annealing at 1025°C forms thermally stable framework structures with large chromium carbides and borides. As a result, improved hardness and wear resistance of the coating are maintained when heated to 1000°C. Stabilizing annealing also increases the frictional thermal resistance of the NiCrBSi coating. Under high-speed (3.1– 9.3 m/s) sliding friction, when the surface layer temperature reaches about 500 –1000°С and higher, the wear resistance of the coating increases by 1.7 – 3.0 times. The proposed approach to the formation of heat-resistant coatings is promising, in particular, for a hot deformation tool and other components of metallurgical equipment operating under high thermal and mechanical loads. Such products include crystallizer walls of continuous casting machines. For the walls, the development of laser cladding technology for wear-resistant composite coatings on copper alloys is relevant as an alternative to thermal spraying. The cladding of composite NiBSi-WC coatings of 0.6 and 1.6 mm thickness on a Cu-Cr-Zr bronze substrate heated to 200 – 250°C with a diode laser is considered. The presence of boron causes the formation of the W(C, B) carboboride phase, whose hardness is higher than that of WC in the initial powder. Depending on the thickness of coatings and, accordingly, on the duration of heating and the subsequent cooling, the process of secondary carboborides precipitation from the solid solution can be suppressed (in the “thin” coating) or activated (in the “thick” coating). This leads to a higher wear resistance under friction sliding 1.6 mm thickness coating. © 2019, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved.Institute of Education Sciences, IES: АААА-А18-118020790147-4Russian Science Foundation, RSF: 19-79-00031АААА-А18-118020190116-6The work was supported by the state orders of IMP UB RAS on the subjects “Laser” and “Structure” №АААА-А18-118020190116-6 and IES №АААА-А18-118020790147-4. The study of the evolution of the structure of NiCrBSi coatings during heating was carried out with financial support from the Russian Science Foundation, grant № 19-79-00031. The structural studies were done on the equipment installed at the Plastometriya Collective Use Center of IES UB RAS

Eddy-current testing of fatigue degradation upon contact fatigue loading of gas powder laser clad NiCrBSi-Cr 3 C 2 composite coating

The possibilities of the eddy-current method for testing the fatigue degradation under contact loading of gas powder laser clad NiCrBSi-Cr 3 C 2 composite coating with 15 wt.% of Cr 3 C 2 additive have been investigated. It is shown that the eddy-current testing of the fatigue degradation under contact loading of the NiCrBSi-15%Cr 3 C 2 composite coating can be performed at high excitation frequencies 72-120 kHz of the eddy-current transducer. At that, the dependences of the eddy-current instrument readings on the number of loading cycles have both downward and upward branches, with the boundary between the branches being 3×10 5 cycles in the given loading conditions. This is caused, on the one hand, by cracking, and, on the other hand, by cohesive spalling and compaction of the composite coating, which affect oppositely the material resistivity and, correspondingly, the eddy-current instrument readings. The downward branch can be used to monitor the processes of crack formation and growth, the upward branch - to monitor the degree of cohesive spalling, while taking into account in the testing methodology an ambiguous character of the dependences of the eddy-current instrument readings on the number of loading cycles. © 2017 Author(s)

Features of frictional treatment of the composite NiCrBSi-Cr3 C2 laser clad coating

The authors conducted a comparative analysis of the effectiveness of frictional treatment with a sliding indenter of a NiCrBSi coating and a composite coating formed by laser cladding of a powder mixture of 85 wt.% NiCrBSi and 15 wt.% Cr3 C2 . The criteria were intensive strain hardening, favorable compressive stresses, and low surface roughness. Frictional treatment with an indenter made of cubic boron nitride at a load of 350 N provides less intense deformational hardening of the NiCrBSi-Cr3 C2 coating (microhardness growth from 900 to 940 HV 0.025) than the NiCrBSi coating (from 570 to 850 HV 0.025). This is due to the significantly higher initial hardness of the composite coating, because its structure, in addition to the phases characteristic of the NiCrBSi coating, contains large primary Cr3 C2 carbides, which did not dissolve during cladding, as well as elongated Cr23 C6 carbides, precipitated during cooling from a solid solution supersaturated with chromium as a result of the partial dissolution of Cr3 C2 carbides during cladding. Frictional treatment also results in a lower level of compressive residual stresses (−250 MPa) on the composite coating surface than on the NiCrBSi coating surface (−390 MPa). In contrast to frictional treatment of the NiCrBSi coating, when a smoothed surface with a nano-roughness is formed (Ra = 60 nm), frictional treatment of the composite coating forms a surface with a higher roughness (Ra = 310 nm) due to the creation on the surface of supporting “island frame” of large Cr3 C2 chromium carbides protruding 2 – 5 μm. © 2020, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved.The work was performed with the financial support of the Grant from the President of the Russian Federation for young scientists MK-391.2019.8 and at the expense of funds making up the income from the trust management of the target capital for the development of UrFU, formed with the participation of UMMC-Holding Corp, as well as within the state order for IES UB RAS (AAAA-A18-118020790147-4) and IMP UB RAS (AAAA-A18-118020190116-6 and АААА-А19-119070490049-8). The experimental research was performed on the equipment of the Plastometriya Collective Use Center of IES UB RAS

Effect of frictional treatment with a dense cubic boron nitride indenter on the micromechanical properties of the NiCrBSi-Cr3C2coating

Coatings based on NiCrBSi alloys with Cr3C2 addition can effectively resist wear, corrosion, and oxidation at high temperatures. The use of frictional treatment by sliding indenters as finishing is a modern way to create high surface quality and to enhance the strength and wear resistance of the surface of parts. The article studies the characteristics determined by instrumented microindentation of the surface of a NiCrBSi-Cr3C2 laser clad coating subjected to frictional treatments with a sliding indenter made of dense cubic boron nitride DBN in the air at loads on the indenter of 350, 500 and 700 N, and after grinding. Frictional treatment in the entire considered range of loads contributes to an increase in strength performance, as well as parameters indicating an increased ability of the coating surface to resist elastoplastic deformation. The highest growth of the parameters is observed after frictional treatment at a load of 700 N. © Published under licence by IOP Publishing Ltd

КОМПЬЮТЕРНАЯ ТОМОГРАФИЯ В ДИАГНОСТИКЕ ПОВРЕЖДЕНИЙ ПРОКСИМАЛЬНОГО ОТДЕЛА ГОЛЕНИ

The article assesses the capability and adequacy of computed tomography in patients with complex intra-articular and juxta-articular fractures of the lower leg bones. The research includes modified methodology of these studies and systemized symptoms of fractures.The conclusion has been made about the place of computed tomography in medical treatment for patients with such fractures, including the CT over time in the postoperative period.В статье проведен анализ возможности и целесообразности выполнения компьютерно-томографических исследований у пострадавших со сложными внутри- и околосуставными переломами костей проксимального отдела голени, приведена модификация методики этих исследований, систематизирована семиотика повреждений.Сделаны выводы о месте метода компьютерной томографии в алгоритме лечебного процесса у этих пострадавших, в том числе — при динамическом контроле в послеоперационном периоде