Vol 120, No 9 (2019)

Abstract—The structure and magnetoresistive properties of Ta(5 nm)/NiFeCr(5 nm)/[FM(t_FM)/Cu(2.2 nm)]_n/ Ta(5 nm) superlattices prepared by magnetron sputtering are studied in this work. The ferromagnetic layer thickness t_FM is varied in a 1.1–1.5 nm range. The Co₉₀Fe₁₀, Co₈₅Fe₁₂Ni₃, Co₇₇Fe₁₇Ni₆, and Co₇₀Fe₂₀Ni₁₀ alloys with an fcc structure and close saturation magnetization values are used as the ferromagnetic (FM) materials. It is shown that, as the Ni and Fe contents in the CoFeNi alloy increase, the magnetoresistance of superlattices containing eight bilayers remains high and equal to 24–28%; in this case, the twofold decrease in the hysteresis occurs. As the number of bilayers in the superlattices, which contain CoFeNi alloys differing in composition increases to 12, the close values of magnetoresistance 30–31% are obtained. The correlation between the saturation magnetization of the ferromagnetic material of superlattice layers and maximum value of magnetoresistance is discussed.

Abstract—This work has demonstrated the possibility of joining (“welding”) a coating of intermetallic compound NiAl to an Mo substrate using the self-propagating high-temperature synthesis (SHS) method, without melting the Mo substrate. It has been revealed that an intermediate layer is formed between the Mo substrate and the welded NiAl coating. The main component of this layer is a cellular rod-like pseudobinary NiAl–Mo eutectic consisting of branched Mo threads 200 nm thick and of a NiAl matrix. It has been found that the microhardness of the Mo/NiAl transition layer is higher (2860 MPa) than that of the welded NiAl coating (2360 MPa) and of the Mo substrate (1830–1990 MPa). This indicates the occurrence of a strengthening of the NiAl intermetallic compound owing to the dissolution of Mo in it and to the formation of a pseudobinary NiAl–Mo eutectic and of Mo nanoprecipitates in the NiAl dendrites. Upon mechanical fracture of the sample, the Mo threads in the eutectic cells undergo significant plastic deformation. Using the selective chemical etching method in a mixture of HCl + H₂O₂, Mo-based structural components in the form of branched bundles of threads with a thickness of about 200 nm and a length of up to 300 μm have been separated.

Abstract—X-ray diffraction, Mössbauer and Raman spectroscopy have been used to study structural phase transformations during mechanosynthesis of Fe–С_60/70 in toluene with 20 and 25 at % С_60/70 fullerite. The quantitative carbon content determines the phase composition of mechanocomposites. (Fe₃C)_D forms at 20 at % С_60/70, whereas Fe₇C₃ and a paramagnetic phase form at 25 at % С_60/70 at the initial stage of mechanical alloying. Free carbon is in an amorphous state in the sample. The formation mechanism of carbides and a paramagnetic component is discussed.

Abstract—Special misorientations between the bainite crystals in a high-carbon manganese–silicon steel, which were obtained during isothermal γ → α transformation at 300°C, have been studied using EBSD-based orientation microscopy. Sets of special boundaries have been compared with theoretical calculations of possible angles and axes of rotation of α crystals arising in the initial γ phase as a consequence of three types of orientation relationships: Kurdjumov–Sachs, Nishiyama–Wasserman, and intermediate. It has been shown that the special misorientations of α crystals taking into account the Brandon criterion correspond to Nishiyama–Wasserman and Kurdjumov–Sachs orientation relationships.

Abstract—Cryogenic treatments including shallow and deep cryogenic treatment are supplemental operations designed to improve wear resistance and increase the hardness of a variety of tool and hardening steels. In this research, the effect of cryogenic treatment was investigated on the microstructure and wear behavior (wear behavior in environment temperature and at 550°C) in H11 hot work tool steel. To do so, the samples were austenitized in 1050°C for 60 min and were quenched in oil. Then, the samples were put into dry ice (‒80°C) and liquid nitrogen (–196°C) under shallow and deep cryogenic treatments. Later, the samples were tempered at 550°C for 60 min. Scanning electron microscopy (SEM), optical microscopy (OM), and X-ray diffraction (XRD) analysis were used to analyze the microstructure and the pin on disk method was used to analyze the wear behavior. The results showed that the percentage of retained austenite reaches from 6.5% in quench–temper treatment (QT) to 3% in shallow and to less than 1% in deep cryogenic treatments. Moreover, the tiny carbides are generated (after tempering at 550°C) as a result of deep cryogenic treatment (DCT) and the amount of carbides reaches from 5.5% in QT treatment to 8.2% in DCT treatment. Moreover, in both deep and shallow cryogenic treatments compared to a quench-temper one with the hardness of 4 and 9%, wear resistance at ambient temperature reached 31 and 36% and the wear resistance at high temperature reached 30 and 40%. Additionally, the wear mechanism becomes an adhesive and tribochemical wear in the environment temperature and becomes an abrasive and tribochemical wear in the high temperatures. Conducting cryogenic treatment reduces the amount of adhesive and abrasive wear at the environment and high temperatures.

Abstract—The fracture profiles and microhardness distribution in some regions of the compression region of Charpy samples of a high-viscous steel with a filamentary structure formed by the non-recrystallization controlled rolling with accelerated cooling have been studied. The mechanism of the plastic flow in the compression region of impact samples with different types of notches has been investigated. It has been shown that, as a result of intense plastic flow, two plastic hinges with axes containing a high density of slip lines appear in the compression regions.

Abstract—The fracture profiles and distribution of the microhardness in regions adjacent to the fracture surface in the region of tension of Charpy samples of the high-viscous 08G2B steel (0.08 C; ~2 Mn; 0.2 Mo; ≈0.15 Σ(Ti–V–Nb); 0.004 N; 0.04 Al; 0.004 S; 0.007 P wt %) with a filamentary structure formed by non-recrystallization controlled rolling with an accelerated cooling have been studied. The factors that provide the extremely high impact toughness of steel in the case of the fracture of the Charpy samples perpendicular to the surface of filaments have been revealed.