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In the present work, low cycle fatigue (LCF) behavior and fracture characteristic of Ti–6Al–4V-0.55Fe alloy with bimodal microstructure, consisted of equiaxed primary α (αp), lamellar α (αl) and β matrix, are systematically investigated at room temperature. Results indicate that Ti–6Al–4V-0.55Fe alloy mainly exhibits a continuous softening behavior both at high and low strain amplitudes, due to the interaction of back stress(σb) and friction stress(σf) mainly related to the plastic deformation heterogeneity and precipitates shearing, respectively. Compared with Ti–6Al–4V alloy, LCF life of Ti–6Al–4V-0.55Fe is similar at high strain amplitudes (Δεt/2 > 1.0%), while much higher at low strain amplitudes (Δεt/2 < 1.0%), which could be attributed to the extra resistance to dislocation movement and crack propagation produced by Fe microalloying. The fractography shows remarkably different characteristics for these imposed strain amplitudes. At low strain amplitude, there is only one crack initiation site caused by dislocations pile-ups and stress concentration on the specimen surface, accompanied with narrower fatigue striation, while more cracks initiated on the surface with wider fatigue striation due to strain accumulation at high strain amplitudes.

High-pressure torsion (HPT) processing under a pressure of 6.0 GPa was applied to Ti 29.7 Ni 50.3 Hf 20 (at.%) alloy. Two types of structure were observed after HPT with 3 revolutions: first one is the mixture of amorphous phase and retained nanocrystalline; second is the alternating bands of amorphous phase and high defect density crystalline. As a result, post deformation annealing (PDA) at 500−700 °C leads to the non-uniform distribution of martensite and parent phase grains. The grains of martensite are twice larger compared to that of parent phase. The nanocrystalline and ultrafine grains form after annealing at 500−600 °C and 700 °C, respectively. The twinning mechanism does not change with the reduction of martensitic grains up to ∼35 nm. The relationship between strength and grain size in Ti 29.7 Ni 50.3 Hf 20 alloy obeys the classical Hall-Petch relationship with a coefficient of 10.80 ± 0.39 GPa nm1/2. [ABSTRACT FROM AUTHOR]

TiNi alloys, with their unique shape memory effects and super elastic properties, occupy an indispensable place in the family of metallic biomaterials. In the past years, surface treatment is the main technique to improve the bioinert nature of microcrystalline TiNi alloys and inhibit on the release of toxic nickel ions to obtain excellent osteogenesis and osseointegration function. In the present study, nanocrystalline Ti 49.2 Ni 50.8 alloy has been fabricated via equal channel angular pressing (ECAP), and the in vitro and in vivo studies revealed that it had enhanced cell viability, adhesion, proliferation, ALP (Alkaline phosphatase) activity and mineralization, and increased periphery thickness of new bone, in comparison to the commercial coarse-grained counterpart. These findings indicate that the reduction of grain size is beneficial to increasing the biocompatibility of Ti 49.2 Ni 50.8 shape memory alloy. [ABSTRACT FROM AUTHOR]

Microstructure evolution of an Al-0.4Zr(wt.%) alloy after isothermal aging (AG) and subsequent high pressure torsion (HPT) and its impact on strength and electrical conductivity has been investigated. Microstructure was characterized by X-ray diffraction, electron backscatter diffraction, transmission electron microscopy (TEM) and electron energy-dispersive X-ray spectroscopy in TEM. The initial Al-0.4Zr(wt.%) alloy obtained by combined casting and rolling presents solid solution of Zr in Al matrix. Aging at 375 °C for 60 h leads to formation of uniformly distributed metastable Al3Zr precipitates with the average diameter of 13 nm, resulting thereby in a decrease of strength sUTSfrom 128 to 95 MPa and in increase of conductivity from 50.7 to 58.8% IACS at ambient temperature. The subsequent HPT processing leads to grain refinement and partial dissolution of the Al3Zr precipitates that is accompanied by enrichment of solid solution by Zr atoms and by coarsening of the remaining Al3Zr precipitates. The combination of AG and HPT provides the strength and the conductivity at ambient temperature which do not decrease under annealing up to 230 °C. Moreover, additional strengthening accompanied by an increase in conductivity was found for AG-HPT samples after annealing at Tan=230 °C for 1 h, that provides the best combination of the strength of sUTS=142 MPa and the conductivity of 58.3% IACS. Contribution of different possible mechanisms into strength and charge scattering are analyzed on the basis of specific microstructural features. The analysis indicates a suppression of strengthening by the Orowan mechanism in AG and AG-HPT samples. In all the studied states, i.e. initial, after AG, and subsequent HPT, grain boundary strengthening is found to be the main strengthening mechanism.

This paper presents the results of a computer and experimental study of a promising severe plastic deformation (SPD) technique, called Multi-ECAP-Conform (M-ECAP-C), for the fabrication of long-length nanostructured billets (wire rods) with an enhanced strength and electrical conductivity from the aluminum alloy EN-AW 6101 per one processing cycle. On the basis of the obtained results, a new rational geometry of the pressing channel for the M-ECAP-C process has been developed. The strained state of pilot samples of wire rods have been studied. Using the method of dividing grids shows the character of accumulation and the achieved level of deformation shear during the experimental treatment, and the average value of the shear deformation of the central region of the workpiece is 3.015. It was found that the error between the obtained values of the experimental method of grids, computer modeling and calculation is, respectively, 10 % and 17 %. The error between the experimental and computer modeling is not so important, so application of the computer modeling to estimate the strain state of the method of the Multi-ECAP-Conform is completely adequate.

Ferrite has been transformed to austenite at room temperature in an initially pearlitic steel. This occurs under high shear strain conditions once the alloy has been grain‐refined down to a nanoscale dimensions by high‐pressure torsion deformation. This transformation must have occurred by a martensitic mechanism and plays the role of an additional deformation mechanism for the nanostructured material.

Severe plastic deformation (SPD) can lead to emergence of microstructural features and properties in materials which are fundamentally different from the ones well known for conventional cold deformation. In particular, the instances of unusual phase transformations resulting in development of highly metastable states associated with formation of supersaturated solid solutions, disordering or amorphization and their further decomposition during heating, high thermal stability of the SPD‐produced nanostructures, and the paradox of strength and ductility in some SPD‐processed metals and alloys are discussed.

Severe plastic deformation (SPD) can lead to emergence of microstructural features and properties in materials which are fundamentally different from the ones well known for conventional cold deformation. In particular, the instances of unusual phase transformations resulting in development of highly metastable states associated with formation of supersaturated solid solutions, disordering or amorphization and their further decomposition during heating, high thermal stability of the SPD-produced nanostructures, and the paradox of strength and ductility in some SPD-processed metals and alloys are discussed.

Recent results of the development of the severe plastic deformation methods to fabricate bulk nanostructured materials as well as results of their thorough structural characterization and investigations of their unusual deformation behavior and novel mechanical properties are presented. The structural model of nanomaterials processed by severe plastic deformation methods is developed on the basis of the obtained results.

The microstructural stability of an Al3%Mg solid solution alloy with a submicrometergrained (SMG) structure (∼ 0.2 μm) was evaluated using both static annealing and transmission electron microscopy over a range of temperatures from 443 to 803 K and differential scanning calorimetry (DSC) up to 773 K. The results show that the SMG structure contains many non-equilibrium grain boundaries but recrystallization occurs at the higher temperatures giving large grains with boundaries having high-angle equilibrium configurations. There are significant differences between the DSC curves of the SMG alloy and a standard cold-rolled Al3%Mg alloy, due primarily to the advent of significant heat release at low temperatures in the SMG alloy because of recovery at the non-equilibrium grain boundaries. A temperature of ∼ 500 K, close to half the absolute melting temperature, represents an effective upper limit for utilization of the SMG structure in this material.

Magnetic hysteretic properties of high purity nickel were studied in a broad range of structural states from a submicron grained state achieved by means of large deformation on the Bridgman anvils to a coarse-grained state obtained after high-temperature annealing. The structure was studied in different states using electron microscopy and X-ray analysis. At the initial state, the coercivity (Hc) of 5.1 kA/m was achieved for nickel. The contribution of intragrain dislocations and grain boundaries to the value of the coercivity was shown. The value of residual magnetization Ir= 0.5 Isobtained for a highly strained state coincides with the theoretically calculated value. Factors causing a sufficiently complicated dependence of Iron the annealing temperature are specified.

AbstractBulk samples of nanocrystalline Ni were produced by severe plastic deformation consolidation of ball-milled powders. The processed samples are characterized by reduced values of saturation magnetization and Curie temperature. Relying on transmission electron microscopy and X-ray data, an assumption has been made to explain the origin of the observed phenomena.

The grain size distribution of copper and nickel processed by severe plastic deformation was studied by transmission electron microscopy. The temperature dependence of electrical resistivity in the temperature range from 20 to 300 K is presented. The tunnel model of electrical resistivity of grain boundaries is discussed. The width of the potential barrier at grain boundaries in copper and nickel is determined. Larger values of potential barriers are noted in ultrafine grained materials in comparison to the crystallographic width of grain boundaries.

An Al-3% Mg solid solution alloy was subjected to intense plastic deformation, using either equal-channel angular (ECA) pressing or torsion straining, to produce grain sizes in the submicrometer range. Static annealing at elevated temperatures led to grain growth and average grain sizes of up to > 100 μm. As-fabricated and statically annealed specimens were used to determine the variation in microhardness with grain size, and results confirm that the Hall-Petch relationship persists down to at least the finest grain size examined experimentally (∼90 nm). The results provide no evidence to support the claims of a negative Hall-Petch slope when the average grain size is very small, but there is evidence of a decrease in the slope of the Hall-Petch plot at the very finest grain sizes (< 150 nm); this is attributed to the increased participation of mobile extrinsic dislocations in the boundary regions when taking the hardness measurements.