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Several pure metals exhibit softening when imparting large strains at room temperature. This study investigates the nature of this strain softening. Torque measurements during high-pressure torsion using ring specimens, which appear to be more suitable than disk specimens for the evaluation of the strain response on the in situ flow stress, suggest that the softening in aluminum occurs mainly by dynamic recrystallization and recovery, whereas no appreciable dynamic softening occurs in copper. The softening in aluminum is associated with decreasing the dislocation density and increasing the grain size and missorientation angles, whereas copper exhibits ultrafine grains of higher dislocation density and few nanotwins. A significant static recrystallization is detected in HPT-processed pure copper by argon irradiation during ion milling.

Nanostructured intermetallics generally exhibit high strength but limited plasticity due to the covalent nature of their bonding. In this study, high-pressure torsion followed by annealing was used to produce TiAl intermetallics with two microstructural features: (i) bimodal microstructure composed of nanograins and submicrometer grains; and (ii) nanotwins. An exceptional performance, combining ultrahigh yield strength, ∼2.9 GPa, and high strain to failure, ∼14%, was achieved with micropillar compression tests. Twinning, dislocation slip and grain boundary sliding appear to be active under compressive stress.

This work presents a study related to the grain refinement of an aluminum A2618 alloy achieved by High-Pressure Torsion (HPT) known as a process of Severe Plastic Deformation (SPD). The HPT is conducted on disks of the alloy under an applied pressure of 6 GPa for 1 and 5 turns with a rotation speed of 1 rpm at room temperature. The HPT processing leads to microstructural refinement with an average grain size of ~250 nm at a saturation level after 5 turns. Gradual increases in hardness are observed from the beginning of straining up to a saturation level. This study thus suggests that hardening due to grain refinement is attained by the HPT processing of the A2618 alloy at room temperature.

Micropowder mixtures of W–50% Al, W–50% Ti and W–50% Ni were subjected to severe plastic deformation at 573 K using high-pressure torsion (HPT). The powder mixtures were consolidated and nanocomposites of W/Ti, W/Ti and W/Ni, with average grain sizes as small as ∼9, ∼15 and ∼12 nm, respectively, were formed by imposing large shear strains. The nanocomposites exhibited Vickers microhardness as high as ∼900 Hv, a level that has rarely been reported for metal–matrix composites. X-ray diffraction analyses together with high-resolution transmission electron microscopy showed that in addition to grain refinement, an increase in the fraction of grain boundaries up to 20%, the dissolution of elements in each other up to ∼15 mol.%, an increase in the lattice strain up to 0.6%, and an increase in density of edge dislocations up to 1016 m−2 occurred by HPT. The current study introduces the HPT process as an effective route for the production of ultrahigh-strength W-base nanocomposites, fabrication of which is not generally easy when processing at high temperatures because of interfacial reaction and formation of brittle intermetallics.

Micropowder mixtures of Al–50 mol.% Ni were severely deformed by high-pressure torsion and Al 3 Ni 2 /Ni nanocomposites were produced. The hardness increased with straining, as a consequence of nanograin formation and high-strain-induced solid-state reactions, and saturated to a steady-state level, 920 Hv. The reactions were completed and nanostructured AlNi intermetallics were produced by subsequent annealing. The formation of nanostructured intermetallics was feasible in this process at significantly low temperatures because of the rapid diffusion and short diffusion paths resulting from intense shearing.

High purity elements such as magnesium, aluminum, silicon, titanium, vanadium, iron, nickel, copper, zinc, zirconium, molybdenum, palladium, silver, indium, tin, hafnium, gold and lead were processed by high-pressure torsion and subsequently evaluated by microstructural examinations and Vickers microhardness measurement. The grain size at the steady state, where the grain size and hardness remain unchanged with straining, was determined using either transmission electron microscopy, electron back-scatter diffraction analysis and/or optical microscopy. It is found that the steady state grain sizes are at the submicrometer level in elements with metallic bonding and at the nanometer level in elements with covalent bonding. The correlations between the steady-state grain size and the physical properties of metals are examined and it is found that the atomic bond energy and the homologous temperature are important parameters influencing the steady-state grain size after processing by HPT. A linear correlation between the hardness and grain size at the steady state is achieved by plotting the hardness normalized by the shear modulus against the grain size normalized by the Burgers vector in the logarithmic scale.

Pure Cu (99.99%) is processed by equal-channel angular pressing (ECAP) and by high-pressure torsion (HPT). The electrical resistivity aswell as the microhardness increases with an increase in the equivalent strain at an early stage of straining, but saturates to a steady state at theequivalent strains more than ³20. At the steady state, the samples processed by ECAP and HPT show a significant increase in the hardness(³270%) but little decrease in the electrical conductivity (³12%) when compared to the annealed state. Transmission electron microscopyconfirms that the microstructure does not change at the saturated level with further straining. Evolutions of hardness, electrical conductivity andmicrostructures are also investigated after post-HPT annealing. [doi:10.2320/matertrans.MD201109](Received June 30, 2011; Accepted August 9, 2011; Published September 21, 2011)Keywords: severe plastic deformation, equal-channel angular pressing, high-pressure torsion, ultrafine grain, electrical conductivity

Severe plastic deformation using high-pressure torsion (HPT) is successfully applied at room temperature to partially stabilized ZrO2. X-ray diffraction and Raman spectroscopy analyses reveal that appreciable strain is introduced in the sample and a phase transformation with a coherent interface occurs from the metastable tetragonal phase to the monoclinic phase during HPT. The fraction of the stress-induced monoclinic phase increases with straining, reaches a saturation level. Transmission electron microscopy shows that nanograins of high dislocation density but with no twins are formed during HPT.

Nanocomposites of Ti–18 vol.% Al2O3 were fully consolidated by applying severe plastic deformation to powder mixtures using high-pressure torsion (HPT). The HPT-processed composites exhibited an unusual increase in the hardness from 350 Hv to 650 Hv when they were annealed at 973 K for 1 h. Microstructural observations including elemental mappings were conducted using scanning electron microscopy with an electron probe X-ray micro-analyzer and scanning transmission electron microscopy with an energy dispersive X-ray spectrometer. It was shown that the Al2O3 particles are fragmented and the grain size of the Ti matrix is reduced to the nanometer level (

The grain size in pure elements (magnesium, aluminum, silicon, titanium, vanadium, chromium, iron, nickel, copper, zinc, germanium, zirconium, niobium, molybdenum, palladium, silver, indium, tin, hafnium, tantalum, gold and lead) after processing by high-pressure torsion (HPT) reaches steady-state levels where the grain size remains unchanged with straining. The steady-state grain sizes decrease by atomic bond energy and related parameters such as specific heat capacity, activation energy for self-diffusion and homologous temperature and are reasonably independent of stacking fault energy. A good correlation exists between the hardness normalized by the shear modulus and grain size normalized by the Burgers vector, indicating that the important factor for strengthening HPT-processed pure metals is the average size of grains having high angles of misorientation.

High purity metals with low melting temperatures such as indium (99.999%), tin (99.9%), lead (99%), zinc (99.99%) and aluminum (99.99%) were processed using high-pressure torsion (HPT). An unusual softening behavior was observed in all these metals after processing by HPT at room temperature. Pure copper (99.99%) and palladium (99.95%) were used to simulate the softening behavior due to a thermal effect by processing and subsequently holding at the temperatures equivalent to room temperature of pure Al. It is shown that a hardness peak appears in any metal by static softening after processing by HPT at a homologous temperature of 0.32 which is equivalent to room temperature of pure Al. The contribution of dynamic softening on hardness decrease becomes more important as the homologous temperature and stacking fault energy increase. Microstructural examinations indicate that, although the stacking fault energy influences the rate of the microstructural evolution, the homologous temperature appears to be a dominant parameter to determine the steady-state grain size after processing by HPT.

Experiments and finite element simulations were conducted to measure the temperature increase in processing disc samples by high-pressure torsion. Aluminum, copper, iron and molybdenum were selected as model materials. The temperature increases at the early stages of straining but saturates to steady-state levels at large strains. The increase of temperature is proportional to the hardness and rotation speed and is higher at higher imposed pressures and is somewhat higher at larger distances from the disc center.

A newly developed severe plastic deformation method, continuous high-pressure torsion (CHPT), was modified for continuous processing of metallic wires. In this study, using the CHPT, wires of high-purity aluminum (99.99%) and copper (99.999%) with diameters of 2 mm and total lengths of 100 mm were successfully processed by employing the same features as conventional high-pressure torsion (HPT) technique. The results of hardness measurements, 35 Hv for Al and 116 Hv for Cu, after CHPT at an imposed equivalent strain of ~13 were consistent with those of conventional HPT using disk and ring specimens, as well as with those of CHPT using sheet specimens. Transmission electron microscopy (TEM) demonstrated that the microstructural elements are elongated in the shear direction after CHPT. The average grain size reaches the steady-state level, ~1.3 μm, in Al, but the microstructure is at the non-steady state in Cu with subgrain sizes in the range of 0.3–4 μm.

Pure Mg (99.9%) is processed by high-pressure torsion (HPT) at room temperature. The hardness behavior with imposed strain is similar to pure Al (99.99%), having a hardness maximum followed by a steady state. HPT processing increases the hardness and tensile strength. A bimodal microstructure with an average grain size of ∼1 μm is developed by HPT with some grains free of dislocations. Hydrogen absorption is improved by HPT after 10 revolutions, and a total hydrogen absorption of 6.9 wt.% is achieved.

High-purity elements (magnesium, aluminum, silicon, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, germanium, zirconium, niobium, molybdenum, palladium, silver, indium, tin, tellurium, neodymium, hafnium, tantalum, tungsten, rhenium, platinum, gold and lead) were processed by high-pressure torsion and subsequently evaluated by Vickers microhardness measurements. The hardness at the steady state was expressed as a unique function of atomic bond energy, specific heat capacity, specific latent heat of fusion, linear thermal expansion coefficient and activation energy for self-diffusion.

Pure metals of 30 elements with various crystal structures (bcc, fcc, hcp, diamond cubic, complex cubic, primitive hexagonal and tetragonal) are processed by high-pressure torsion (HPT) and their mechanical properties are subsequently evaluated by Vickers microhardness measurements. For all metals, the hardness reaches steady states at large strains where the hardness remains unchanged with further straining. It is shown that the hardness values at the steady state are characteristics of each metal and are successfully expressed as a unique function of the homologous temperature, shear modulus and physical parameters of metals such as melting temperature, specific heat capacity and diffusion coefficient except for a few elements. The findings are well applicable to predict the ultimate steady-state hardness of metals attained by HPT processing through the correlation established in this study.

Continuous high-pressure torsion (CHPT) was developed as an expeditious process to effect severe plastic deformation. Using the CHPT, sheets of high purity aluminum, copper, and iron were successfully processed by introducing intense shear strain under high pressure. The results of hardness measurements after CHPT were well consistent with those of CHPT using disk and ring specimens. Microstructural observations demonstrated that CHPT can be used as a continuous process for grain refinement.

Alumina (α-Al 2 O 3 ) powders were successfully consolidated by application of high-pressure torsion (HPT) at ambient temperature and by a subsequent annealing process. Introduction of strain by HPT was confirmed by peak broadening in X-ray diffraction analysis. It was shown that consolidation was greater, giving rise to increased hardness with increasing imposed strain, annealing temperature and annealing time. Scanning electron microscopy showed that consolidation occurred at lower temperatures due to the presence of strain.

Two body centered cubic (bcc) metals, V and Mo, were processed by high pressure torsion (HPT) at ambient temperature. Hardness variation as well as microstructural evolution was examined with strain under a pressure of 2 to 6 GPa. It was shown that the hardness increases with straining and saturates to a constant level with the grain size of 330–400 nm in V irrespective of the applied pressures. Although the hardness variation with strain is the same for Mo with the grain size of ∼350 nm at the saturation level when the applied pressure is 6 GPa, the hardness level lowers below the saturation level and the grain size becomes coarser as the pressure is lowered. Tensile tests show that the strength significantly increases with some ductility for V after processing under any pressure and for Mo under lower pressures, but brittle fracture occurs in the Mo specimen processed at 6 GPa. The slower evolution of microstructure as well as the lower hardness levels observed in Mo is due to the applied pressure which is lower than the yield stress and thus due to the insufficient generation of dislocations for grain refinement.

Pure Ti powders were subjected to ball milling and subsequently high-pressure torsion (HPT) for consolidation. It is found that a fully dense (99.9%) disc with ultrafine grained structure (~50-300 nm) was produced. The strength and ductility were well comparable to those of ball-milled Ti-6%Al-4%V powders after hot roll sintering.

Pure Hf (99.99%) is processed by high-pressure torsion (HPT) under pressures of 4 and 30 GPa to form an ultrafine-grained structure with a gain size of ∼180 nm. X-ray diffraction analysis shows that, unlike Ti and Zr, no ω phase formation is detected after HPT processing even under a pressure of 30 GPa. A hydride formation is detected after straining at the pressure of 4 GPa. The hydride phase decomposes either by application of a higher pressure as 30 GPa or by unloading for prolong time after HPT processing. Microhardness, tensile and bending tests show that a high hardness (360 Hv) and an appreciable ductility (8%) as well as high tensile and bending strength (1.15 and 2.75 GPa, respectively) are achieved following the high-pressure torsion.

alloywereprocessedbyhigh-pressuretorsion(HPT).ItwasconfirmedthatthemachiningchipscanbeconsolidatedusingHPTatroomtemperaturetodisc-shapedsampleswith10mmdiameterand0.6mmthicknesshavinga relative densityof 96.7%.The hardnessforthe consolidatedchips was wellcomparableto thoseobtainedusingthe bulksampleswhenthe imposed strain is large. No crystallization was detected after HPT processing of chips and bulk samples.[doi:10.2320/matertrans.MB200914](Received August 24, 2009; Accepted October 20, 2009; Published December 2, 2009)Keywords: high-pressure torsion, severe plastic deformation, amorphous, bulk metallic glasses, machining chips

High purity Al (99%), Al (99.99%), Au (99.999%), Ag (99.99%), Cu (99.99%), Pt (99.9%), Ni (99.996%), Fe (99.96%), Co (99.99%), Ti (99.4%), Zr (99.9%), Hf (99.99%), Cu-30%Zn and commercial purity Al (99%) were received in the form of rods and/or plates. The as-received specimens were annealed for 1 hour under an argon atmosphere at a temperature of 773 K for Al, 793 K for Ag and Cu30%Zn, 873 K for Au and Cu, 973 K for Ni, 1073 K for Co, Ti and Zr, 1273 K for Fe and Hf, and 1323 for Pt. The annealed specimens were cut to discs with 4 and/or 10 mm diameters and 0.8 mm thickness and to rings with inner and outer diameters of 24 and 30 mm and 0.8 mm thickness using a wire-cutting electric discharge machine. HPT was carried out on the annealed discs using the facilities described earlier. 12,15) The disc samples with 4 and 10 mm diameters were processed under a selected pressure in the range of 14–40 GPa and 0.6–6 GPa, respectively, for N ¼ 1{20 revolutions with a rotation speed of ! ¼ 0:2 or 0.5 rpm. The ring samples were processed for one revolution under a pressure in the range of 0.6–2 GPa with ! ¼ 0:5 rpm. It should be noted that the pressure was calculated by dividing the applied load by the area of the central hole or circular groove on the anvil. The samples after HPT were polished to a mirror-like surface and evaluated in terms of Vickers microhardness and

High-pressure torsion (HPT) was conducted on commercial grade pure titanium (99.4%) by applying pressures in a wide range from 1.2 to 40 GPa. When the microhardness was plotted against equivalent strain, the hardness saturates to a constant level at each applied pressure. Such a level at the saturation depends on the applied pressure: for up to the pressure of 4 GPa, the saturation level is independent of the pressure but, for the pressures above 4 GPa, the hardness gradually increases with pressure because of the formation of an  phase. Bending tests showed that an excellent ductility as well as high bending strength was achieved for the sample processed at 2 GPa. The bending ductility was reduced for the sample at 6 GPa because of the  phase formation.

High purity Al (99.99 wt.%) and high purity Cu (99.99 wt.%) were processed using high pressure torsion. The mechanism for unusual softening in Al after the resultant intense plastic straining was investigated. The pure Cu was used to simulate a thermal effect on the hardness behavior and microstructural evolution after processing. This simulation consists of processing and subsequently keeping the pure Cu at the temperature equivalent to room temperature for pure Al. It is shown that the softening of the processed Cu occurs by static recrystallization. It is then suggested that the softening in Al should be due to recovery and/or recrystallization. Whereas the softening in Cu occurs rather slowly, it is very quick in Al and it may even be dynamic during processing by high pressure torsion.

Pure Zr is processed by high-pressure torsion (HPT) at pressures in the range of 1–40 GPa. A phase transformation occurs from α to ω phase during HPT at pressures above ∼4 GPa while the total fraction of ω phase increases with straining and saturates to a constant level at higher strain. This phase transformation leads to microstructural refinement, hardness and strength enhancement and ductility reduction. Lattice parameter measurements confirm that c for α phase is expanded about 0.6% by the presence of ω phase. The temperature for reverse transformation from ω to α phase increases with straining and thus, straining under high pressure increases thermal stability of ω phase. The ω phase obtained by HPT is stable for more than 400 days at room temperature.

Pure Ti (99.4 pct) is processed by high-pressure torsion (HPT) at applied pressures in a wide range of 1.2 to 40 giga-pascals (GPa) for equivalent strain up to ~200. X-ray diffraction (XRD) analysis clearly reveals that a pressure-induced phase transformation occurs from α phase to ω phase during HPT processing when the applied pressure is more than ~4 GPa and the straining facilitates this phase transformation. The hardness and the tensile strength increase, but the ductility decreases by the phase transformation. Hardness measurements demonstrate that all values obtained at each pressure fall on a single curve when they are plotted as a function of equivalent strain. The hardness increases with an increase in the equivalent strain at an early stage of straining and saturates to a constant level, where the hardness remains unchanged with further straining. It is shown that the saturation level as well as the onset of the saturation depends on the applied pressure.

Digital radiography has been studied extensively for thickness measurement in recent years. This has resulted in enhanced image quality and improved overall evaluation. In this research, an innovative numerical method was used for image enhancement and radiographic interpretation through the use of MATLAB software. Film digitising was carried out by a scanner. Thickness profiles of specimens were extracted from the optical density of radiographs by a numerical method. Therefore, digital imaging and optical density measurements were combined to evaluate the thickness profile of samples. Results were used to create a three-dimensional mapping of the non-complex specimens for further investigation. Then the volumetric information could be used for the evaluation of various defects, such as corrosion, erosion and pitting. The most important challenge in the calculations was measuring the exact effective atomic attenuation coefficient for the samples. For this purpose, some reference blocks were designed, fabricated and used. In addition to practical experiments, Monte Carlo simulation was carried out for accurate assessment of the developed method. Although results show a high correlation between real and calculated values for plates, insulated and non-insulated pipes, this method cannot be used for the volumetric rendering of samples with a complex geometry. Ordinary computerised tomography has to be used for complex specimens.

A 100 mm-diameter ring sample of high purity Al (99.99%) was processed by high-pressure torsion (HPT). It was confirmed that the results of hardness measurements were consistent with those obtained using disk samples and demonstrated that scaling-up the HPT process was feasible using the ring-shaped sample. Evaluating the advantage of using ring sample, the potential for the scaling-up arises from the fact that the ring diameter can be increased by the amount corresponding to the inner central area of disk sample. Furthermore, the applied load is entirely used for the introduction of intense strain and thus for the development of a homogeneous microstrcuture throughout the ring sample. [doi:10.2320/matertrans.MD200822]

Pure Fe (99.96%) was processed by high pressure torsion (HPT) using disc and ring samples. When the microhardness and tensile properties are plotted against the equivalent strain, the individual properties fall well on unique single curves, level off at the equivalent strain of � 40. At the saturated level, the tensile strength of 1050 MPa and the elongation to failure of 2% are attained. Transmission electron microscopy showed that a subgrain structure containing dislocations develops at an initial stage of straining. More dislocations form within the grains and the subgrain size decreases with further straining. At the saturation stage, the average grain size reaches � 200 nm, the misorientation angle increases and some grains which are free from dislocations appear. It is suggested that at the saturation stage, a steady state condition should be established through a balance between hardening by dislocation generation and softening by recrystallization. [doi:10.2320/matertrans.MD200812]

Experiments were conducted to measure the extent of slippage occurring when thin disks are processed by high-pressure torsion. Separate tests were conducted on aluminum, copper and iron. The results show the extent of slippage varies between these three materials such that there is very little slippage in aluminum, slightly more slippage in copper and significant slippage when using iron. For all materials, the extent of slippage increases at both faster rotational speeds and lower imposed pressures.

Pure Cu was subjected to severe plastic deformation through high-pressure torsion (HPT) using disc and ring samples. Vickers microhardness was measured across the diameter and it was shown that all hardness values fall well on a unique single curve regardless of the types of the HPT samples when they are plotted against the equivalent strain. The hardness increases with an increase in the equivalent strain at an early stage of straining but levels off and enters into a steady-state where the hardness remains unchanged with further straining. It was confirmed that the tensile strength also follows the same single function of the equivalent strain as the hardness. The elongation to failure as well as the uniform elongation also exhibits a single unique function of the equivalent strain. Transmission electron microscopy showed that a subgrain structure develops at an early stage of straining with individual grains containing dislocations. The subgrain size decreases while the misorientation angle increases and more dislocations are formed within the grains with further straining. In the steady-state range, some grains appear which are free from dislocations, suggesting that recrystallization occurs during or after the HPT process. The mechanism for the grain refinement was discussed in terms of dislocation mobility.

This study introduces a process of high-pressure torsion (HPT) using ring samples and compares with the results of conventional disk HPT. Both types of HPT were conducted at room temperature on pure Al and pure Cu. The microhardness was measured along the diameters of the disks and rings. Microstructures were examined using transmission electron microscopy. When hardness values were plotted against equivalent strain, all data points fell on a single line for each material. There was a hardness maximum for pure Al but no such a maximum was present in pure Cu. In pure Al, many dislocations were visible within grains up to the equivalent strain corresponding to the hardness maximum but beyond this strain, grains with low dislocation density appear. All materials exhibited steady state where the hardness remains constant with respect to imposed equivalent strain. This study concludes that use of ring samples is effective as an alternative to the disk samples.

Radiographic image quality, which is quantified by radiographic sensitivity measurements, is significantly influenced by parameters such as scattering, effective attenuation coefficient and image contrast. In the present work, the Monte Carlo method has been utilized to simulate Gamma ray scattering and image contrast for double wall radiography of pipes and some experiments have been designed to determine the radiographic sensitivity and measure the effective attenuation coefficient. Wire type image quality indicators were simulated as artificial defects and the threshold contrast and minimum optical density difference for viewing each wire were investigated. It was found that the maximum allowable source to film distance for double wall exposure and single wall viewing technique was 1.4 times the outside diameter of the pipe and the image contrast and radiographic sensitivity were higher for this technique in comparison with the double wall viewing technique. The double wall exposure and double wall viewing technique is proposed to be used when the minimum source to film distance is higher than 1.4 times the outside diameter.

In this study of pipes of 150 mm diameters, thickness ranging from 4.2 to 15.0 mm was determined by using two radiography techniques: tangential radiography and double wall radiography. It was concluded that thickness losses of 10%, 20% and 50% could be determined by these methods. Formulae were developed for the double wall radiography method with a high precision of thickness measurement for non-insulated pipes. The precision was comparable with ultrasonic measurement results. Corrosion type and corrosion surface could be observed by these methods. Internal or external corrosion produced different effects in tangential radiography. Insulation removal was not necessary using the radiographic techniques.

Radiographic inspection is one of the most appreciated techniques among non-destructive testing methods due to the production of a film which acts as a unique fingerprint record. Converting radiographs to a digital format and further digital image processing is the best method of enhancing the image quality and assisting the interpreter on his evaluation. In this research, different algorithms were used for image enhancement and radiograph interpretation in MATLAB environment. A graphical user interface (GUI) was created for implementation of different algorithms. Both spatial and frequency domains techniques were used for image enhancement. The main enhancement technique was a spatial technique based on morphological transformation (top-hat and bottom-hat transforms). The wavelet filtering was implemented as the frequency domain technique. A third technique, based on pseudo-colouring, was also used for a better comparison between different methods. Wavelet-based techniques are used very often nowadays. However, we show that wavelet applications are more complicated and a supervised and intelligent usage has to be carried out. A wisely established spatial technique can result in reasonably proper results. The diagnostic test reliability was carried out for the quantitative evaluation of the results with the help of industrial radiography interpreters. The obtained results indicated that the defect recognition probability can be increased effectively in both domains. However, it was concluded that better results can be achieved using a morphological method.

The influence of silicon carbide and ferrosilicon as silicon carriers on the cooling curve characteristics, fluidity, microstructure, chill depth and hardness of hypoeutectic gray cast irons poured at different temperatures has been investigated. It has been found that the addition of SiC instead of FeSi as a silicon carrier resulted in variations in the thermal analysis characteristics and microstructure together with increasing fluidity as well as decreasing chill depth for the whole range of pouring temperatures explored. Microstructural studies revealed that SiC addition resulted in the maximum amount of A-typed graphite with a more uniform distribution. The finest microstructure (i.e. refined eutectic cells) was also obtained with SiC addition. These observations were attributed to the pre-inoculation behavior of SiC in gray cast iron with a slow fading tendency within the melt during solidification.

The most technically available NDT method for in-service inspection of heat exchanger tubes is eddy current testing. Using a differential ID bobbin probe, tubes can be tested with high speed, but for accurate estimation of tube condition, precisely machined calibration blocks from the same material are necessary. The purpose of this work was to calibrate the eddy current system by radiography without the use of expensive calibration blocks. Wall thickness measurement and deterioration determination due to corrosion/erosion/pitting was evaluated in this study by using radiograph ie film density measurements. It was found that this method can determine the remaining wall thickness as well as pitting corrosion in the tubes using differential and absolute film density measurements. Results show that good precision can be obtained with this method of eddy current system calibration.

The influence of inoculant additions on the cooling curve characteristics, microstructure and chill depth of hypoeutectic grey cast iron melts treated with FeSi or SiC as silicon carriers has been investigated. The effect of SiC content, when used simultaneously with FeSi as a silicon carrier, on the solidification behaviour of melts with an identical carbon equivalent has also been studied. It has been found that the addition of SiC instead of FeSi as a silicon carrier resulted in variations in the thermal analysis characteristics and microstructure together with decreasing chill depth. These effects were more pronounced for inoculated melts. It was also observed that the maximum amount of A-type graphite, the finest microstructure and the minimum chill depth were obtained with 1.6–2.0 wt-%SiC additions, for grey cast iron melts (treated with SiC and FeSi) having carbon equivalents of 4.2%.

We measured the electrical conductivity of bulk nanostructured silver prepared by high-pressure torsion (HPT) in a contactless manner by observing the AC magnetic susceptibility resulting from the eddy current, so that we could quantitatively analyze the dissipation process of the residual strain with sufficient time resolution as a function of temperature T and initial shear strain γ. The HPT process was performed at room temperature under a pressure of 6 GPa for revolutions N = 0–5, and we targeted a wide range of residual shear strains. The contactless measurement without electrode preparation enabled us to investigate both the fast and slow dissipation processes of the residual strain with sufficient time resolution, so that a systematic study of these processes became possible. The changes in the electrical conductivity as a function of N at room temperature were indeed consistent with changes in the Vickers microhardness; furthermore, they were also related to changes in structural parameters such as the preferred orientation, the interplanar distance, and the crystallite size. The dissipation process at N = 1, corresponding to γ ≈ 30, was the largest and the fastest. For N = 5, corresponding to γ ≈ 140, we considered the effects of grain boundaries, as well as those of dislocations. The strain dissipation was quite slow below T = 290 K. According to the analytical results, it became successful to conduct the quantitative evaluation of the strain dissipation at arbitrary temperatures: For instance, the relaxation times at T = 280 and 260 K were estimated to be 3.6 and 37 days, respectively.

Microstructural modifications of a biomedical Ti-6Al-7Nb alloy were accomplished via heat treatment in 3 different quenching mediums and then processed by High-Pressure Torsion (HPT) at room temperature. The microstructure of the as-received condition is composed of an equiaxed duplex (α+β) structure. After the heat treatment, a combination of primary α phase and lamellar structures was obtained with an increasing fraction of the martensitic lamellar with increasing cooling rate. After HPT processing, refinement of the microstructures was observed for N=5 revolutions. Transmission electron microscopy (TEM) of the sample quenched in liquid nitrogen confirmed the nanostructure with grain sizes below 100 nm and high density of lattice defects after HPT processing for N=5 revolutions. High-temperature tensile tests were carried out at 800 °C with an initial strain rate of 2×10−3 s−1 on specimens with different combinations of heat treatment and HPT straining. The test in the as-received condition presented a maximum elongation to failure of ~400% after HPT processing for N=5 revolutions. The highest elongation to failure in the heat-treated samples was ~580% in the sample quenched in liquid nitrogen and processed for N=5 revolutions.

Wall thickness measurement and deterioration determination of 6 and 10 inch pipes due to corrosion/erosion/pitting was evaluated by using radiographic film density measurements. Special reference blocks were prepared withdefined step wall reductions and artificial defects. Gamma radiography with a Ir-192 source was used. A double-wall technique with longitudinal film arrangement was used for this purpose. Formulae were developed from the experiments for numerical calculations. It was observed that this method can determine remaining wall thickness as well as pitting corrosion in insulated and non-insulated pipes with differential and absolute density measurements. The purpose of the work was the optimisation of techniques, quality control, evaluation of radiographs and parameters affecting the results. Furthermore, the studies included investigation on the limitations of each technique and stability of test conditions. Results show good precision - above 97% - between real and calculated values.

Micro-powders of Al were mixed with 50 mol.% micro-powders of Ni and severely deformed by high-pressure torsion (HPT). Following the HPT, the powder mixtures were consolidated and their average grain size is reduced to ~28 nm. Structural analysis using high-resolution transmission electron microscopy showed that higher fractions of Al3Ni and Al3Ni2 intermetallics are formed in the Ni matrix by the HPT processing. The HPT-processed materials were transformed to a nanostructured AlNi intermetallic with an average grain size of ~50 nm by annealing at 673 K. The current findings suggest that the HPT processes can be used successfully for production of bulk nanostructured intermetallics at low temperatures.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.