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SUS 304 austenitic stainless steel (ASS) was deformed by high pressure torsion (HPT) to obtain 100% volume fraction of martensite (α') from a fully austenitic (γ) matrix. Deformation caused an increase in hardness (Hv) from 1.6 GPa in the as annealed state to 6.4 GPa after HPT. Deformed samples were then annealed in the range 200 – 600oC and peak hardness of 7.8 GPa was observed after annealing at 400oC for 1 hour. Differential scanning calorimetry (DSC) and electrical resistivity tests showed that the deformed alloy undergoes a two stage phase transformation on heating from room temperature up to 700oC. The first stage of transformation was associated with hardening behavior while the second one which is reverse α' → γ transformation resulted in a reduction in hardness. Annealing at 400oC after deformation was found to increase the magnetization saturation (Msat) values.

Among the various severe plastic deformation (SPD) processes, high pressure torsion (HPT) has several unique characteristics. These are applicability of very large strain and deformation under high pressure. Due to these abilities of HPT, several unique phenomena have been observed. In the present paper, three topics were reviewed; 1) work-softening in pure Cu, 2) high pressure phase formation in pure Ti and 3) synthesis of Cu-NbC composite. Work softening in pure Cu was observed when low strain rate and high pressure were applied. In Ti high pressure ω phase is obtained after unloading only when the deformation at high pressure was applied. The volume fraction of ω phase increased with the increase in the amount of strain. In pure Fe, high pressure ε phase was not retained at ambient pressure. The bulk Cu-NbC composite was synthesized starting from elemental powders. This demonstrates that HPT is an efficient tool for mechanical alloying and cold consolidation.

The investigation of the behavior of CO2 absorption into the low Al2O3 electric arc furnace (EAF) oxidizing slag under wet grinding was investigated in this paper. The slag was wet ground in the vibration ball mill in the presence of CO2 at room temperature. The observation of the CO2 absorption was made with constant pressure method. The CO2 absorption increased steeply in the early stage of grinding. It occurred simultaneously with the grinding and immediately ceased when the grinding was stopped. The CO2 absorption occurred at the interface between the slag and the water which was saturated with CO2. The CO2 absorption increased as the finer particles were formed by the grinding process, and as the interface between slag and water was increased by the vibration process. A large amount of CO2 absorption and high conversion ratio was observed in the oxidizing slag with low Al2O3 in comparison with those of the slag with the high Al2O3 content.

SUS 304 austenitic stainless steel was subjected to severe plastic deformation (SPD) by the method of high pressure torsion (HPT). From a fully austenitic matrix (γ), HPT resulted in phase transformation to give a two phase structure of austenite (γ) and martensite (α') by the transformation γα'. The phase transformation was accompanied by an increase in hardness (Hv) from 1.6 GPa in the as annealed form to 5.4 GPa in the deformed state. Subsequent annealing in temperature range 250oC to 450oC resulted in an increase in both α' volume fraction and hardness (6.4 GPa). Annealing at 600oC resulted in a decrease in α' volume fraction hardness.

In the present work, effects of loading scheme and strain reversal on structure evolution are studied by using high pressure torsion (HPT) and twist extrusion (TE) techniques. High purity aluminum (99.99%) was processed at room temperature up to a total average equivalent strain of ~4.8 by TE and HPT with two deformation modes: monotonic and reversal deformation with a step of 12˚ rotation. It was revealed that microstructural change with straining observed in pure Al was a common consequence of the SPD processing and was not affected significantly by the loading scheme. At the same time, it was found that strain reversal retarded grain refinement in comparison with monotonic deformation.

Two unique characteristics of HPT as a SPD process, namely deformation with strain gradient and deformation under high pressure, were investigated. The effect of strain gradient was examined using low carbon steel. HPTed samples showed hardening at the center of the specimen where shear strain is principally zero and saturation hardness was higher than those without strain gradient such as ECAP or ARB. HPT experiments using specimen with different radial strain gradient in one sample also showed strain gradient hardening. The effect of high pressure during HPT was examined using pure Ti which transformed from α phase to ω phase when HPTed at high pressure. The volume fraction of ω phase increases with strain and with decreasing oxygen content. The ω phase is metastable at ambient conditions and it transforms back to α phase during heating.

The microstructure and the mechanical properties of pure Fe after HPT-straining at a rotation-speed of 0.2 rpm under a compression pressure of 5 GPa were investigated. The elongated grains with 300 nm thick and 600 nm long were observed at r = 1.5 mm away from the disk center regions after HPT-straining for 5 turns ( εeq = 45). The obtained Vickers microhardness in the submicrocrystalline Fe after 5 turns was around Hv 3.6 GPa. The engineering tensile strength and total elongation of the HPT-processed Fe for 10 turns were 1.9 GPa and 30 %. These facts suggest that HPT-straining leads to significant refinement of microstructure and increase in strength with good ductility.

Effect of chemical composition was investigated on martensitic transformation temperatures, Curie temperature, magnetization and microstructures for Ni-(Mn, Fe, Co)-Ga and Cu-Mn-Ga systems. In the Ni-(Mn, Fe, Co)-Ga alloys, which is a modification of Ni-Mn-Ga systems, the Af and TC over 400 K were achieved. Cu-Mn-Ga alloy exhibited shape memory effect at temperatures above 373 K and had TC over 400 K. Furthermore, Cu-Mn-Ga exhibits good ductility even in polycrystalline condition unlike the case of Ni-Mn-Ga. Effect of addition of the fourth element to improve the magnetic property is under investigation.

Formation of nanocrystalline structure by severe plastic deformation has studied extensively. Although ultra fine grained structure (grain size larger than 100 nm) had been obtained in many processes such as heavy cold rolling, equal channel angular pressing (ECAP) or accumulative roll bonding (ARB), the formation of nano grained structure (< 100 nm) is limited to processes such as ball milling, shot peening or drilling. In the present study, high pressure torsion (HPT) deformation and drilling were carried out to understand the conditions necessary to obtain nano grained structure in steels. The results of HPT experiments in pure Fe showed that HPT has superior ability of strengthening and grain refinement probably due to a strain gradient but the saturation of grain refinement occurs before reaching nano grained structure. Drilling experiments in high carbon martensitic steel revelaed that nano grained ferrite forms at the drilled hole surface only when the transformation from ferrite to austenite takes place during drilling. Considering various other processes by which nano grained ferrite was produced, it is proposed that heavy strains with large strain gradients together with dynamic transformation are necessary to reach nano grained ferrite structure.

Application of TiNi shape memory alloy in biomedical field is rapidly expanding. Some of the applications calls for non-conventional properties, which may require new methods of thermomechanical treatment and surface modification. In the present study, the effect of nanocrystallization/amorphization by various method of severe plastic deformation, such as, shot peening, cold rolling and high pressure torsion, was investigated on properties of TiNi shape memory alloys. Shot peening using iron based metallic glass media was found to be an effective method to obtain the amorphous surface. Surface amorphization improved the corrosion resistance. Nanocrystalline TiNi exhibited peculiar superelastic properties. Correlation between the microstructure and phase transformation in nanostructured TiNi was discussed.

Effect of isothermal aging on martensitic transformation temperatures, mechanical properties and microstructure was investigated for a Ni-rich Ti-Zr-Ni shape memory alloy at temperatures ranging from 673 K to 773 K. The aging behaviour was two stage process: the first stage associated with an increase in the Vickers hardness and a decrease in martensitic transformation temperatures and the second stage with a decrease in the hardness and increase in the transformation temperatures. Second stage was also characterized by the appearance of nano-scale precipitates, which has never been reported.

The mechanical behavior of the sintered nanostructured intermetallic alloys, Al67Ti25Mn8 and Al67Ti25Fe8 has been investigated by means of compression tests as a function of temperature. These intermetallic materials are produced by mechanical alloying and spark plasma sintering. The sintered alloys have been characterized by X-Ray Diffraction and Transmission Electron Microscopy. Their nanostructure consists of a single-phase with an L12 (cubic) structure and an average grain size in the nanoscale (lower than 30 nm). These nanostructured intermetallics show considerably high ductility in compression at high temperature but are brittle at temperatures below 400 °C. In such cases the compressive fracture strength can reach values as high as 1.8 GPa (Al67Ti25Fe8). At 500 °C, some ductility is found together with a relatively high flow stress (around 1 GPa), the corresponding deformation curve shows strain hardening and in some cases stress serrations (strain aging). At 600 °C, a low flow stress is measured (~300 MPa) with high ductility. At 700 and 800 °C, a quasi-superplastic behavior is found with a total deformation of around 45 and very low flow stresses. No evidence of dislocation motion is found at temperatures above 700 °C suggesting a deformation mechanism based on grain boundary sliding.

The formation of nanocrystalline structure in steels by ball milling, shot peening and drilling were studied. In ball milling and shot peening, nanocrystalline layers form with sharp boundaries from deformed structure regions. Nanocrystalline layer showed extremely high hardness. By annealing, nanocrystalline layer showed substantially slow grain growth without recrystallization. The temperature of the specimen during deformation is low and deformation is done in ferrite state. In drilling, several μm thick nanocrystalline layers form at the top surface of a drill hole. Nanocrystalline layers showed high hardness and good thermal stability. The fresh martensite and retained austenite near a drill hole indicate that the temperature reached above Ac3 and nanocrystalline layers are produced in austenite condition. It is recognized that nanocrystalline layers produced in the processes studied in the present investigation has similar characteristics irrespective of the temperature it produced. It is proposed that deformation with a large strain gradient is an important condition to produce nanocrystalline structure.

Thermal- and stress-induced martensitic transformation was investigated on TiNi shape memory alloys subjected to severe plastic deformation (SPD) by cold rolling. TEM observation revelaed the sample is a mixture of nanocrystalline and amorphous after 40% cold rolling. DSC analysis suggested that the martensitic transformation was suppressed when the thickness reduction was over 25% reduction. Aging at lower temperatures (573 ~ 673 K, 3.6 ks) restores the phase transformations, but to a limited extent. The stress-strain curves of nanocrystalline/amorphous TiNi are characterized by absence of stress-plateau and small hysteresis.

The effects of the shot peening (SP) condition and the initial hardness of specimens on the formation and thickness of nanocrystalline (NC) layer were investigated. The NC structure is found to be independent of the SP techniques, air blast, impeller and ultrasonic SP. In the SP condition, the increase in the kinetic energy per one shot is effective to increase the thickness of NC layer. It is also found that there is a certain critical initial hardness of specimens to produce the NC structure by SP. The NC structure forms when the specimen hardness is lower than the shot hardness.

Dissolution behavior of cementite in eutectoid steels with pearlitic and spheroidite structures by severe plastic deformation was studied. Applying a long time milling, cementite dissolved completely and matrix turned out to be nanocrystalline ferrite. By a ball drop deformation (at high strain rates), heavily deformed layers in which cementite dissolves completely or partially were produced. By applying pulsed laser irradiation, re-austenitized zone which transformed to fresh martensite during quenching was produced. The boundary between the re-austenitized zone and matrix exhibited similar microstructure with that observed in specimens subjected to a ball drop deformation. It was suggested that the dissolution of cementite by heavy deformation at high strain rates are probably due to thermal effect, that is, re-austenitization.

Deformation and dissolution behavior of the cementite in eutectoid steels with pearlitic and spheroidite structures were studied using high resolution SEM and AFM. Cementite lamellae in deformed pearlite exhibited inhomogeneous slip, smooth thinning or necking, fragmentation and cleavage fracture. Complete dissolution of cementite lamellae and spheroidal cementite particles was observed in specimens deformed with large strains at high strain rates. The dissolution mechanism of cementite by heavy deformation was discussed.

Half metallic ferromagnets are candidate materials for novel electronic devices, which can control the spin character of the conducting electrons. Electronic band calculation predicted that Co2MnGe Heusler compounds may has the half metallic band structure. In the present study, structure and magnetic properties have been investigated of the Co2MnGe for bulk and thin films. In the bulk sample, plate defects have been found.

Surface nanocrystallization in various steels by shot peening (both air blast and ultrasonic) and particle impact processing was investigated. Nanocrystalline layers with several µm thick were successfully fabricated by these methods. In all the case, the nanocrystalline layers have extremely high hardness and separated from adjacent deformed structure regions with sharp boundaries. By annealing, the nanocrystalline layers showed substantially slow grain growth without recrystallization. Those characteristics are similar to those observed in the samples experienced ball milling and ball drop deformation.

Surface amorphization by shot peening in intermetallic compounds was examined. The formation of amorphous layer has been verified in Ti-Ni and Zr-Co-Ni alloys. In Ti-Ni alloy, an amorphous phase and nanocrystalline grains were detected by TEM for 120 s peening duration. However, recrystallization and grain growth occurred, when peening duration was up to 400 s. In Zr-Co-Ni alloy, an amorphous phase coexisting with nanocrystalline grains was observed in Zr-37Co-13Ni alloy. For other alloy compositions (Zr-50Co and Zr-50Ni), an amorphous phase was not observed, and nanocrystalline grains were observed. All the observed nanocrystalline grains may be recrystallized from amorphous phase, because their shape was spherical.

Using the ultrafine laminate method, thin foils (50 µm) of Ni-rich TiNi shape memory alloys were produced. Overall composition of the Ti/Ni laminate is Ti-50.7%Ni. TiNi (B2) phase was obtained after different diffusion treatments at 1073 K for 36 ks. Aging treatment at 773 K for 3.6, 18, 36, 72 and 144 ks were also performed. Phase transformation behavior of aged foils changed from two-step, to three-step and then to two-step transformation, which is similar to the case of bulk TiNi alloys. Uniform distribution of Ti3Ni4 phase was observed for aged samples by transmission electron microscopy. Two-way shape memory effect of the aged TiNi foil was also demonstrated.

The deformation behavior of cementite was studied using eutectoid steels with pearlitic and spheroidite structures and fine grained bulk cementite prepared by sintering the mechanically alloyed powders. Cementite lamellae in deformed pearlite exhibited inhomogeneous slip, thinning by deck-of-cards slip, homogeneous bending, fragmentation, cleavage fracture and cracking by shear bands. Complete dissolution of cementite lamellae and spheroidal cementite was also observed in specimens deformed at high strain rates. The polycrystalline bulk cementite is brittle and fractures within elastic limit when deformed below 573 K. However, large plastic deformation was observed when compressed at high temperatures (over 773 K) and low strain rates (10 -5 ~ 10 -3 s -1 ). The artificial pearlite was successfully fabricated by hot compression starting from the

Using the bulk cementite (Fe3C, θ) fabricated by mechanical alloying (MA) and spark plasma sintering (SPS), the mechanical properties of cementite such as Young's modulus, hardness and compression strength were measured. The abnormal decrease in Young's modulus and the abnormal increase in hardness with a decrease of temperature were observed at around the Curie temperature. It has been found that the hardness and Young's modulus of the alloyed cementite increased in the order of V, Cr, Mn and Mo. At elevated temperatures, cementite could deform in compression superplastically to large strain without cracks. Multilayers of cementite and ferrite with the layer thickness less than 100 µm could be fabricated by compression at elevated temperatures and this indicated a cooperative deformation of these two phases.

An effect of aging on shape memory behavior was investigated for Mn - 15 at.% Cu alloy. It was revealed that aging of the alloy at 693 K significantly improves both shape memory effect (SME) and reversible shape memory effect (RSME). The reason of improved SME can be attributed to the decrease in the axial ratio, c/a, of fct martensite phase at room temperature, The enhancement of RSME might be related to the formation of Mn-rich zones associated with a higher antiferromagnetic ordenng temperature.

The effect of mechanical milling on C 60 (C 70 ) (a mixture of 87 vol.% C 60 and 13 vol.% C 70 ) and mechanical alloying on metal-0.3 mol% C 60 (C 70 ) (M-C 60 (C 70 ) ), where M=Al,Cu,Fe,Ni,Sn or Zn was studied. Liquid chromatography and infrared absorption measurements done on the mechanically milled C 60 (C 70 ) showed that when milled the C 60 (C 70 ) was stable for 3600 ks. However, milling results in a reduced fraction of C 60 and for the same time, showed the formation of probably a dimer of C 60 and C 60 polymer. After milling C 60 (C 70 ) with a metal for 720ks, a small fraction of the initial C 60 (C 70 ) retained its identity in Al- and Zn-C 60 (C 70 ) systems, whereas the molecular structure of C 60 (C 70 ) is lost when the metal was Cu, Fe, Ni or Sn. The sintered compacts made from the MA powder of a M-C 60 (C 70 ) and a M-graphite showed similar hardness in the cases of M=Cu, Fe and Ni. However, the sintered compacts made from an Al-C 60 (C 70 ) MA powder showed about a 40% increase in hardness compared with that made from an Al-graphite MA powder. While in the case of Zn, the hardness of the sintered compact made from the Zn-C 60 (C 70 ) MA powder was less than half of that made from a Zn-graphite MA powder. The stability of C 60 in a metal after MA was discussed according to which element group the metal belonged to on the periodic table.