Severe plastic deformation has the fascinating power of alloying equilibrium-immiscible elements, overriding the thermodynamic driving force (positive heat of mixing) that would dictate phase separation in equilibrium. This article briefly reviews the current understanding of this subject, in terms of experimental evidence for atomic-level alloying and phase selection, and in particular the models proposed to explain the driven intermixing. Outstanding issues that await future research are also discussed.

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We review our recent results of the formation, fundamental properties, workability and applications of late transition metal base bulk glassy alloys which have been developed after the first synthesis of Fe-based bulk glassy alloys by the copper mold casting method in 1995. The late metal transition base bulk glassy alloys were obtained in Fe–(Al,Ga)–(P,C,B,Si), Fe–(Cr,Mo)–(C,B), Fe–(Zr,Hf,Nb,Ta)–B, Fe–Ln–B(Ln=lanthanide metal), Fe–B–Si–Nb and Fe–Nd–Al for Fe-based alloys, Co–(Ta,Mo)–B and Co–B–Si–Nb for Co-based alloys, Ni–Nb–(Ti,Zr)–(Co,Ni) for Ni-based alloys, and Cu–Ti–(Zr,Hf), Cu–Al–(Zr,Hf), Cu–Ti–(Zr,Hf)–(Ni,Co) and Cu–Al–(Zr,Hf)–(Ag,Pd) for Cu-based alloys. These bulk glassy alloys exhibit useful engineering properties of high mechanical strength, large elastic elongation and high corrosion resistance. In addition, Fe- and Co-based bulk glassy alloys have good soft magnetic properties which cannot be obtained for conventional amorphous and crystalline type magnetic alloys. The Fe- and Ni-based bulk glassy alloys have already been used in some application fields. These late transition metal base bulk glassy alloys are promising as new metallic engineering materials.

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In order to improve the fatigue strength of Zr₅₀Cu₄₀Al₁₀ BGAs during 10³–10⁴ cycles, we tried to use the small additive element. As a result, Pd, Ag, Pt, and Au are effective addition elements to enhance the fatigue strength. Especially, the additive Pd element has a beneficial effect on the fatigue-strength enhancement. The additive Pd element promotes the glass-structure expansion, which can be recognized from the volume change due to the structural relaxation. Consequently, we found the linear relationship between the fatigue limit and volume change in Zr₅₀Cu_40−XAl₁₀Pd_X [X: 0–7 atomic percent (at%)] glassy alloys. Furthermore, we conclude that the origin of the unique hardness distribution on the fatigue-fractured surface is probably related to hydrogen hardening. The Zr₅₀Cu₃₇Al₁₀Pd₃ glassy alloy, which exhibits the highest fatigue limit of 1,050 MPa, shows a superior resistance force against the hydrogen hardening. Thus, maintaining the balance between the hardening and embrittlement around the fatigue crack tip by hydrogen is the significant factor to enhance the fatigue strengths.

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Bulk Zr_62−xNb_xCu_15.4Ni_12.6Al₁₀ (x=0–10 at%) glassy alloys were prepared via copper mould casting. XRD, DSC, SEM and compression test show appropriate niobium addition can enhance the glass forming ability (GFA) and thermal stability of these alloys. The bulk amorphous alloy with x=2.5 displays the largest temperature interval of supercooled liquid region (ΔT_x) up to 105 K and the largest γ value 0.428. However, the largest critical diameter is not achieved at x=2.5 but at x=5 instead, indicating a larger ΔT_x and γ value does not necessarily mean a higher glass-forming ability. At x=10, no glass transition but crystallization takes place, suggesting too much Nb may promote crystallization. The compression test shows increasing Nb content increases the strength and reduces the plasticity of the Zr_62−xNb_xCu_15.4Ni_12.6Al₁₀ glassy alloy, which is apparently attributed to the decrease in the number of microstructural heterogeneities in the metallic glasses, resulting in much less severe multiplication and interaction of shear bands.

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Refraction-enhanced X-ray imaging method using extremely parallel X-ray beams from a so-called third generation synchrotron radiation source was applied to observe titanium-hydride in titanium and titanium-aluminide polycrystals. Hydride in titanium was formed by an annealing in 1 atm hydrogen gas and electrolytic-charging for cross-sectional observation. Although the hydride in titanium cannot be observed by conventional radiography that utilizes absorption of X-rays, we visualized a high-contrast projection image of hydride using refraction-contrast radiography. This is a promising new technique for non-destructive inspection in bulk material systems with only small differences between refraction indexes such as hydride in titanium.

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The β-Al₅FeSi platelets have long been thought to be brittle and responsible for the inferior mechanical properties of Al-Si cast alloys. Two typical cracks, transverse and longitudinal, are commonly observed in β-Al₅FeSi platelets. It is thought that the cracks are probably due to the presence of doubled-over oxide films (bifilm) though some transverse cracks may be due to the brittleness. The crack is actually the gap between the two dry sides of an entrained oxide film. Its wetted sides are the favoured substrates for the nucleation and growth of β-Fe platelets. This discovery of the formation of β-Fe platelets on folded films has answered many previously intractable questions encountered in β-Fe phase. For the future, one may speculate that if oxide films could be eliminated from Al melts, it may prove possible to create alloys with unusually high toughness, despite high Fe contents.

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A two-point orientation auto-correlation function (TP-OACF) was developed in order to quantify the spatial distribution of targeted texture components. An example of a TP-OACF was demonstrated using an idealized orientation map. Characteristics of the spatial distribution of major texture components in 6022-T4 Al sheets deformed in plane-strain tension were also quantified using a TP-OACF. The results showed that {110}⟨1\\bar12⟩ and {123}⟨63\\bar4⟩ orientations (in {ND}⟨PD⟩ notation, where PD is the pulling direction) tend to form localized diagonal and horizontal bands through the thickness, respectively, after the plane-strain deformation. The cube orientation on the surface initially showed a relatively strong texture band along the RD, but this banding behavior was less significant after the plane-strain deformation.

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A supersaturated solid solution of Cu-44.5 at%Ni-22.5 at%Fe alloy was produced by ball milling of a pure chemical elemental mixture for 1080 ks. An fcc supersaturated solid solution with a grain size of about 20 nm was obtained after milling. This alloy was subsequently aged at 803, 898 and 1003 K for different times. The growth kinetics of the modulation wavelength was determined from the X-ray diffraction results and followed the Lifshitz-Slyozov-Wagner theory for a diffusion-controlled coarsening in the MA alloy after aging. The growth kinetics of composition modulation wavelength for the MA alloy was faster at 803 and 898 K than that for the same alloy composition obtained by a conventional processing and then aged at the same temperatures. The activation energy for the decomposed phase coarsening process in the MA alloy was lower than that corresponding to the conventionally-processed alloy.

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In this paper, 1 vol% TiC/Ti-1100 composite was prepared, and the β transus temperature of the composite was measured using metallographic techniques. The composite was forged at 1173, 1333 and 1423 K, respectively. Microstructure of forged samples was studied by optical microscopy (OM) and transmission electron microscopy (TEM). The forging in the upper α phase field was investigated especially. Mechanical properties of the composite after hot forging were tested by tensile tests at ambient temperature. It was found that there is an about 100 K increase in β transus temperature compared to monolithic Ti-1100 alloy. Widmanstatten microstructure, bimodal microstructure and microstructure containing aligned α plate were obtained after forging at various temperatures. Compared to Widmanstatten microstructure or bimodal microstructure, there is an increase about 200 MPa in ultimate tensile strength for the microstructure containing aligned α plate. The increase in tensile strength for the microstructure containing aligned α plate may result from two factors: one is the work hardening during the forging process, and the other is the interaction between α⁄β interface and dislocations in α phase during tensile process.

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The shape memory effect (SME) of Fe-15Mn-5Si-9Cr-5Ni-(0.5–1.5)NbC alloys pre-extended at room temperature was investigated. It shows that the pre-deformation result is similar for the SME of three composition alloys, i.e., the SME increased with increasing pre-extension and then decreased when they were over 12–14% pre-extended at room temperature. X-ray diffraction showed that there are two kinds of martensite transformations γ (fcc) → ε (hcp) and γ→ε→α′ (bcc) occurring in the Fe-15Mn-5Si-9Cr-5Ni-(0.5–1.5)NbC alloys when the alloys were deformed at room temperature. It was found by magnetic saturation measurements that when the alloy was 8% extended at room temperature, α′ phase appeared and obviously increased with increasing deformation. Furthermore, TEM observations showed that α′ phase exists in the cross section of the ε martensite and reverses in the different path of γ→ε. The effect of pre-deformation and aging on SME was correspondingly explained in view of martensite transformations and its nucleation, i.e., stacking faults and associated contribution of NbC precipitation, for γ→ε transformation.

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Creep testing was carried out at around 650°C for a martensitic 8Cr-2WVTa steel (F82H), which is a candidate alloy for the first wall of the fusion reactors of the Tokamak type. Rupture strength of the double tempered steel (F82HD) is lightly higher than that of simply tempered steel (F82HS). On the other hand, creep rate of F82HD is obviously smaller than that of F82HS in acceleration creep, though creep strain of F82HD in transition creep, where creep rate decreases with increasing strain, is larger than that of F82HS. Hardness of the crept F82HD decreases with increasing creep strain, which corresponded with the transmission electron microscopy (TEM) observation. On the contrary, X-ray diffraction and electron back-scattered diffraction pattern measurements show that fine sub-grains are created during transition creep. The creep curves were analyzed using an exponential type creep equation and the apparent activation energy, the activation volume and the pre-exponential factor were calculated as a function of creep strain. Then, these parameters were converted into two parameters, i.e. equivalent obstacle spacing (EOS) and mobile dislocation density parameter (MDDP). While EOS decreases with increasing creep strain, MDDP increases with increasing strain during transition creep. The decrease in EOS and the increase in either EOS or MDDP are rate-controlling factors in transition and acceleration creep, respectively. On the other hand, in case of F82HS, EOS increases and MDDP decreases during transition creep. In this case, the decrease in MDDP controls the creep rate during transition creep of F82HS. It is concluded that both EOS and MDDP are representative parameters of the change in substructure during creep.

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Vapor pressure of zinc from the Fe_tO-CaO-SiO₂-Al₂O₃ slag system was measured by the Knudsen effusion method under conditions with varying parameters such as temperature, slag compositions, and initial contents of zinc and chlorine. In the thermodynamic estimations using thermodynamic parameters under the experimental temperature range, for slag samples without Cl addition, it suggests that metallic Zn is the only vapor species. In the case of Cl addition, gaseous ZnCl₂ is predominant and the formation ratio of metallic Zn and FeCl₂ can be neglected. In the measurements, the vapor pressures of metallic Zn and ZnCl₂ increase with increasing temperature. For ZnCl₂, the logarithm of vapor pressure (lnP) is a linear function of the reciprocal of temperature (1⁄T), while in the case of gaseous metallic Zn, a non-linear relationship is observed between lnP and 1⁄T. The slag basicity exhibits the different effects on the vapor pressures of metallic Zn and ZnCl₂. The former increases with increasing the slag basicity, while the latter decreases. A high FeO content in the slag tends to increase the vapor pressure of metallic Zn and ZnCl₂.

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Pure aluminum and magnesium cube samples were heated at a specific temperature for a given time after being polished by abrasive papers. The amorphous layer that formed on the sample surface was transformed into a crystallized oxide film during the heating and holding period. We discuss how this thermally-formed oxide film progressively developed on the surface of the cubic samples. Gibbsite (Al(OH)₃) forms on pure aluminum during the initial stage of heating, after which it is then transformed to complex oxides, diaspore and γ-alumina. After an extended holding time at 883 K, the thermally-formed oxide film will be comprised of gibbsite, diaspore, α-Al₂O₃ and γ-alumina. This thermally-formed oxide film is compact and contains evenly-distributed microchannels. With pure magnesium, the transformation of periclase from brucite is associated with the formation of microcracks. In this study we use TGA (thermo-gravimetric analysis) to describe the progressive development of complex oxides and periclase films on pure Al and Mg respectively.

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The authors have investigated the factors causing undesirable deformations of extruded sections subjected to a quasi-uniform bending moment. These deformations include flattening distortion, wrinkling and folding. In this report, the basic mechanism of the flattening distortion of the cross section is explained and effective methods for controlling the undesirable deformation are proposed. The flattening distortion appears as a primary deformation at the beginning of the bending operation and corresponds to the shape of the cross section and the degree of bending. It is clarified that the thickness of the wall, the shape of the cross section and the position of the neutral axis influence the configuration of the flattening distortion. As an example, the bend degree of the wrinkling limit is approximately fourfold when the thickness of the workpiece is doubled.

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It is known that cooling rate from the liquid state is an important factor for producing the bulk metallic glasses. However, almost no other factors such as electric and/or magnetic fields were investigated. The present authors have reported that a new method for producing Mg-Cu-Y bulk metallic glasses by using electromagnetic vibrations is effective in forming the metallic glass phase. However, effects of the electromagnetic vibrations on glass-forming ability in other alloy systems are not investigated. Thus, this study aims to investigate effects of the electromagnetic vibrations on glass-forming ability in Fe-Co-B-Si-Nb bulk metallic glasses. As a result, it was found that glass-forming ability of Fe-Co-B-Si-Nb alloys also enhances with increasing the electromagnetic vibration force. Moreover, the electromagnetic vibrations were found to affect the increase of the cooling rate and the decrease in the number of crystal nuclei directly, but not to affect the crystal growing rate.

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Although the microstructure, hot crack susceptibility and porosity of aluminum alloy laser welds are affected by many welding parameters, the effects of the shielding gas flow rate and the power waveform are particularly significant. In this study, a high-power Nd:YAG laser is used to weld A5754-O aluminum alloy sheets of 1 mm in thickness. Initially, bead-on-plate (BOP) welding is performed using a rectangular waveform with a constant mean output power and three different levels of ΔP (ΔP=P_p−P_b, where P_p is the peak power and P_b is the base power). Butt welding is then performed using the appropriate BOP welding speed, which is lower than the welding speed for just full penetration, and one of two levels of ΔF (ΔF=F_f−F_b, where F_f is the face shielding gas flow rate and F_b is the back shielding gas flow rate). The BOP welding results show that reducing the value of ΔP increases the welding speed required for full-penetration, and therefore increases the penetration depth to bead width ratio and the micro-hardness of the weld bead. The butt welding results show that the tensile strength and total elongation properties of the high ΔF (ΔF_H) specimens are approximately three times higher than those of the low ΔF (ΔF_L) specimens. This is primarily due to the absence of hot cracking in the ΔF_H specimens, together with a finer microstructure and a lower level of porosity. This study demonstrates that the effect of ΔF on the weld bead geometry, microstructure, hot crack susceptibility and mechanical properties is far higher than that of ΔP. However, the effect of ΔP on the change of welding speed is higher than that of ΔF.

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The instrumented pulse electric discharge consolidation method is used to provide a way of in process nanocrystalline control densification of the amorphous ZrO₂-20 mol%Al₂O₃ powder as prepared by rotating-arm reaction ball milling. The cylindrical compact height (h_f) of the amorphous ZrO₂-20 mol%Al₂O₃ powder is found to be a dominant process variable; at 1 mm, it leads to the densification prior to major crystallization after a high relative density of roughly 0.86 at 800 K, and significant decreases down to 1284 K in temperature necessary to obtain the full densification under 100 MPa. The rapid densification for amorphous and nanocrystalline supersaturated cubic ZrO₂-20 mol%Al₂O₃ is fairly well expressed by an Arrhenius-type equation of Newtonian viscous flow: η_p=η_poexp(Q⁄kT) having greatly decreasing apparent activation energy Q from 300 to 72 kJ mol⁻¹ and process viscosity η_p at 1200 K with decreasing h_f from 14.6 to 1 mm. The Berkovich indentation testing permits us to derive a relatively low level of 4.4 GPa for the value of the yield stress at room temperature in the full-density nanocrystalline ZrO₂-20 mol%Al₂O₃ sample having the Vickers hardness number of approximately 800 DPN.

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A pulsated orifice ejection method (POEM) has attained mass-production of monosized spherical micro particles of solder. In this method, the micro droplet melts are emitted from a small orifice by applying both mechanical pulses and constant gas pressure to the melt. This paper reports further development of this method for alternative monosized copper spherical particles with a size in the order of 100 μm. The possibility of the droplet formation was strongly determined by the wettability of orifice material to the melt. Droplets of molten copper could be stably formed at a particularly high contact angle. Using an orifice with the low wettability, monosized copper particles are obtained in a wide range of process parameters such as the rod displacement and gas pressure. Their particle size was also clarified to vary with changes in the two parameters. Especially, the gas pressure may linearly control the particle size from 75 to 120 μm, which is equivalent to 75 to 120% of the orifice diameter. All monosized particles produced by the POEM have an excellent mono-dispersivity less than 2.0 in standard deviation.

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Calcium titanate (CaTiO₃) films were prepared by metal-organic chemical vapor deposition (MOCVD) using Ca(dpm)₂ and Ti(O-i-Pr)₂(dpm)₂ precursors. The phases, composition and morphology of Ca-Ti-O system films changed depending on molar ratio of Ca to Ti (R_Ca/Ti), total pressure (P_tot) and substrate temperature (T_sub). CaTiO₃ films in a single phase were obtained at the condition of R_Ca/Ti=0.95, T_sub=1073 K and P_tot=0.8 kPa, and R_Ca/Ti=0.78, T_sub=973 K and P_tot=0.8 kPa. The CaTiO₃ films prepared at T_sub=1073 K had a well-developed columnar texture, and significant (010) orientation was observed at R_Ca/Ti from 0.59 to 0.72. The deposition rate showed the highest value of 1.25×10⁻⁸ m s⁻¹ at T_sub=1073 K, P_tot=0.4 kPa and R_Ca/Ti=0.95.

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The aim of this study was to investigate the in vivo performance of implants coated with hydroxyapatite (HAp) with different surface morphologies. HAp coatings were formed on commercially pure titanium rods (2 mm in diameter, 5 mm in length) by the thermal substrate method in an aqueous solution that included Ca(H₂PO₄)₂ and CaCl₂. The coating experiments were conducted at 40–140°C and pH=8 for 15 or 30 min. All the specimens were covered with HAp, which had different morphologies such as net-like, plate-like, and needle-like. The coated rods were implanted in the tibiae of 10-week-old male rats. Noncoated titanium rods were used as the control in this study. The constructs were retrieved 14, 28, and 56 days postimplantation and examined for new bone formation and tissue response in the cancellous and cortical bone, respectively. After 14 days implantation, new bone formed on both the HAp-coated and noncoated titanium rods in the cancellous and cortical bone. However, the bone-implant contact ratio, which was used for the evaluation of new bone formation, was significantly dependent on the surface morphology of the HAp, and the results demonstrated that the needle-like coating appears to promote rapid bone formation.

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High-entropy Al_0.5CoCrCuFeNiTi_x alloys are synthesized using the well-developed arc-melting and casting method. The molar ratio (x) of titanium is varied from 0 to 2.0. The microstructure, hardness and wear resistance of the alloys are investigated. The alloys exhibit simple FCC, BCC, CoCr-like and Ti₂Ni-like phases. For a small addition of titanium, the alloys form a monolithic FCC solid-solution phase. Two phases of β₁ and β₂ based on BCC appear at the titanium content of x=0.4 and the β₁ phase becomes ordered at x=1.4. With the increase of titanium content, copper segregates to the interdendrite region in which nano-precipitates form. A CoCr-like phase forms when x ranges from 0.8 to 1.2. Ti₂Ni-like phase forms when the titanium content exceeds x=1.0. The hardness value increases with titanium content. The alloys with lower titanium content exhibit similar wear resistance to Al_0.5CoCrCuFeNi. The wear resistance is rapidly improved at titanium contents from 0.6 to 1.0, and reaches a maximum at x=1.0. This is followed by a gradual decrease with further increase of the titanium. The mechanisms behind the strengthening and wear resistance of the alloys are discussed.

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Effects of Ti carbide precipitates on the ductility and toughness of 30 mass%Cr steels containing above 0.1%C and 1%Ti were investigated by tensile and impact tests at low temperatures. Two kinds of heat treatments of aging after solution treatment (process SA) and annealing without solution treatment (process A) were performed for the test pieces. The ductility and toughness were evaluated by ductile-brittle transition temperature (DBTT) in reduction of area and DBTT in absorption energy, respectively. Both the processes SA and A produce coarse globular Ti carbide particles within the grains in the 2 μm size range and cluster-like coarse globular Ti carbides at grain boundaries. The process SA does not bring about numerous fine Ti carbides at grain boundaries for the specimens containing above 0.1%C, which is contrary to those for the specimens containing below 0.07%C. The DBTTs determined by the tensile test (tensile DBTTs) for the specimens with above 0.1%C after the process SA are lower than the tensile DBTTs for the specimens in the range from 0.04% to 0.07%C, while the impact DBTTs for the former specimens are higher than the impact DBTTs for the latter specimens. The effect of the morphology of Ti carbides on the tensile DBTT and that of the morphology of Ti carbides on the impact DBTT are different. The numerous fine Ti carbides at grain boundaries exert detrimental effects on the tensile DBTT. On the other hand, the numerous fine Ti carbides at grain boundaries and the coarse globular Ti carbides exert detrimental effects on the impact DBTT.

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The activation enthalpies and frequency factors for interdiffussion of Al and Re in the γ-phase of Ni-Al-Re ternary system were estimated by a series of experiments using diffusion couples in the temperature range from 1200 to 1300°C. The method developed by Whittle and Green was applied to obtain the interdiffusion coefficients of the solutes (Al, Re) in the system. The activation enthalpies Q and the frequency factors \\ ildeD_o obtained from the experiments confirmed the slower diffusion of Re than Al. In addition, it was found that the influence of Re on the diffusion of Al in the γ-phase of Ni-Al-Re system was insignificant.

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Influence of oxygen content on the microstructure and thermoelectric properties of bismuth-telluride based (Bi,Sb)₂(Te,Se)₃ alloys has been investigated. The consolidated specimens in a disc form of 10 and 26 mm in diameter and 8 mm in height were prepared by hot-pressing of rapidly solidified foils produced by a single-roller melt spinning method. Oxygen content was analyzed to be enriched in the range of 4.1 nm depth from the foil or powder surface. By the reduction-treatment process in a hydrogen atmosphere, the enriched oxygen content on the surface was decreased. For the hot-pressed specimens, the highest oxygen content was 519 ppm and the oxygen-rich area lies along the grain boundaries. As the oxygen content decreased, the carrier mobility (μ) was increased and the electrical resistivity (ρ) was decreased. The reduction of oxygen content by the reduction process using hydrogen gas causes the increase of μ, leading to high value of figure of merit (Z). For the specimens containing the oxygen content of 79 ppm, the maximum Z value of 3.4×10⁻³ K⁻¹ was obtained. There was a tendency for grain size to increase with increasing oxygen content in the hot-pressed specimens.

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Copper electroplating has been used for making interconnections in large-scale integration (LSI). Sub-100-nm-wide, deep trenches with aspect-ratios over 6 were fully filled by optimizing DC and pulse electroplating processes. Grain sizes of Cu of sub-100-nm wide trenches after electroplating were 70 nm for DC electroplating and 58 nm for pulse electroplating. The Cu grain sizes of Cu interconnects by DC plating after electroplating increased with the annealing temperature.

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