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An Al-8Mg-based alloy with high strength and high ductility was developed by adding a grain boundary strengthening element. Zr was predicted to be the most effective element for grain boundary strengthening at 298 K from first-principles calculations. Then, an Al-8Mg-0.2Zr alloy was developed. Grain boundary analysis by high-angle annular dark-field scanning transmission electron microscopy and Auger electron spectroscopy revealed that the added Zr segregated at grain boundaries in the Al-8Mg-0.2Zr alloy. The Al-8Mg-0.2Zr alloy exhibited tensile elongation of 49% with transgranular fracture, whereas the Al-8Mg alloy exhibited tensile elongation of 28% with intergranular fracture after tensile tests at room temperature. We succeeded in developing a high strength and high ductility Al-8Mg-0.2Zr alloy which compensates for the trade-off between strength and ductility in comparison with commercial Al alloys.

High productivity and bath stability of electrodeposition for Al and its alloys from a dimethylsulfone (DMSO2)-aluminum chloride bath are highly desirable characteristics for a wide range of critical applications. However, a long-standing problem for such electrodeposits is S and Cl contamination, which results in limited ductility. In this study, we explored a reduction method for S and Cl in Al electrodeposits from a DMSO2 bath to facilitate plastic elongation of the electrodeposited Al. For 2–5:10 M ratios of aluminum chloride to DMSO2, tailoring the conditions of electrodeposition decreased the S and Cl contents to ∼0.2 at%. The addition of various metal salts revealed that gallium chloride further reduced the S and Cl contents to less than 0.1 at%. This reduction permitted the electrodeposited Al–Ga alloys to exhibit plastic elongation in tensile tests. Based on the results of experiments and first-principles calculations, we discuss the role of Ga in the growth mode of electrodeposits and its effect on grain boundary cohesion. Thus, we elucidate the mechanisms for realizing high strength and ductility in electrodeposited Al alloys.

We electrodeposited bulk nanocrystalline Fe–Ni alloys with a tensile ductility of 12%–24%. We explored the intrinsic ductility of these alloys, taking into consideration the relationship between the ductility and the orientation index and contents of the grain boundary embrittlement element. Applying multiple regression analysis to our findings and those from the literature we found that the ductility of Fe–Ni alloys can be predicted from their orientation index for the (2 0 0) plane and sulfur content. The analysis of our study points to the potential for intrinsic ductility in nanocrystalline Fe–Ni alloys greater than that of the present highest value of 24%.

Al and Al alloys electrodeposited from a dimethylsulfone (DMSO2) bath are typically contaminated with S and Cl. Electrodeposited Al and Al alloys suffer from limited ductility since undesired impurities decrease plastic deformability. Herein, we report an electrodeposition process involving the use of a DMSO2 bath that realizes an Al product with tensile elongation as large as ∼30%. Doping of tin chloride in the DMSO2 bath resulted in a micrometer-scale grain microstructure with sub-µm Sn precipitates distributed along the grain boundaries of the electrodeposited Al. These Sn precipitates on the electrodeposits prevented S and Cl contamination, which is likely the main factor underlying the large tensile elongation in the electrodeposited Al. Furthermore, electrodeposition with varying concentrations of tin chloride pointed to that tin chloride showed enough impurities reducing ability even in trace amounts.

The small amount (0.1 at%) of V addition to Fe–Al alloys promotes AlN precipitation during nitriding and results in substantial surface hardening, in contrast to the normal sluggish precipitation kinetics of AlN during nitriding of Fe–Al binary alloys. The addition of V to Fe–Al alloys can increase the surface hardness to a greater extent than the addition of Ti. First-principles calculations of the interaction energy between an Al atom and an N–s cluster (s = V, Ti, Cr, or Al) show that a V–N cluster has an attractive interaction with an Al atom, and this interaction is stronger than that between a Ti–N cluster and an Al atom, in good agreement with the greater hardening induced by V addition than by Ti addition. These experiments and calculations indicate that solute clusters not only contribute directly to the hardening but also induce alloy nitride precipitation.

Effects of third alloying elements on the transformation strains and phase stabilities of Ti-Nb based alloys at 0 K were investigated using the first-principles calculations. In binary Ti-Nb alloys, the transformation strains and the body-centered cubic high-temperature beta (β) phase stabilities decrease with increasing Nb concentration. In Ti-12.5Nb-6.25X (at.%) alloys, the effects of 46 different alloying elements X on the transformation strains and phase stabilities were also investigated. The addition of Al, Be, Ca, Cu, Ga, Ge, Hf, La, Mg, Sc, Si, Sn, Sr, Y, Zn, and Zr increase the transformation strains, and all alloying elements except for Sc act as the β-phase stabilizing element. Using the calculated values of the effects of alloying elements, x M values were calculated for the different 46 alloying elements, where x M are the X contents of Ti-12.5Nb-X (at.%) ternary alloys where the martensitic transformation start temperatures were equal to 300 K. Then, the transformation strains of Ti-12.5Nb- x M X (at.%) alloys were predicted. The Ti-12.5Nb-17.8Hf (at.%) alloy shows the largest transformation strain value.

Texture change during superplastic deformation was examined and compared in two magnesium alloys with different chemical composition. These alloys were extruded to refine the microstructure. The pre-existing basal texture of both alloys became slightly more random within the bulk probably owing to grain boundary sliding and the accompanying grain rotation. However, the texture changes differed between tensile and compressive deformation along the extrusion (longitudinal) direction. This fact suggests that dislocation slip is important in superplastic deformation. It was concluded that dislocation slip acts primarily as an accommodation mechanism for grain boundary sliding.

Friction stir processing (FSP) is one of the severe plastic deformation (SPD) processes. It has been reported that SPD-processed Al with various purities attained a minimum grain size when Zener-Hollomon parameter is larger than 1016 s-1. The minimum grain size is different by purity level and alloying elements. We investigated the influence of Fe solute atoms on grain refinement of high-purity Al on the condition that Zener-Hollomon parameter was larger than 1016 s-1. FSP was conducted on Al-0.01%Fe, which was fabricated by using 5N Al (99.999% purity). FSP-ed Al-0.01%Fe exhibits the minimum grain size of 1.4 μm, although high-purity aluminums with more than 99.998% exhibits much larger minimum grain sizes of 30-40 μm. Only 101 at.ppm Fe played a critical role in the grain refinement of pure aluminums.

Bulk nanocrystalline Fe-Ni alloys with Ni content of 40-55 at.%, grain size of 12-15 nm, and hardness of 3.9-4.6 were prepared by an electrodeposition. The decrease in the hardness values as grain size decreased was discussed in terms of grain refinement effect, solid solution strengthening, and grain boundary relaxation strengthening. It was found that the change of Ni content could not significant solid solution strengthening, and there were no difference in the state of grain boundary for each sample. Micro X-ray diffraction analysis on the sample after tensile tests showed that the (200) texture was developed but full width at half maximum was not changed. This indicated the potency that the grain boundary activity would be induced by a tensile loading. The softening behavior of electrodeposited Fe–Ni alloys would be related to the transition of the dominant deformation mechanisms.

Parameters for evaluating the glass-forming ability (GFA) in Ti–Cu system metallic glasses were considered by investigating the effect of additional elements (Fe, Co, Ni, Si, Zr, Cr) on structural changes and onset temperatures associated with each exothermic peak on heating. The differential scanning calorimetry curves of Ti–Cu system metallic glasses (added Ni, Cr, Zr) exhibited two exothermic peaks. Moreover, the sample containing Zr maintained its halo peak when the sample was annealed at first exothermic peak. The results indicate that the onset temperature of the second exothermic peak ( T x 2 ) is an important temperature reflecting the resistance of the supercooled liquid to crystallization. The GFA of Ti–Cu system metallic glasses are expressed well by parameters containing T x 2 .

A method for reducing the sulfur content of electrodeposited bulk nanocrystalline Fe–Ni alloys was developed to improve the tensile ductility of the materials and prevent thermal embrittlement caused by the grain boundary segregation of sulfur. Bulk nanocrystalline Fe–Ni alloys were prepared using electrolytes that primarily consisted of iron sulfate and nickel sulfamate combined with manganese chloride (MnCl 2 ). The addition of MnCl 2 in the deposition bath did not produce any significant changes in the Ni content and grain sizes of the electrodeposited alloys. In contrast, the sulfur content in the materials decreased from 840 to 620 at ppm. The bulk nanocrystalline Fe–Ni alloys with low sulfur content exhibited a higher tensile elongation of 16–19% compared to the materials with high sulfur content. Furthermore, after annealing at 200 °C for 3 h, The bulk nanocrystalline Fe–Ni alloys with low sulfur content exhibited a high tensile elongation of 9–10%, whereas the elongation of the materials with high sulfur content was 3%. The results indicate that the plastic elongation of electrodeposited bulk nanocrystalline Fe–Ni alloys can be improved by reducing the amount of sulfur in the materials.

A method for enhancement of the mechanical properties of electrodeposited bulk nanocrystalline Fe–Ni alloys was explored. Bulk nanocrystalline Fe–Ni alloys were prepared using electrolytes that primarily consisted of iron sulfate and nickel sulfamate with propionic acid. Varying the concentration of propionic acid in the deposition bath produced no significant change in the C, S, or Ni content or grain sizes of the electrodeposited alloys. In contrast, the hardness of bulk nanocrystalline Fe–Ni alloys increased from 4.0 to 5.0 GPa with the increase of propionic acid concentration from 0 to 3.0 g/L. In addition, the tensile strength also increased from 1.6 to 1.7 GPa while maintaining a good tensile ductility of ~10%. These increases for electrodeposited alloys can be explained by grain boundary relaxation strengthening. After annealing at relatively mild temperatures, the alloys electrodeposited without propionic acid exhibited higher strength than at the as-deposited state, while the strength of the alloys electrodeposited using 3.0 g/L propionic acid remained unchanged. The results of this study indicate that the addition of propionic acid to the deposition bath could remove the excess grain boundary defects of Fe–Ni alloys in as-deposited states, requiring no additional thermal treatments and enhancing the mechanical strength to high levels.

In order to develop a high strength and heat-resistant magnesium alloy, we focused on controlling microstructure of Mg96Zn2Y2 (at %) casting alloy by the addition of a 4th element. Initially, we investigated the effects of zirconium addition and cooling rate for grain refinement on microstructure and mechanical properties. Consequently, Mg95.8Zn2Y2Zr0.2 casting alloy contains fine equiaxed grains (approx. 0.01 mm), and it exhibits tensile and fatigue properties equivalent to or higher than those of commercial aluminum alloys at high temperature above 473 K. At 523 K, this alloy exhibited a tensile strength of 223 MPa nearly twice that of A4032-T6 alloy used in typical automotive pistons. The Mg95.8Zn2Y2Zr0.2 casting alloy also reveals sufficient ductility and good castability, characteristics not common in current heat-resistant magnesium alloys. Next, we focused on controlling microstructure of Mg96Zn2Y2 casting alloy by the addition of Ag. Mg96Zn2Y2 cast alloy is composed of alpha-Mg phase, long-period stacking ordered phase and Mg3Zn3Y2 phase; on the other hand, Mg-Zn-Y-Ag cast alloy had 4th phase by an addition of Ag. A substantial increase in yield strength at room temperature, without grain refining, was the result.

The tensile behavior of electrodeposited bulk nanocrystalline Fe–Ni alloys with a grain size of approximately 15 nm was investigated. Electrodeposited alloys with a nickel content of 43–56 wt% have a single-phase face-centered cubic structure. These alloys exhibited a good combination of tensile strength and ductility in tensile tests at room temperature. In particular, bulk nanocrystalline Fe–44 wt% Ni exhibited the high tensile ductility of 1.7 GPa and significant ductility of 16%, and the tensile specimen after fracture showed clear necking. Fracture surface observation indicated that dimples, the size of which was 10 times the grain size, developed in electrodeposits with high ductility of above 10%. The results of this study point out that grain clusters can have a role in plastic deformation during tensile loading.

Al was electrodeposited from a dimethylsulfone (DMSO 2 ) bath using a new pre-electrodeposition process to investigate the effect of sulfur and chlorine on the tensile ductility. Al electrodeposited from a DMSO 2 bath contains sulfur and chlorine, which are impurities are incorporated into the electrodeposits as sulfide and chloride, respectively. By pre-electrodeposition, the sulfur and chlorine contents of electrodeposited Al decreased from approximately 0.64 and 0.71 at% to 0.15 and 0.17 at%, respectively. This reduction in the sulfur and chlorine contents affects the microstructure, hardness, and ductility of the electrodeposits. The grain size increased from approximately 200 nm to 4 μm, and the microhardness decreased from 1.67 to 0.24 GPa. In tensile tests, electrodeposited Al before pre-electrodeposition exhibited failure even in the elastic regime, while electrodeposited Al after pre-electrodeposition exhibited good tensile ductility of approximately 30%.

Effect of orientation on tensile ductility of electrodeposited bulk nanocrystalline Ni–W alloys was studied. Bulk nanocrystalline Ni–W alloys with different textures were prepared by electrodeposition, varying the amount of saccharin sodium and the bath temperature. An elongation of 0–13.4% was obtained in a tensile test. Although there was no relationship between tensile ductility and the grain size or W content, there was the relationship between tensile ductility and the orientation index for the (200) plane in the bulk nanocrystalline Ni–W alloys. In fact, no plastic deformability was observed when the index was below 1, while the tensile ductility increased with increasing orientation index above a value of 1. The cross-sectional TEM observations indicate the colony structure of electrodeposits varied in orientation. The results of this study point to that the colony structure of electrodeposits has an effect on the tensile ductility.

Changes in the lattice constants of 55 Al-based solid solutions, as well as local lattice distortions induced by solute atoms, were studied on the basis of first-principles calculations using 3.70, 3.13, 1.56, and 0.93 at.% alloys. The first nearest-neighbor interatomic distances between the solute and the solvent Al atoms were relatively constant for all calculated Al–X systems. The calculated volume size factor and the misfit strain were in good agreement with the experimental data available in the literature. The linear relationship observed between the misfit strain and the volume size factor was explained by using the Eshelby approach. A discussion of the application of the misfit strains to the estimation of increasing yield stress due to the solid solution strengthening was also presented. The calculated extent of solid solution strengthening was in good agreement with the available experimental values.

The effects of solute X (Mo, Nb, V and W) on the phase stability of ¢-Ti alloys were studied from first-principles calculations. The firstprinciples calculations yielded solution enthalpies for hexagonal close-packed (hcp)-Ti35X1 and hcp-X35Ti1 and body-centered cubic (bcc)Ti26X1 and bcc-X26Ti1 solid solution alloys. The enthalpy curves for the i (hcp)- and ¢ (bcc)-phases of Ti­X alloys were described as a function of the X concentration by using the calculated solution enthalpies and sub-regular solution model. While the enthalpies of the i-phases increased with increasing concentrations of Mo, Nb, Vand W, the enthalpies of the ¢-phases decreased with increasing concentrations. This is consistent with the experimental results, showing that Mo, Nb, V and W are ¢-stabilizers. The ¢-stabilizing strength of solute elements in Ti alloys is gauged using the experimental critical concentration. We found a good linear correlation between the experimental critical concentration and the theoretical metastable equilibrium concentration at which the enthalpy of the i-phase is equal to that of the ¢-phase. The metastable equilibrium concentration decreased with the increasing lattice stability of the bcc structure with reference to hcp structure. [doi:10.2320/matertrans.MC201209]

A textured Mg–9Al–1Zn alloy rod exhibited highly isotropic flow along the longitudinal and transverse directions during superplastic deformation, indicating that crystallographic orientation had a negligible effect on flow stress. Although there was an overall weakening of the initial basal texture during deformation due to grain boundary sliding, the texture changes differed between tensile and compressive deformation along the longitudinal direction. This indicates that dislocation slip plays an important role in superplastic deformation. Macroscopic specimen shape anisotropy, on the other hand, would be expected to appear under the preferential activation of basal slip during compression along the transverse direction, but was not observed experimentally. These results imply that dislocation slip acts primarily as an accommodation mechanism for local stress concentration produced by grain boundary sliding.

In this study, calcium, Ca-, and strontium, Sr-added AZ91 magnesium alloys, which were composed of magnesium, Mg–9 wt.% aluminum, Al–0.8 wt.% zinc, Zn–x wt.% Ca–y wt.% Sr, were formulated and designated as AZXJ91xy alloys. The optimum composition of die-cast AZXJ alloys has been studied by micro-structural analysis and through the application of the constitutive equation of deformation behavior at elevated temperatures that includes the stacking fault energy. The normalized plots of the tensile test results of AZXJ alloys at 448 K by the constitutive equation of deformation behavior indicated that the deformation mechanism of the alloys was climb-controlled dislocation creep. The value of the constant A′ in the constitutive equation differs in the different AZXJ alloys, even though the effect of the solid solution of added elements, which is considered in the stacking fault energy term, was eliminated from A′. Using A′ as an indicator parameter of the creep resistance with the tensile strength at ambient temperature, the optimum composition of the creep-resistant Mg–Al–Zn–Ca–Sr alloy has been determined, and its creep resistance was comparable to those of known heat-resistant magnesium alloys.

Bulk nanocrystalline (nc) Al was electrodeposited from a mixture of dimethylsulfone-based electrolytes (DMSO 2 bath). The DMSO 2 bath demonstrates characteristics suitable for the fabrication of bulk nc Al, such as high current efficiency, good thermal stability, and low toxicity. The bulk nc Al having a thickness of 250 μm was electrodeposited from a dimethylsulfone bath. It displayed high hardness of about 1.7 GPa. The hardening source was analyzed on the basis of the Hall–Petch relationship and solid solution strengthening models. These analyses indicate that grain size reduction to approximately 40 nm and solid solution hardening by trace impurities contribute to the high hardness of the bulk nc Al.

The effects of adding small amounts of Zn and conducting an aging treatment at elevated temperatures on the microstructure and tensile properties of low-Ag Sn–Ag–Cu alloys were investigated. The addition of Zn to Sn–Ag–Cu alloys inhibited the growth of intermetallic compounds. As the amount of Zn increased, the flow stress increased both before and after the aging treatment. In particular, the Sn–1Ag–0.3Cu–1Zn alloy exhibited the highest flow stress among all the examined alloys. Although the flow stress of the Sn–3Ag–0.5Cu alloy was originally higher than that of the Sn–1Ag–0.1Cu–0.4Zn and Sn–1Ag–0.3Cu–0.7Zn alloys, the flow stress of these two alloys was higher after aging for 500 h at 398 K than that of the Sn–3Ag–0.5Cu alloy. The addition of small amounts of Zn in Sn–Ag–Cu alloys suppressed the decline in the flow stress after the aging treatment.

13Þ½110� grain boundary were investigated in aluminum using the first-principles calculation. The relationship between the grain boundary segregation energies and the volume size factors were examined to understand the role of elastic strain energy in the grain boundary segregation energy. The grain boundary segregation energy decreased with the increase in the volume size factor. It has been explained that the solute atom larger in size than Al, which stores greater strain energy in the bulk, prefers the looser site at the grain boundary plane rather than in the bulk, to release the elastic strain energy. Furthermore, on the basis of the Rice­Wang model, the effects of grain boundary segregation on the embrittlement at the grain boundary were studied. The embrittlement potency indicates that the Mg, Na, Ca, K and Sr atoms serve as embrittler in the grain boundary. [doi:10.2320/matertrans.M2012108]

We applied first-principles calculations to study the relationship between the grain boundary energy (GBE) and grain boundary excess free volume (BFV) at the tilt grain boundaries in aluminum. GBE increased linearly as the grain BFV increased and the value of the proportionality constant between them, i, was 13.8GPa for aluminum. The grain boundary elastic energies calculated on the basis of first principles using a dummy boundary as well as the classical elasticity theory were close to the grain boundary energies. We examined the free volume in nanocrystalline and ultrafine-grained materials and proposed a method for estimating GBE using the density of nanocrystalline and ultrafinegrained materials with the proportionality constant i. The GBE of nanocrystalline aluminum fabricated by ball milling and subsequent consolidation was estimated to be comparable to or lesser than that in coarse-grained aluminum. [doi:10.2320/matertrans.L-M2013816]

Friction stir processing (FSP) is one of the severe plastic deformation processes that have been developed to improve the mechanical properties of both metals and alloys by producing an ultrafine-grained structure. In this study, it was used to realize the minimum grain size in Al–Mg alloys. The results indicate that the grain size in Al–Mg alloy decreases with increasing Mg content because of the influence of stacking fault energy in the Al–Mg alloy.

We examined the grain boundary energy (GBE) and grain boundary excess free volume (BFV) by applying the first-principles calculation for six [110] symmetric tilt grain boundaries in aluminum to clarify the origin of GBE. The GBE increased linearly as BFV increased. The elastic energy associated with BFV, namely the grain boundary elastic energy, was estimated as a function of BFV and the shear modulus. The grain boundary elastic energies were close in value to the GBEs. The charge density distributions indicated that the bonding in the grain boundary region is significantly different from the bonding in the bulk. The grain boundary elastic energies were 15–32% higher than the GBEs. This overestimation of the grain boundary elastic energy is caused by the characteristics of the electronic bonding at the grain boundary, which is different from bonding in the bulk. We have concluded that GBE results mainly from the grain boundary elastic energy.

Homogeneous bulk amorphous Ni-W alloy with thickness of more than 2 mm is fabricated by an electroforming process. By suppressing the side reaction and by preserving the mass balance between consumed ions by electrodeposition and supplemented ions by the solution of Ni and W anodes in the electroforming system, the standard deviation of W-concentration throughout the specimen is kept to 1.3 at%. As the result of micro-Vickers hardness tests, the standard deviation of micro-hardness decreases about 90% in bulk materials in comparison with thin-film materials fabricated by conventional electroforming process. This result indicates that it is important to minimize the fluctuation of Wconcentration in the specimen for obtaining the micrometer-scale high reliability of hardness. The compressive strength of bulk amorphous Ni-W alloy is about 2.7 GPa. High compressive strength of amorphous Ni-W alloy can be clearly shown. [doi:10.2320/matertrans.M2010288]

The dynamic friction coefficients of the commercial aluminum alloys (A2014, A2024 and A6061) and a superplastic IN9021 alloy were measured by ring-compression tests in a temperature range from 573 to 753K and a stain rate range from 1.0 × 10-2 to 4.0 × 100s-1. In general the friction coefficients (m values) increase slightly with increasing the compressive strains even under the well-lubricated test conditions. The m values of the Al-Cu based alloys, including A2014, A2024 and IN9021, were almost same at 0.2∼0.4 at the temperatures below 723K, but increased rapidly at the temperatures above 723K. On the other hand those of A6061 were almost constant at about 0.4 at the temperatures below 753K. The analysis based on the constitutive equation with consideration of the effect from an existence of the particles indicated that the dominant deformation mechanisms under the investigated conditions were dislocation creep for A2014, and were superplasticity for IN9021 except for the test condition at 573K with 1.0 × 10-1s-1. The m values of the IN9021 were lower than those of A2014, even if the flow stresses of IN9021 were higher than those of A2014. So it was concluded that the m value under a superplasticity region was lower than that under a dislocation creep region. It suggested that the superplastic forming had more benefits for the engineering applications.

The dynamic friction properties of the extruded AZ31 magnesium alloy with the initial average grain size of 15 μm were investigated by the ring compression test at 473 and 523 K and in a strain rate range from 1.0×10−2 to 3.0 s−1. Two types of the tool, WC-Co tool (WC) and WC-Co coated with diamond like carbon tool (DLC) were used. At 523 K, few differences in terms of the friction coefficient were observed due to the difference with or without DLC. At 473 K, the friction coefficient for the sample deformed by DLC tool was smaller than that done by WC tool. The investigation of the texture near the surface of the tested work pieces with different tools reveals that the integration degree of the grains within 10 degree from 〈0001〉 direction to compressive axis in the sample deformed by the DLC tool was smaller than that done by WC tool. It was concluded that the larger friction could enhance alignment of the planes perpendicular to the compressive direction to the basal plane even if under same testing condition.

We investigated the influence of bath composition on characteristics in an electrodeposited bulk nanocrystalline Ni (nc-Ni). This study was aim to establish the fabrication process of bulk nc-Ni with good tensile property. The bulk nc-Ni was electrpdeposited from a sulfate bath and a sulfamate bath. The nc-Ni was evaluated for microstructure and mechanical properties, such as microhardness, tensile strength. As a result, bulk nc-Ni obtained from a sulfamate bath exhibited enhanced tensile property (ultimate tensile strength of 1006 MPa and ductility of 8.8%) compared to that obtained from a sulfate bath. Dimple pattern was observed in fracture surface of bulk nc-Ni obtained from a sulfamate bath. However, dimple pattern and brittle fracture surface were observed in bulk nc-Ni obtained from a sulfate bath. We consider the ductility of electrodeposited nc-Ni was influenced by internal stress generated from electrodepostion. These experiments and analyses suggest that it is important to control internal stress on fabrication of bulk nc-Ni with high tensile strength and good ductility.

We investigate the energy of segregation of solute Ca at symmetric tilt grain boundary in aluminum from the first-principles calculations. As energy of segregation of Ca is negative, Ca atoms tend to segregate at the grain boundary. Furthermore, on basis of the Rice-Wang model, we study the effect of the segregation of Ca on the grain boundary embrittlement of aluminum. Our first-principles calculations of energies of segregation at grain boundary and free surface show that Ca behaves as embrittler.

Nanocrystalline materials with high strength have been reported in large numbers. In particular, there has been considerable research on electrodeposited nanocrystalline Ni (nc-Ni) and nc-Ni alloys. However, reported data vary widely especially in ductility. Therefore, it is necessary to obtain the true characteristic value of nc-Ni and nc-Ni alloys. In the present study, nc-Ni and nc-Ni-W was electrodeposited under different conditions in order to obtained bulk nc-Ni and nc-Ni-W with high tensile strength and good ductility. At first, bulk nc-Ni-W was fabricated using a sulfamate bath. Although the resulting bulk nc-Ni-W had inhomogeneous grain size and W-concentration, this sample exhibited plastic deformation behavior. Then, nc-Ni was fabiricated by four types of sulfamate baths. As a result, the nc-Ni obtained from a sulfamate bath containg added saccharine and 2-butyne-1,4-diol exhibited brittle behavior. In contrast, bulk nc-Ni obtained from sulfamate bath with a grain size of about 60 nm exhibited a tensile strength of about 1000 MPa and ductility of 8.8 %.

The dynamic friction properties of the extruded AZ31 magnesium alloy of the grain size of 20 mm were investigated by ring upsetting method test at 523, 548 and 573 K at strain rate of 1:0 � 10 � 2 s � 1 , where all the initial testing conditions were the climb-controlled dislocation creep. The MoS2 lubricant maintained lower dynamically friction coefficient (m value) than the oil lubricant. The difference in m values between machined surface and polished surface was unclear. The m values for WC-Co and diamond like carbon (DLC) tools were similar in MoS2 lubricant. The m values for DLC tool were lower than those for the WC-Co tool in the oil lubricant. The extruded direction influenced to the friction properties. The aspect ratio of the inner diameter on 90 � to extruded direction after testing was almost isotropic; on the other hand, the anisotropy occurred on 0� and 45� . The extent of anisotropy at 548 K was the highest, although the lower temperature, the higher the critical shear stress of non-basal plane. The condition at 523 K, where the fine grain sizes less than 3 mm could be obtained by dynamic recrystallization during deformation, is suitable temperature to make superplasticity at the given strain rate. [doi:10.2320/matertrans.P-M2010811]

The effect of the coating materials of the tools on the dynamic friction characteristics and microstructural evolution with straining was investigated by the ring-typed compressive test at a temperature of 473 K and at a strain rate of 10 � 2 s � 1 in the extruded AZ31 magnesium alloy with an average grain size of 15 mm. The values of the dynamically recrystallized grain size in the samples compressed up to about 45% by using the WC-Co tools with and without the DLC coating were 3.8 mm and 4.8 mm, respectively. The dominant deformation mechanism under all the testing condition for the present alloy was the climb-controlled dislocation creep. The dynamic friction coefficient, m value, for the sample compressed by the WC-Co tool was higher than that done by the DLC tool, even if though there was identical tendency in stress level. The integration degree of the grains within 10 degree from h0001i direction to compressive axis in the sample compressed by the WC-Co tool was larger than that done by the DLC tool. It was concluded that the higher m value could enhance an alignment of the planes perpendicular to the compressive direction to the basal plane even if under same testing condition. [doi:10.2320/matertrans.MBW200914]

Sn-based alloys with high creep resistance are required for soldering applications. This paper describes the effect of solid solution strengthening on the creep resistance of Sn-Zn alloys. The maximum solubility limit of Zn is 0.34 mass% in Sn. The creep behaviors of Sn, Sn0.1 mass%Zn and Sn-0.4 mass%Zn were examined at 298 and 398 K under constant strain rates ranging from 1 � 10 � 4 to 1 � 10 � 2 s � 1 . The creep resistance of Sn was improved significantly by the addition of a small amount of Zn owing to the solid solution strengthening. The creep resistance of Sn-0.4 mass%Zn was at the same level as that of Sn-37 mass%Pb. We obtained a stress exponent of about 7 and an activation energy of 41–45 kJ/mol, which indicates that the creep behavior was climb-controlled dislocation creep controlled by pipe diffusion. The finding that a small addition of Zn improves the creep resistance is useful for developing new Pb-free solders. [doi:10.2320/matertrans.MJ201023]

We investigated the effect of pre-introduced shear bands direction on compressive deformation behavior in Zr55Al10Ni5Cu30 bulk metallic glass. The compressive deformation behavior varied with the difference of the direction of pre-introduced shear bands with respect to loading direction. The specimen in which shear bands were introduced at an angle of 45 degree to the loading direction showed largest plastic strain. This large plasticity was achieved due to the activity of pre-introduced shear bands and formation of multiple shear bands. The direction of preintroduced shear bands is an important factor to improve the plasticity in bulk metallic glasses. [doi:10.2320/matertrans.MAW200920]

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