Showing papers in "Materials Transactions in 2001"
TL;DR: In this paper, the RS P/M alloys exhibited excellent elevated-temperature yield strength that was 510 MPa at 423 K. The specific tensile yield strength was four times as high as that of a commercial AZ91-T6 alloy, and was higher than those of conventional titanium (Ti-6Al-4V) and aluminum (7075-T 6) alloys.
Abstract: Nanocrystalline magnesium alloys having high tensile strength, high elevated-temperature tensile strength, high-strain-rate superplasticity and high thermal stability have been developed in Mg 97 Zn 1 Y 2 (at% I alloy by rapidly solidified powder metallurgy (RS P/M) processing. The tensile yield strength and elongation that were dependent on the consolidation temperature were in the ranges of 480 to 610MPa and 5 to 16%, respectively. Young's modulus of the RS P/M alloy was 45 GPa. The specific tensile yield strength was four times as high as that of a commercial AZ91-T6 alloy, and was higher than those of conventional titanium (Ti-6Al-4V) and aluminum (7075-T6) alloys. The RS P/M alloys exhibited excellent elevated-temperature yield strength that was 510 MPa at 423 K. The RS P/M alloy also exhibited high-strain-rate superplasticity at a wide strain-rate range from I × 10 - to I × 10 0 s -1 and at a low temperature of 623 K. It is expected that the Mg 97 Zn 1 Y 2 RS P/M alloy can he applied in some fields that requires simultaneously the high specific strength at ambient and elevated temperatures and high workability.
908 citations
TL;DR: In this article, the authors studied the mechanical behavior of Zr 40 Ti 14 Ni 10 Cu 12 Be 24 through uniaxial compression and nanoindentation experiments and found that shear is more likely caused by changes in viscosity associated with increased free volume in the shear bands.
Abstract: We have studied the mechanical behavior of Zr 40 Ti 14 Ni 10 Cu 12 Be 24 through uniaxial compression and nanoindentation experiments. Quantitative measurements of the serrated plastic flow observed during uniaxial compression are reported. These data are used to predict temperature increases in single shear bands due to local adiabatic heating caused by the work done on the sample as shear propagates progressively across the sample. Since the predicted temperature increases are insufficient to reach the glass transition temperature, it is unlikely that localized heating is the primary cause of flow localization. Instead, localization of shear is more likely caused by changes in viscosity associated with increased free volume in the shear bands. The orientation of the shear bands in compression tests and an indentation size effect for the onset of plastic flow in nanoindentation both point to increased free volume as the cause of localization.
354 citations
TL;DR: In this article, the deformation twinning results in a twin mechanism of DRX, which processes strain softening at an initial stage of deformation at high strains, followed by strain hardening.
Abstract: Microstructural evolution of commercial grade pure magnesium was studied during plastic deformation by torsion under high pressure at ambient temperature and by compression at temperatures ranging from 293 to 773 K and at a strain rate of 3 x 10 -3 s -1 . Grain refinement takes place by operation of dynamic recrystallization (DRX) at all examined temperatures. The mechanisms of DRX change with temperature and strain. As a result, unusual dependencies of recrystallized grain size against strain and recrystallized volume fraction against temperature are observed. In the temperature interval of 293-623 K the deformation twinning results in twin mechanism of DRX, which processes strain softening at an initial stage of deformation. At T ≤ 423 K the other mechanism of low temperature DRX takes place at high strains. Such DRX is accompanied by strain hardening. In contrast, continuous DRX (CDRX) yielding a steady-state flow operates frequently at temperatures ranging from 523 to 773 K. CDRX occurs mainly in overall recrystallization process at elevated temperatures. Discontinuous DRX (DDRX) takes place by bulging of boundaries of coarse recrystallized grains evolved from twins at T = 723 K. DDRX occurs repetitively, but gives an insignificant contribution into total recrystallization process. The present results suggest that the mechanisms of DRX and the deformation mechanisms are closely related.
288 citations
TL;DR: In this article, the individual contributions of Gadolinium and Yttrium to age hardening and high temperature strength of magnesium alloys containing both elements were investigated using alloys with different Gd:Y mole ratios of 1:0, 3:1 1:1, 1:3 and 0:1 with a constant Y+Gd content of 2.75 mol%.
Abstract: The individual contributions of Gadolinium and Yttrium to age hardening and high temperature strength of magnesium alloys containing both elements are investigated using alloys containing different Gd:Y mole ratios of 1:0, 3:1 1:1, 1:3 and 0:1 with a constant Y+Gd content of 2.75 mol%. All investigated alloys exhibit remarkable age hardening by precipitation of β phase with DO 19 crystal structure and β' phase with bco crystal structure even at aging temperatures higher than 200°C. Both precipitates are observed in peak-aged specimens. The precipitates contributing to age hardening are fine and their amount increases as Gd content increases, and this results in increased peak hardness, tensile strength and 0.2% proof stress but decreased elongation. On the other hand, higher Y content increases the elongation of the alloys but results in decreased strength.
272 citations
TL;DR: In this paper, the phase equilibria, the martensitic and magnetic phase transformations in the β (B2) phase region of the Co-Ni-Ga and CoNi-Al systems have been investigated.
Abstract: The phase equilibria, the martensitic and magnetic phase transformations in the β (B2) phase region of the Co-Ni-Ga and Co-Ni-Al systems have been investigated. It is shown that some compositions in the range Co-(15-30)at%Ni-30 at%Ga and Co-(30-40)at%Ni-30 at%Al exhibit both the β to β' (L1 0 ) thermoelastic martensitic transformation and the para/ferromagnetic transition. Some of these undergo the martensitic transformation from the paramagnetic β to the ferromagnetic β'. The introduction of a small amount of the y phase into the β phase by heat treatment, based on the results of the β/γ phase equilibria study in these systems, is shown to significantly improve the ductility in both alloy systems. The new β single phase and β + y two-phase ferromagnetic shape memory alloys (FSMAs) of the Co-Ni-Ga and Co-Ni-Al systems hold great promise as new smart materials.
262 citations
TL;DR: In this article, high temperature creep properties of Mg-Gd-Y-Zr alloys have been evaluated quantitatively under a stress range of 50-100 MPa and a temperature range of 250-300°C.
Abstract: High temperature creep properties of Mg-Gd-Y-Zr alloys have been evaluated quantitatively. Creep test was carried out under a stress range of 50-100 MPa and a temperature range of 250-300°C. Within the limits of the creep test conditions used in this study, the activation energy for creep of investigated alloys is in the range of 160-240 kJ/mol, and the stress exponent is in the range of 3.7-5.2. Accordingly, the creep mechanism of the investigated alloys is considered to be power law creep. Creep resistance of the investigated alloys depends on chemical composition, it improves with increase in gadolinium content, which implies an increase in the quantity of precipitates. The creep resistance of the high gadolinium-containing alloys exceeds that of the existing heat resistant magnesium alloy, WE54A alloy.
210 citations
TL;DR: In this paper, the chemical behavior of pure pure magnesium (3N-Mg) in Hank's solution (HBSS) for various holding time (25-700 h).
Abstract: A new artificial bone concept by magnesium alloys is proposed to think much importance on its homogenization with a surrounding natural hard and soft tissue. Magnesium is an essential element for human body, so that magnesium hone implants can be expected to be toxicity free even though magnesium dissolved into human soft tissue. In addition, magnesium base artificial bone has vivo-adaptively to growing bone cells once vivo-coating is formed on the surface of magnesium in the inside of soft tissue. In the present paper, its chemical behavior in Hank's solution (HBSS (+)) is described to simulate biochemical reactions of magnesium in the human body. An effect of heat treatment of magnesium on its chemical behavior is also investigated. Specimens of 10 x 20 x 2 mm 3 were used for examining chemical behaviors of commercial grade pure magnesium (3N-Mg) in a HBSS (+) for various holding time (25-700 h). Specific mass gain of each specimen was measured, the surface microstructure was observed by a scanning electron microscope, identification of reaction products were examined by x-ray diffraction measurements, Chemical compositions of reaction products were also analyzed by an energy dispersion x-ray spectrometry, Mass change of heat-treated 3N-Mg, which was heat-treated at 803 K for 90 ks increased with immersing time in HBSS (+) though that of other heat-treated 3N-Mg unstably decreased in HBSS (+). Magnesium reacted with HBSS (+) and then a magnesium apatite was precipitated on the heat-treated 3N-Mg specimen surface. The magnesium apatite should he described as (Ca 0.86 Mg 0.14 ) 10 (PO 4 ) 6 (OH) 2 .
182 citations
TL;DR: In this article, cyclic deformation of ultra-fine grain (UFG) materials processed by severe plastic deformation is reviewed in light of recent experimental results and common concepts of fatigue.
Abstract: Cyclic deformation of ultra-fine grain (UFG) materials processed by severe plastic deformation is reviewed in light of recent experimental results and common concepts of fatigue. High strength bulk metals with a characteristic structural element size of 200–300 nm were obtained through the so-called equal-channel angular pressing (ECAP) technology. Fatigue properties are discussed in terms of stress-controlled and strain-controlled fatigue. Enhancement of fatigue life under constant stress amplitude is emphasized in comparison with some shortening in fatigue life under constant plastic strain amplitude. Fine structure and surface morphology of post-fatigued materials are characterized on different scale levels to account for the fatigue behaviour observed. Mechanisms of fatigue in ECA-processed materials are discussed within frameworks of a simple one-parameter model of dislocation kinetics.
163 citations
TL;DR: In this paper, a phenomenological constitutive equation was developed in order to provide a guideline for the control of the grain size of hot deformed AZ61 alloy, and grain refinement was observed during deformation.
Abstract: Dynamic recrystallization (DRX) behavior was systematically examined in two commercial Mg-Al-Zn alloys in order to clarify the relationship between deformation conditions and the resulting microstructure. The materials were deformed by upset forging at temperatures ranging from 473 to 673 K at an initial strain rate of 3.3 x 10 -2 s -1 . Grain refinement was observed during deformation. It was found that the dynamically recrystallized grain size decreases with an increasing Zener-Hollomon parameter and/or a decreasing initial grain size. A phenomenological constitutive equation was developed in order to provide a guideline for the control of the grain size of hot deformed AZ61 alloy.
158 citations
TL;DR: In this paper, a new Cu-based bulk glassy alloy with high tensile fracture strength above 2000 MPa was formed in a (Cu 0.6 Zr 0.3 Ti 0.1 ) 98 Y 2 alloy by copper mold casting.
Abstract: A new Cu-based bulk glassy alloy with high tensile fracture strength above 2000 MPa was formed in a (Cu 0.6 Zr 0.3 Ti 0.1 ) 98 Y 2 alloy by copper mold casting. The maximum sample thickness for glass formation is 4 mm for Cu 60 Zr 30 Ti 10 and increases to 5 mm for the 2%Y-containing alloy. The addition of 2%Y also causes an increase in the supercooled liquid region (ΔT x = T x - T g ) from 36 to 50 K and in the reduced glass transition temperature (T g /T l ) from 0.62 to 0.63. The increase in the glass-forming ability (GFA) is presumably due to the increase in ΔT x and Tg/T. The bulk glassy (Cu 0.6 Zr 0.3 Ti 0.1 ) 98 Y 2 alloy exhibits good mechanical properties, i.e., 1780 MPa for yield strength, 2030 MPa for tensile fracture strength, 2100 MPa for compressive fracture strength, 1.7% for elastic elongation and 1.5% for plastic elongation. The distinct plastic elongation indicates good ductile nature of the Cu-based bulk glassy alloy. The success of synthesizing the new Cu-based bulk glassy alloy with high GFA and good mechanical properties allows us to expect the extension of application fields as a new engineering material.
147 citations
TL;DR: In this paper, the tensile properties at room temperature of Mg-9Al-1Zn were compared with those processed by equal channel angular (ECA) extrusion, and the effect of the grain size rapidly decreased with testing temperature.
Abstract: The tensile properties at room temperature ∼ 573 K of Mg-9Al-1Zn processed by normal extrusion were compared with those processed by equal channel angular (ECA) extrusion. The strength at room temperature was strongly affected by the grain size. However, the effect of the grain size rapidly decreased with testing temperature. At room temperature, the normal extruded alloy showed the stronger grain size dependence of 0.2% proof stress than the ECA extruded alloy because of the microscopic orientation effect. Also, the grain size dependence was reduced when grain boundaries were in a non-equilibrium state.
TL;DR: In this article, an improvement of tensile mechanical properties under dynamic loading has been demonstrated for a pure magnesium and a ZK60 magnesium alloy, which exhibits yielding at a dynamic strain rate of 1.8 x 10 3 s -1.
Abstract: Magnesium alloys are generally brittle owing to their HCP structure. In this study, improvement of tensile mechanical properties under dynamic loading has been demonstrated for a pure magnesium and a ZK60 magnesium alloy. The solution-treated ZK60 alloy exhibits yielding at a dynamic strain rate of 1.8 x 10 3 s -1 , which was not observed in a pure magnesium. The yield stress of the ZK60 alloy increases at the dynamic strain rate with a similar slope of Hall-Petch relation at a quasi-static strain rate. Enhancement of ductility can he also achieved by refining grain structures for the ZK60 alloy. The high ductility of the fine-grained alloy is due to the absence of macroscopic cracking at mechanical twin boundaries. It is found that the absorption energy per weight in the fine-grained ZK60 is twice higher than that of high strength aluminum alloys.
TL;DR: In this article, the authors deal with some general aspects of magnesium alloy development and casting as well as some other production technologies for magnesium alloys with improved properties and for several applications.
Abstract: Among the light metal alloys, magnesium is the lightest structural material with a density of 1.74 g/cm 3 and many attractive physical and mechanical properties combined with processing advantages. Therefore, it represents a very attractive material for a large amount of applications from main user automotive industry up to other industry fields like sport, robotic and electronic industry. But the usage of magnesium alloys in more complex applications is limited by insufficient properties regarding the ductility, corrosion and creep resistance. Additionally, the high reactivity of magnesium alloys leads to an increased tendency of contamination. In this regard, the paper deals with some general aspects of magnesium alloy development and casting as well as some other production technologies for magnesium alloys with improved properties and for several applications. An emphasis is put on new magnesium-lithium alloy systems with lower density, improved ductility and corrosion resistance. The basic component of metallurgical processing is a magnesium-suitable furnace system which is designed modularly with universal, adaptable components and automatic pressure metering technology. It is used in a wide range of casting processes like chill casting, cold chamber die casting, continuous casting and break-mould casting. Further applications are methods of rapid solidification technology. In the powder metallurgy and spray casting a microstructure with line and homogeneous phase distribution is generated. Based on the represented processing technology new magnesium alloy systems with lower density, improved ductility and corrosion resistance will he shown. A special peculiarity of magnesium alloys is their application in the medicine sector where they are used as implant materials for surgery.
TL;DR: In this paper, the authors examined the hydrogen flow in amorphous alloys and found that hydrogen flow increased with an increase of the temperature or the difference in the square-root of hydrogen pressures across the membrane.
Abstract: We prepared the melt-spun (Ni0:6Nb0:4)100� xZrx (x ¼ 0 to 40 at%) and other amorphous alloy membranes and examined the permeation of hydrogen through those alloy membranes. The interatomic spacing in the Ni–Nb–Zr amorphous structure increased with increasing Zr content. The crystallization temperature of the Ni–Nb–Zr amorphous alloys decreased with increasing Zr content. The hydrogen flow increased with an increase of the temperature or the difference in the square-roots of hydrogen pressures across the membrane, � ffiffiffi p . At relatively higher temperature up to 673 K or at relatively higher hydrogen pressure difference, � ffiffiffi p up to 550 Pa 1=2 , the hydrogen flow was more strictly
TL;DR: In this article, the effects of annealing and changes in stress state on the toughness of Zr-Ti-Ni-Cu-Be alloy have been determined in amorphous state, both notched and fatigue precracked specimens have been tested.
Abstract: The effects of annealing and changes in stress state on the toughness of both 4 mm thick and 7 mm thick plates of a Zr-Ti-Ni-Cu-Be alloy have been determined In the amorphous state, both notched and fatigue precracked specimens have been tested The effects of changing the notch root radius from a fatigue precrack to that of a blunt notch on the fracture toughness are dramatic The toughness increases from approximately 179 ± 18 MPa√m in the fatigue precracked specimens to in excess of 130 MPa√m in the notched specimens These results are compared to similar tests on a range of structural materials, including aluminum alloys, steels, Ti alloys, and metal matrix composites The increased toughness obtained by increasing the notch root radius in this bulk metallic glass far exceeds that typically observed in other structural materials Possible reasons for this are presented In addition, the effects of changes in loading rate and various annealing treatments on the toughness are presented and rationalized via both crack path and fracture surface observations Annealing of this bulk metallic glass at temperatures below Tg produces increases in strength/hardness, rapid decreases in toughness, and a corresponding change in the fracture morphology Changes in loading rate did not have a significant effect on the toughness for either notched or fatigue precracked specimens
TL;DR: A new Co-based bulk glassy alloy Co 43 Fe 20 Ta 5.5 B 31.5 exhibiting a large supercooled liquid region before crystallization and good soft magnetic properties was synthesized by the copper mold casting method.
Abstract: A new Co-based bulk glassy alloy Co 43 Fe 20 Ta 5.5 B 31.5 exhibiting a large supercooled liquid region before crystallization and good soft magnetic properties was synthesized by the copper mold casting method. The glass transition temperature (T g ) is 910K and the supercooled liquid region (ΔT x ) reaches 70 K. The high thermal stability of the supercooled liquid enabled us to produce bulk glassy alloys with diameters up to 2 mm. These bulk glassy alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.5 T, very low coercivity of 0.9 A/m and very high permeability of 40000 at 1 kHz. It is noticed that the diameter of 2 mm is the largest value for Co-based bulk glassy alloys reported up to now. The success of forming the large-scale size Co-based bulk glassy alloy with high thermal stability of supercooled liquid and good soft magnetic properties is encouraging for future uses of bulk amorphous soft magnetic materials.
TL;DR: The Platform Science and Technology for Advanced Magnesium Alloys (PSME-MAG) project as mentioned in this paper was a four-year project with financial support from the Ministry of Education, Science, Sports and Culture of Japan.
Abstract: The four year project on Platform Science and Technology for Advanced Magnesium Alloys started in September 1999 with financial support from the Ministry of Education, Science, Sports and Culture of Japan. The project members consisting mainly of Professors in Japanese Universities are going to make various efforts for the advancement of studies on magnesium alloys. The background and concept of the research project is described, and then the contents and practical activities of the group are briefly explained.
TL;DR: In this article, a new class of magnesium alloys containing alkaline earth elements such as Ca and Sr, which offers excellent creep performance is discussed, and an example of a rare-earth containing magnesium diecasting alloy with good creep resistance at 150°C is the Mg-4Al-2 rare earth alloy AE42.
Abstract: The automotive use of magnesium is currently restricted to low-temperature structural components. Its use in elevated-temperature structural components such as transmission and engine parts requires the development of cost-effective alloys that can meet the elevated-temperature (150-175°C) performance requirements of these components for strength and creep resistance. Rare-earth additions such as Ce Nd, Pr to Mg are known to improve the creep performance. An example of a rare-earth containing magnesium diecasting alloy with good creep resistance at 150°C is the Mg-4Al-2 rare-earth alloy AE42. This paper discusses a new class of magnesium alloys containing alkaline earth elements such as Ca and Sr, which offers excellent creep performance.
TL;DR: In this article, the authors classified the Fe-based glassy alloys into five groups, i.e., (1) Fe-(Al, Ga)-(P, C, B), (2) (Nd, Pr)-Fe(Al, Si), (3) Fe(Zr, Hf, Nb)-B, (4) Fe-Co-Ln-B, and (5)Fe-(Cr, Mo)-B-C.
Abstract: Ferromagnetic bulk glassy alloys were synthesized in a variety of alloy systems by the copper mold casting process for the last five years after 1995. Their typical alloy systems are classified into five groups, i.e., (1) Fe-(Al, Ga)-(P, C, B) and Fe-Ga-(P, C, B), (2) (Nd, Pr)-Fe-(Al, Si), (3) Fe-(Zr,Hf,Nb)-B, (4) Fe-Co-Ln-B, and (5) Fe-(Cr, Mo)-B-C. The Fe-based glassy alloys exhibit a large supercooled liquid region exceeding 50 K before crystallization and the largest value reaches approximately 100 K. The maximum sample thickness of glass formation in the alloy systems belonging to the groups (1) to (5) is about 3 mm, 12 mm, 6 mm, 1 mm and 3 mm, respectively. These bulk glassy alloys exhibit good soft magnetic properties with a maximum saturation magnetization of 1.3 T and low coercive forces below 5 A/m except for hard magnetic properties only for the Nd- or Pr-based alloys. In addition, the application of the consolidation technique using the viscous flow phenomenon to the Fe-(Al, Ga)-(P,C, B) alloys caused the formation of fully dense bulk glassy alloys with rather good soft magnetic properties, e.g., 1.2T for saturation magnetization, 10 A/m for coercive force, 9000 for maximum permeability and 0.1 1 W/kg at 50 Hz for core loss. The combination of good magnetic properties, high glass-forming ability and good workability into a bulk form is promising the future development as a new type of magnetic material.
TL;DR: In this paper, Fe-based glassy alloys of Fe 45 Cr 16 Mo 16 C 18 B 5, Fe 45Cr 16 Mo 14 Nb 2 C18 B 5 and Fe 45cr 16Mo 14 Ta 2 C 18B 5 were synthesized and shown to have high corrosion resistance in 1, 6 and 12 mol.
Abstract: New Fe-based glassy alloys of Fe 45 Cr 16 Mo 16 C 18 B 5 , Fe 45 Cr 16 Mo 14 Nb 2 C 18 B 5 and Fe 45 Cr 16 Mo 14 Ta 2 C 18 B 5 were synthesized. They exhibit a large supercooled liquid region (ΔT x ) reaching 58 K before crystallization and high reduced glass transition temperatures (T g /T m ) up to 0.62. These values indicate that these Fe-based alloys have a glass-forming ability which is high enough to enable the formation of bulk glassy alloys. The Fe-based glassy alloys have high corrosion resistance in 1, 6 and 12 mol.L -1 HCl solutions al room temperature. The corrosion rates are in the range of 10 -4 -10 -2 mm.y -1 . The glassy alloys are spontaneously passivated in 1 and 6 mol.L -1 HCl solutions with wide passive region and low passive current density in the range of 10 -2 -10 0 A.m -2 . No pitting corrosion is seen even in 12 mol.L -1 HCl solution. The addition of Nb or Ta to the glassy alloys is effective on enhancing the corrosion resistance.
TL;DR: In this paper, a new manufacturing process for Zr-based bulk glassy alloys has been developed to increase the coefficient of restitution at the impact between a golf club and a golf ball.
Abstract: Bulk glassy alloys have high tensile strength, while the Young's modulus is lower by 20 to 40% than those for the corresponding crystalline alloys. These unique mechanical properties are effective to increase the coefficient of restitution at the impact between a golf club and a golf ball. Bulk glassy alloys have in general been produced by the copper mold casting and die casting methods. We have developed a new manufacturing process for Zr-based bulk glassy alloys. By the use of the new process, we have succeeded in producing a glassy Zr-Al-Ni-Cu alloy in a shell shape with a dimension of about 90 x 40 mm and a thickness of 3 mm for glassy driver golf clubs. It exhibits excellent mechanical properties such as tensile strength of 1700MPa, Young's modulus of 81 GPa, and impact fracture toughness of 130 kJ/m 2 . These properties are suitable for the material for driver golf club heads. The glassy driver golf club with the shell shape in the impact region was confirmed to have a high coefficient of restitution.
TL;DR: In this article, a new Cu-based bulk glassy alloys with high glass-forming ability and good mechanical properties were formed in Cu-Zr-Ti-Be system.
Abstract: New Cu-based bulk glassy alloys with high glass-forming ability and good mechanical properties were formed in Cu-Zr-Ti-Be system. The glass transition temperature (T g ), supercooled liquid region defined by the difference between crystallization temperature (T x ) and Tg, ΔT x (=T x -T g ) and reduced glass transition temperature (T g /T l ) are 728 K, 50 K and 0.64, respectively, for the (Cu 0.6 Zr 0.3 Ti 0.1 ) 92.5 Be 7.5 and 720 K, 42 K and 0.64, respectively, for the Cu 54 Zr 27 Ti 9 Be 10 alloy. The use of the 7.5%Be and 10%Be alloys has enabled us to form glassy alloy rods with diameters up to 5 mm. The bulk glassy 10%Be alloy exhibits high tensile fracture strength of 2450 MPa and Vickers hardness of 710, in combination with Young's modulus of 146 GPa, compressive fracture strength of 2500MPa and compressive elongation of 3.5%. The tensile strength level is the highest among all bulk metallic glasses and hence the new Cu-based bulk glassy alloys have significant importance in basic science and engineering aspects.
TL;DR: In this article, the effect of adding Ag up to 1'mass% on the microstructural and mechanical properties of Sn-Cu eutectic solder alloy was examined, and the DSC experiment revealed the presence of four endothermic reactions on heating for Sn-cu-Ag alloys.
Abstract: The effect of adding Ag up to 1 mass% on the microstructural and mechanical properties of Sn–Cu eutectic solder alloy was examined. Without Ag, primary β–Sn grains are surrounded by the eutectic network band of Cu6Sn5 needle precipitates/β–Sn. With increasing Ag content, the primary β–Sn grain size and the eutectic network size become finer. In the eutectic band fine Ag3Sn particles appear in addition to Cu6Sn5 precipitates. The DSC experiment revealed the presence of four endothermic reactions on heating for Sn–Cu–Ag alloys; the two peaks near 217°C correspond to the Sn–Cu–Ag ternary eutectic melting reaction and those at 223–225°C/224–226°C are for Sn–Cu binary melting. The 0.2% proof stress and tensile strength decrease with the addition of 0.1 mass%Ag and then gradually increase up to 1 mass%Ag. Even with 1% Ag, they are less than the values for a Sn–0.7Cu binary alloy. In contrast, elongation increases with increasing Ag content up to 1%. Thus, the addition of Ag to Sn–0.7Cu alloy can effectively improve its ductility. The strain rate dependence of 0.2% proof stress of Sn–0.7Cu–0.5Ag is similar to that of Sn–Ag eutectic alloy but is different from that of Sn–Cu eutectic alloy. A small amount of added Ag results in a change of the deformation mechanism of Sn–Cu alloy.
TL;DR: In this paper, a cold rolling treatment leading to the rolled structure with high-density slip bands was performed, and the first slip bands were found to slant significantly with increasing reduction ratio in thickness.
Abstract: With the aim of improving ductility and plasticity of a Zr 55 Cu 30 Al 10 Ni 5 bulk glassy alloy, a cold rolling treatment leading to the rolled structure with high-density slip bands was performed. A number of slip bands were introduced along the maximum shear stress plane by cold rolling, and the first slip bands were found to slant significantly with increasing reduction ratio in thickness. At the critical reduction ratios, the second slip bands were introduced at a reduction ratio of 30%, followed by the third slip bands at a reduction ratio of 60%. Mechanical properties of the rolled samples were examined by bending test and Charpy impact test. The maximum bend deflection value before failure increased with an increase of reduction ratio, indicating that the cold rolling improves the plasticity of the bulk glassy alloy. Since the Charpy impact value depends on the rolling direction, we selected an optimum rolling direction in which the maximum Charpy impact value is obtained. The control of the rolling direction causes an increase in the Charpy impact value by 36% as compared with the unrolled alloy. Consequently, the cold rolling process is concluded to be a valuable method for improving the ductility and plasticity of the bulk glassy alloy.
TL;DR: In this article, the amorphous-forming composition range (AFCR) was calculated for 338 ternary AMO-alloyed systems on the basis of the database given by Miedema's model in order to examine the applicability of the model and to determine the dominant factors influencing the ability to form an amomorphous phase.
Abstract: The amorphous-forming composition range (AFCR) was calculated for 338 ternary amorphous alloy systems on the basis of the database given by Miedema's model in order to examine the applicability of the model, to analyze the stability of the amorphous phase, and to determine the dominant factors influencing the ability to form an amorphous phase. The mixing enthalpies of amorphous and solid solution phases were expressed as a function of alloy compositions on the basis of chemical enthalpy. Based on the Eshelby and Friedel model, an elastic enthalpy term was added to the model for the solid solution. Furthermore, an average melting temperature of the constituent elements was added to the model as the topological enthalpy in an amorphous phase. An amorphous phase was assumed to have been formed at the composition where the enthalpy of an amorphous phase was smaller than that of a solid solution. The AFCR was calculated for 335 systems except for the Al-Cu-Fe, Al-Mo-Si and Au-Ge-Si systems. The calculated results are in agreement with the experimental data for Cu-Ni- and Al-Ti-based systems. For typical amorphous alloy systems exemplified by the Zr-, La-, Fe- and Mg-based systems, it was recognized that the calculated AFCR had been overestimated as a result of the model being simplified. We have also shown that the elastic enthalpy term arising in a solid solution phase stabilizes the amorphous phase, and the stabilization mechanism is particularly notable in Mg-based amorphous alloy systems. Short-range order plays an important role in the formation of Al-, Fe- and Pd-metalloid based systems. The following factors have a great influence on amorphous-forming ability: (1) three empirical rules for the achievement of high AFA, (2) melting temperature and viscosity at the melting temperature, (3) elastic enthalpy arising in a solid solution, and (4) short-range order observed in an amorphous phase. The importance of the latter two factors was only identified as a result of the present study.
TL;DR: In this article, the properties of powder compacts were mainly subject to the behavior of oxide film between the powder particles and the interfaces between Al powder particles were investigated using high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy.
Abstract: Pure Al powder was sintered by spark plasma sintering (SPS) process at various sintering temperatures and loading pressures. The density, electrical resistivity, tensile properties and microstructure of powder compacts were investigated. The powder compacts with the similar properties as base aluminum metal was obtained at sintering temperature above 873 K, loading pressure above 23.5 MPa. For the powder compacts with the similar density but with the large difference in the electrical resistivity and tensile properties, the interfaces between Al powder particles were investigated using high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). Two types of interfaces, with metal/metal bonding and metal/oxide film layer/metal bonding, were observed in Al powder compacts. The properties of powder compacts were mainly subject to the behavior of oxide film between the powder particles.
TL;DR: In this paper, the surface modification with sodium hydrogen carbonate made it possible to apply metal magnesium in biomedical, dental, and other industrial usage, and the surface structure of needle-shaped crystals was observed by scanning electron microscopy (SEM).
Abstract: The present study was carried out to improve the corrosion resistance of pure magnesium in Hank's Balanced Salt Solution (HBSS) through the surface modification. Three kinds of alkaline compounds, such as sodium hydrogen carbonate, sodium carbonate, and lithium hydroxide, were used for treatment. Only magnesium treated with aqueous sodium hydrogen carbonate solution gave a good corrosion resistance in HBSS solution at 25°C up to 75 days, while almost no effect in sodium carbonate and lithium hydroxide. It was likely that hydrogen carbonate ions were essential for the surface improvement of magnesium. X-ray diffraction patterns of modified magnesium showed new peaks of magnesium carbonate and others on the surface. New surface structure of needle-shaped crystals was observed by scanning electron microscopy (SEM). Both elemental mapping, and energy dispersive (EDX) techniques in SEM showed the precipitation of calcium magnesium phosphate (low crystallinity whitlockite:(Ca,Mg)3(PO 4 ) 2 ) on the surface of magnesium specimen. It could be concluded that surface modification with sodium hydrogen carbonate made it possible to apply metal magnesium in biomedical, dental, and other industrial usage.
TL;DR: The intrinsic threshold behavior of fatigue cracks and the disappearance of any cyclic plastic deformation below a threshold value can be understood by taking into account the discreteness of plasticity with recourse to discrete dislocation models as discussed by the authors.
Abstract: The intrinsic threshold behavior of fatigue cracks and the disappearance of any cyclic plastic deformation below a threshold value can be understood by taking into account the discreteness of plasticity with recourse to discrete dislocation models. The aim of this paper is to document the progress in the discrete dislocation modelling within the past twenty years and the resulting increase in the understanding of fatigue cracks. The problems addressed are (1) the nature of the intrinsic fatigue threshold, (2) the influence of microstructure and/or of the mean stress level on the crack tip deformation and (3) the physical reason for the minimum striation spacing at small stress intensity ranges. A particular purpose of this paper is to compare the different dislocation models proposed in the literature in order to differentiate aspects of fatigue crack growth that do and do not depend on modelling and on microstructural details.
TL;DR: In this article, an equiaxed ultra-fine grained structure of ∼ 0.3 µm was obtained in a commercial 5083 Al alloy with an initial grain size of ∼ 200 µm using the equal channel angular pressing (ECAP) technique.
Abstract: An ultra-fine grained (UFG) structure was introduced in a commercial 5083 Al alloy with an initial grain size of ∼ 200 \\micron using the equal channel angular pressing (ECAP) technique. ECAP was successfully conducted at 473 K on the same sample up to a total of 8 pressings through the die such that the sample was rotated 180° around its longitudinal axis between pressings. The microstructure was reasonably homogeneous after a single pressing and consisted of parallel bands of elongated substructure having an average width of 0.2 \\micron and an average length of 0.8 \\micron. An equiaxed ultra-fine grained structure of ∼ 0.3 \\micron was obtained in the present alloy after 4 pressings. The ultra-fine grains were thermally stable at 523 K . The yield stress of as-received 5083 Al alloy was 129 MPa, whereas it increased to 249 MPa after a single pressing and finally became 290 MPa after 8 pressings, which was superior to that of a conventional 5083-H321 Al alloy. In addition, in this study, the feasibility of low temperature superplasticity of a UFG 5083 Al alloy was examined. It was found that the 5083 Al alloy with a grain size of ∼ 0.3 \\micron exhibited a superplastic-like behavior with elongation to failure in excess of 200% below 523 K.