Showing papers on "Alloy published in 2001"

Rapidly Solidified Powder Metallurgy Mg97Zn1Y2Alloys with Excellent Tensile Yield Strength above 600 MPa

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.

Strengthening Mechanisms of Creep Resistant Tempered Martensitic Steel

Abstract: The creep deformation resistance and rupture life of high Cr ferritic steel with a tempered martensitic lath structure are critically reviewed on the basis of experimental data. Special attention is directed to the following three subjects: creep mechanism of the ferritic steel, its alloy design for further strengthening, and loss of its creep rupture strength after long-term use. The high Cr ferritic steel is characterized by its fine subgrain structure with a high density of free dislocations within the subgrains. The dislocation substructure is the most densely distributed obstacle to dislocation motion in the steel. Its recovery controls creep rate and rupture life at elevated temperatures. Improvement of creep strength of the steel requires a fine subgrain structure with a high density of free dislocations. A sufficient number of pinning particles (MX particles in subgrain interior and M 23 C 6 particles on sub-boundaries) are necessary to cancel a large driving force for recovery due to the high dislocation density. Coarsening and agglomeration of the pinning particles have to be delayed by an appropriate alloy design of the steel. Creep rupture strength of the high Cr ferritic steel decreases quickly after long-term use. A significant improvement of creep rupture strength can be achieved if we can prevent the loss of rupture strength. In the steel tempered at high temperature, enhanced recovery of the subgrain structure along grain boundaries is the cause of the premature failure and the consequent loss of rupture strength. However, the scenario is not always applicable. Further studies are needed to solve this important problem of high Cr ferritic steel. MX particles are necessary to retain a fine subgrain structure and to achieve the excellent creep strength of the high Cr ferritic steel. Strengthening mechanism of the MX particles is another important problem left unsolved.

Improving the mechanical properties of magnesium and a magnesium alloy through severe plastic deformation

Abstract: Pure Mg and Mg alloys generally exhibit only limited ductilities at ambient temperatures. Experiments were conducted to evaluate the potential for improving the mechanical properties of pure Mg and an Mg–0.9% Al alloy at room temperature by subjecting these materials to severe plastic deformation through the procedure of equal-channel angular pressing (ECAP). It is shown that ECAP may be applied successfully to these materials at elevated temperatures and this leads to grain refinement due to the occurrence of recrystallization during the pressing process and to significant improvements in the strength and ductility of these materials. Since these improvements are apparent after only a single pass through the ECAP die, it is concluded that the introduction of ECAP provides a simple and effective procedure for improving the ambient temperature mechanical properties of materials, such as hcp metals, where the measured ductilities are generally limited.

High temperature resistant part, made of single-crystal or polycrystalline nickel-base superalloy

Abstract: Component made from a nickel-based super alloy contains (in wt.%) 9-11 chromium (Cr),3-5 tungsten (W), 0.5-2.5 molybdenum (Mo), 3-3.5 aluminium (Al), 3-5 titanium (Ti), 3-7 tantalum (Ta), 0-12 cobalt (Co), 0-1 niobium (Nb), 0-2 hafnium (Hf), 0-1 zirconium (Zr), 0-0.05 boron (B), 0-0.2 carbon (C), 1-5 rhenium (Re), 0.1-5 ruthenium (Ru), balance nickel (Ni) and impurities. Preferably the alloy contains at least 2 wt.% Re and a maximum of 3 wt.% Ru. The component is a monocrystalline structure having an isotropic distribution of the orientation of the grain structure.

Copper and Copper Alloys

Abstract: This book is a comprehensive guide to the selection and applications of copper and copper alloys, which constitute one of the largest and most diverse families of engineering materials. The handbook includes all of the essential information contained in the 20-volume ASM Handbook series, as well as important reference information and data from a wide variety of ASM publications and industry sources. In addition to extensive property data for wrought, cast, and powder-metallurgy products, this book provides practical information on the casting, forming, joining, machining, and finishing of copper alloys. The principles of physical metallurgy, including the relationships among heat treatment, structure, and properties, are also examined. Specifications for copper and its alloys are cross referenced in useful tabular form. Recent alloy developments - such as low-lead free-machining alloys, high-strength alloys with resistance to corrosion in hot 'sour' environments, and thermally stable, high-conductivity electronic packaging materials-are also reviewed. Contents: Metallurgy, alloys, and applications Fabrication and finishing Metallurgy, microstructures, and phase diagrams: Metallography and microstructures of copper alloys and beryllium-copper alloys Solidification structures Phase diagrams. Engineering properties and service characteristics Appendices.

Metalorganic vapor-phase epitaxial growth and photoluminescent properties of Zn1−xMgxO(0⩽x⩽0.49) thin films

Abstract: High-quality Zn1−xMgxO(0.00⩽x⩽0.49) thin films were epitaxially grown at 500–650 °C on Al2O3(00⋅1) substrates using metalorganic vapor-phase epitaxy. By increasing the Mg content in the films up to 49 at. %, the c-axis constant of the films decreased from 5.21 to 5.14 A and no significant phase separation was observed as determined by x-ray diffraction measurements. Furthermore, the near-band-edge emission peak position showed blueshifts of 100, 440, and 685 meV at Mg content levels of 9, 29, and 49 at. %, respectively. Photoluminescent properties of the alloy films are also discussed.

Novel hexagonal structure and ultrahigh strength of magnesium solid solution in the Mg–Zn–Y system

Abstract: A magnesium (Mg) solid solution with a long periodic hexagonal structure was found in a Mg97Zn1Y2 (at.%) alloy in a bulk form prepared by warm extrusion of atomized powders at 573 K. The novel structure has an ABACAB-type six layered packing with lattice parameters of a = 0.322 nm and c = 3 × 0.521 nm. The Mg solid solution has fine grain sizes of 100 to 150 nm and contains 0.78 at.% Zn and 1.82 at.% Y. In addition, cubic Mg24Y5 particles with a size of about 7 nm are dispersed at small volume fractions of less than 10% in the Mg matrix. The specific density (ρ) of the extruded bulk Mg–Zn–Y alloy was 1.84 Mg/m3. The tensile yield strength (σy) and elongation (δ) are 610 MPa and 5%, respectively, at room temperature, and the specific yield strength defined by the ratio of σy to ρ is as high as 3.3 × 105 Nm/kg. High σy values exceeding 400 MPa are also maintained at temperatures up to 473 K. It is noticed that the σy levels are 2.5 to 5 times higher than those for conventional high-strength type Mg-based alloys. The Mg-based alloy also exhibits a high-strain-rate superplasticity with large δ of 700 to 800% at high strain rates of 0.1 to 0.2 s−1 and 623 K. The excellent mechanical properties are due to the combination of the fine grain size, new long periodic hexagonal solid solution containing Y and Zn, and dispersion of fine Mg24Y5 particles. The new Mg-based alloy is expected to be used in many fields.

Pb-free solders for flip-chip interconnects

Abstract: A variety of lead-free solder alloys were studied for use as flip-chip interconnects including Sn-3.5Ag, Sn-0.7Cu, Sn-3.8Ag-0.7Cu, and eutectic Sn-37Pb as a baseline. The reaction behavior and reliability of these solders were determined in a flip-chip configuration using a variety of under-bump metallurgies (TiW/Cu, electrolytic nickel, and electroless Ni-P/Au). The solder micro-structure and intermetallic reaction products and kinetics were determined. The Sn-0.7Cu solder has a large grain structure and the Sn-3.5Ag and Sn-3.8Ag-0.7Cu have a fine lamellar two-phase structure of tin and Ag3Sn. The intermetallic compounds were similar for all the lead-free alloys. On Ni, Ni3Sn4 formed and on copper, Cu6Sn5Cu3Sn formed. During reflow, the intermetallic growth rate was faster for the lead-free alloys, compared to eutectic tin-lead. In solidstate aging, however, the interfacial intermetallic compounds grew faster with the tinlead solder than for the lead-free alloys. The reliability tests performed included shear strength and thermomechanical fatigue. The lower strength Sn-0.7Cu alloy also had the best thermomechanical fatigue behavior. Failures occurred near the solder/intermetallic interface for all the alloys except Sn-0.7Cu, which deformed by grain sliding and failed in the center of the joint. Based on this study, the optimal solder alloy for flip-chip applications is identified as eutectic Sn-0.7Cu.

Mechanical behavior and microstructure of a thermally stable bulk nanostructured Al alloy

Abstract: A commercial aluminum alloy, 5083, was processed using a cryomilling synthesis approach to produce powders with a nanostructured grain size. The powders were subsequently degassed, hot isostatically pressed, and extruded. The grain size at each processing step was measured utilizing both X-ray diffraction and transmission electron microscopy (TEM). The mechanical properties of the n-5083 extruded material were determined utilizing ASTM E8-93, Standard Test Methods for Tension Testing of Metallic Materials. This processing technique was found to produce a thermally stable nanostructured aluminum alloy which maintained an average grain size of 30 to 35 nm through several processing steps up to 0.61 T mp . The thermal stability was attributed to Zener pinning of the grain boundaries by AIN and Al2O3 particles and solute drag of numerous atomic species. The nanostructured 5083 was found to have a 30 pct increase in yield strength and ultimate strength over the strongest commercially available form of 5083, with no corresponding decrease in elongation. The enhanced ductility is attributed to the presence of a few large, single-crystal aluminum grains acting as crack-blunting objects.

Bulk Amorphous Alloys

Abstract: This chapter aims to review our recent research results on new bulk amorphous alloys. The main topics are the following: (1) the finding of new amorphous alloys with high glass-forming ability in a number of alloy systems; (2) the mechanism for achieving high glass-forming ability; (3) the fundamental properties of the new amorphous alloys; (4) successful examples of producing bulk amorphous alloys by different techniques of water quenching, metallic mold casting, arc melting and unidirectional zone melting, etc.; (5) the high tensile strength, low Young’s modulus, and high impact fracture energy of nonferrous metal-based bulk amorphous alloys; (6) the soft magnetic properties of Fe- and Co-based bulk amorphous alloys; (7) hard magnetic properties of Nd- and Pr-based bulk amorphous alloys; (8) the viscous flow and microformability of bulk amorphous alloys in a supercooled liquid region, and (9) future aspects of applications. These new results enable eliminating of the limitation of sample shape which has prevented the development of amorphous alloys as engineering materials. They are expected to give rise to a new era of amorphous alloys.

Alloying: Understanding the Basics

Abstract: Alloying: Understanding the Basics, is a comprehensive guide to the influence of alloy additions on mechanical properties, physical properties, corrosion and chemical behavior, and processing and manufacturing characteristics. The coverage considers alloying, to include any addition of an element or compound that interacts with a base metal to influence properties. Thus, the book addresses the beneficial effects of major alloy additions, inoculants, dopants, grain refiners, and other elements that have been deliberately added to improve performance, as well as the detrimental effects of minor elements or residual (tramp) elements included in charge materials, or that result from improper melting or refining techniques. The content is presented in a concise, user-friendly format. Numerous figures and tables are provided. The coverage has been weighted to provide the most detailed information on the most industrially important materials. Contents include: Principles of alloying; Cast irons; Carbon and alloy steels; High-strength low-alloy steels; Tool steels; Maraging and high-fracture-toughness steels; Austenitic manganese steels; Stainless steels; Superalloys; Refractory metal alloys; Ordered intermetallics (nickel, iron, and titanium aluminides); Aluminum alloys; Titanium alloys; Magnesium alloys; Copper alloys; Nickel alloys; Zinc alloys; Tin alloys; Lead alloys; Cobalt alloys; Noble metal alloys; Special-purpose materials (cemented carbides, cermets, low-expansion alloys, electrical contact alloys, magnetic alloys); Index.

Nonlinear macroscopic polarization in III-V nitride alloys

Abstract: We study the dependence of macroscopic polarization on composition and strain in wurtzite III-V nitride ternary alloys using ab initio density-functional techniques. The spontaneous polarization is characterized by a large bowing, strongly dependent on the alloy microscopic structure. The bowing is due to the different response of the bulk binaries to hydrostatic pressure and to internal strain effects (bond alternation). Disorder effects are instead minor. Deviations from parabolicity (simple bowing) are of order 10% in the most extreme case of AlInN alloys, much less at all other compositions. Piezoelectric polarization is also strongly nonlinear. At variance with the spontaneous component, this behavior is independent of microscopic alloy structure or disorder effects, and due entirely to the nonlinear strain dependence of the bulk piezoelectric response. It is thus possible to predict the piezoelectric polarization for any alloy composition using the piezoelectricity of the parent binaries.

Microstructural factors governing hardness in friction-stir welds of solid-solution-hardened Al alloys

Abstract: Microstructural factors governing hardness in friction-stir welds of the solid-solution-hardened Al alloys 1080 and 5083 were examined by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effect of grain boundary on the hardness was examined in an Al alloy 1080 which did not contain any second-phase particles. The weld of Al alloy 1080 had a slightly greater hardness in the stir zone than the base material. The maximum hardness was located in the thermomechanically affected zone (TMAZ). The stir zone consisted of recrystallized fine grains, while the TMAZ had a recovered grain structure. The increase in hardness in the stir zone can be explained by the Hall-Petch relationship. On the other hand, the hardness profiles in the weld of Al alloy 5083 were roughly homogeneous. Friction-stir welding created the fine recrystallized grains in the stir zone and recovered grains in the TMAZ in the weld of this alloy. The stir zone and the TMAZ had slightly higher dislocation densities than the base material. Many small Al6(Mn,Fe) particles were detected in all the grains of the weld. The hardness profiles could not be explained by the Hall-Petch relationship, but rather by Orowan hardening. The results of the present study suggest that the hardness profile is mainly affected by the distribution of small particles in friction-stir welds of Al alloys containing many such particles.

Enhanced plastic strain in Zr-based bulk amorphous alloys

Abstract: Bulk metallic glasses subjected to quasistatic uniaxial compression at room temperature typically display large elastic strains but limited plastic flow of 0--2% before failure. We have developed an amorphous alloy, ${\mathrm{Zr}}_{59}{\mathrm{Ta}}_{5}{\mathrm{Cu}}_{18}{\mathrm{Ni}}_{8}{\mathrm{Al}}_{10},$ which experiences an average macroscopic plastic strain of 4.5% before failure. The as-cast alloy shows no evidence for the presence of crystalline phases, and displays a distinct glass transition temperature and a wide supercooled liquid region. Upon compression beyond the yield point, the alloy develops shear bands which show a pronounced tendency for branching. We propose that this shear band branching distributes the plastic strain on the shear band, thereby suppressing crack initiation and allowing the material to experience a large macroscopic plastic strain before failure.

AC Impedance Spectroscopy in Characterizing Time-Dependent Corrosion of AZ91 and AM50 Magnesium Alloys Characterization with Respect to Their Microstructures

Abstract: The corrosion behavior of as-cast magnesium alloys (AM50, AZ91, and AZ91Si) was investigated in a 0.1 M sodium sulfate solution at the corrosion potential (E corr ) using electrochemical impedance spectroscopy. Transmission electron microscopy was used to analyze the corrosion product layer, and phase shifting interferometric microscopy was carried out to characterize the reactivity of intermetallic particles. Due to its microstructure, the AM50 alloy presented uniform corrosion during immersion, whereas corrosion of the AZ91 alloys began in the grain body and progressively spread to the eutectic areas. For the AZ91 alloys, the dissolution of the α-eutectic phase led to a strong aluminum enrichment of the corrosion product layer and, when a threshold was reached in the level of Al 2 O 3 in the magnesium oxide (or hydroxide) layer a change of phenomenology occurred in the impedance diagrams. In addition, electrochemical results revealed that an increase of silicon concentration for the AZ91 alloys decreased the corrosion resistance, This was attributed to an increase of the number of Mg 2 Si particles, accelerating the dissolution n of eutectic areas.

Nanostructure formation on the surface of railway tracks

Abstract: The microstructure of the surface layer of railway tracks is investigated. It is shown that the surface layer of the rail transforms during exploitation into a nanocrystalline Fe–C alloy. The mechanism of the nanostructure formation is discussed. It is shown that the transformation of pearlite to the nanostructured Fe–C alloy layer is caused by the heavy plastic deformation at the wheel–rail contact zone. The transformation of the microstructure of the surface may take place at rail–wheel contact temperatures less than 230°C and its mechanism is similar to that taking place during mechanical alloying.

Spatial correlations in GaInAsN alloys and their effects on band-gap enhancement and electron localization.

Abstract: In contrast to pseudobinary alloys, the relative number of bonds in quaternary alloys cannot be determined uniquely from the composition. Indeed, we do not know if the ${\mathrm{Ga}}_{0.5}{\mathrm{In}}_{0.5}{\mathrm{As}}_{0.5}{\mathrm{N}}_{0.5}$ alloy should be thought of as $\mathrm{InAs}+\mathrm{GaN}$ or as $\mathrm{InN}+\mathrm{GaAs}$. We study the distribution of bonds using Monte Carlo simulation and find that the number of In-N and Ga-As bonds increases relative to random alloys. This quaternary-unique short range order affects the band structure: we calculate a blueshift of the band gap and predict the emergence of a broadband tail of localized states around the conduction band minimum.

Effects of pitting corrosion on the fatigue behavior of aluminum alloy 7075-T6: modeling and experimental studies

Abstract: The effects of pitting corrosion on the fatigue behavior of bare 7075-T6 aluminum alloy were investigated. Pitting corrosion decreased the fatigue lives by a factor of about 6 to 8. The fatigue lives were also calculated assuming an equivalent initial flaw corresponding to pits of average and maximum dimensions. The measured fatigue lives generally agreed with the predictions using the average rather than the maximum pit size as the initial crack size. This result could be explained by the pit size distributions offering a significantly larger population of pits near the average size. This work has demonstrated the promise of standardized spray tests for obtaining quantitative measures of corrosion that can be used as inputs in analytical models for fatigue life prediction for evaluating integrity of aircraft structures.

Precipitation of Al3Sc in binary Al–Sc alloys

Abstract: The precipitation of coherent Al 3 Sc particles in Al–Sc alloys containing 0.06, 0.12 and 0.18 at.% Sc was investigated. The alloys were aged at 350°C for times up to 4663 h and the kinetics of particle growth, the particle size distributions and the evolution of particle morphology were measured and evaluated using transmission electron microscopy. Al 3 Sc precipitates did not nucleate homogeneously in the most dilute alloy; this result was unexpected because 0.06 at.% Sc exceeds the solubility limit at 350°C. Persistent dislocation networks were observed in the alloy containing 0.12 at.% Sc under normal solution treatment conditions (e.g. 1 h at 600°C) and the dislocations acted as heterogeneous nucleation sites. The dislocations were ultimately eliminated using a very long solution treatment time of ∼70 h near the melting temperature. Aging of both of the more concentrated alloys produced coherent precipitates. At short aging times the particles in the alloy containing 0.12% Sc were cauliflower-shaped and became spherical at longer times. At 4663 h some of the precipitates in this alloy were cuboidal, while others appear to have become semicoherent. The precipitates in this alloy were highly resistant to coarsening, and their size distributions were for the most part narrower than that predicted by the classical theory of Lifshitz, Slezov and Wagner (the LSW theory). The shapes of the precipitates in the alloy containing 0.18% Sc evolved from spherical to cuboidal with increasing aging time. The kinetics of growth of the precipitates in this alloy were consistent with the predictions of the LSW theory, the average size, 〈 r 〉, increasing with aging time, t , according to an equation of the type 〈 r 〉 3 ≃ kt . The experimentally measured rate constant, k , was in very good agreement with that calculated theoretically for this alloy.