Showing papers on "Alloy published in 1990"

Gas-dynamic spraying method for applying a coating

Abstract: A cold gas-dynamic spraying method for applying a coating to an article introduces into a gas particles of a powder of a metal, alloy, polymer or mechanical mixture of a metal and an alloy, the particles having a particle size of from about 1 to about 50 microns The gas and particles are formed into a supersonic jet having a temperature considerably below a fusing temperature of the powder material and a velocity of from about 300 to about 1,200 m/sec The jet is directed against an article of a metal, alloy or dielectric, thereby coating the article with the particles

Static compression of iron to 300 GPa and Fe0.8Ni0.2 alloy to 260 GPa: Implications for composition of the core

Abstract: Results are reported on a room temperature static compression study of iron and the Fe(0.8)Ni(0.2) alloy to above 260 GPa, which provide direct pressure-volume measurements on geophysically important materials at the conditions close to those at the inner core boundary. The diffraction patterns obtained by XRD indicate that pure iron remains in the hcp structure to 304 GPa and that Fe(0.8)Ni(0.2) is stable to at least 255 GPa. The results of this study, in conjunction with work at higher temperatures, will make it possible to address directly the question of the composition of the inner core with a level of certainty that were previously applicable only to the mantle.

Transition metal-based hydrogen electrodes in alkaline solution — electrocatalysis on nickel based binary alloy coatings

Abstract: Nickel-molybdenum, nickel-zinc, nickel-cobalt, nickel-tungsten, nickel-iron and nickel chromium binary alloy codeposits, obtained through electrodeposition methods on mild steel strips, have been characterized with the objective of qualitatively comparing and assessing their electrocatalytic activities as hydrogen electrodes in alkaline solution. It has been concluded that their electrocatalytic effects for the hydrogen evolution reaction rank in the following order: Ni-Mo > Ni-Zn (after leaching Zn in KOH) > Ni-Co > Ni-W > Ni-Fe > Ni-Cr > Ni plated steel. Further investigations on the alloy electrocatalysts have revealed that the cathodic overpotential contribution to the electrolysis voltage can be brought down by 0.3 V when compared with conventional cathodes. The best and most stable hydrogen evolving cathode, based on nickel-molybdenum alloy, exhibited an overpotential of about 0.18 V for over 1500 h of continuous electrolysis in 6m KOH at 300 mA cm−2 and 353 K. The salient features of the coatings, such as physical characteristics, chemical composition, crystal structure of the alloy phases and the varying effects of the catalytic activation method were analysed with a view to correlating the micro-structural characteristics of the coatings with the hydrogen adsorption process. The stability under open-circuit conditions, the tolerance to electrochemical corrosion and the long term stability of nickel-molybdenum alloy cathodes were very encouraging. An attempt to identify the pathway for the hydrogen evolution reaction on these alloy coatings was made, in view of the very low apparent activation energy values obtained experimentally.

Brittle fracture and grain boundary chemistry of microalloyed NiAl

Abstract: The room-temperature tensile properties, fracture mode, and grain boundary chemistry of undoped stoichiometric NiAl, as well as NiAl doped with boron, carbon, and beryllium, have been investigated, Pure, stoichiometric NiAl fractures with limited tensile ductility in a predominantly intergranular manner. Auger analyses revealed that the grain boundaries in NiAl are extremely clean and free of any segregated impurities, indicating that they are intrinsically brittle. Boron, when added to stoichiometric NiAl at a bulk level of 300 wt. ppm, segregates to the grain boundaries and suppresses intergranular fracture. However, there is no attendant improvement in tensile ductility because boron is an extremely potent solid solution strengthener in NiAl, more than doubling its yield strength. As a result, any potential benefit of improving grain boundary strength is more than offset by the increase in yield strength. Unlike boron, both carbon (300 ppm) and beryllium (500 ppm) are ineffective in suppressing intergranular fracture in NiAl, and Auger analyses of the C-doped alloy revealed that carbon did not affect the fracture mode because it did not segregate to the grain boundaries. Although neither beryllium nor carbon suppressed grain boundary fracture, their effects on the tensile ductility of NiAl were quite different: the ductility of the Be-doped alloy was higher than that of the B-doped alloy because beryllium, unlike boron, has a rather modest strengthening effect in NiAl, whereas the C-doped alloy was brittle like the B-doped alloy, because carbon is a potent solid solution strengthener, just like boron. These observations were rationalized by considering a hard-sphere model for interstitial and substitutional sites in NiAl. It was concluded that boron and carbon occupy interstitial sites, whereas beryllium dissolves substitutionally. In all the alloys that were investigated, the Ni and Al contents of the grain boundaries were not significantly different from the bulk levels, and no evidence was found for B–Ni cosegregation.

Some observations on the wetting and bonding of nitride ceramics

Abstract: Several series of experiments have been conducted to gain information about the wettability of AlN, BN, Si3N4 and two sialon ceramics by potential braze materials. It was possible to achieve wetting of all five ceramics using aluminium, copper-titanium alloys, and a Ag-28Cu-2Ti alloy. Wetting by aluminium and the Ag-28Cu-2Ti alloy was usually good. Both wetting and non-wetting alloys containing titanium reacted to form TiN and it is argued that the achievement of wettability is associated with a certain degree of hypostoichiometry. While aluminium should also have reacted, no clear evidence was obtained. In supplementary experiments it was found that bonds formed by brazing with aluminium at 1000 °C could have shear strengths as great as 60MPa. Although the experimental work was preliminary in nature, it suggested that good brazing systems could be developed.

The influence of small amounts of added elements on various anode performance characteristics for LaNi2.5Co2.5-based alloys

Abstract: The addition of small amounts of elements such as silicon, aluminium and titanium to LaNi2.5Co2.5 greatly influenced anode performance characteristics such as usable temperature range, capacity and its decay rate during repeated cycles, rate capability, low temperature dischargeability and self-discharge rate. The capacity decay was suppressed by the addition of silicon, but the rate capability decreased and the self-discharge rate increased. The alloy containing titanium exhibited a much longer cycle life, but much lower storage capacity and worse low temperature dischargeability. The addition of aluminium was very useful for improving the usable temperature range, cycle life and charge retention, and it did not cause too great a decrease in capacity and/or increase in overpotentials.

Oxidation Effects on Porcelain-Titanium Interface Reactions and Bond Strength

Abstract: Titanium is strong, resists corrosion and has a low density and excellent biocompatibility. Conventional ceramic-metal restorations have been extensively used in dentistry because of their esthetic appearance and good mechanical properties. This study investigates oxidation effects on the porcelain-titanium interface reactions and bond strength. Pure titanium was treated in a porcelain furnace at temperatures of 600 to 1000°C under either vacuum or air. X-ray diffraction analysis of the surface of pure titanium revealed that the relative peak intensity of α-Ti decreased and that of TiO2 increased, with increasing firing temperature. The Vickers hardness number of titanium increased with temperature especially over 900°C, and was harder in air than in vacuum. The tension-shear bond strength of the porcelain-titanium system was the highest in the green stage and lowest after 900°C treatment. Metallographic microscopy of the porcelain-titanium interface revealed a thick band-like zone in the sample treated over 900°C. The excess thick layer of TiO2 apparently weakened the bond strength of porcelain-titanium. Unlike the conventional ceramic-gold alloy system the recommended degassing procedure was not suitable for porcelain-pure titanium restoration.

Corrosion Mechanisms for Iron and Low Alloy Steels Exposed to the Atmosphere

Abstract: Despite extensive study over the years, the chemical processes involved in the atmospheric corrosion of iron and its alloys remain poorly understood. Most conceptual studies have ignored the chemical influence of the trace anions (Cl−,, , , etc.) present in the atmosphere and in precipitation. This review, presented from the perspective of atmospheric chemistry and mineralogy, provides an analysis of rust layer formation, evolution, morphology, and composition, together with information on iron‐containing minerals and other crystalline structures that are likely to be present. The chemical reactions involved in the formation of these constituents during the corrosion process are then presented. The reactions are not spatially homogeneous, but favor pits, voids, and crevices in the metal surface. It is demonstrated that (i) the pH of the moisture on the surface is crucial to the corrosion process, since it controls the dissolution of the passive oxyhydroxide surface; the pH is largely controlled by atmospheric and dissolved in the moisture or by fog or rain deposited on the surface; (ii) the extant data suggest that the rate of iron oxyhydroxide formation is slow; hence, the presence of reactive anions generally results in their blending into mixed hydroxy‐anion products; (iii) the interactive chemistry of readily available hydrogen peroxide and bisulfite ion in the aqueous surface film can either enhance or impede the rate of corrosion; (iv) photon‐driven reactions can promote the corrosion of iron and its alloys. This analysis unifies the analytical information, as well as the data on kinetic processes, and provides the basis for a full understanding of the atmospheric corrosion of iron and low alloy steels.

Relationship between crystallization process and magnetic properties of Fe‐(Cu‐Nb)‐Si‐B amorphous alloys

Abstract: The effect of Cu and/or Nb addition on crystallization processes and soft magnetic properties for Fe‐Si‐B alloys has been investigated. For Fe‐Si‐B, Fe‐Cu‐Si‐B, and Fe‐Nb‐Si‐B alloys annealed at various temperatures, the effective permeabilities were very low and decreased considerably as they crystallized, while for Fe‐Cu‐Nb‐Si‐B alloy annealed at a temperature above Tx , a very good soft magnetic property was obtained. From DTA analysis of Fe‐Cu‐Nb‐Si‐B alloys, it became clear that the combined addition of Cu and Nb expanded largely the temperature range over 100 °C where a single phase of α‐Fe solid solution can exist. Above 580 °C, the second crystalline phase such as Fe2 B and some unidentified phases other than the α‐Fe phase precipitated, and soft magnetic properties deteriorated rapidly. It is concluded that the combined addition of Cu and Nb makes the α‐Fe single phase stable in a broad temperature range, which is considered to be the necessary condition for the superior soft magnetic properties.

Microscopic examination of the interface region in 6061-Al/SiC composites reinforced with as-received and oxidized SiC particles

Abstract: Aluminum (6061) matrix composites reinforced with different SiC particles were processed. Black SiC particles were used in their as-received form or after artificial oxidation, leading to a 50-nm-thick SiO2 layer surrounding the SiC particles. The manufacturing route used was the compocasting technique, which allows maintenance of the semisolid slurry at relatively low temperatures (<650 °C) during the incorporation of the reinforcement. Before squeeze casting, the liquid alloy is held at 700 °C for 5 to 10 minutes. The interface between the aluminum matrix and SiC was characterized by transmission electron microscopy (TEM). Results show that no reaction takes place during compocasting between the as-received SiC particles and the molten aluminum. This is a consequence of the low temperatures and short holding times in the liquid state of the 6061 alloy, possible with this process. Prolonged holding at 800 °C of this material leads to extensive formation of A14C3. In the case of artificially oxidized SiC particles, the SiO2 layer surrounding the SiC particles reacts with the molten Al-Mg-Si alloy to produce MgAl2O4. However, the amount of Mg from the base alloy lost to form this spinel phase is not sufficient to prevent age hardening of the material.

Pit Morphology of Aluminum Alloy and Silicon Carbide/Aluminum Alloy Metal Matrix Composites

Abstract: Pit morphology of Al 5456 (UNS A95456), Al 6061 (UNS A96061), SiCw/Al 5456, and SiCw/Al 6061 is studied in order to compare pitting processes of SiCw/Al metal matrix composites with that of corresponding unreinforced alloys. Work on anodized samples of Al 6061 and SiCw/Al 6061 is also included. Pits on the composites are significantly more numerous, shallow, and widespread than on the monolithic materials. Studies of pit structure suggest there are two stages in pit development. The first involves the initial dissolution of metal atoms and opening of the pit, and the second involves pit enlargement or growth. For both materials, pits initiate at secondary particles within the metal matrix. In the case of Al 5456 and SiCw/Al 5456, it is shown that these particles are intermetallic phases composed of alloying elements Mg, Cr, Mn, and Al, as well as, Fe, which is an impurity of the metal. Under equivalent conditions of preparation and processing, a greater number of intermetallic phases form in the ...

Tensile Properties of Short Fiber-Reinforced SiC/AI Composites: Part I. Effects of Matrix Precipitates

Abstract: The tensile behavior of aluminum matrix composites reinforced with 8 and 20 pet SiC whiskers or paniculate was characterized. Two matrix alloys were employed, a solution-hardened Al-Mg alloy (5456) and a precipitation-hardened Al-Cu-Mg alloy (2124). The precipitation-hardened alloy was aged to develop a variety of precipitate microstructures. It was found that additions of SiC caused monotonie increases in the elastic modulus, 0.2 pct offset yield stress, work-hardening rate, and ultimate tensile stress. The proportional limit, however, was found to first decrease and then increase with SiC content. Whiskers caused a greater increase in the longitudinal elastic modulus than particles. For the 2124 alloy, it was found that the proportional limit could be varied between 60 and 650 MPa by changing the precipitate microstructure, while changes in the SiC content had much smaller effects. These observations are discussed in relation to current theories of the strengthening of short fiber composites, with primary emphasis being placed on the effects of SiC additions on the elastic modulus and the work-hardening rate.

The influence of aluminium content to the stacking fault energy in Fe-Mn-Al-C alloy system

Abstract: Four Fe-30Mn-0.9C-XAl alloys are employed to investigate the influence of aluminium content to the stacking fault energy in Fe-Mn-Al-C alloy system. The range of aluminium content is zero to 8.47 wt%. Based on the thermodynamic model, the stacking fault energy can be obtained through calculation. Increasing the aluminium content will make the stacking fault energy of Fe-30Mn-0.9C based alloys increase at 300 K.

Mechanical stress as a function of temperature for aluminum alloy films

Abstract: Aluminum alloys have virtually replaced aluminum thin films for interconnections in very large‐scale integration because of their improved reliability. Mechanical stress is a problem of growing importance in these interconnections. Stress as a function of temperature was measured for thin aluminum films on an oxidized silicon substrate and several aluminum alloys and layered films consisting of silicon, copper, titanium, tungsten, tantalum, vanadium, and TiSi2. Solid‐state reactions of the aluminum with the additives and with the ambient during thermal cycling will occur, and depending on what compounds have formed and at what temperature, this will determine the morphology and reliability of the metallization. The measurement technique, based on determination of wafer curvature with a laser scanning device, directly measures the total film stress and reflectivity in situ as a function of temperature during thermal cycling. Changes in stress were detected when film composition and structure varied and wer...

Hydrogen assisted cracking in C-Mn and low alloy steel weldments

Abstract: Hydrogen assisted cracking (cold cracking) in the heat affected zones of welded C-Mn and low alloy steels and their weld metals is discussed with regard to hydrogen diffusion, residual stress, and microstructure. The features of the hydrogen-assisted cracking tests so far proposed are reviewed and correlations between results by different cracking tests are discussed. The effects of steel chemical composition, including microalloying elements and impurities, are discussed, and the adequateness of various carbon equivalents proposed, depending on the type of steel, is described. On the basis of factors influencing hydrogen cracking, methods to determine safe welding conditions are discussed.

Chromium addition and environmental embrittlement in Fe3Al

Abstract: Iron aluminides based on Fe[sub 3]Al afford excellent oxidation properties at relatively low cost, making them candidates for use as structural material in corrosive environments. Recently, efforts have been devoted to understanding and improving their ductility through control of grain structure, alloy additions and material processing. Studies at this laboratory have shown that the ambient temperature ductility can be increased significantly by additions of up to 6% Cr. This increase in ductility was earlier attributed to increased cleavage strength, easier cross slip due to lower antiphase boundary (APB) energy, and solid softening. Very recent studies of FeAl and Fe[sub 3]Al in various tensile testing environments have indicated that both alloy systems are relatively more ductile at room temperature when tested in vacuum or dry oxygen. Ductilities of 12--18% were attained in both iron aluminide systems in an oxygen pressure of 6.7 [times] 10[sup 4] Pa, while only 2--4% ductility was achieved in normal laboratory air. It seems appropriate to reexamine the mechanism by which chromium produces improved ductility at room temperature in laboratory air and to correlate it with the environmental effects on mechanical properties. In the current investigation, the authors have evaluated room temperature tensile properties of the binary more » alloy (Fe-28Al, at.%) and ternary alloy containing chromium (Fe-28Al-4Cr) as a function of surface condition and heat treatment. The results indicate that, although chromium may affect cleavage strength and APB energies, its most significant effect on room temperature ductility is to modify the protective surface oxide, resulting in a minimization of environmental embrittlement. « less

A comparison of the solidification behavior of INCOLOY 909 and INCONEL 718

Abstract: The solidification behavior of two commercial aerospace superalloys, INCOLOY 909 and INCONEL 718, has been examined. Specifically, differential thermal analysis (DTA) revealed that INCOLOY 909 terminates solidification with the formation of a single minor constituent at ≈1198 °C. INCONEL 718 terminates solidification with the formation of two minor constituents, at ≈1257 °C and ~1185 °C, respectively. Metallography performed on the DTA samples confirmed that a single minor constituent was present in INCOLOY 909 while two minor constituents were present in INCONEL 718. Differential thermal analysis samples were also examined by electron probe microanalysis to reveal the patterns of elemental segregation. Arc welds of these alloys were examined by transmission and analytical electron microscopy (TEM and AEM). It was observed that the arc welds of INCOLOY 909 contained only a y/Laves eutectic-like constituent, while the arc welds of INCONEL 718 contained both y/Laves and γ/MC eutectic-like constituents. Compositional analyses of these minor phases revealed that all were enriched in Nb relative to the bulk alloy. The Laves phases were also enriched in Si relative to the bulk alloy concentration. Comparisons of the observed solidification sequences in these alloys with other Nb-bearing austenitic matrix alloys are made.

Superplastic behavior of a fine-grained two-phase Mg-9wt.%Li alloy

Abstract: A two-phase Mg-9Li alloy (where the composition is in weight per cent) was made fine grained (d≈6–35 μm) by extensive cold rolling into foils and press bonding the foils at low homologous temperatures. The material exhibited superplastic properties in the temperature range 423–523 K ((0.49–0.61)T/Tm) with elongations to failure as high as 460%. The creep rate was determined to be inversely proportional to approximately the square of grain size and to the second power of stress. The activation energy for superplastic flow was equal to that for lattice diffusion in the major b.c.c. β phase. The Mg-9Li laminate alloy was found to be similar in its flow characteristics to MA-21, a multicomponent Mg-8.1Li fine-grained commercial Soviet alloy.

Melting relations in the iron-sulfur system at ultra-high pressures - Implications for the thermal state of the earth

Abstract: The melting temperatures of FeS-troilite and of a 10-wt-pct sulfur iron alloy have been measured to pressures of 120 and 90 GPa, respectively The results document that FeS melts at a temperature of 4100 (+ or - 300) K at the pressure of the core-mantle boundary Eutecticlike behavior persists in the iron-sulfur system to the highest pressures of measurements, in marked contrast to the solid-solutionlike behavior observed at high pressures in the iron-iron oxide system Iron with 10-wt-pct sulfur melts at a similar temperature as FeS at core-mantle boundary conditions If the sole alloying elements of iron within the core are sulfur and oxygen and the outer core is entirely liquid, the minimum temperature at the top of the outer core is 4900 (+ or - 400) K Calculations of mantle geotherms dictate that there must be a temperature increase of between 1000 and 2000 K across thermal boundary layers within the mantle If D-double-prime is compositionally stratified, it could accommodate the bulk of this temperature jump

Development of anodes for aluminium/air batteries -- solution phase inhibition of corrosion

Abstract: The discharge characteristics of aluminium in inhibited and uninhibited 4 M KOH at 50°C have been explored. The performance of pure aluminium as a fuel is compared with that for two leading alloy fuels that had been evaluated in our previous work, Alloy BDW (Al−1Mg−0.1In−0.2Mn) and Alloy 21 (Al−0.2Ga−0.1In−0.1Tl). The inhibitors employed in this study, SnO 3 2− , In(OH)3, BiO 3 3− , Ga(OH) 4 − , MnO 4 2− , and binary combinations thereof, are either present in Alloys BDW and 21 or have been investigated previously (SnO 3 2− ). We found that potassium manganate (K2MnO4) and Na2SnO3+In(OH)3 are effective inhibitor systems, particularly at high discharge rates (400 mA cm−2), but at low discharge rates only manganate offers a significant advantage in coulombic efficiency over the uninhibited solution. Alloy BDW exhibits a very low open circuit (standby) corrosion rate, but its coulombic efficiency under discharge, as determined by delineating the partial anodic and cathodic reactions, was found to be no better than that of aluminium in the same uninhibited solution. Alloy 21 was found to exhibit a comparable performance to Alloy BDW under open circuit conditions and a much higher coulombic efficiency at low discharge rates (100 mA cm−2), but the performance of this alloy under high discharge rate conditions was not determined. Alloy 21 has the significant disadvantage that it contains thallium.

Disproportionation in Nd16Fe76B8-type hydrides

Abstract: This work has shown that heating Nd 16 Fe 76 B 8 -type materials in a hydrogen atmosphere, with subsequent vacuum annealing at greater than 750°C produces coercive powders which are suitable for the production of polymer-bonded magnets. A study of the material at different stages of the process has confirmed that the Nd-Fe-B alloy disproportionates into iron, Fe 2 B and neodymium hydride before recombining during the vacuum annealing stage to produce the fine-grained microstructure necessary for highly coercive material. The grain size of the final microstructure has been found to be very dependent on the temperature at which the hydrogenation-disproportionation-desorption cycle is carried out with optimum properties for the Nd 16 Fe 76 B 8 alloy being obtained for a desorption temperature of 785°C for 1 h.

Soft magnetism of crystalline Fe based alloy sputtered films

Abstract: The physical origin of soft magnetic properties in Fe-based alloy films with large magnetocrystalline anisotropy and magnetostriction is systematically examined. The relations between the microstructure of the film and soft magnetic properties are discussed for various kinds of Fe-based alloy films such as Fe-N, Fe-Si-Al, and Ni-Fe-Nb fabricated by DC magnetron sputtering. Magnetic anisotropy dispersion is analyzed based on the micromagnetic ripple theory proposed by H. Hoffmann (1969). Analysis of dynamic differential susceptibility suggests that initial permeability is strongly related to the structure constant S, which must be reduced in order to realize high initial permeability. It has been demonstrated that the reduction of grain size and induced lattice deformation are very effective in decreasing the value of S with respect to controlling the microstructure of the film. Several factors which must be taken into account for achieving high initial permeability in Fe-based alloy films are examined. >

Structure and properties during aging of an ultra-high strength Al-Cu-Li-Ag-Mg alloy

Abstract: The structure and properties of the strengthening phases formed during aging in an Al-Cu-Li-Ag-Mg alloy (Weldalite 049) were elulcidated, by following the development of the microstructure by means of TEM. The results of observations showed that the Weldalite 049 alloy has a series of unusual and technologically useful combinations of mechanical properties in different aging conditions, such as natural aging without prior cold work to produce high strengths, a reversion temper of lower yield strength and unusually high ductility, a room temperature reaging of the reversion temper eventually leading to the original T4 hardness, and ultrahigh-strength T6 properties.

Characterization of oxide structures formed on nickel-chromium alloy during low pressure oxidation at 500–600°C

Abstract: Low pressure oxidation studies of Ni-18%Cr alloy were carried out at temperatures of 500–600°C for very brief periods. Detailed XPS, AES, SEM, and TEM studies identified four stages in the initial oxidation. These are: (1) formation of a mixed nickel-chromium oxide overlayer; (2) growth of submicron-sized oxide nodules; (3) development of dark “hole-like” patches on the surface; and (4) growth of “second generation” oxide nodules. Both types of nodules consist primarily of a nickel structure depleted in oxygen. Their formation appears to result from a very rapid outward movement of nickel from localized defects in the metal. The dark patches result from the presence of a chromium oxide-rich underlayer, which appears to form by a lateral migration of chromium from adjacent oxide/metal interface regions and from grain boundaries.