AgMn Alloys Research Articles

Effects of CrxMo(0.2-x) addition on the dispersoids evolution and mechanical properties of Al–Cu–Mg–Ag–Mn alloy

Unlike the rod-like T–Al20Cu2Mn3 dispersoids, the spherical Al7(Cr, Mn) and Al6(Fe, Mn, Mo) precipitated in Al–Cu–Mg–Ag–Mn alloys with CrxMo(0.2-x) addition, retained the deformed substructure, and acted as a dispersion reinforcement. In this study, the precipitation behavior of dispersoids in Al–Cu–Mg–Ag–Mn alloys with various CrxMo(0.2-x) (x = 0.15, 0.10, 0.05 wt.%) at 400 °C/12 h + 515 °C/24 h homogenization was investigated. The compositional and structural evolution of dispersoids in Al–Cu–Mg–Ag–Mn alloys were investigated by optical microscopy and atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The effects of CrxMo(0.2-x) addition on morphology, size and number density of dispersoids inhibited the recrystallization behavior and improved the mechanical properties of alloys in varying degrees. When x = 0.15 in CrxMo(0.2-x), the large amount of Al7(Cr, Mn) precipitates to refine the T–Al20Cu2Mn3, and dispersoid-free zones (DFZ) significantly decreases. As x decreases to 0.05, the homogeneous Al6(Fe, Mn, Mo) dispersoids present the opposite precipitation trend of T–Al20Cu2Mn3 to compensate for the DFZ. During the deformation and subsequent heat treatment, the Al–Cu–Mg–Ag–Mn alloy with Cr0.05Mo0.15 addition maintains the highest substructure and dislocation density owing to the highest number density of spherical dispersoids, demonstrating excellent mechanical properties at ambient and elevated temperatures.

Preparation and Characterization of Orthorhombic AgMn Alloys by the Pulsed Laser Welding Technique

AbstractHerein, AgMn alloys are prepared by the pulsed laser welding technique in an argon atmosphere. The effect of the laser pulses width and stoichiometric composition of the alloys on the structural, compositional, morphological, and electrical properties are investigated. In contrast to the traditional preparation techniques which reveal cubic structure of AgMn alloys, the pulsed laser welding technique reveals the orthorhombic phase of the alloys. The lattice parameters of the orthorhombic phase of AgMn are . It is observed that pulse widths of 50 ms are the optimum from preparing these alloys. From an electrical point of view, the AgMn alloys exhibit negative dielectric constant and negative conductance effect in the microwave frequency domain. The impedance spectroscopy analyses in the frequency domain of 0.01–1.80 GHz have shown that AgMn alloys can be employed as band filters with return loss value of ≈16 dB. The features of the AgMn alloys which are achieved by the pulsed laser welding technique nominate them for use as negative capacitance and negative conductance transistors. These devices are suitable for noise reduction and parasitic capacitance cancellation.

Interdiffusion and atomic mobilities in fcc Ag–Mg and Ag–Mn alloys

On the basis of Ag/Ag–Mg and Ag/Ag–Mn semi-infinite diffusion couples together with electron probe microanalysis technique, the interdiffusion coefficients in fcc phases of Ag–Mg and Ag–Mn alloys were measured between 873 and 1173 K via the Sauer-Freise method. A statistic method was applied to evaluate the errors of the identified interdiffusivities in terms of the propagation of errors. Based on available thermodynamic information and the experimental interdiffusion coefficients, the atomic mobilities for the fcc Ag–Mg and Ag–Mn systems are obtained by using the DICTRA software package. The quality of the assessed atomic mobilities was confirmed by the comprehensive comparisons between calculated concentration profiles and the experimental data.

Short-range structural and magnetic order in rapidly-solidified Ag[sbnd]Mn alloys

Short-range structural and magnetic order in rapidly solidified nanostructured Ag100−xMnx alloys featuring nominal large Mn content (x=25, 32, 40at.%), well above the maximum equilibrium concentration (x~14at.%), are quantified using X-ray, neutron and magnetic probes. These inhomogenous alloys contain coexisting Mn-rich and Mn-deficient nanoscopic face-centered-cubic-type phases. Interaction between these regions provides large exchange bias at low temperature, with the magnitude of the unidirectional anisotropy field increasing gradually with increased Mn concentration. Neutron diffraction data reveal no evidence of long-range antiferromagnetic ordering but instead identifies short-range structural order from the presence of a diffuse scattering peak that evolves with Mn content. Moderate annealing temperatures (Tann=350°C) promote homogenization of the Mn content in the alloys with subsequent suppression of exchange bias, confirming the above model. A strong interfacial exchange density between Mn-deficient and the Mn-rich nanocrystalline phases exists that is determined to be of the same order of magnitude as that found in other exchange-biased ferromagnetic/antiferromagnetic systems. The intriguing behavior of these AgMn alloys as a function of temperature, of Mn content and of annealing condition highlights options to manipulate and tailor their magnetic attributes such as interface exchange and magnetic anisotropy.

Tuning exchange anisotropy in nanocomposite AgMn alloys

Silver manganese alloys of composition Ag100−xMnx (25 ≤ x ≤ 40) were prepared by rapid solidification to investigate their reported antiferromagnetic character. Thorough characterization of their structural, compositional, and magnetic features indicates the formation of a phase-separated fcc-type structure in all studied alloys with lattice parameters and coherently diffracting region sizes on the order of 40–100 nm that are strongly correlated with the Mn content. Magnetic measurement reveals a blocking temperature TB ∼ 105 K that is accompanied by unprecedented exchange bias values up to 1.7 T (17 kOe) at low temperatures. The magnitudes of the exchange bias field and the blocking temperature increase with increasing Mn concentration, suggesting a very sensitive balance between Mn content and magnetic character in these alloys that fosters tuning of the resultant exchange bias.

A Subnanoscale Investigation of Sb Segregation at MnO/Ag Ceramic/Metal Interfaces

We have studied Sb segregation at MnO/Ag(Sb) ceramic/metal heterophase interfaces employing three-dimensional atom-probe (3DAP) microscopy. Specimens are prepared by the internal oxidation of Ag(Mn) alloys, leading to the formation of nanometer-size MnO precipitates within a Ag(Mn) matrix. Sb is introduced into the internally oxidized specimens with a vapor diffusion treatment. Appreciable Sb segregation is observed only after a subsequent segregation anneal is performed, and the measured interfacial excess of Sb at the MnO/Ag(Sb) interfaces, ΓSbMnO/Ag, is determined directly. The temporal evolution of the MnO precipitates is followed for the different processing steps employed. It is shown that the concentration of silver within the MnO precipitates decreases from an initial value of 45–50 at.% Ag to less than 5 at.% Ag with increasing annealing time at the different processing temperatures. Thus the MnO precipitates form under paraequilibrium conditions and the precipitates inherit Ag from the matrix. With increasing aging time orthoequilibrium conditions prevail and the MnO precipitates reject the silver atoms they inherited from the matrix.

Effect of Pd or Au addition on age-hardening in AgMn-based alloys

Objective: The objective of this research was to characterize the age-hardening behavior of AgMn alloys modified with Au or Pd. These alloys are being studied as possible alternatives to Type III dental alloys. Methods: The age-hardening reactions in Ag-37 at% Mn alloys with 5 at% Au or Pd were investigated by optical microscopy, electrical resistivity, X-ray diffraction and hardness tests. Results: Optical microscopy showed no grain boundary precipitates formed after overaging. The maximum hardness reached by aging in all alloys is about 260 (Hv) and identical to that of traditional AgPdCu dental alloys. The precipitation reactions were retarded with the addition of 5 at% Au or Pd. X-ray diffraction studies suggest a fine precipitate, α-Mn, is dispersed within the grain interior. The activation energy for the precipitation reaction is 114 kJ/mol for the AgMn and AgMnAu alloys. This value is about one-half of the activation energy for volume diffusion of manganese in AgMn alloys. Significance: The age-hardenable AgMn-based alloys modified with Au or Pd can achieve hardness values comparable to those of traditional AgPdCu alloys. Provided the in vivo corrosion resistance of these alloys is adequate, they show promise as a Cu-free alternative material for cast restorations.

Characteristics of strengthened Ag substrates for Bi2Sr2CaCu2Ox doctor-bladed tapes

The characteristics of Ag-(Mg,Ni) and Ag-Mn alloys as substrate materials for Bi2Sr2CaCu2Ox (Bi-2212) tapes and their influence on the superconducting properties were studied. Alloying with Mg+Ni or Mn drastically decreased the grain size of Ag after heat treatment. The additives in Ag-(Mg,Ni) and Ag-Mn alloys were oxidized during heat treatment in air. Both the fine grain structure and the internal oxidation of the additives increased the mechanical strength of the Ag alloys. Both alloys were 3–6 times stronger than pure Ag. The superconducting properties of Bi-2212 prepared on these Ag alloys were slightly degraded; however the critical current densities at 4.2 K in 8 T were still well over 104 A/cm2.

The oxidation and oxide overlayer stability of AgMn alloys

AbstractThe oxidation of several compositions (5, 9 and 14% Mn) of polycrystalline Ag‐Mn alloys from room temperature to 650 °C in high vacuum and in 5 m Torr O2 has been investigated by x‐ray photoelectron spectroscopy (XPS). The behavior of the oxidation and the nature of the oxide films are controlled by tempearature, oxygen pressure, bulk alloy composition and the stability of the oxide overlayers. At low temperatures and pressures, the oxidation process is controlled by the relative free energies of oxide formation of the alloy components. At high temperatures the oxide of stabilities play a large role in determining the oxidation state of the oxide overlayer. The chemical state and the morphology of the oxide of manganese formed during the alloy oxidation has been examined. The chemical state and the morphology of the oxide overlayers have been studied by XPS, x‐ray diffraction (XRD) and scanning electron microscopy (SEM). The complex oxidation process has been delineated.

Ion intensity thermal analysis of Ag-Mn alloy.

Ion intensity thermal analysis by means of a Knudsen cell-mass spectrometer combination was applied to the study of invariant reactions in the Ag-Mn alloy system. In this study, the ion intensity of a component of the sample was measured as an index of temperature of the sample. Sensitivity and features of the ion intensity thermal analysis were discussed in comparison with the conventional thermal analysis with thermocouples. Temperature and type of the invariant reactions in Ag-Mn alloys were reported. Comparison of several published phase diagrams for this system was made in the light of the present study.

Thermodynamic stabilities of AgMn alloys

The activities of manganese in four AgMn alloys ( N Mn = 0.048, 0.090, 0.138 and 0.174) were determined with a twin-chamber Knudsen cell mass spectrometer in the temperature range 1050–1220 K. From the measured a Mn values, the Gibbs enthalpies of formation ΔG m of these four alloys were calculated as − 446, − 709, − 975 and − 1172 cal mol −1 respectively at 1150 K.

Non-equilibrium Ag-TM alloys produced by vapour quenching (TM ≡ Cr, Mn, Fe and Co)

AgCr, AgMn, AgFe and AgCo alloys were produced by a sputter-deposition method. Wide ranges of primary solid solutions were formed on water-cooled substrates, although the equilibrium phase diagrams of these alloys are immiscible except for AgMn. In AgFe alloys, the single-phase body-centered cubic (b.c.c.) and face-centred cubic (f.c.c.) regions were greatly extended on liquid-nitrogen-cooled substrates. The phase boundaries of silver-rich f.c.c. phases are roughly consistent with the results estimated from the classical elastic model.

Photoemission from Magnetic Metals and Alloys

Angle-resolved uv photoelectron spectroscopy has proved to be the most useful probe of the electronic structure in metallic solids. For the investigation of magnetic systems spin-resolved measurments are often preferred. However, considerable detailed information about the electronic structure in certain magnetic metals and alloys can be obtained using conventional and inverse spin-integrated photoemission techniques. In this paper a selection of results from such studies on spin-glass Ag-Mn alloys and on the rate-earth metal Gd are described and compared, where appropriate, with theory.

Magnetic diffuse scattering in AgMn spin glass alloys

Magnetic diffuse peaks observed around the (1 1 2 ± δ 0) type positions in reciprocal space have been studied in AgMn spin glass alloys by using neutron diffraction techniques. The position parameter δ of AgMn alloys coincides with that for CuMn alloys with the same Mn content even though the former has a larger lattice spacing than the latter by about 10%. The results suggest that the origin of the satellite diffuse peaks comes from a Fermi surface effect such as the RKKY interaction.

Very thin films of Mn, Ag, and Ag–Mn epitaxially deposited on Ru

Mn, Ag, and Ag–Mn alloys have been deposited on 001 Ru in an MBE system for the study of the epitaxy of the first few layers when the lattice constants have large mismatches. A new phase of Mn metal is reported. XPS studies of the splitting of the 3s peak of Mn is essentially the same in various metallic environments. If this splitting reflects the 3d–3s exchange interactions, it appears that Mn metal has 5 μβ per atom on the time scale of XPS measurements.

Irreversibility onset in spin glasses from torque measurements

Improved torque measurements on CuMn and AgMn alloys show a field independent torque onset temperature for fields from 0.5 kG to 9 kG. This result is compatible with mean field transverse freezing (GT line) predictions.

Changes in the Fermi surface of Cu-Ni and Ag-Mn random alloys deduced from studies of the photoemission from (111) surface states

Features are observed in the uv photoemission spectra from (111) faces of Cu-Ni and Ag-Mn random substitutional alloys which arise from Shockley-type surface states located around the ⌈ point of the 2-dimensional Brillouin zone. The variations in intensity of these features and their dispersion have been measured in the ⌈ LWK and ⌈ LUX planes using Arl photons. Since the dimensions of the Fermi surface in the vicinity of the L point are related to the dispersion of the surface state, the results indicate that in the case of Cu-Ni alloys the neck radius around [111] decreases as the bulk concentration of Ni increases, in good agreement with previous investigations using alternative techniques. In Ag-Mn alloys, however, the ϵF−L′2 gap and the neck radius both increase as Mn is added to Ag.

Magnetic Gruneisen parameters for some spin glasses

Values for the magnetic Gruneisen parameter gamma M for CuMn, (Cu-10 at.% Al)Mn and AgMn alloys determined form low-temperature thermal expansion and specific heat capacity measurements are reported. mu M is found to be both temperature- and concentration-dependent in contrast to the simple RKKY model for the spin-glass ordering. The concentration dependence of mu M differs significantly from that reported earlier based upon a combination of thermal expansion and specific heat capacity measurements made independently on different samples. Dipolar anisotropy is discussed as a possible cause of the dependence of mu M on temperature and magnetic impurity concentration.

Magnetic susceptibility and single-impurity effects in dilute AgMn alloys

The magnetic susceptibility, chi , of AgMn alloys with concentrations, c, between 10 at ppm and 4 at.% has been measured in the temperature and field ranges 1.4-300K and 0.9-8.5 kOe. The impurity susceptibility has been analysed according to a modified Curie-Weiss law chi = chi 0+(C/(T+ theta )). The effective magnetic Mn moment is p=(5.1+or-0.1) mu B and theta =(0.05+or-0.04)K for c or approximately=0.5 at.%, theta is dependent on the concentration and p=(5.4+or-0.1) mu B. The susceptibility is independent of concentration over the whole temperature range for c<or approximately=100 at ppm and a characteristic temperature TK approximately=20-30 mK has been estimated from a comparison with the calculations of the temperature dependence of chi by Krishna-Murthy et al. (1975) in which a spin value S=5/2 was used as a scaling parameter. Special attention has been given to the sample control and a reliable determination of the magnetic solute concentration.

Nuclear orientation of AgMn alloys

Interactions between magnetic impurities in a dilute alloy, long regarded as a hindrance to the study of the single-impurity problem, have in recent years become themselves the subject of considerable interest. Variation of the concentration of impurities can produce a broad range of magnetic behavior ranging from a slight depression of the characteristic temperature in Kondo systems through spin-glass interactions to magnetic ordering. The nuclear orientation technique is particularly suited to the study of impurity-impurity interactions, since it is applicable to a large number of impurity ions over a wide concentrationand applied-field range, and since it is espeically sensitive to local disalignment of the impurity spins.