Atom configurations in Pd–Au and Pd–Au–D alloys: A neutron total scattering and Reverse Monte Carlo study

The effect of the alloying elements on the distribution of deuterium in Pd–Au has been investigated by total neutron scattering. The data are analyzed by Reverse Monte Carlo modeling in order to assess the type of interstitial sites occupied with deuterium and how this is correlated with the distribution of the Pd and Au atoms on the host metal lattice. The results show that in Pd–Au alloys deuterium occupies both octahedral and tetrahedral interstitial sites: the overall occupancy of tetrahedral sites increases with increasing Au content and decreasing overall D content. Short-range ordering (SRO) is identified in the D occupancy of interstitial sites in the sample with higher Au content. Indications of SRO and D-induced reorganization in the metal lattice are discussed.     

Phase diagram calculation and predication of Au–Pd–Zr ternary system

Au-Pd-Zr ternary alloy phase diagram at 25℃ was calculated by Panda phase calculation software,and the thermodynamic data were based on three binary alloy phase diagrams:Pd-Au,Au-Zr,and Pd-Zr.Five composition points in the ternary phase diagram were selected to predict the precipitation order.One(32Au-32Pd-36Zr) of the five composition points in ternary phase diagram was chosen to verify the correctness of the phase diagram calculation and the precipitation order by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD).The unknown phase in XRD patterns was predicated by EDS and materials studio(MS) software.The experimental results show that there are seven key ternary reactions points and 17 phase regions in all isothermal sections at 25℃.The thermodynamic process and microstructure for the alloy phase can be described in order according to the vertical section in phase diagram.The phase compositions of the chosen one point are consistent with calculation prediction.The unknown phase in XRD patterns should be Zr_2AuPd by the first principle X-ray simulation.     

Nanoquasicrystalline phase formation in binary Zr–Pd and Zr–Pt alloys

This paper reports nanoquasicrystalline phase formation in Zr_100−xPd_x (x=30 and 35) and Zr₈₀Pt₂₀ binary alloys and the kinetics of the nanoquasicrystallization process. While the icosahedral phase (i-phase) forms as a metastable phase in the transient stage during the crystallization of Zr–Pd amorphous alloy, it forms directly from the liquid during melt-spinning of Zr–Pt alloy. The isothermal kinetics studies show that i-phase forms from the Zr₇₀Pd₃₀ amorphous alloy by the primary crystallization process with the Avrami exponent in the range of 1.5–2.5. Three-dimensional atom probe analysis results suggest that the i-phase is slightly enriched with Zr with respect to the matrix and its composition is close to Zr₇₅Pd₂₅. The tendency of quasicrystallization of Zr-based alloys appears to have correlation with the enthalpy of mixing of the system.     

Analysis of surface and bulk behavior in Ni–Pd alloys

The most salient features of the surface structure and bulk behavior of Ni–Pd alloys have been studied using the Bozzolo–Ferrante–Smith (BFS) method for alloys. Large-scale atomistic simulations were performed to investigate surface segregation profiles as a function of temperature, crystal face, and composition. Pd enrichment of the first layer was observed in (1 1 1) and (1 0 0) surfaces, and enrichment of the top two layers occurred for (1 1 0) surfaces. In all cases, the segregation profile shows alternated planes enriched and depleted in Pd. In addition, the phase structure of bulk Ni–Pd alloys as a function of temperature and composition was studied. A weak ordering tendency was observed at low temperatures, which helps to explain the compositional oscillations in the segregation profiles. Finally, based on atom-by-atom static energy calculations, a comprehensive explanation for the observed surface and bulk features will be presented in terms of competing chemical and strain energy effects.     

Solute concentrations and stresses in nanograined H–Pd solid solution

In the present work, we applied the Gibbs-approach-based adsorption isotherm for nanograined polycrystals to H–Pd solid solutions. Using the published experimental data of lattice strain and sample strain of the nanograined Pd, with an average grain size of 10 nm and in thermodynamic equilibrium with an H₂ partial pressure, we determined H concentrations and stresses, as a function of the H₂ partial pressure, in both grains and grain boundaries. More importantly, we determined the intrinsic properties of grain boundaries, such as the grain boundary bulk modulus, the grain boundary excess thickness, and the difference in chemical potential between grains and grain boundaries. With the determined intrinsic properties, the Gibbs-approach-based adsorption isotherm predicted the segregation of H in grain boundaries of nanograined Pd with an average grain size of 5 nm. The predication was verified by other reported experimental data.     

Supercooling investigation and critical cooling rate for glass formation in Pd–Cu–Ni–P alloy

Based on the previous results of undercooling investigation, the critical cooling rate for glass formation (R_c) and crystallization behavior of the Pd₄₀Cu₃₀Ni₁₀P₂₀ alloy are determined and compared with theoretical calculation results using the classical nucleation theory (CNT). As nucleating homogeneously, the R_c is evaluated to be 2.08×10⁻⁵ K/s under continuous cooling, which is underestimated by four orders of magnitude against the experimental results. Actual crystallization of the alloy is dominated by a heterogeneous nucleation mechanism. Considering foreign substrate-induced nucleation, the wetting angle (θ) between crystalline embryo and undercooled melt is evaluated to be about 62.5°. Furthermore, other heterogeneous nucleation mechanisms beyond the CNT are discussed to fit the experimental results.     

Composition dependence of the microstructure and mechanical behavior of Ti–Zr–Cu–Pd–Sn–Nb bulk metallic glass composites

Ti-based bulk metallic glass composite alloys Ti₅₆Zr₆Cu_19.8Pd_8.4Sn_1.8Nb₈, Ti₆₄Zr₄Cu_13.2Pd_5.6Sn_1.2Nb₁₂ and Ti₆₈Cu_13.2Pd_5.6Sn_1.2Nb₁₂ were designed to obtain the microstructure composing of β-Ti dendrites and glassy matrix. The compressive and three-point bending properties were investigated. It was found that the actual microstructure of the Nb-added alloys consisted of primarily precipitated β-Ti dendrites, network-like glassy matrix, and extra island-like Ti₂Cu intermetallic phase with different volume fractions. Under compressive loading, all the Nb-added alloys presented higher yield strength combined with remarkably increased plasticity. Under bending condition, however, the alloys Ti₅₆Zr₆Cu_19.8Pd_8.4Sn_1.8Nb₈ and Ti₆₄Zr₄Cu_13.2Pd_5.6Sn_1.2Nb₁₂ with higher Ti₂Cu volume fractions became completely brittle. The alloy Ti₆₈Cu_13.2Pd_5.6Sn_1.2Nb₁₂ could keep its plastic deformability due to the decreased Ti₂Cu volume fraction. Compressive deforming behavior of the Nb-added alloys was determined by the ductile β-Ti phase and glassy matrix, nevertheless, bending deforming behavior of the alloys was determined by the volume fraction and distribution of the brittle intermetallics.     

The ferromagnetic shape memory system Fe–Pd–Cu

A new ferromagnetic shape memory thin film system, Fe–Pd–Cu, was developed using ab initio calculations, combinatorial fabrication and high-throughput experimentation methods. Reversible martensitic transformations are found in extended compositional regions, which have increased fcc–fct transformation temperatures in comparison to previously published results. High resolution transmission electron microscopy verified the existence of a homogeneous ternary phase without precipitates. Curie temperature, saturation polarization and orbital magnetism are only moderately decreased by alloying with nonmagnetic Cu. Compared to the binary system; enhanced Invar-type thermal expansion anomalies in terms of an increased volume magnetostriction are predicted. Complementary experiments on splat-fabricated bulk Fe–Pd–Cu samples showed an enhanced stability of the disordered transforming Fe₇₀Pd₃₀ phase against decomposition. From the comparison of bulk and thin film results, it can be inferred that, for ternary systems, the Fe content, rather than the valence electron concentration, should be regarded as the decisive factor determining the fcc–fct transformation temperature.     

Oxidation of Pd and Pd-RE Alloys

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Recrystallization behavior,microstructure evolution and mechanical properties of biodegradable Fe–Mn–C(–Pd) TWIP alloys

In this study the interplay between recrystallization and precipitation in a biodegradable TWIP (twinning-induced plasticity) steel developed for use in temporary implants was investigated. Microstructural and mechanical properties were studied and a thermomechanical treatment was designed with the aim of achieving an overall performance suitable for the intended application as temporary implant material. The formation of Pd-rich precipitates in the cold-worked state was found to considerably retard recrystallization during an annealing treatment. The formation, morphology and interaction with dislocations of these precipitates were studied by means of scanning and transmission electron microscopy. Grain boundary pinning by Pd-rich precipitates (Zener drag) and reduced dislocation mobility due to a solute drag effect caused by the enrichment of dislocation cores with Pd were both identified as mechanisms which impede recrystallization. A model is reported which explains the interplay between recrystallization and precipitation, and provides the basis for the optimized thermomechanical treatment then presented. The resulting mechanical properties, in particular the combination of high strength and ductility with a pronounced strain-hardening response, exceed the performance of other TWIP steels and alloys typically used in biomedical implants, such as stainless steel, titanium or cobalt–chromium alloys. The specific property profile developed is especially advantageous for the production and deployment of cardiovascular stents.     

Age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental Au–Ag–Cu–Pd–Zn alloy

The age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental casting gold alloy composed of 56Au–25Ag–11.8Cu–5Pd–1.7Zn–0.4Pt–0.1Ir (wt.%) were elucidated by characterizing the age-hardening behaviour, phase transformations, changes in microstructure and changes in element distribution. The fast and apparent increase in hardness at the initial stage of the aging process at 400°C was caused by the nucleation and growth of the metastable Ag–Au-rich phase and the Cu–Au-rich phase by the miscibility limit of Ag and Cu. The transformation of the metastable Ag–Au-rich phase into the stable Ag–Au-rich phase progressed concurrently with the ordering of the Cu–Au-rich phase into the AuCu I phase through the metastable state, which resulted in the subsequent increase in hardness. The further increase in hardness was restrained before complete decomposition of the parent α₀ phase due to the initiation of the lamellar-forming grain boundary reaction. The progress of the lamellar-forming grain boundary reaction was not directly connected with the phase transformation of the metastable phases into the final product phases. The heterogeneous expansion of the lamellar structure from the grain boundary caused greater softening than the subsequent further coarsening of the lamellar structure. The lamellar structure was composed of the Ag–Au-rich layer which was Cu-, Pd- and Zn-depleted and the AuCu I layer containing Pd and Zn.     

Estimation of Transformation Temperatures in Ti–Ni–Pd Shape Memory Alloys

The present study focused on estimating the complex nonlinear relationship between the composition and phase transformation temperatures of Ti–Ni–Pd shape memory alloys by artificial neural networks (ANN). The ANN models were developed by using the experimental data of Ti–Ni–Pd alloys. It was found that the predictions are in good agreement with the trained and unseen test data of existing alloys. The developed model was able to simulate new virtual alloys to quantitatively estimate the effect of Ti, Ni, and Pd on transformation temperatures. The transformation temperature behavior of these virtual alloys is validated by conducting new experiments on the Ti–rich thin film that was deposited using multi target sputtering equipment. The transformation behavior of the film was measured by varying the composition with the help of aging treatment. The predicted trend of transformational temperatures was explained with the help of experimental results.     

Liquid–solid equilibria in the quasicrystalline regions of the Al–Pd–Mn phase diagram

Phase equilibria were investigated in the Al–Pd–Mn phase diagram in the region where quasicrystals and approximant phases form. With respect to previous thermodynamic studies, the extents of the liquidus phase fields of several approximant phases are either established or precisely determined. In particular, compositional profiles across interfaces show the ternary character of the T(AlPdMn) and ξ′ phases which are close to the binary Al–Mn and Al–Pd limits respectively. It is pointed out that the relative stability of some of the phases involves very small energy differences leading to very long transformation times and the solidification of metastable phases.     

Structure of quenched alloys of the Ti–Pd system

The quenched alloys of the Ti–Pd system containing 2–15 at % Pd have been studied using X-ray diffraction analysis, optical metallography, transmission electron microscopy, and measurements of the microhardness. It has been found that, in the course of quenching, epy alloys containing 2, 3, and 5 at % Pd undergo a eutectoid decomposition into the α phase and Ti₂Pd intermetallic compound, and the Ti–7 at % Pd and Ti–9 at % Pd alloys undergo a β → α' martensitic transformation. In the alloys with Pd contents of more than 9 at %, the β phase is fixed in the metastable state. The complete stabilization of the β phase takes place in the alloys containing 11 at % Pd and more. It has been found that the formation of the orthorhombic α" phase and metastable ω phase in the quenched alloys of this system does not occur.     

Effect of Mn addition on the structural and magnetic properties of Fe–Pd ferromagnetic shape memory alloys

The effect of Mn addition on the structural and magnetic properties of Fe–Pd ferromagnetic shape memory alloys is investigated. In particular, a complete characterization of the influence of the partial substitution of Fe by Mn has been performed on Fe_69.4?xPd_30.6Mn_x (x = 0, 1, 2.5 and 5) alloys. The substitution of 1% Fe by Mn fully inhibits the undesirable irreversible face-centered tetragonal to body-centered tetragonal transformation without decreasing the face-centered cubic to face-centered tetragonal temperature. In addition, the substitution of 2.5% Fe by Mn gives rise to the highest thermoelastic transformation temperature observed to date in the Fe–Pd system, probably due to an increase in the valence electron concentration. The magnetocaloric effect has been evaluated in this alloy system for the first time. Nevertheless, the low values obtained suggest that the Fe–Pd alloys are not good candidates for magnetic refrigeration applications.     

The compositional stability of the P-phase in Ni–Ti–Pd shape memory alloys

The precipitation of the P-phase in Ni–Ti–Pd and Ni–Ti–Pt shape memory alloys has been shown to dramatically increase the martensitic transformation temperature and strength in Ni-rich ternary alloys, yet little is known about the phase's compositional stability. Therefore, the compositional limits of the P-phase have been systematically studied by varying the Pd and Ni content while maintaining the general P-phase Ti₁₁(Ni + Pd)₁₃ stoichiometry. Each alloy was solutionized at 1050 °C followed by water quenching, and aging at 400 °C for 100 h. Four distinct phases were identified by electron and x-ray diffraction: Ti₂Pd₃, B2 NiTi, P- and P1-phases. The latter precipitate phases became more stable with increasing Ni at the expense of the Pd content. Atom probe tomography revealed the P-phase composition to be 45.8Ti–29.2Ni–25Pd (at.%) or Ti₁₁(Ni₇Pd₆) as compared to the P1-phase 44.7Ti– 45.8Ni–9.4Pd (at.%) or Ti₅Ni₅Pd.     

Interfacial microstructure and the kinetics of interfacial reaction in diffusion couples between Sn–Pb solder and Cu/Ni/Pd metallization

The interfacial microstructure and the kinetics of interfacial reaction between eutectic Sn–Pb solder and electroplated Ni/Pd on a Cu substrate have been studied by scanning, transmission and analytical electron microscopies. Besides PdSn₄ and Ni₃Sn₄, small grains of Ni₃Sn₂ with a hexagonal structure are also observed after long-time aging of the diffusion couples at 125°C. The presence of intermetallic phases is correlated with the diffusion paths in the calculated Pd–Pb–Sn and Ni–Pb–Sn isothermal sections. The growth kinetics of the Ni₃Sn₄ scallops in the submicrometer length scale was analyzed with an Arrhenius type of equation. The thickening kinetics yields a time exponent n=3.1 and an apparent activation energy (Q_h) of 25,750 J/mol, while the radial growth kinetics data yield a time exponent m≈6.6 and an apparent activation energy (Q_d) of 15,300 J/mol. The radial size distributions (RSDs) of Ni₃Sn₄ scallops were also quantified. The parameters describing RSDs are consistent with the theories of coarsening in two-phase systems containing a very high volume fraction of the second phase. Selective etching of solder revealed the three-dimensional morphology of PdSn₄ and Ni₃Sn₄, and also the dynamical phenomena, such as faceting, competitive growth and coalescence of Ni₃Sn₄ scallops during interfacial reaction. Non-parabolic growth kinetics is discussed in terms of the existing theories and characteristics of the evolving microstructure.