Sputtering of two-phase AgxCux alloys

Elemental sputtering yields from two phase AgCu alloys were measured for 20, 40 and 50 at% Ag. Argon ion bombardment energies were in the range 35–55 keV and the ion dose was 1×10¹⁹ ions cm^–2. The sputtering yield for silver was found to be considerably below what was expected by simple selective sputtering of a two component alloy. Analysis by electron probe X-ray microanalysis and scanning electron microscopy of the eroded surface indicated that surface diffusion of copper from copper rich grains and geometrical constraints in the dense cone forest on Cu/Ag eutectic regions combine to reduce the sputtering yield for silver.     

Models of tensile behaviour of two-phase alloys from their components

Abstract

The main models (mixture laws, finite element methods, self-consistent methods) proposed to describe the stress–strain curve of a two-phase material from the stress–strain curves of its components have been considered. None of these models exactly describes the behaviour of the two-phase alloys (each phase equal vol.-%) studied (Cu–Ag and Cd–Zn).

MST/473     

Residual thermal stresses in two-phase alloys

Regularities in the formation of residual thermal stresses in two-phase alloys in relation to structure and the physicomechanical properties of phases are studied. Results are given for the calculation of intergranular reaction forces in the vicinity of pores filled with binder occurring as a result of the difference in thermal expansion coefficients for the phases. The dependence of the magnitude of intergranular reaction on the percentage content of binder is analyzed.Translated from Problemy Prochnosti, No. 9, pp. 81–86, September, 1990.     

Fatigue crack growth in two-phase alloys

Abstract

Stress intensity levels at the tip of cracks approaching and growing past second-phase particles have been computed using finite element methods. It is predicted that particles having a lower modulus than the matrix (i.e. ‘soft’ particles) attract and accelerate cracks growing into their vicinity, whereas ‘hard’ particles deflect them and retard local growth. A reverse, but weaker, effect is indicated once the crack has extended past a particle. Using a ferrite matrix with either spheroidized cementite or spheroidal graphite as the second phase, these predictions have been largely verified experimentally. An apparent anomaly is the cross-over in the growth rate curves of the cast iron and the totally ferritic microstructure. However, this may be explained by the requirement for the crack to reinitiate following its interaction with each graphite particle, during which decohesion of the particle/matrix interface occurs.

MST/417     

Crack formation in sintered two-phase alloys

Al/Al₂O₃ alloys are characterised by a pronounced high-temperature brittleness which is not yet fully understood. The authors postulated that microcrack formation plays a fundamental role in determining the ductility in tensile and creep tests of these alloys. To investigate the appearance and generation of cracks, density measurements and electron microscope examinations were carried out on samples broken in tensile tests (20 to 620° C temperature range) and in accelerated creep tests (450° C) of two Al/Al₂O₃ alloys (SAP-ISML and Fibroxal). Some investigations were also made on samples deformed by swaging.The experimental results (morphology, dimensions, distribution and volume of microcracks in the broken samples as a function of temperature and deformation time) confirmed the crack-formation hypothesis and showed that during the deformation of sintered aluminium two-phase alloys, voids may be generated by two mechanisms. The first involves the opening of pre-existing pores which are due to imperfect bonding between matrix and particles, the second involves the creation of new cracks by dislocations blocked at second phase particles.     

Grain growth in the two-phase Al-Cu alloys

Grain and phase growth in the two-phase Al-Cu alloys containing 6, 11, 1 7, 24 and 33 wt % Cu were investigated by annealing at 535 °C for 0.5–100 h. The grain and phase sizes of the phase are seen to be larger than that of the phase. The size of phase decreases whereas the size of phase increases with increasing copper content in the alloy. As such, the phase- and grain-size distributions are broader than the phase- and grain-size distributions, but the size range depends on annealing time and alloy composition. The grain sizes of the ,d , and ,d , phases can be related to the volume fraction of the phase,f , according to the equationd = 0.497d /f .     

Electrolytic preparation of chemically resistant alloys for radionuclide immobilization

An electrolytic method for preparing chemically resistant Pm-Ni alloys was developed. Optimal electrolysis conditions ensuring maximal Pm recovery from the electrolyte (up to 95%) with the alloy formation were determined. Side steps of the process were examined. The main of them is reduction of Pm in the bulk of the electrolyte with alkali metal subions.     

A criterion for cavitation of two-phase superplastic alloys

Microduplex 60/40 brass and Zn-AI eutectoid were used as models to represent cavitating and non-cavitating classes of the two superplastic alloys, respectively. In addition, a series of alloys were produced to represent the individual phases, over a wide range of temperatures, in these model systems. Hardness, Young's modulus and tensile tests were carried out on all these alloys at temperatures between 20 and 700° C. Analysing the above data, a criterion for the occurrence of cavitation in two-phase superplastic alloys is proposed.[/p]     

Microstructural evolution in two-phase alloys processed by high-pressure torsion

The Zn-22 % Al eutectoid alloy and the Pb-62 % Sn eutectic alloy were processed by high-pressure torsion (HPT) over a range of experimental conditions. Both alloys exhibit similar characteristics with significant grain refinement after processing by HPT but with a reduction in the hardness values by comparison with the initial unprocessed conditions. It is shown that there are generally smaller grains at the edges of the disks by comparison with the disk centers. The hardness results in these two alloys are mutually consistent, but they are different from those generally reported for conventional single-phase materials. The significance of this difference is examined.     

Hall-Petch relationship in two-phase TiAl alloys with fully lamellar microstructures

The dependences of the room temperature tensile properties of two-phase TiAl alloys with fully lamellar microstructures on colony size and the effects of alloying elements on the k value of Hall-Petch relationship were investigated. It is found that the ultimate tensile strength and the yield strength show Hall-Petch dependences on colony size, but the ductility does not obey a Hall-Petch dependence on colony size. The k value of Hall-Petch relationship increases when Ti-47Al (at.%) is alloyed with interstitial elements C or B, but the additions of substitutional elements Cr or Nb don’t lead to its apparent change.     

Stress-strain rate relations for high-temperature deformation of two-phase Al-Cu alloys

Al-Cu alloys containing 6, 11, 17, 24 and 33 wt% Cu, annealed for 0.5–100 h, were deformed by the differential strain-rate test technique over a strain-rate range of 4×10^–6 to 3×10^–2s^–1 at temperatures ranging from 460–540°C. Superplastic behaviour, with strain-rate sensitivity, m0.5, and activation energy, Q=171.5 kJ mol^–1, is shown by the Al-24Cu and Al-33Cu alloys at lower strain rates and higher temperatures. All the alloys show m0.20 at higher strain rates, but the average activation energy for deformation of the Al-6Cu, Al-11Cu, and Al-17Cu alloys is evaluated to be 480.7 kJ mol^–1, in contrast to a lower value of 211 kJ mol^–1 for the Al-24Cu and Al-33Cu alloys. Instead of grain size, the mean free path between particles is suggested to be a more appropriate microstructural parameter for the constitutive relationship for deformation of the Al-Cu alloys.     

Characterization of two-phase nickel aluminides produced by pressure-assisted combustion synthesis

Two-phase (B2+L1₂) nickel aluminide intermetallic compounds were synthesized by the pressure-assisted volume combustion synthesis (CS). The production and characterization of the samples containing NiAl+Ni₃Al were investigated. Aluminum (99% pure, 15 μm) and carbonyl nickel (99.8 pure, 4-7 μm) powders were used. The production of intermetallic compound was carried out at 1050 °C under 150 MPa uniaxial pressure in open air atmosphere in an electrical resistance furnace for 60 min. The formation temperature of intermetallic compound was determined by differential scanning calorimeter (DSC) analysis, and exothermic temperature of powder mixture was determined as 653 °C. The characterization of samples was confirmed by optical microscope, SEM and XRD analysis. It was observed that the structure of compound has very low porosity and the formation of NiAl was completed successfully. The relative density of test materials measured according to Archimedes’ principle was 98.04%. The microhardness of test materials was about 351 HVN₁.     

Structural transformations produced during tempering of Fe-Ni-Co-Mo alloys

In an attempt to resolve the difficulties in interpreting the behaviour of the industrial maraging steel of VASCOMAX 300 type, we have studied the influence of separate or simultaneous additions of Co and Mo on the structural transformations taking place during the heating cycles at moderate rates (300° Ch^–1) for the Fe-Ni base alloys. An interpretation of the mechanisms of the M transformation, implying preponderantly diffusional mechanisms, has been proposed for the alloys Fe-Ni, Fe-Ni-Co, Fe-Ni-Mo and Fe-Ni-Co-Mo for which the Ni/Fe, Mo/Fe ratios are equal to those of the reference maraging steel. The ageing phenomena in the martensite of the alloys containing Mo have been studied and show the formation of G.P. zones having a diameter of a few tens of Å and spaced at an average distance of 120 Å, in the case of the quaternary alloy, at temperatures of 400 to 450° C.     

Effect of grain-structure topology in modelling aggregate irradiation creep behaviour of two-phase alloys

The two-phase alloy Zr–2.5Nb, a high-strength alloy for nuclear applications, has a grain structure in which the hcp -phase is surrounded by the bcc β-phase. A satisfactory method for the macroscopic overall properties of this type of materials has yet to be developed. Based on the small volume fraction of the β-phase, some existent models of polycrystalline aggregates of Zr–2.5Nb argued to completely ignore the presence of the β-phase, and hope that errors cancel by fitting to experimental data. This may not introduce significant errors if the β-phase is randomly distributed, and if the deformation mechanisms are not an important part of the investigation. However, for highly correlated distributions of the two phases, the dependence of the overall polycrystalline properties in the topology of the distribution of the β-phase is intuitively feasible, or at least, the contrary has not been established. In this paper, we are interested in ascertaining the effect, if any, of the grain structure topology on the irradiation-induced deformation of this type of alloys. We compare the behaviours of three model polycrystalline aggregates with topologically different grain structures, one made up of “grains” in which the -phase is embedded periodically in a β-phase, and another in which the β-phase is embedded periodically in the -phase, and the third in which the β-phase is neglected. All have the same texture, and the first two have the same :β volume ratio, and therefore cannot be distinguished within the existent models. The double interaction method (DIM) is introduced for the treatment of this type of quasi-periodic textured polycrystalline aggregates. In this method, the overall properties of the constituent grains with a periodic structure, are first calculated. The interaction direction derivation (IDD) method is used to consider the interactions among the “intra-granular” periodic elements. The overall properties of the textured polycrystalline aggregate can then be calculated, by considering the inter-granular interaction using the usual self-consistent method (SCM). It is found that, the β-phase may not be neglected in the usual self-consistent model treatment, unless the magnitudes of the creep compliances of the two phases are not very different.     

Prediction of creep deformation in ductile two-phase alloys by a continuum mechanics model

The creep deformation of the ductile two-phase alloys was analysed on the basis of the continuum mechanics model which incorporated the projection concept proposed by Evans and Wilshire. The calculated creep curves were compared with the experimental ones in ferrjte-pearlite steels. It was found that the continuum mechanics model was able to predict the whole creep deformation process of the ductile two-phase alloys from the onset of creep loading to the final rupture, if the creep-deformation and creep-rupture data of the individual phases which constituted the two-phase alloys were known. A steady-state creep in the ductile two-phase alloys was predicted by the continuum mechanics model to occur, even if the constituent phases did not have the inherent steady-state creep. This was caused by the internal stresses arising from the creep-strength difference between second-phase and matrix in the two-phase alloys. This steady-state creep was observed in ferrite-pearlite steels during creep at 873 K. The predicted rupture life on the basis of the continuum mechanics model was correlated well with the experimental results in ferrite-pearlite steels, although the former was somewhat shorter than the latter under higher creep stresses. The continuum mechanics model was able to apply to the life prediction and the creep-strength design of the ductile two-phase alloys.     

Effect of Al content on the microstructure and mechanical behavior of two-phase FeNiMnAl alloys

The effects of varying the Al content in the range of 11–15 at.% on the microstructure and room-temperature mechanical properties of lamellar-structured FeNiMnAl alloys with compositions close to Fe₃₀Ni₂₀Mn₃₅Al₁₅ have been studied, and the temperature dependence of the yield strength of one composition, i.e., Fe₃₆Ni₁₈Mn₃₃Al₁₃, has been investigated. All alloys consisted of B2 and fcc phases. Decreasing the Al content initially (13 and 14 at.% Al) led to marked increases in both the fcc phase fraction and fcc lamellar spacing, λ, but, on further reducing the Al content (11 and 12 at.% Al), the lamellar structure was no longer present. The elongation to fracture of the FeNiMnAl alloys increased with the decreasing Al concentration from 6.5 % at 15 at.% Al to 31.1 % at 11 at.% Al with a concomitant decrease in the yield stress from 820 to 255 MPa. For the lamellar-structured alloys, the yield stress, σ _y, obeyed a Hall–Petch-type relationship with λ, i.e., $ \sigma_{y } = \sigma^{\prime}_{0} + k^{\prime}\lambda^{ - 1} $ , where $ \sigma^{\prime}_{0} $ is the lattice resistance, and k′ is a constant. The compressive yield stress of Fe₃₆Ni₁₈Mn₃₃Al₁₃ was found to be independent of temperature up to 700 K, after which it decreased dramatically because of the softening of the B2 phase. All alloys showed ductile fracture modes.