The effect of Ag additions on the microstructure of aluminium–lithium alloys

Minor quantities of Ag have been added to Al–Li–Cu–Mg–Zr alloys. Their microstructure has been studied by means of optical metallography, transmission electron microscopy and X-ray diffraction. In the high Li, low Cu : Mg ratio alloys the main phases found were , , S and T₁, while fewer T₂ and Al₇Cu₂Fe precipitates were also observed. The addition of up to 0.5 wt% Ag diminishes the and T₁ precipitates size. This is attributed to a small increase of Li solubility in the matrix. In the low Li, high Cu : Mg ratio alloy the addition of 0.2 wt % Ag resulted in the precipitation of phase simultaneously with , , S and T₁ phases. Due to the low Li concentration an unusual growth of the / precipitates at the expense of the precipitates was also observed.     

The effect of Ag additions on the microstructure of aluminium–lithium alloys

Minor quantities of Ag have been added to Al–Li–Cu–Mg–Zr alloys. Their microstructure has been studied by means of optical metallography, transmission electron microscopy and X-ray diffraction. In the high Li, low Cu:Mg ratio alloys the main phases found were , , S and T1, while fewer T2 and Al7Cu2Fe precipitates were also observed. The addition of up to 0.5 wt% Ag diminishes the and T1 precipitates size. This is attributed to a small increase of Li solubility in the matrix. In the low Li, high Cu:Mg ratio alloy the addition of 0.2 wt% Ag resulted in the precipitation of phase simultaneously with , , S and T1 phases. Due to the low Li concentration an unusual growth of the / precipitates at the expense of the precipitates was also observed. © 1998 Kluwer Academic Publishers     

The influence of carboxylate ions on the growth of β-FeOOH particles

Colloidal -FeOOH particles were produced by hydrolysis of FeCl₃ solutions doped with varied amounts of formate, lactate, oxalate, tartarate, pyromellitate and EDTA ions at 100 °C. The resulting particles were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric-differential thermal analysis, Fourier transform-infrared spectroscopy, elemental analysis, and the adsorption of nitrogen and water. With increasing concentration of added carboxylate ions, the mean modal size of the particles formed increased at low concentrations and decreased after passing the maximum. The crystallite sizes also revealed a maximum on adding EDTA, oxalate and lactate ions, while they monotonically decreased with the addition of other ions. Doping with tartarate and pyromellitate ions by more than 7 and 10 mol%, respectively, produced amorphous particles containing a large amount of these ions. The particles formed with 20 mol% tartarate ions adsorbed water selectively.     

A study on the influence of Mo, Al and Si additions on the microstructure of annealed dual phase Cr–Ta alloys

The effects of additions of 5 at.% Mo, Al and Si on the long-term annealed microstructures of a two phase Cr–Cr₂Ta alloy have been studied. Following 200 h at 1300 °C, the lamellar eutectic constituent of all the alloys disintegrated into discrete particles of the Laves phase embedded within a Cr-rich solid solution phase, along with the formation of fine Laves phase precipitates. One of the predominant differences between the three alloying additions was the extent of the C14 to C15 polytypic transformation of the Cr₂Ta-based Laves phase. With Mo and Al additions, the Cr₂Ta Laves phase transformed from C14 to either C15 or intermediate hexagonal polytypes following 200 h annealing at 1300 °C. In contrast, Si additions stabilised the C14 polytype, with no transformation to other polytypes observed after prolonged annealing at 1000, 1100 and 1300 °C.     

PLD bioactive ceramic films: the influence of CaO–P2O5 glass additions to hydroxyapatite on the proliferation and morphology of osteblastic like-cells

This work consists on the evaluation of the in vitro performance of Ti6Al4V samples PLD (pulsed laser deposition) coated with hydroxyapatite, both pure and mixed with a CaO–P₂O₅ glass. Previous studies on immersion of PLD coatings in SBF, showed that the immersion apatite films did not present the usual cauliflower morphology but replicated the original columnar structure and exhibited good bioactivity. However, the influence of glass associated to hydroxyapatite concerning adhesion, proliferation and morphology of MG63 cells on the films surface was unclear. In this study, the performance of these PLD coated samples was evaluated, not only following the physical–chemical transformations resulting from the SBF immersion, but also evaluating the cytocompatibility in contact with osteoblast-like MG63 cells. SEM and AFM confirmed that the bioactive ceramic PLD films reproduce the substrate’s surface topography and that the films presented good adherence and uniform surface roughness. Physical–chemical phenomena occurring during immersion in SBF did not modify the original columnar structure. In contact with MG63 cells, coated samples exhibited very good acceptance and cytocompatibility when compared to control. The glass mixed with hydroxyapatite induced higher cellular proliferation. Cells grown on these samples presented many filipodia and granular structures, typical features of osteoblasts.     

The effect of Ni additions on the oxidation behaviour of Co–Re–Cr high-temperature alloys

Abstract

The present study focused on the influence of Ni on the microstructure and oxidation behaviour of Co–Re–Cr-based alloys. Alloys with three different Ni contents were tested in laboratory air at 800–1100 °C. A refinement and a reduction of the σ phase volume fraction as well as a change in the matrix microstructure were observed. Thermogravimetric measurements showed that the alloys with higher Ni contents possess a better oxidation resistance when exposed to higher temperatures. All alloys suffered from continuous mass loss during oxidation at 800 °C due to the formation of porous oxides scales, consisting of Co₃O₄, Co(Ni)O and Ni-doped CoCr₂O₄, which allow the evaporation of Re-oxides. At 900–1100 °C, only the alloy with 25 at. % Ni showed parabolic oxidation kinetics after a short period of transient oxidation. This is a result of the fast formation of a protective Cr₂O₃ layer. It was also found that exposure to air at 1000 °C leads to a phase transformation of the bulk material; an oxidation-induced formation of fine hexagonal close-packed (hcp) grains was observed near the oxide scales. It is supposed that the improved oxidation resistance of Ni-containing Co–Re–Cr alloys is a result of enhanced Cr diffusion caused by the Ni addition. The extensive formation of the fcc phase in the alloy matrix had a detrimental effect on the oxidation behaviour of the Ni-containing Co–Re–Cr-based alloys.     

The effect of iron additions on the microstructure and properties of the “Tribaloy” Co-Mo-Cr-Si wear resistant alloys

The effect of iron additions in the range 5 to 15 wt % iron inclusive on the microstructure and properties of two Co-Mn-Cr-Si wear resistant alloys (Tribaloys T400 and T800) has been investigated. Iron additions were found to stabilize the f c c form of the cobalt solid solution, to give a fully eutectic matrix and to decrease the volume fraction of the primary Laves phase. These microstructural modifications have little effect on the plane strain fracture toughness but result in a significant increase in the modulus of rupture. The addition of iron induces only minor changes in the corrosion and oxidation resistance of T800, whereas the performance of T400 deteriorates.     

The influence of ageing on the stability of β-γ/γ′ derived microstructures in Ni-Al-Cr-(Co) alloys

Multiphase Ni-Al-(Fe)-(Cr)-(Co)-based intermetallics with (B2)- (A1)/(L1₂), - or - microstructures can exhibit significant room-temperature tensile ductility. In the case of Ni-Al-Cr-based alloys, microstructural development is complicated by the precipitation of -Cr, which can supplant the -phase during ageing of three-phase -/ microstructures. An investigation of the stability, during ageing, of cast Ni-Al-Cr-(Co) alloys with microstructures derived from -/ is reported. In the as-cast condition, the materials investigated consisted of a dendritic matrix containing L1₀ type martensite and interdendritic /. Extensive intra- and interdendritic -Cr precipitation was also observed. The stability during ageing of the interdendritic / microstructure is also considered and transformation of the L1₀ martensite is examined.     

The influence of process parameters on the structure and morphology of pulsed plasma‐polymerized octafluorotoluene films

Abstract

This work describes amorphous fluorinated polymer films deposited by pulsed plasma polymerizations of octafluorotoluene (PPP‐OFT) monomers on ITO glass as the hole‐injection layer of organic electroluminescent (EL) devices, in order to study the influence of sample position and duty cycle on PPP‐OFT film characteristics, and also to find a good process to yield a higher retention degree of monomers and lower roughness of PPP‐OFT fluorocarbon films. Experimental results revealed that PPP‐OFT films deposited at positions far away from the RF coil and close to the monomer inlet showed less roughness than films deposited near the high RF‐flux regions. In addition, the retention of the monomers in the PPP‐OFT layer will be high if the deposition is conducted near the monomer inlet but some distance away from the RF electrode. Moreover, amorphous fluorinated polymer films can be deposited with higher fluorine to carbon (F/C) ratios and CF₂ contents at proper substrate positions by means of different sticking coefficients of free radicals dissociated by octafluorotoluene monomers.     

The effect of titanium additions onM s of β-CuZn

The effect of titanium additions to binary -CuZn alloys was investigated: the concentration range of at high temperatures (860° C), solid solution hardening of this phase, and the change in martensite temperature,M _s. Titanium in solution produces considerable solid solution hardening, both by replacing copper or zinc. Only replacement of zinc leads to a constant or increasingM _s, while replacing copper decreases it. Ageing of the -phase causes strong hardening and a decrease inM _s. The results have been interpreted considering the role of thermodynamic and mechanical properties in determiningM _s.     

A study of Mg and Cu additions on the foaming behaviour of Al–Si alloys

Aluminium casting alloys containing Mg and Cu in addition to Si were investigated with respect to their potential to be foamed. The kinetics of foam expansion of different alloys was studied and the resulting structures were characterised. Of the stages of evolution of foams, namely (i) pore nucleation, (ii) foam growth in the semisolid state, (iii) further expansion in the fully liquid state, the latter two were explored. Expansion in the semisolid state could be related to the available liquid fraction. Mg-containing Al–Si alloys yielded a less coarse and more uniform pore structure than the other alloys investigated. However, achieving a high volume expansion required restriction to a narrow process window and led to the suggestion of AlMg4Si8 as a practical alloy.     

Influence of additions on the solidification behaviour of Ni-B alloys — crystallography of Ni-Ni3B eutectic

The influence of small additions (1 to 2 at.%) of some elements (chromium, copper, silicon, aluminium, iron, titanium, vanadium) on the solidification behaviour and crystallography of Ni()-Ni₃B eutectic composition is examined by differential thermal analysis, X-ray and electron diffractions, scanning and transmission electron microscopy. With the exception of Fe-doped eutectic alloys, all the alloys whether doped or undoped exhibit a very large undercooling for the nucleation of Ni₃B. We give an interpretation of the controversial hypothesis of this undercooling. We propose a crystallographic orientation relationship between the cubic phase Ni() and the orthorhombic phase Ni₃B in the lamellar eutectic Ni-Ni₃B. We also examine a complex transformation which occurs in Ni₃B during slow cooling.     

The influence of antioxidants on the Spreadability of α-Tocopherol Gels

Abstract

This study is based on the elaboration of α-Tocopherol gels containing the antioxidants butylated hydroxitoluene and ascorbic acid for the purpose of subjecting them to a Theological study aimed at evaluating the influence of the components of the various preparations.     

Effect of rare earth element additions on the impression creep of Sn–9Zn solder alloy

Creep behavior of the Sn–9Zn–RE alloys containing 0.1, 0.25 and 0.5 wt.% rare earth (RE) elements was studied by impression testing and compared to that of the eutectic Sn–9Zn alloy. The tests were carried out under constant punching stress in the range 40–135 MPa and at temperatures in the range 298–420 K. Results showed that for all loads and temperatures, Sn–9Zn–0.25RE had the lowest creep rate, and thus the highest creep resistance among all materials tested. This was attributed to the formation of Sn–RE second phase precipitates which act as the main strengthening agent in the RE-containing Sn–Zn alloys. RE contents higher than 0.25 wt.%, resulted in a lower creep resistance due to a reduction in the volume fraction of Zn-rich phase caused by the formation of Sn–Zn–RE intermetallics. The average stress exponents of 6.8, 6.9, 7.1, 6.8 and activation energies of 42.6, 40.6, 43.0 and 44.9 kJ mol⁻¹ were obtained for Sn–9Zn, Sn–9Zn–0.1RE, Sn–9Zn–0.25RE, and Sn–9Zn–0.5RE, respectively. These activation energies were close to 46 kJ mol⁻¹ for dislocation climb, assisted by vacancy diffusion through dislocation cores in the Sn. This, together with the stress exponents of about seven suggests that the operative creep mechanism is dislocation climb controlled by dislocation pipe diffusion.     

The intergranular embrittlement of Cu-AI-Ni β-phase alloys

Intergranular embrittlement in the Cu-Al-Ni -phase alloys has been investigated. Results of various experiments, which included an Auger electron spectroscopic analysis of freshly fractured grain boundary surfaces, lead to the conclusion that impurities do not play any significant role in the intergranular embrittlement of these alloys.     

The effect of notch plasticity on the behaviour of fatigue cracks emanating from edge-notches in high-strength β-titanium alloys

The present paper is aimed at investigating the behaviour of fatigue cracks emanating from edge-notches for two different microstructures of the Ti-6246 alloy, produced by two specific thermo-mechanical treatments and defined as β-annealed and β-processed, respectively. Pulsating four point bending tests were performed on double-edge-notched specimens. The initiation and early propagation of fatigue cracks were investigated at two relatively high nominal stress levels corresponding to 88 and 58% of the 0.2% material’s yield stress. Plastic deformation at the notch tip initially produced a local stress redistribution followed by elastic shake down due to the high cyclic strain hardening rates exhibited by both microstructures, as confirmed by finite element modelling. Crack closure effects, measured by an extensometric technique, and variations in crack aspect ratio were considered in the ΔK calculation. The obtained crack growth rate data were compared with those of long cracks measured on standard C(T) specimens as well as of microcracks measured on round, unnotched S-N type of specimens to evaluate the intrinsic fatigue crack propagation resistance of the two microstructures. The contribution of notch plasticization to crack closure was estimated by finite element modelling.     

The influence of Ca on the corrosion behavior of new die cast Mg–Al-based alloys for elevated temperature applications

In this study, the corrosion behavior of Mg–5Al alloys with different quantities of calcium was investigated by DC and AC polarization and immersion tests. The alloys’ microstructure was investigated by optical microscopy and SEM with EDS. It was found that increasing the Ca content from 0.9 to 1.8 wt% improves the corrosion resistance of the alloy; the corrosion resistance of the alloy with 1.8 wt% Ca equals that of the base Mg–5Al alloy. Ca addition causes a reduction of the average grain size, which increases corrosion resistance as the precipitates located at grain boundaries are more continuous and act as a barrier to the advance of corrosion. The precipitates located at grain boundaries contain Al and Ca and are much less cathodic than the β phase, thus making the microgalvanic effect in the specimen less effective.     

Effect of small alloying additions on behaviour of rapidly solidified Cu–Cr alloys

Abstract

The mechanical properties of as well as microstructural changes in rapidly solidified ternary Cu–Cr based alloys were studied for various ternary additions. The flow stresses of the binary and various ternary alloys are explained in terms of Orowan strengthening mechanisms. Zirconium, magnesium, and, to a lesser extent, silicon affected the age hardenability of the alloys, refining the chromium dispersion by modifying the precipitation sequence described by Tang. The coarsening kinetics was insensitive to the presence of a third alloying element, showing that these additions did not affect chromium transport within the copper matrix. Nevertheless, these additions influenced the morphology of the chromium particles during coarsening; zirconium tended to keep the particles spherical, while titanium additions increased their aspect ratio. Titanium reduced dramatically the age hardenability of the alloy by provoking heterogeneous nucleation of bcc chromium on small Ti0₂ particles present in the as cast structure, resulting in a coarser particle size distribution at peak strength.

MST/1171