The kinetics of transformation in amorphous germanium alloy films

The kinetics of the amorphous-to-crystalline transformation were studied in amorphous germanium (a-Ge) and its alloys with aluminium, silicon, indium, copper, iron, nickel, gallium and tin by using isochronal and isothermal annealing of the room temperature resistivity, differential thermal analysis and electron microscopy measurements. It was shown that the transformations in a-Ge and a-Ge alloy films are nucleation and growth controlled. The activation energy of 3.0 eV obtained for the amorphous-to-crystalline transition in a-Ge was found to decrease on alloying with metals, and the decrease depended on the nature of the alloying element.     

Wettability and contact interaction of gallium-containing melts with non-metallic solids

The wettability of sapphire, quartz and graphite by gallium, gallium-based binary alloys with indium, tin, copper, silver, nickel, manganese, chromium, vanadium and titanium and by ternary Cu-Ga-Ti, Cu-Ga-Cr and Cu-Ga-Mn alloys has been studied by sessile drop, plate weight and meniscus form methods. The character and intensity of contact reactions and the composition of transition layers at the solid—melt boundary have been investigated by X-ray analysis and profilographic measurements and the correlation between the wettability and the contact reaction intensity has been established. The condition for high wettability of non-metallic solids by multicomponent melts is shown to be a combination of high affinity of a component for solid phase atoms with high thermodynamical activity of this component in the melt.     

Compatibility of chromium carbide coated graphite fibres with metallic matrices

Chromium carbide coating on graphite fibres was obtained by diffusing chromium through a coating of copper on a graphite fibre. Coated fibres, then, were infiltrated with liquid copper, aluminium and nickel alloys in a vacuum furnace. Chromium carbide proved to be reasonably wetted by those alloys, although the wettability is affected by the alloying elements.     

A study on dental nonprecious cast alloys

The ternary nickel-copper-manganese (Ni-Cu-Mn) cast alloys were studied on hardening by the addition of elements such as aluminium and indium to the ternary alloys. Tensile tests showed that both the 20 Ni-40 Cu-40 Mn (which has the lowest melting temperature of all the Ni-Cu-Mn ternary alloys investigated) and the 50 Ni-30 Cu-20 Mn (with the highest melting temperature) exhibited a ductile behaviour. Dendritic structures seen by optical microscopy were constituted of ternary alloys containing aluminium and indium and the amount of dendritic structures increased in the indium-containing alloys rather than in the aluminium containing alloys, and as a result the hardness (VHN) had larger values in the latter alloy than in the former alloy.     

High-temperature oxidation behaviour of base metal elements in nickel-base alloys

Oxidation of non-precious metals nickel, chromium and copper, nickel-base alloys in an air atmosphere was studied under differential thermal analysis. The results suggest that adding chromium and copper to high-purity nickel metal reduces the amount of oxidation and gives a slower oxidation than in untreated high-purity metals. It is then shown that the activation energy for oxidation in nickel-base alloys is almost the same as that in high-purity nickel metal when alloying elements are added to nickel.     

Differential scanning calorimetry and reaction kinetics studies of γ + α2 Ti aluminide

Reaction synthesis method for titanium aluminide processing consists of an exothermic reaction among alloying elements present and primarily between titanium and aluminium particles at specific temperature range. Study of this reaction helps in understanding the process of aluminide formation. Differential scanning calorimetry (DSC) study is the suitable method to study such reactions. In the present work, five different alloy mixtures based on Ti48Al2Cr2Nb0.1B are prepared and DSC study is carried out. Onset temperature, peak temperature and completion temperature of the major exothermic reaction is analyzed at different heating rates. Further, kinetics of the reaction is studied using Johnson–Mehl–Avrami equation. Activation energy and Avrami parameter are calculated and compared with the reported works on binary alloy. It has been observed that exothermic reaction is triggered by melting of aluminium. Boron assists in increasing the enthalpy of reaction by boride formation. Primary reaction product is found to be TiAl₃. Activation energy as well as Avrami parameter is found to have marginal variation due to small change in alloying elements in different alloys and due to heating rates in the same alloy.     

Wetting of aluminium oxide by molten aluminium and other metals

The sessile drop technique has been used to measure the contact angle of molten aluminium, aluminium-nickel and aluminium-copper alloys, copper and gold, with sapphire, ruby and recrystallised alumina. Measurements were madein vacuo, and as a function of time and temperature over the range 800 to 1500° C. Cinematography and time-lapse photography were used. At temperatures below 950° C, sessile drops of aluminium reached equilibrium only after a period of time which increased with decrease in temperature and could be in excess of one hour. A rapid increase in contact area occurred around 900° C. Above 1150° C drops of aluminium and of the aluminium alloys were observed to spread and contract repeatedly. Contractions were observed with both polycrystalline and single-crystal alumina, although they were much more pronounced with the latter, and were associated with the formation of a series of reaction rings on the plaque. Ruby and sapphire behaved similarly. The shape of the rings depended on the crystallographic orientation of the plaque: the reaction profile tended to terminate in certain low index directions. Neither contractions nor reaction was observed with copper or gold. The observations are discussed in terms of the combined effects of evaporation, chemical reactivity and interfacial tensions in the system.     

The effect of the annealing of indium electrode films on the electrical resistivity of thin metal films

The resistances of thin films of gold, silver, copper and aluminium deposited onto glass substrates were measured using annealed and unannealed films of indium as electrodes. The percentage variation in resistance for the different metal films differs with annealed and unannealed electrodes. The effect of factors such as oxide formation, bubble formation and alloying at the electrode-film junction are discussed in the light of the observed variations in resistance of the films. An attempt is also made to correlate this variation with the microscopic features observed at particular electrode-film junctions.     

Dental application of the 30Ni-30Cu-40Mn ternary alloy system

Experimental nickel-based alloys for dental application were made on the basis of the measurement of dissolved oxygen in the liquid state of the alloys. The improved Ni-Cu-Mn-based alloys were examined for hardness, microstructures and dimensional change. The alloys had a low concentration of dissolved oxygen, and each experimental Ni-Cu-Mn-based alloy containing a single additive element (either aluminium or tin) and complex additive elements (aluminium and tin, aluminium and indium, and aluminium, indium and tin) was constituted mainly by dendrite structure, but the aluminium, indium and tin-containing ones had a smaller amount of dendrite structure than the others, representing a fineness of dendrite structure. In addition, the metal crowns of the improved Ni-Cu-Mn-based alloys showed a better fit than that of the original Ni-Cu-Mn ternary alloy.     

The solid phase bonding of copper,nickel and some of their alloys to diamonds

The bonding achieved by vacuum hot-pressing cylinders of copper, nickel and a few of their alloys against diamond plaques has been measured. Alloying with carbide-forming elements such as titanium can have a markedly beneficial effect on the bonding of copper and, to a lesser extent, of nickel. The strengths obtained also depended on the fabrication time and temperature, at first increasing and then decreasing with time. These phenomena are compared to those observed previously in a study of bonding between diamonds and molten copper alloys. Some evidence is presented that relates the phenomena to the abrasiveness of diamond grit compacts.     

Effects of alloy additions on the fatigue properties of cast Co-Cr-Mo alloy used for surgical implants

As the second part of the present study, the effects of modifying the composition of the Co-Cr-Mo alloy with additions of nickel and some trace elements aluminium, titanium and boron, have been investigated. A great improvement in the fatigue crack growth resistance of the cast alloy is obtained by nickel additions to the base alloy, mainly because of a significant increase in the alloy's stacking fault energy. In addition, the fatigue fracture ductility is observed to be improved strikingly with the nickel additions. Much smaller facets and better ductility with a mixed fatigue crack propagation mode, as compared to the base alloy, are observed in the alloys with low nickel content level, and in the alloys with high nickel content level, localized ductile fatigue striations are observed. It is also indicated that minor additions of such elements as aluminium, titanium and boron can be used to improve further the fatigue crack growth resistance resulting from the elimination of some microstructural casting defects.     

Compatibility between carbon fibre and binary aluminium alloys

Compatibility between carbon fibre and various binary aluminium alloys is investigated. Series of aluminium alloys are coated onto the fibre surface and the wetting behaviour of these alloys are observed by scanning electron microscopy after heating the coated fibres at 1073 K, well above the melting point of the alloys. It is found that the aluminium alloys containing such elements as indium, lead and thallium showed excellent wetting behaviour. These alloying elements have significantly smaller surface energies as compared to aluminium and they are practically insoluble with aluminium, even in the liquid states. Tensile test shows that the strength of carbon fibres is not degraded after heating at 1073 K when fibres are coated with an Al-1 at % Tl alloy. The reasons for these elements in aluminium to substantially improve the compatibility against carbon fibres are discussed from the thermodynamical point of view.     

Synthesis,microstructure and mechanical properties of Al2O3 reinforced Ni3Al matrix composite

A new method to synthesize alumina reinforced Ni₃Al intermetallic matrix composites has been described. The powder mixture of nickel and aluminium was mechanically alloyed. The powder mixture was excessively heated during mechanical alloying and then exposed to atmosphere for oxidation. The oxidized powder mixture was transformed into alumina reinforced nickel aluminide matrix composite on subsequent pulse current processing. Alumina reinforcements were generated in the nickel aluminide matrix by in situ precipitation. The microstructure of the composite showed that the alumina reinforcements were 50–150 nm in size. The fine alumina reinforcements were homogeneously distributed in the matrix phase. The mechanical properties of the alumina reinforced nickel aluminide matrix composite fairly exceeded the nickel aluminide alloys. This novel synthesis approach allowed the rapid and facile production of high strength alumina reinforced Ni₃Al matrix composites.     

The effect of the annealing of electrode films on the electrical resistivity of thin aluminium films

The resistance of aluminium films, coated on glass substrates with annealed and unannealed thick films of gold, silver, copper and aluminium as electrodes, was measured. The percentage variation in resistance of the aluminium films differs with the use of annealed and unannealed electrodes. This variation was found to be greater for gold, silver and copper electrodes and not very marked for aluminium electrodes. The respective roles of factors such as oxide formation and alloying at the film-electrode junction are discussed by considering the observed variation in the resistance of the films. An attempt is also made to correlate this variation with the microscopic features seen at particular electrode-film junctions.     

Joining of sialon ceramics by Sn-5 at % Ti based ternary active solders

The effect of a third element, such as silver, copper, indium, nickel or aluminium, on the joining of sialon ceramics with tin-5 at % titanium based ternary active solders was investigated. The content of the third element in the Sn-based solders was varied from 5–40% for Cu, from 5–10% for Ag and Al from 5–20% for In and from 1–5% for Ni. The joining was carried out in vacuum at 1100 K for 20 min. The four point bend testing of a butt joint of a ceramic/ceramic structure with dimensions 40 mm long, 3 mm wide and 4 mm high was used to study the bond strength between the ceramic and the Sn-based solders. The results show that the bond strength of the Sn-based solder with the sialon ceramic varied from 54–103 MPa. Small additions of Cu or Ag (about 5–10%), In (about 5–10%), or Ni (about 1–3%) to the solder is beneficial, but too much Ni (more than 5%) or In (more than 10%) is detrimental. On the other hand, Al in the active solder considerably decreased the bond strength of the solders with the ceramic. Suggestions are made for the selection of the third element in order to improve the bond strength of the soft solders with the ceramic. These include a high surface energy, improving the wetting of the solder on the ceramic and strengthening of the solder. This revised version was published online in November 2006 with corrections to the Cover Date.     

Resulting morphologies on quenching of titanium aluminide alloys

Abstract

The effect of alloying elements (aluminium, silicon, niobium, and zirconium) on the mechanism and morphology of the allotropic transformation Ti-β(bcc) → Ti-α(hcp), occurring during the quenching of binary, ternary, and quaternary titanium aluminide alloys, has been studied. The alloys investigated were (at.-%) Ti–16Al, Ti–16Al–1Si, Ti–16Al–3·5Si, Ti–14Al–1Si–1Nb, Ti–14Al–1Si–1Zr, Ti–22Al, Ti–22Al–1Si, Ti–22Al–3·5Si, Ti–20Al–1Si–1Nb, and Ti–20Al–1Si–1Zr. The allotropic transformation in these alloys presented a very narrow temperature range for the formation of all possible α morphologies resulting from quenching. The different morphologies of α phase observed have been correlated with the competing mechanisms of β decomposition. The morphological observations indicated that small variations in thermodynamic and kinetic conditions in the β phase might account for changes in the mechanisms of formation and growth of the α phase. Additionally, the effect of the alloying elements on the ordering reaction α → α₂ occurring during quenching has been investigated. Silicon addition promoted the formation of columnar α₂ domains during quenching.     

Cyclic oxidation of copper doped Ti-48Al-2Cr-2Nb

The widespread use of titanium aluminide alloys will require effective joining techniques for primary fabrication and repair. One such technique is Transient Liquid Phase (TLP) bonding, which has been used to join titanium aluminide alloys. A successful TLP bonding process uses a copper-containing composite interlayer and thus introduces a small amount of copper into the alloy. Although even relatively small alloying additions can be detrimental to the oxidation resistance of titanium aluminide alloys, the amount of copper added to the alloy during the TLP bonding process has previously been shown to be neutral or beneficial to the isothermal oxidation resistance of the alloy. In this paper, a small amount of copper introduced during TLP bonding is shown to have no detrimental effect on the cyclic oxidation of Ti-48 at% Al-2 at% Cr-2 at% Nb.     

Study of the properties of low-cost powder metallurgy titanium alloys by 430 stainless steel addition

Titanium is a lightweight metal with an outstanding combination of properties which make it the material of choice for many different applications. Nonetheless, its employment at industrial level is not widespread due to higher production costs with respect to competitor metals like steel and aluminium. In this work the production of low-cost titanium alloys is attempted by combining the utilisation of a powder metallurgy process and cheap alloying elements (i.e. commercial 430 stainless steel powder optimised for the powder metallurgy industry). Low-cost titanium alloys are fabricated by blending elemental titanium with stainless steel. The behaviour of the powders as well as that of the sintered materials are analysed and compared to that of a master alloy addition Ti6Al4V alloy. The produced low-cost titanium alloys show comparable properties to both wrought and powder metallurgy titanium alloys and, therefore, they are proposed as an alternative to obtain structural component made out of titanium alloys.     

The wetting of alumina and vitreous carbon by copper-tin-titanium alloys

The wetting behaviour of copper-rich copper-tin-titanium alloys on alumina and vitreous carbon substrates at 1050 to 1150° C has been determined using the sessile drop technique. Substantial additions of titanium induce copper to wet, but tin has no significant effect. However, the simultaneous addition of tin and titanium is markedly beneficial, particularly with vitreous carbon. Metallographic and EPMA studies showed that titanium-rich reaction products were formed at the interfaces. The wetting and reactivity data are interpreted in terms of surface enrichment of the alloys by tin and of a disproportionately greater activity of titanium in tin.     

Electromechanical polishing of alloys of copper and gold with the transition metals of the first long period

The electromechanical polishing of binary alloys of copper and gold with the Periodic Table elements from Ti to Se inclusive has been investigated with special reference to the inter-relation between the polishing response and the systematics of alloying behaviour. The electrolyte contained 12 wt% sodium thiosulphate with varying additions of potassium thiocyanate. Wide ranges of composition of primary solid solution of the transition metals and B Group elements in copper and gold, and also a few chromiumand vanadium-base alloys, polish satisfactorily. Brief mention is also made of the polishing of Ag-Al alloys and Fe-Mn-P-C metallic glasses.