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The 18kt gold-based bulk glass-forming composition Au49Ag5.5Pd2.3Cu26.9Si16.3 is modified in order to reduce its fast surface tarnishing caused by internal oxidation of Si, partitioning and fast out-diffusion of Cu and Au. By partially substituting Cu by the species Ga or Sn, the formation of Si as primary crystalline phase is facilitated and a distinct increase of the liquidus temperature is observed. It is found that a reduction of the Si content recovers the glass-forming ability of the novel Ga/Sn-containing alloys, reflected by an increasing reduced glass transition temperature, Trg, and a decreasing driving force for crystallization. This strategy is used to reduce the amount of Cu and Si, which are responsible for the fast surface tarnishing. Corrosion studies of the novel alloys reveal that the Cu release into an artificial saliva test solution is up to eight times lower than that of the mother alloy and the corrosion depth in artificial saliva is drastically lowered by 50% for the Ga-bearing alloys and by 80% for the Sn-bearing alloys. Keywords: Bulk metallic glass, Gold, Corrosion, Alloy development, Jewelry application

Effective strategies to improve the tarnishing resistance of the 18 K (karat) gold-based bulk glass-forming composition Au49Ag5.5Pd2.3Cu26.9Si16.3 were recently found, with the addition of Ga at the expense of Cu and a sufficient reduction of Si. However, the modification of the alloy is accompanied by a reduction of the glass-forming ability (GFA) from 5 to 2 mm in terms of the critical casting thickness, and eventually collapses for Ga contents higher than about 9 at%. In this work, thermodynamic and kinetic studies of the newly discovered 18 K Au-Ag-Pd-Cu-Ga-Si system shed light on the reason for the loss in GFA with increasing Ga content. Investigations of the liquid kinetics in terms of viscosity and transition time, assessed by three-point beam bending and the Tg-shift method, reveal an unexpected change of the fragility to stronger liquid kinetics with increasing Ga concentration, which is usually attributed to an increase in the GFA. Thermodynamic considerations based on specific heat capacity measurements reveal, in contrast, an ascending driving force for crystallization with an increasing Ga-content, accountable for the drop in GFA. Therefore, a Ga-rich melt beyond the threshold concentration of 9 at% is not desirable for the production of bulk metallic glasses (BMGs) from the liquid state. With the intention to outrun this barrier, while preserving the amorphous structure, Ga-ion implantation with a liquid metal focused ion beam source is used as a post-processing routine for a cast Ga-containing 18 K Au-BMG. Hence, the thermodynamic borderline concentration is successfully crossed with additional tremendous improvement of the tarnishing resistance in the Ga-enriched areas.

Surface quality and dimensional accuracy of titanium components produced by investment casting are limited by the conventional dip-coating procedure of the lost-wax process. This study presents a novel approach with spraying and centrifugation as alternative coating technologies. Aiming at improved surface quality, calcium zirconate slips and coatings based on alginate gelation were developed. Scanning electron microscopy and computed tomography revealed a homogeneous spray coating. The alginate-based spray coating was used for producing functionally graded calcium zirconate shell molds. These molds exhibited a fine-grained microstructure with pores in the lower μ m range. Applying an intermediate layer between the fine-grained spray coating and the coarse-grained dip-coating layers as well as the alternating application of dip-coating layers prevented cracking. The characteristic microstructure showed a bridging zone and a homogeneous distribution of coarse grain across the diameter. Ti6Al4V cast parts with no presence of an alpha case layer were obtained.

A series of iterative wear and corrosion tests were conducted on two 950 platinum alloys, two 585 white gold alloys and two 750 white gold alloys. Testing followed standardised industrial procedures in order to provide comparable and reproducible conditions. Wear testing comprised a sequence including abrasion testing, corrosion testing and polish testing. Mass loss was recorded after each test cycle. Five complete test cycles were followed by two long-term polish tests. The total testing time was ca. 250 h. A pronounced difference in the mass and volume loss between the platinum and the gold alloys was observed. The absolute volume loss per surface area of the platinum alloys was a factor of two to three times lower than that of the gold alloys. The highest volume loss was observed for 750AuPd, followed by 585AuPd, 585AuNi and 750AuNi with the latter three showing similar wear behaviours. The mass loss increased linearly with testing time. No measurable mass loss was observed by corrosion testing in our limited duration test cycle and the only alloy exhibiting significant corrosion was 585AuNi. Hardness of the alloys was determined by Vickers microhardness testing at a 100 g load. Notably, higher hardness levels were not found to be an indicator for low mass or volume loss.

The use of biodegradable materials for implants is a promising strategy to overcome known long-term clinical complications related to permanent implants. Ideally, biodegradable implants support the damaged tissue for a certain period and then degrade, while the physiological function of the surrounding tissue is restored. Although Mg-based alloys nearly ideally lend themselves to biodegradable implants, a few critical shortcomings promoted the development of alternative alloy systems. Due to their reasonably good biocompatibility, moderate corrosion rate without hydrogen evolution and adequate mechanical properties, increasing attention has been paid to Zn alloys. In this work, precipitation-hardening alloys in the system Zn-Ag-Cu were developed relying on thermodynamic calculations. After casting the alloys, their microstructures were refined by thermomechanical treatment. The processing was tracked and directed, respectively, by routine investigations of the microstructure, associated with hardness assessments. Although microstructure refinement increased the hardness, the material proved to be susceptible to aging as the homologous temperature of zinc is at 0.43 Tm. Besides mechanical performance and corrosion rate, long-term mechanical stability is another crucial factor that must be taken into consideration to ensure the safety of the implant and thus requires a profound understanding of the aging process.

Additive manufacturing of jewellery alloys has been actively investigated during the last 10 years. Several, but limited studies have been conducted on gold and platinum jewellery alloys. Platinum is of increased interest due to the technological challenges in investment casting. In the present paper, typical platinum jewellery alloys have been tested by laser track experiments on sheet materials. The effect of alloy composition on width and depth of the laser tracks was studied by metallography. Optimum parameters of the LPBF process were determined for a typical 950Pt jewellery alloy by the preparation of dedicated test samples. Densities of >99.8% were reached for a wide range of processing parameters. However, in case of real jewellery parts the resulting density was found to depend significantly on the part geometry and on the chosen support structure. The supports have to take into account the geometrical orientation of the part relative to the laser build direction and the orientation on the build plate. Local overheating gives rise to porosity in these areas. Therefore, the supports play an important role in the thermal management and have to be optimized for each part. The design of suitable supports was successfully demonstrated for a typical jewellery ring sample.

Zinc (Zn) alloys have been considered as promising absorbable metals, mainly due to their moderate degradation rates ranging between magnesium alloys and iron alloys. The degradation behavior depends on the specific physiological environment. Released metallic ions and corrosion products directly influence biocompatibility. The initial contact of orthopedic implants or vascular stents after implantation will be with blood. In this study, fetal bovine serum (FBS) was used as a model system of blood components. We investigated the influence of FBS on in vitro degradation behavior and cytotoxicity of pure Zn, and Zn-4Ag and Zn-2Ag-1.8Au-0.2 V (wt%) alloys. The initial degradation rates in FBS were assessed and compared with the degradation and toxicity in four other common physiological model systems: DMEM cell culture medium ± FBS and McCoy's 5A medium ± FBS. Test samples in pure FBS showed the highest initial degradation rates, and accordingly, FBS supplemented media accelerated the degradation process as well. Moreover, an extract test according to ISO 10993-5 and -12 with L929 and Saos-2 cells was performed to investigate the role of FBS in the extraction medium. The cytotoxic effects observed in the tests were correlated with FBS-mediated Zn2+ release. These findings have significant implications regarding the selection of appropriate media for in vitro degradation and cytotoxicity evaluation of Zn and its alloys. Statement of Significance Metallic zinc and its alloys have been considered as promising biodegradable metals, mainly due to their moderate degradation rates. However, in vitro cytotoxicity tests according to the current ISO 10993 standard series are not suitable to predict biocompatibility of Zn alloys due to the inconsistent correlation between in vitro and in vitro biocompatibility. In this study, we show that the outcomes of standardized in vitro cytotoxicity tests of Zn and Zn alloys are influenced by fetal bovine serum in the extraction vehicle because FBS promotes Zn2+ release during the extraction process. The results of the study provide significant information for selection of appropriate model systems to evaluate in vitro degradation behavior and cytotoxicity.

Owing to the physical properties of copper and its alloys it is challenging to achieve good surface quality and low porosity by the widely used laser-based additive manufacturing processes. This paper deals with the role of alloy composition, powder size and process parameters in additive manufacturing with laser beam melting machine (with power up to 100 W). Test parts were produced in pure copper and CuNiSi(Cr) alloys. The porosity was investigated as a function of different process parameters and powder size ranges. The effects of the alloy physical properties (reflectivity, thermal conductivity, melting range and surface tension) are discussed. Moreover, the effect of thermal treatment on the properties of CuNiSi parts was assessed in conventional two-step heat treatments.

Zn-based biodegradable metallic materials have been regarded as new potential biomaterials for use as biodegradable implants, mainly because of the ideal degradation rate compared with those of Mg-based alloys and Fe-based alloys. In this study, we developed and investigated a novel Zn-4 wt % Ag alloy as a potential biodegradable metal. A thermomechanical treatment was applied to refine the microstructure and, consequently, to improve the mechanical properties, compared to pure Zn. The yield strength (YS), ultimate tensile strength (UTS) and elongation of the Zn-4Ag alloy are 157 MPa, 261 MPa, and 37%, respectively. The corrosion rate of Zn-4Ag calculated from released Zn ions in DMEM extracts is approximately 10.75 ± 0.16 μg cm

Diffusion couples of copper alloys are presented as screening tool for high-throughput alloy development. It allows estimating the precipitation hardening potential in multicomponent alloys of a va...

Copper is a material used in a wide range of applications. The combination of electrical conductivity and mechanical strength is a feature which is especially important when it comes to conductive and contact materials. This combination of properties in low-alloy copper-based alloys can be achieved when the material is subjected to a thermomechanical treatment consisting of rolling and annealing. Samples of the alloy CuNi1.5Si0.3 were taken at distinctive steps of the industrial manufacturing process for semi-finished products in order to examine the influence of the manufacturing parameters on the microstructure during solution annealing, rolling, and aging. The sample material for the respective chosen conditions was aged in the laboratory at various temperatures. Quasi-static tensile tests were performed, the electrical conductivity was determined, the microhardness was measured, and the microstructure was examined on metallographic sections in order to characterize the material conditions.

Investment casting allows the near net shape production of complex cast parts, but the investment casting of high melting and highly reactive titanium alloy melts is very difficult. Calcium zirconate ( C a Z r O 3 ) is a novel ceramic refractory material, which is particularly stable in a highly reducing atmosphere and in contact with extremely reducing titanium alloy melts such as Ti6Al4V. Besides the refractory, the choice of the binder is equally important because conventional silicate binders significantly impair the corrosion resistance. Although there have been successful attempts to develop CaZrO 3 investment casting molds, silica-free CaZrO 3 investment casting molds using a water-based binder have not yet been reported. For the first time, CaZrO 3 investment casting molds using a silica-free water-based binder system were successfully produced. Moreover, the rheological behavior of the slips and the chemical, physical and microstructural properties of the molds were extensively described. Investment casting of Ti6Al4V led to an exceptionally low hardness increase of the cast part, suggesting that only a slight corrosion reaction took place. Thus, the silica-free CaZrO 3 investment casting molds contributed to an improved investment casting of titanium alloys.

Zinc (Zn) and Zn-based alloys have been proposed as a new generation of absorbable metals mainly owing to the moderate degradation behavior of zinc between magnesium and iron. Nonetheless, mechanical strength of pure Zn is relatively poor, making it insufficient for the majority of clinical applications. In this study, a novel Zn–2Ag–1.8Au–0.2V (wt.%) alloy (Zn–Ag–Au–V) was fabricated and investigated for use as a potential absorbable biocompatible material. Microstructural characterization indicated an effective grain-refining effect on the Zn alloy after a thermomechanical treatment. Compared to pure Zn, the Zn–Ag–Au–V alloy showed significantly enhanced mechanical properties, with a yield strength of 168 MPa, an ultimate tensile strength of 233 MPa, and an elongation of 17%. Immersion test indicated that the degradation rate of the Zn–Ag–Au–V alloy in Dulbecco’s phosphate buffered saline was approximately 7.34 ± 0.64 μm/year, thus being slightly lower than that of pure Zn. Biocompatibility tests with L929 and Saos-2 cells showed a moderate cytotoxicity, alloy extracts at 16.7%, and 10% concentration did not affect metabolic activity and cell proliferation. Plaque formation in vitro was reduced, the Zn–Ag–Au–V surface inhibited adhesion and biofilm formation by the early oral colonizer Streptococcus gordonii, indicating antibacterial properties of the alloy.

Zinc (Zn) and its alloys are proposed as promising resorbable materials for osteosynthesis implants. Detailed studies should be undertaken to clarify their properties in terms of degradability, biocompatibility and osteoinductivity. Degradation products of Zn alloys might affect directly adjacent cellular and tissue responses. Periosteal stem cells are responsible for participating in intramembranous ossification during fracture healing. The present study aims at examining possible effects emanating from Zn or Zn–4Ag (wt%) alloy degradation products on cell viability and osteogenic differentiation of a human immortalized cranial periosteal cell line (TAg cells). Therefore, a modified extraction method was used to investigate the degradation behavior of Zn and Zn–4Ag alloys under cell culture conditions. Compared with pure Zn, Zn–4Ag alloy showed almost fourfold higher degradation rates under cell culture conditions, while the associated degradation products had no adverse effects on cell viability. Osteogenic induction of TAg cells revealed that high concentration extracts significantly reduced calcium deposition of TAg cells, while low concentration extracts enhanced calcium deposition, indicating a dose-dependent effect of Zn ions. Our results give evidence that the observed cytotoxicity effects were determined by the released degradation products of Zn and Zn–4Ag alloys, rather than by degradation rates calculated by weight loss. Extracellular Zn ion concentration was found to modulate osteogenic differentiation of TAg cells. These findings provide significant implications and guidance for the development of Zn-based alloys with an optimized degradation behavior for Zn-based osteosynthesis implants.

Titanium alloys are very difficult to process via investment casting due to their high melting temperature and reactivity. The objective of the present work was to evaluate new shell mould materials for the suitability for titanium casting in comparison to conventional materials. A new corrosion-resistant material for crucibles and shell moulds based on calcium zirconate (CaZrO3) is proposed with the aim of improving the casting quality of titanium alloys. Tilt casting trials into CaZrO3 shell moulds using three different crucible materials were conducted. The results were compared to a commercial shell system containing silica. The reactivity with the titanium melt was extensively studied as a function of melt temperature, part dimensions and shell mould temperature by hardness profiles and oxygen measurements. The reaction of the CaZrO3 shell was very low, indicated by small oxygen contents and thereby low surface hardness. The formation of an α-case was avoided by choosing appropriate casting parameters.

Zinc (Zn) and its alloys have been considered as potential materials for osteosynthesis implants. Nonetheless, the relatively slow degradation rates within bone environments impede their further application. Herein, sandblasting surface treatment with two Al2O3 particle sizes (125 μm and 250 μm) was employed to accelerate the degradation rates of Zn and two Zn alloys, a Zn 4Ag and a Zn-2Ag-1.8Au-0.2V (wt%). The degradation processes of Zn and Zn alloys were significantly increased after sandblasting treatment mainly due to the increased surface roughness and embedded Al2O3 particles in the surfaces. However, an increase of sandblasting particle size from 125 μm to 250 μm did not affect the degradation rates. Moreover, the mean relative metabolic activities of Saos-2 osteoblasts below 70% were observed for alloys treated with 250 μm Al2O3 particles, indicating apparent cytotoxic effects. The results showed that the size of the sandblasting particles had no direct effect on the degradation rate but on the cytotoxicity. Therefore, sandblasting treatment with appropriate particles might be a promising surface modification to accelerate the biodegradability of Zn and its alloys.

cited By 2; International audience; The dynamic mechanical relaxation behavior of an Au49Cu26.9Si16.3Ag5.5Pd2.3 (at.%) bulk metallic glass was investigated by mechanical spectroscopy as a function of temperature or driving frequency. The mechanical spectra show the evidence of a secondary relaxation (or β) process at low temperature or high driving frequency. The main relaxation (α) is clearly evident at higher temperature or lower frequency. Crystallization induces an increase in elastic modulus, in two steps, which correspond to the formation of two different crystalline phases, as determined by in-situ X-ray diffraction experiments. Master curves could be obtained based on the time-temperature superposition principle. From these curves the apparent activation energies for the two relaxation phenomena were determined: Eβ = 1.10 eV and Eα = 3.65 eV, respectively. These values indicate that the secondary relaxation may be attributed to local atomic movements, while the α relaxation corresponds to correlated movements. © 2016 Elsevier B.V.

cited By 2; International audience; The present investigation addresses the impact of crystallinity on the mechanical properties: hardness (HV) and toughness (KIC) in an Au49Cu26.9Ag5.5Pd2.3Si16.3 BMG which appears especially attractive for applications in jewelry and watch making industries. Thermal stability is first determined using differential scanning calorimetry (DSC), X-ray diffraction and thermo-mechanical analysis (TMA). Then the conditions (time, temperature) in which crystallization is observed (during annealing above the glass transition temperature) and the kinetics are determined. Results show an increase of hardness proportional to the volume fraction of the crystalline phase (φ) (from about 350 HV up to about 480 HV), and a drastic reduction in fracture toughness from about 20 MPa√m down to 1.5 MPa√m for fully crystalline structure. Finally the conditions required achieving a good compromise between hardness and toughness are established. © 2016 Elsevier B.V.

Zn-based biodegradable metallic materials have been regarded as new potential biomaterials for use as biodegradable implants, mainly because of the ideal degradation rate compared with those of Mg-based alloys and Fe-based alloys. In this study, we developed and investigated a novel Zn-4 wt % Ag alloy as a potential biodegradable metal. A thermomechanical treatment was applied to refine the microstructure and, consequently, to improve the mechanical properties, compared to pure Zn. The yield strength (YS), ultimate tensile strength (UTS) and elongation of the Zn-4Ag alloy are 157 MPa, 261 MPa, and 37%, respectively. The corrosion rate of Zn-4Ag calculated from released Zn ions in DMEM extracts is approximately 10.75 ± 0.16 μg cm–2 day–1, which is higher than that of pure Zn. In vitro cytotoxicity tests showed that the Zn-4Ag alloy exhibits acceptable toxicity to L929 and Saos-2 cells, and could effectively inhibit initial bacteria adhesion. This study shows that the Zn-4Ag exhibits excellent mechanical properties, predictable degradation behavior, acceptable biocompatibility, and effective antibacterial properties, which make it a candidate biodegradable material.

Zn-based biodegradable metallic materials have been regarded as new potential biomaterials for use as biodegradable implants, mainly because of the ideal degradation rate compared with those of Mg-based alloys and Fe-based alloys. In this study, we developed and investigated a novel Zn-4 wt % Ag alloy as a potential biodegradable metal. A thermomechanical treatment was applied to refine the microstructure and, consequently, to improve the mechanical properties, compared to pure Zn. The yield strength (YS), ultimate tensile strength (UTS) and elongation of the Zn-4Ag alloy are 157 MPa, 261 MPa, and 37%, respectively. The corrosion rate of Zn-4Ag calculated from released Zn ions in DMEM extracts is approximately 0.75 ± 0.16 μg cm–2 day–1, which is higher than that of pure Zn. In vitro cytotoxicity tests showed that the Zn-4Ag alloy exhibits acceptable toxicity to L929 and Saos-2 cells, and could effectively inhibit initial bacteria adhesion. This study shows that the Zn-4Ag exhibits excellent mechanical properties, predictable degradation behavior, acceptable biocompatibility, and effective antibacterial properties, which make it a candidate biodegradable material.

In earlier research a better understanding of the solidifi cation characteristics for a number of platinumbased alloys was established (1). The fi ndings demonstrated a strong tendency toward the formation of shrinkage and gas porosity upon solidifi cation, and HIP, a high-pressure thermal treatment developed as a densifi cation process, was proven to be an effective method to minimise or eliminate this porosity. While the previous results made it clear that porosity had been signifi cantly reduced following the HIP process, the authors had not yet explored the full range of HIP’s effects in terms of post-processed microstructure and mechanical properties. The goal of this new phase of research is to further our understanding by characterising the post-HIP effects on platinum based castings with respect to grain size and shape, chemical distribution and mechanical strength.

The amorphous 18 K white gold alloy of the composition Au49Ag5.5Pd2.3Cu26.9Si16.3 at% possesses a premium white-gold color and a Vickers hardness value 1.5 times that of conventional white gold alloys. These properties, together with the low melting temperature of ca. 370 °C and its good processability are highly desired for jewelry applications. Nevertheless, the premium white color of this alloy is unstable and turns into a yellowish brown color after some time. The intense tarnishing of the Au49Ag5.5Pd2.3Cu26.9Si16.3 at% bulk metallic glass alloy under various different environmental conditions has been investigated by SEM, STEM, TEM, and Auger spectroscopy (AES) and linked to a chemical interaction between the copper and the silicon of the alloy. A mechanism behind the tarnishing is discussed in detail and suggestions are made for future alloy development towards a tarnish resistant 18 K amorphous white gold alloy.

Platinum and copper along with their alloys have been used in a broad range of applications including jewelry, coinage, electrical and electronic devices, and many others. Their thermophysical properties play an important role in casting processes and are required as input data for casting simulation. The focus of this work was to investigate these properties by different methods. Platinum, copper, and four platinum-copper alloys, namely, Pt96Cu04, Pt68Cu32, Pt50Cu50, and Pt25Cu75, were investigated within this work. The melting range and thermal expansion were measured at fem by differential scanning calorimetry and dilatometry, respectively. At TU Graz, wire-shaped samples were investigated by an ohmic pulse heating technique. This technique delivers thermophysical properties of electrically conducting materials far into the liquid phase. These measurements allow the calculation of specific heat capacity and the temperature dependencies of electrical resistivity, enthalpy, and density of these alloys in the solid and liquid phases. Thermal conductivity and thermal diffusivity as a function of temperature are estimated from resistivity data using the Wiedemann–Franz law at the end of the solid phase and at the beginning of the liquid phase. The results are compared with the available literature values.

Solid state diffusion bonding has been successfully employed to join γ-TiAl alloys. Processed in vacuum, at high temperature and pressure, the thin interfaces and the lack of structural discontinuity across the interface are the main advantage of this joining technique. An interlayer made of alternated Ti and Al nanometric layers that increases the diffusivity at the joint interface, was used in order to assist the bonding process of γ-TiAl alloys. The use of Ti/Al interlayer has efficiently reduced the joining temperature. Sound joints have been achieved at a temperature of 900 °C under a pressure of 50 MPa in vacuum. In the present work Cu was added as third element to the Ti/Al multilayers and its effect improved the bonding quality. The interface microstructure was studied by scanning and transmission electron microscopy.

In this study phase equilibria in the Fe–Ni–Ti–Al system were investigated experimentally, with special emphasis on the FeAl–NiAl–TiAl section. Individual alloys with chemical compositions from this section were prepared by arc-melting in an argon atmosphere, and were examined by differential thermal analysis (DTA). Microstructural characterization of as-cast and samples equilibrated at 800 °C and 1000 °C was performed by scanning electron microscopy (SEM), and the compositions of the coexisting phases were established by electron probe microanalysis (EPMA). The crystal structure of selected alloys was characterized by X-ray diffraction (XRD) and Rietveld refinements. A complete solid solubility of the B2 phase from FeAl to NiAl was observed and the solubility for Ti was seen to decrease with decreasing temperature. The ternary phase Al2FeTi (τ2) also shows a significant extension into the quaternary. In contrast, TiAl has a very low solubility for Fe and Ni.

The Cu–Sn–Ti ternary system has been studied via experiments and thermodynamic modelling. In the experimental section, the composition of the alloys was selected based on the preliminary calculations and available literature data. Metallography, scanning electron microscopy and electron probe microanalysis were employed to analyse alloy samples prepared by arc-melting after annealing at 800 °C for 760 h. Solid phase relations at 800 °C were established. In contrast to earlier reports, the CuSn 3 Ti 5 phase was interpreted as a binary intermetallic compound (Sn 3 Ti 5 ) with extended Cu solubility. In the modelling section, three binary sub-systems were critically evaluated and updated according to the new experimental data and theoretical calculations reported in literature. According to their crystal structures and homogeneity ranges, appropriate sublattice models were proposed for SnTi 3 ,SnTi 2 ,Sn 3 Ti 5 and Sn 5 Ti 6 . A set of self-consistent thermodynamic parameters for the Cu–Sn–Ti ternary system was obtained by considering the present experimental results and reported experimental information. The calculated results compare with the available experimental data to validate the present thermodynamic assessment.

Despite its significant technical relevance, a number of uncertainties remain regarding the Fe–Ni–Ti ternary system. These concern phase relations, the solidus–liquidus range and the liquidus projection, especially in the Ti-rich corner. In this study the melting and solidification behaviour of Tirich Fe–Ni–Ti alloys was characterized using differential thermal analysis, electrical conductivity measurements and high-temperature X-ray diffraction. Combining these different methods allowed us to determine the liquidus temperatures more precisely than with differential thermal analysis measurements alone. The results were compared with calculated values using the ThermoCalc software package.

The Research Institute for Precious Metals and Metals Chemistry (FEM), Katharinenstrasse 17, D-73525 Schwabisch Gmund, Germany; *E-mail: klotz@fem-online.de Platinum is a challenging material for casters because of its physical properties, which result in possible crucible and flask reactions during melting and casting, high shrinkage porosity and difficulties in filling of filigree items. This paper summarises the results of a collaborative research effort by several industrial partners and FEM on the influence of casting process parameters. Two common platinum jewellery alloys (platinum with 5 wt% cobalt and platinum with 5 wt% ruthenium) and four different investment materials were used for casting experiments with variation of atmosphere, casting and flask temperature, tree design and centrifugal machine parameters. Detailed sample investigation found shrinkage porosity and surface defects to be the main problems. Optimised process parameters for heavy and filigree items were identified. Future research on platinum casting should focus on casting simulation in order to reduce experimental effort and costs.

In this investigation phase relations in the Fe–Ni–Ti system were studied and two isothermal sections at 800 °C and 1000 °C as well as a revised liquidus projection were established. Microstructural characterisation of the as-cast alloys and of samples equilibrated at 800 and 1000 °C was performed by scanning electron microscopy (SEM), chemical compositions of the phases were analysed by electron probe microanalysis (EPMA), and liquidus temperatures were examined by differential thermal analysis (DTA). The experimental results clarify some uncertainties concerning the melting behaviour and the solid-state phase equilibria between the phases (Ni,Fe)Ti2, (Fe,Ni)Ti and β-Ti. The present data also confirm that the solid solubility of Ti in γ-(Fe,Ni) varies in dependence on the Fe:Ni ratio and decreases with decreasing temperature. The liquidus projection as well as the reaction scheme in the Ti-lean part are modified because two ternaries eutectic E1: L ↔ γ-(Fe,Ni) + Fe2Ti + Ni3Ti and E2: L ↔ Fe2Ti + Ni3Ti + (Fe,Ni)Ti are found at 1108 and 1099 °C, respectively.

Blue and purple gold alloys form in the alloying systems of gold with gallium/indium and aluminium respectively and are known to be very brittle and to possess low corrosion resistance. Taking into account these drawbacks this paper describes the results of a European funded research project. The properties of the blue and purple gold alloys and coatings such as corrosion resistance, metal release rates, hardness and colour and the influence of alloying additions on these properties are presented and discussed. Surface engineering techniques and investment casting were used for manufacturing of jewellery items with selectively coated coloured surface. Coatings of AuGa2 and AuIn2 blue gold alloys were applied on 18kt gold and Sterling silver jewellery by electroplating, laser/torch cladding or dipping into liquid gallium. The suitability of blue gold coatings for jewellery purposes will be discussed in the light of reliability and feasibility. The work consists of two parts. Part I describes properties and surface processing techniques while Part II deals with investment casting and related alloy design of coloured gold alloys.

The structures of Sn1– x Ti x (x = 0.00; 0.02, 0.05, 0.15, 0.25; 0.35; 0.45) alloys were studied by X-ray diffraction at different temperatures. The structure factors, pair correlation functions, and parameters obtained were analysed. It is shown that the structures of the liquid alloys are inhomogeneous in the pre-crystallisation temperature region. The solidified phases are in agreement with the equilibrium phase diagram. The X-ray diffraction data were used for the specification of the liquidus line position.

The Sn – Ti – Zr system is an important subsystem for Cu based active brazing filler metals. Experimental results on this system, however, are rather scarce. The diagram is rather uncertain regarding most of the liquidus, especially on the Sn rich side. In this work, the atomic structure and temperature dependence of structure-sensitive physical properties (dynamic viscosity and electrical conductivity) of liquid Sn – Ti – Zr alloys in the Sn-rich corner were investigated in a wide temperature range with special attention to the melting – solidification region. The results allowed the liquidus line position to be specified.

In this work, a nominally new Fe-Mn-Si based shape memory alloy with a small amount of VC was designed. After an optimized thermo-mechanical treatment, a shape recovery of more than 90% after an elongation of 4% could be achieved when the alloys were heated up to 225°C. In addition, high recovery stresses of up to 380 MPa could be obtained after heating to 225°C, whereas 330 MPa were obtained after heating to 160°C.

Active brazing is an effective technique for joining diamond or cBN grit to metallic substrates. This technique is currently used to manufacture superabrasive, high-performance tools. The investigation of interface reactions between diamond and active brazing alloys plays an important role in understanding and improving the brazing process and the resultant tool performance. Focused ion beam (FIB) milling enabled the high resolution investigation of these extremely difficult to prepare metal–diamond joints. The interfacial nanostructure is characterized by the formation of two layers of TiC with different morphologies. First a cuboidal layer forms directly on the diamond and reaches a thickness of approximately 70 nm. Then a second layer with columnar TiC crystals grows on the first layer into the brazing filler metal by a diffusion-controlled process. The combined thickness of both TiC layers varies between 50 nm and 600 nm depending on the brazing temperature and holding time.

Successful solid state bonding of titanium aluminides requires the use of high temperature and pressure. In previous works, authors have demonstrated that the use of Ti/Al multilayer thin film as an interlayer, deposited by d.c. magnetron sputtering onto the joining surfaces, can effectively lower the bonding temperature. The enhanced diffusivity of these nanometric layers and the heat evolved by the formation of γ-TiAl improves the joinability of titanium aluminide by solid-state diffusion bonding. In the present work, further improvement of the process was pursued by doping the interlayer with 2.8 at.% of Ag; previous studies have confirmed that silver favours the transformation Ti+Al→γ-TiAl. The solid-state diffusion bonding experiments were performed in vacuum by applying 50 MPa at 900°C for 1 h. The effect of the third element on the microstructure and chemical composition along the bonding interface has been analyzed. Microstructural characterisation of the interface was performed by scanning and transmission electron microscopy. Chemical compositions were analysed by energy dispersive X-ray spectroscopy. No defects were observed at the interface and sound bonding was achieved between the interlayers and base γ-TiAl. The bonding interface shows a fine-grained microstructure, slightly coarser than the one formed at the same temperature with the undoped Ti/Al multilayer.

The Cu–Ti–Zr system has attracted increasing interest in recent years due to its good glass-forming ability and the use of its alloys as active brazing filler metals. However, only limited phase diagram data are available in the literature. In the first part of this work we describe experimental investigations. Samples were investigated by means of EPMA and DSC. At 800 °C an isothermal section was determined by the diffusion couple technique and individual alloy compositions. This combination of methods is deemed to be effective, as it only involves limited experimental effort. The binary systems Cu–Ti and Cu–Zr show a series of intermetallic phases. One of these – Cu(Ti,Zr)2 – forms an isomorphous solid solution. The binary phases in the Cu–Zr system, in particular Cu51Zr14, show remarkable solubility for Ti. One ternary compound (Cu2TiZr) in this system is known to be in thermal equilibrium with nearly all binary intermetallic phases and therefore dominates the isothermal section. Based on current data and data in the literature a thermodynamic description of the Cu–Ti–Zr system was obtained which is described in the second part of this work.

In the present work, the applicability of the copper free silver based alloys Ag–15Mn and Ag–5Pd as filler metals for shielding gas brazing of the martensitic stainless steel X3CrNiMo13-4 was investigated. The joints were examined with respect to their microstructure, their corrosion behaviour in aequous NaCl solution as well as – in the case of the specimens brazed with AgPd5 – their mechanical performance under tensile and torsion loading. Specimens brazed with Ag– 15Mn showed pronounced oxidation in the Ar/H2 shielding gas atmosphere as well as a low corrosion resistance in 0 ? 5M NaCl solution. The filler metal Ag–5Pd showed very good brazing results. With this filler metal, defect free and corrosion resistant joints with an ultimate tensile strength of 800 MPa and a low cycle fatigue strength of 490 MPa could be produced.

Viscosity and electrical conductivity of liquid Sn–Ti and Sn–Zr alloys on the Sn-rich side were investigated in a wide temperature range above the melting temperature. It was shown that admixtures of Ti and Zr considerably increased the viscosity of liquid Sn. The electrical conductivity of the melts decreased with an increase of the Ti and Zr content. The conductivity results are interpreted in the context of the s–d hybridization model.

The commercial active brazing alloy “Incusil-ABA” was used for the bonding of diamond grits in order to assess their suitability for high performance machining tools. It was found that the microstructure of the brazing alloy matrix consisted of primary precipitates of Cu in a Ag–Cu eutectic matrix and an additional Cu–In–Ti rich intermetallic phase. Interface characterisation revealed the presence of a Ti-rich interfacial layer between the diamond and the alloy matrix. Therefore, good wettability was obtained for the embedded diamond grit particles. This intervening layer comprised nanosized cuboidal TiC which seemed to have acted as a precursor to its formation and fine metastable needles that were identified as cubic Ti3InC. Furthermore it was demonstrated that a three phase crystallographic orientation relationship had been obeyed at the interfacial region between the diamond, TiC and Ti3InC.

The Fe–Ni–Ti alloy system has been evaluated, together with Fe–Ni and Fe–Ti binary subsystems, to provide reliable information for applications and in view of a thermodynamic modelling of the system. Available literature has been critically evaluated, mainly considering phase constitution and phase equilibria, thermochemical and diffusion data, as well as ab initio atomistic calculations. A discussion of the presently available CALPHAD-type thermodynamic assessments is also presented. Finally, new experimental investigations needed to solve uncertain and contradictory data are suggested.

This study pertains to the investigation of interface formation in infiltrated Al-based composites with high-volume fractions of monocrystalline synthetic diamond particles. The interface characteristics are discussed with respect to process conditions and Al matrix chemistry. To this end, two infiltration techniques, i.e., squeeze-casting and gas pressure infiltration are compared and the effect of Si-addition to the Al matrix is addressed. Eventually, thermal properties of the composite materials are presented and are in turn related to the interface characteristics. Electron microscopy investigations reveal a distinct 50–200-nm-thick layer at the interface between the metal matrix and the diamond particle, regardless of process history and matrix chemistry. This layer is amorphous and consists of carbon, aluminium and oxygen. Additionally, nanocrystallites of Al 2 OC and enrichment of Si are observed within this interface layer in the Si-free, squeeze-casted material and in the gas pressure-infiltrated material with 7 wt.% of Si, respectively. Despite the fact that no evidence of SiC is found in the Si-containing composites, the process conditions experienced in gas pressure infiltration are clearly more favourable than those experienced in squeeze casting with respect to interfacial bonding and thermal properties. Actually, between 25 and 50 °C, the gas pressure-infiltrated AlSi/diamond composite yields a thermal conductivity of 375 W/m K along with a coefficient of thermal expansion of 7 × 10 − 6 /K.

Flame aerosol synthesis has been employed to synthesize nanoscale titania (TiO2) particles by oxidation of titanium tetraisopropoxide (TTIP) vapor. The influence of reactant mixing and flow rates on particle morphology, size and phase composition has been studied for two different diffusion flame configurations using transmission electron microscopy, X-ray diffraction and photon correlation spectroscopy. Spherical, loosely agglomerated powders with a minimum secondary particle size of 90 nm and a rutile content of up to 35 w % were obtained at low oxygen flow rates in the double diffusion flame, while large anatase-rich aggregates formed at high oxygen flow rates. It is shown that the degree of aggregation of the as-synthesized particles is represented better by the ratio of dPCS3/dTEM3, than by the ratio of dBET3/dXRD3 commonly used in literature. The differences observed in particle morphology and phase composition can be explained by considering their time–temperature history as a function of flame configuration and gas flow rates.

Binary TiO2/SiO2 and SnO2/SiO2 nanoparticles have been synthesized by feeding evaporated precursor mixtures into an atmospheric pressure diffusion flame. Particles with controlled Si:Ti and Si:Sn ratios were produced at various flow rates of oxygen and the resulting powders were characterized by BET (Brunauer–Emmett–Teller) surface area analysis, XRD, TEM and Raman spectroscopy. In the Si–O–Ti system, mixed oxide composite particles exhibiting anatase segregation formed when the Si:Ti ratio exceeded 9.8:1, while at lower concentrations only mixed oxide single phase particles were found. Arrangement of the species and phases within the particles correspond to an intermediate equilibrium state at elevated temperature. This can be explained by rapid quenching of the particles in the flame and is in accordance with liquid phase solubility data of Ti in SiO2. In contrast, only composite particles formed in the Sn–O–Si system, with SnO2 nanoparticles predominantly found adhering to the surface of SiO2 substrate nanoparticles. Differences in the arrangement of phases and constituents within the particles were observed at constant precursor mixture concentration and the size of the resultant segregated phase was influenced by varying the flow rate of the oxidant. The above effect is due to the variation of the residence time and quenching rate experienced by the binary oxide nanoparticles when varying the oxygen flow rate and shows the flexibility of diffusion flame aerosol reactors.

Melting experiments of Cu-Sn-Ti-Zr filler metal powder containing cellulose nitrate and graphite, respectively, resulted in the formation of nanosized TiC particles in both Cu-rich phase and CuSn 3 Ti 5 intermetallic regions of the alloy (see figure). The variation of the binder type and content allows to tailor the properties of the filler metals in terms of erosion resistance, decisive for a new generation of superabrasive tools.