Ulrich E. Klotz

Study of microstructure and interfaces in an aluminium–C60 composite material

Abstract This work deals with the study of microstructure and interfacial reactions in an aluminium–fullerene (Al/C 60 ) composite produced by pressurized liquid metal infiltration (squeeze casting) of a tap-packed C 60 powder preform. The obtained composite shows a homogeneous distribution of C 60 crystals in the Al matrix, indicating that the original aggregated crystalline structure of the C 60 fullerenes was not disrupted during the composite fabrication process, even though there is evidence of partial sublimation of C 60 . The C 60 crystals are well integrated in the matrix and there is no hint either of porosity or of weak interfacial bonding. At the interface between Al and C 60 rod-shaped and hexagonal plate-like phases are occasionally observed by TEM. These phases were identified as Al 4 C 3 by XRD and Raman spectroscopy and were shown to nucleate on very thin layers of amorphous carbon at the surface of the C 60 crystals.

Site-specific specimen preparation by focused ion beam milling for transmission electron microscopy of metal matrix composites.

This work describes the application and usefulness of the focused ion beam (FIB) technique for the preparation of transmission electron microscopy (TEM) samples from metal matrix composite materials. Results on an Aldiamond composite, manufactured by the squeeze casting infiltration process, were chosen for demonstration. It is almost impossible to prepare TEM specimens of this material by any other conventional method owing to the presence of highly inhomogeneous phases and reinforcement diamond particles. The present article gives a detailed account of the salient features of the FIB technique and its operation. One of the big advantages is the possibility to prepare site-specific TEM specimens with high spatial resolution. The artifacts occurring during the specimen preparation, for example, Ga-ion implantation, curtain effects, amorphous layers, bending of the lamella, or different milling behaviors of the materials have been discussed. Furthermore, TEM examination of the specimens prepared revealed an ultrafine amorphous layer of graphite formed at the interface between the Al and diamond particles that may affect the interfacial properties of the composite materials. This may not have been feasible without the successful application of the FIB technique for production of good quality site-specific TEM specimens.

Determination of Liquidus Temperature in Sn–Ti–Zr Alloys by Viscosity, Electrical Conductivity and XRD Measurements

Abstract 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.

Determination of liquidus temperature in Ti-rich alloys of the Fe-Ni-Ti system obtained by DTA, electrical conductivity and XRD measurements

Abstract 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.

Bonding γ-TiAl Alloys Using Ti/Al Nanolayers Doped with Ag

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.

Diffusion samples as a high-throughput screening method for alloy development

ABSTRACT 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 vast number of compositions within one sample. The components were diffusion welded and annealed to form compositional gradients which were characterised through a grid of energy dispersive X-ray spectroscopy measurements. After splitting the different sample parts underwent different tempering treatments. Thereafter micro hardness grids matching the spectroscopy data were recorded and displayed in contour plots as a function of alloy composition that instantly show composition areas with hardening potential. A critical assessment of the reliability of the method is provided and checked for cu-Al/mn-Sn-ti systems against literature data. This paper is part of a Thematic Issue on Copper and its Alloys.