Search

A Cu-Sn-Ti-based active brazing filler alloy was in situ reinforced with nanosized TiC particles by adding different amounts of a cellulose nitride-based binder. The TiC particles emanate from a reaction of the Ti within the filler alloy with the carbon from the binder that does not decompose completely during heating. The correlation between the microstructure and mechanical performance was studied. In addition, the effect of different binder amounts on the shear strength and cutting performance of brazed diamond grains was studied in shear tests and single grain cutting tests. The results clearly show that the mechanical performance of the brazed diamond grains can be improved by the formation of TiC particles. This is attributed to particle strengthening of the filler alloy matrix as well as to the decreasing grain size and more homogeneous distribution of the (Cu,Sn)3Ti5 phase with increasing amount of binder.

In this work, Al2O3–Al2O3 and Al2O3–Ti solder joints intended for space applications were realized by applying metallic multilayers both on Ti and on polycrystalline Al2O3 substrates to ensure wetting during the soldering process. The eutectic Au-12Ge (wt%) alloy with a melting point of 361°C was used as solder material and two different multilayer systems on the ceramic (Cr-Ni/Ti-W/Au,Ti/Pt/Au) were investigated. The influence of different thermal pretreatments of the Al2O3 plates on the multilayer properties, the interface reactions during soldering and the mechanical properties were studied using Glow-Discharge Optical Emission Spectroscopy (GDOES), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and a shear test device. It is shown that joints with a good quality can be produced at a soldering temperature of 400°C, whereas their properties and fracture behavior are strongly dependent on the metallization layer properties and the thermal pretreatments.

Au-Ge based alloys are interesting as novel high temperature lead free solder alloys because of their low melting point, good thermal and electrical conductivity and high corrosion resistance. In the present work, the wetting and soldering behaviour of the eutectic Au-28 at.% Ge alloy on Cu and Ni substrates have been investigated. A good wetting on both substrates with final contact angles of 13-14° was observed. In addition, under controlled conditions good solder joints could be produced. Cu substrates exhibit a pronounced dissolution into the Au-Ge filler metal. This was referred to the formation of a reaction layer at the interface with a fcc structure, which allows fast diffusion of Cu and Au. On Ni substrates, the NiGe intermetallic compound was formed at the filler /substrate interface which prevents dissolution of Ni into the solder. Using thin filler metal foils (25 µm), a complete consumption of Ge in the reaction at the Ni interface was observed, leading to the formation of almost pure Au layer in the soldering zone.

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.

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.

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.