Papers by Author: José Lemus-Ruiz

Abstract: The objective of this work was to study various aspects of liquid state diffusion bonding of cylindrical samples of Al₂O₃ and commercially pure niobium (99.7%) by brazing using a 25 µm thick 70Cu-30Zn (wt%) alloy as joining element. Initially, sintering of alumina powder was carried out in order to produce a 7 mm diameter samples at 1550°C by 120 minutes. Joining experiments were carried out on Al₂O₃/Cu-Zn/Nb/Cu-Zn/Al₂O₃ sandwich-like combinations at temperature of 920°C, 950°C and 980°C using different holding times under argon (Ar) atmosphere. The experimental results show a successful joining of alumina to niobium at 950°C and 980°C, however not at 920°C. Joining of Al₂O₃/Cu-Zn/Nb/Cu-Zn/Al₂O₃ occurred by the formation of a homogeneous diffusion zone with no interfacial cracking or porosity at the interface. Scanning electron microscopy (SEM) micrographs show the layer formed in the reaction zone. It was observed that the width of the reaction zone increases with bonding temperature and time. Electron probe microanalysis (EPMA) revealed that at any particular bonding temperature, Nb travel into the Cu-Zn joining element forming a circular precipitate phase near to the alumina ceramic.

Abstract: Solid-state direct diffusion bonding between commercially pure nickel and tungsten carbide (with 6%Cobalt) has been carried out in the temperature of 980°C and 1100°C using different holding times in argon atmosphere. Samples were successfully joined without defects or cracks on the joining interface with the exception of the one joined at 980°C for 5 min. The results showed that joining occurred by the formation of a reaction zone. Scanning electron micrographs show that different intermediate layers are formed in the reaction zone, and the width of these layers increases with an increase in bonding temperature and time. Electron probe microanalysis revealed that at any particular bonding temperature, cobalt travel into the nickel side, whereas nickel travel comparatively larger distances in the tungsten carbide side.

Abstract: Crack disappearance by high-temperature oxidation was studied in alumina (Al2O3) composites toughened by Ni nanoparticles. This process is performed in air at temperature ranging from 1000 to 1300°C for 1 to 48 h. The results showed that crack disappearance depends on both annealing temperature and time. Complete crack disappearance in this composite was confirmed at lower temperatures for long oxidation period, 1100oC for 48 h, and higher temperature for shorter time, 1300oC for 1 h in air. The crack disappearance mechanism was explained on the basis of the formation of NiAl2O4 spinel on sample surfaces produced by the oxidation reaction during the heat treatment.

Abstract: Cemented tungsten carbides are industrially one of the most used composite materials as cutting tools, wear parts and replacements of standard materials for tools, dies and machine components. This work focuses on various aspects of diffusion bonding of tungsten carbide to AISI 304 stainless steel using a Ni-foil interlayer. WC/Ni/AISI 304 combinations were diffusion bonded at 1000°C using different holding times under argon atmosphere. The microstructure characterization of the resulting interfaces was carried out by SEM and EPMA. The results show that successful joining between WC and AISI 304 steel is achieved by the formation of a diffusion zone at both ends of the Ni foil. All WC/Ni/AISI 304 samples have been joined with no severe interfacial cracking or porosity at the interface. The joint strength is determined by four-point bending testing, a maximum of 210 MPa for samples joined at 1000 °C for 60 minutes has been achieved. These results indicate that there is a strong relationship between the thickness of the diffusion interface and the mechanical strength of the joints.

Abstract: This work focuses on various aspects of diffusion bonding silicon nitride to Mo and Ti using a Cu-foil interlayer. Si3N4/Cu/Ti/Cu/Si3N4 and Si3N4/Cu/Mo/Cu/Si3N4 combinations have been diffusion joined at temperatures ranging from 950 to 1150 °C using different holding times in Ar. The results show that Si3N4 could not be bonded to Mo at temperature lower than 1100 °C even for holding times of 60 minutes, however, successful joining is achieved at 1150 °C. On the other hand, successful joining is accomplished at 1050 and 1100 °C for a Si3N4/Cu/Ti/Cu/Si3N4 sample. In the Si3N4/Cu/Ti system, joining occurs by the formation of a reactive interface with several reaction products on the metal side of the joint. All the silicon nitride samples have joined to titanium with no several interfacial cracking and porosity at the interface. The results corresponding to the Si3N4/Cu/Mo system show that a higher temperature is required to join the materials compared with the Si3N4/Cu/Ti system, since the formation of liquid produced by the interaction of Cu with Ti and Si promotes bonding and the high affinity of Ti for Si results in rapid interface formation.