José Lemus-Ruiz

Crack Disappearance by High-Temperature Oxidation of Alumina Toughened by Ni Nano-Particles

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.

Effect on the Microstructure and Mechanical Properties of the Electromagnetic Stirring during GMA Welding of 2205 DSS Plates

Plates, 6.3 mm thick, of 2205 duplex stainless steel (DSS) were gas metal arc welded (GMAW) under the application of an axial magnetic field (0 to 15 mT) with an ER-2209 filler wire using a gas mixture of 98%Ar + 2%O2. Microstructural characterization of the welds revealed that electromagnetic stirring (EMS) increases the content of austenite in both weld center and high temperature heat affected zone (HTHAZ). It induced a grain refining effect during freezing of the ferritic matrix which in turn enabled more sites for nucleation of austenite. This mechanism of solidification was reflected in an increase in the mechanical strength of the welds. Besides, the extent of the HTHAZ was reduced and its microhardness increased when applying the external magnetic field. It is believed that the vibration induced in this region favored the regeneration of austenite in the ferritized HTHAZ enhancing the balance of phases.

WC / Stainless Steel Joints Produced by Direct Diffusion Bonding Using a Ni-Foil Interlayer

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.

Joining of Silicon Nitride to Metal (Mo and Ti) Using a Cu-Foil Interlayer

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.

Corrosion resistance of stainless steel joints bonded with a Ni‐based amorphous interlayer

Purpose – To study the metallurgical characteristics obtained from the process of diffusion bonding of 316L stainless steel (SS) using a commercial Ni‐based amorphous alloy interlayer and its effect on the corrosion resistance of the self‐joined SS‐amorphous alloy‐SS junction zone.Design/methodology/approach – Squared samples of austenitic SS were joined using a brazing metallic foil BMF‐15® in a sandwich‐like arrangement. The samples were then placed into a resistance furnace with a controlled N2 atmosphere. The joining process was carried out at 1105 and 1170°C holding the samples in the furnace for periods of 5, 10, 15, 20 and 40 min. The junction zone was evaluated by scanning electron microscopy (SEM) in order to determine the metallurgical structure induced during the process. The corrosion resistance of the SS/BMF‐15®/SS joints were evaluated using DC electrochemical methods on joined samples immersed in a 3.5 wt% NaCl solution.Findings – The samples of 316L SS showed self‐diffusion bonding at both...

Production, Characterization, and Mechanical Evaluation of Dissimilar Metal/Ceramic Joints

Ceramics and metals are two of the oldest established classes of technologically useful materials. While metals dominate engineering applications, ceramics are used extensively to provide thermal and electrical insulation and are emerging as important structural materials. Properties of individual ceramics and metals can vary widely, but the characteristics of most materials in the two classes diffier significantly (Richerson, 1992). The properties reflect the different lattice binding characteristics of metals and ceramics. Ceramics are neither purely ionic nor purely covalent, and the relative degree of ionicity or covalency of ceramics can be related to the electronegativity of its components. Modern ceramics are gradually becoming important in structural applications because of their high strength to weight ratio, high modulus, high corrosion resistance, excellent high temperature properties, and abundance. The manufacture of component shapes from monolithic engineering ceramics such as Si3N4 is difficult, and this has generated a continued interest in the use of joining technologies to produce complex configurations from assembles of simples shapes. The use of ceramics and ceramics based composites in industrial applications mainly for high temperature has received extensive attention recently. However, the utilization of the full capabilities of ceramics demands an ability to join ceramics to themselves or metals. Significant differences in the mechanical properties of ceramics and metals make it extremely difficult to obtain ceramic/metal joints with adequate mechanical integrity. Silicon nitride (Si3N4) and tungsten carbide (WC) are two of the most attractive advanced ceramics materials for specific applications since the resulting microstructure of these ceramics after sintering is similar to that of whisker or particulate-reinforced composites, respectively. Joining ceramics to metals is a key of technology in the use of advanced ceramics in complex structures. Moreover, the use of advanced ceramics depends on the reliability of ceramic/metal joining processes and the properties of the resulting interfaces. Several methods for joining ceramics to metals have been developed, some need an intermediate liquid phase, brazing, thermal spraying, and others are produced by solid state bonding and co-sintering (Tinsley et al., 1998; Tomsia, 1993). In all cases some problems

Investigation of the effect of inert inclusions on densification during solid-state sintering of metal matrix composites

Abstract Solid-state sintering is the most used process to produce composites. In this paper, the effect of inert inclusions on densification during sintering was evaluated for Cu-WC and Cu-W composites, which have several industrial applications. Dilatometry tests were performed to follow the densification of composites. The effects of the quantity, size, and interphase bonding on densification of the matrix were studied. Distribution of the inert particles inside of the matrix was observed by scanning electronic microscopy. The results show that densification is decreased as the volume fraction of inclusions increases. Two different behaviors are detected when two different sizes of inclusions are used. For <20% vol. of inclusions, smaller tungsten particles have a minor effect on the densification than those of tungsten carbide. On the contrary, higher volume fractions of smaller tungsten particles drastically decrease the densification. The microhardness of the copper matrix is improved up to 15% vol. of inclusions, being higher for tungsten carbide particles. It was found that 15% vol. of inclusions is the maximal quantity of inclusions that can be used, as higher quantities inhibit densification and reduce the mechanical properties of the composite.

Characterization of Constrained Sintering of Powders on Solid Substrate

Nowadays, sintering is a very useful technique to fabricate metal, ceramic and composites parts for different applications. This phenomenon has been extensively studied over 50 years and, most of the research related to it used a model based on two contacting particles. However, just a few jobs were focused on the powder sintering on a solid substrate. This work investigates the effect of two parameters; substrate shape and inclusion of the reinforced particles on the evolving microstructure during sintering of particles on a rigid substrate. Powders and solid bars of copper are used as a model material and particles such as tungsten carbide (WC) as reinforcing particles. Sintering was performed in an electrical furnace at 1050 °C under reducing atmosphere. The progress on sintering was evaluated by measuring the relative density close and far from the solid substrate by means of the image analysis from pictures taken by scanning electronic microscope (SEM). The effects on the constraint sintering were also identified. Heterogeneous densification and delamination of the film from the substrate were observed as densification increased which by the way is reduced by the inclusion of the reinforced particles.

Joining of WC-Co to Ni by Direct Diffusion Bonding

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.

Behavior of the Nano Alumina Powder Conformed by Slip Casting under Microwave Sintering

The effect of the transformation of phase in nanopowders of transition alumina has showed to be detrimental for the final characteristics of the consolidated materials. It was found that the complete transformation from gamma (γ-Al2O3) to alpha (α-Al2O3) alumina generated larger grain sizes and lower relative densities. This work studies the effect of slip casting preformed on the transformation phase of alumina during microwave sintering of α-alumina nanopowders. The sintering of the samples was carried out in a typical unimodal microwave furnace with a 2.5 GHz frequency. Sintering was carried out under air atmosphere at temperatures vary between 1100 and 1500 °C with heating rate of 100 and 200 °C/min and with a sintering plateau of 5 minutes. Sample characterization was performed by XRD, SEM, and TEM. The phase quantification was calculated using the Rietveld software from the XRD patterns. To have a good heating control in the microwave system it is possible by using slip casting to preform compact. It was observed that the heating rate has a strong effect on the phase transformations. Secondary phases like θ, θ’(x, y) appeared in samples sintered with a heating rate of 200 °C/min no matter the sintering temperature. Meanwhile the complete alumina transformation was found when sample were heating at 100 °C/min.