Diffusion Bonding: Influence of Process Parameters and Material Microstructure

Diffusion welding is a solid joining technique allowing for full cross-section welding. There is no heat-affected zone, but the whole part is subjected to a heat treatment. By diffusion of atoms across the bonding planes, a monolithic compound is generated

Comprehensive Study of the Deformation Behavior during Diffusion Bonding of 1.4301 (AISI 304) as a Function of Material Width and Aspect Ratio

In this paper, the impact of material width as well as aspect ratio on deformation during diffusion bonding of layered samples were investigated. For this, six annular samples with a constant cross-sectional area but an increasing diameter and thus decreasing material width were designed. In a first set of experiments, specimens of a constant height of h = 20 mm were examined. Each sample consisted of 10 sheets, 2 mm in thickness each. Diffusion bonding was performed at T = 1075 °C, t = 4 h and p = 15 MPa. Subsequently, additional samples with a constant aspect ratio of about three but different material width were diffusion bonded. For this, additional layers were added. It was expected that the deformation should be nearly constant for a constant aspect ratio. However, comparing the deformation to a sample possessing an aspect ratio of about three from the first batch, a much higher deformation was obtained now. Bonding a third sample, a deformation in the same range as for the other two samples of the second batch was obtained. It was found that due to the evaporation of metals, the thermocouples were subjected to aging, which was proven indirectly by the evaluation of heating power. Since the diffusion coefficient of the metals follows an exponential law, deformation changes considerably with temperature. This emphasizes that exact temperature measurement is very important, especially for bonding microprocessor devices at constant contact pressure. The experiments showed that the deformation depends strongly on geometry. Bonding parameters cannot be generalized. For layered setups, the contribution that thickness tolerances from manufacturing and leveling of surface roughnesses of sheets add to the overall deformation cannot be reliably separated. After diffusion bonding, thickness tolerances increase with a lateral dimension. Obviously, the stiffness of the pressure dies is crucial

Manufacturing of a Burner Plate by Diffusion Bonding to Investigate Premixed Fuel‐Rich Oxy‐Fuel Flames at Increased Pressure and Preheating

Combustion of hydrocarbons with pure oxygen as oxidizer is used, e.g., in high-temperature processes such as the partial oxidation (POX) of hydrocarbons to produce synthesis gas of high purity. Due to the prevailing temperatures, active cooling is required for many parts. For laboratory-scale experiments, the dimensions of key parts are too small for conventional manufacturing processes. One example is the manufacturing of a burner plate especially developed for POX processes. The complex geometries of several hundreds of burner nozzles and perpendicular cooling channels across the diameter of the burner plate cannot be manufactured in a conventional way. For this burner, the advantage of chemical etching of thin sheet material and stacking of multiple sheet layouts was used to assemble the layout of the burner. The burner plate was then diffusion-bonded, allowing the complex design to be realized. The partial oxidation of CH$_4$/O$_2$ flames at the laboratory scale could thus be studied under industrially relevant conditions

Comprehensive Study of the Influence of the Bonding Temperature and Contact Pressure Regimes during Diffusion Bonding on the Deformation and Mechanical Properties of AISI 304

Process parameters for diffusion bonding are temperature, dwell time, and contact pressure. Temperature and contact pressure have opposite effects on deformation. The effect of temperature on deformation was investigated in steps of 20 K from 1015 to 1135 °C. Contact pressure and dwell time were 16 MPa and 4 h, respectively. The deformation increase steadily with temperature. Yield strength and tensile strength decrease slightly with temperature, which is attributed to grain growth. The elongation-at-fracture values are 100–105%. For 925 to 995 °C, values for elongation at fracture decrease. It was investigated if comparable mechanical properties can be obtained at a temperature of 850 °C only. Experiments with higher constant contact pressures were supplemented by tests with superimposed short load peaks. Similar and higher values for the yield strength were achieved. A correlation of yield strength, tensile strengths and elongation-at-fracture values with contact pressure and contact pressure regime was found. The values for elongation at fracture are significantly lower than those for higher temperatures. This even applies to parameter sets at different temperatures, leading to almost identical deformations. Reduced elongation-at-fracture values at 850 °C are attributed to microscopically small defects in the bonding plane and to notch effects

Highly Molybdenum-Alloyed Materials Hastelloy BC-1 (2.4708) and B3 (2.4600): Diffusion Bonding Experiments and Evaluation of both Mechanical Behavior and Corrosion Resistance in Hot 70% Sulfuric Acid

Sulfuric acid is a widely used raw material in the chemical industry. Its corrosive effect on materials varies considerably, depending on impurities, temperature and water content. This is an issue for micro process apparatuses with thin walls. Such devices are often joint by diffusion bonding what may alter materials properties due to high temperatures and long dwell times. In this paper, two high molybdenum alloys, namely Hastelloy B3 and BC-1, were investigated. Diffusion bonding tests were performed at different temperatures. Tensile tests were carried out for different material conditions, to determine the change in mechanical strength and elongation at fracture values. The fracture behavior of both alloys was ductile and the fracture surfaces showed dimple structure. For diffusion bonded samples, weak spots or rather non-bonded areas were found. These obviously caused the onset of material failure and thus, degradation of mechanical properties. Tensile samples, aged in 70% sulfuric acid at 100 °C for 1000 h showed local corrosion attacks at the grain boundaries at the circumferential surfaces and joining planes—for Hastelloy B3 more pronounced than for Hastelloy BC-1. Accordingly, a further decrease of stress and elongation at fracture values was observed. However, 0.2% yield strength used for dimensioning components are found to be reasonable. As conclusion, at least Hastelloy BC-1 reveals both good mechanical properties and an excellent corrosion resistance, regardless of the heat treatment. This is a significant advance compared to the results obtained from a previously research project on four different alloys