Formation Of Interfacial Reaction Layer Research Articles

Effect of material flow behavior on the formation of interfacial reaction layers and fatigue performance of dissimilar friction stir welded S45C and AA6061-T6

Effect of material flow behavior on the formation of interfacial reaction layers and fatigue performance of dissimilar friction stir welded S45C and AA6061-T6

Formation of interfacial reaction layer for stainless steel/aluminum alloy dissimilar joint in linear friction welding

One of the mechanisms for the dissimilar materials joining is the formation of interfacial reaction layers. However, this reaction is disrupted owing to the presence of oxide layers and voids, leading to lower strength, and the elimination of these factors is essential. Thus far, studies on linear fraction welding (LFW) with regard to the relationship between the joint strength and the microstructure of the base alloy and interface are lacking. Therefore, herein, the influence of microstructural changes in base alloys and interfacial structures on the joint tensile strength was investigated for the dissimilar joint between the stainless steel and an A5083 alloy after high-frequency linear friction welding at 245 Hz. After the initial joining process up to 1 s, the joint strength decreased as the friction increased. The crystal orientation analyses using electron backscatter diffraction demonstrated a minimal change in the microstructure of the A5083 alloy, particularly in the grain size in the geometric dynamic recrystallization region. This variation in the microstructure was minimal, regardless of the friction time, which was consistent with the result of the hardness distributions. The observation of microstructure using transmission electron microscopy revealed the formation of metastable Al-Fe intermetallic compounds and Al-Mg-Cr compounds derived from the reaction between the oxide layer and alloying elements in the A5083 after experiencing friction for a short time. Conversely, we confirmed the formation of a fragile boundary within the interfacial reaction layer after the exposure to friction for an extended period due to differences in the formation process of the layer: mechanical mixing or interdiffusion. Hence, it was proposed that mechanical removal as well as the interfacial reaction between the oxide layer and the Mg contained in the aluminum alloy function in removing the surface oxide layer, which plays a significant role in designing the interfacial structure and joint properties.

Formation of Interfacial Reaction Layers in Al2O3/SS 430 Brazed Joints Using Cu-7Al-3.5Zr Alloys

The formation of interfacial reaction layers was investigated in an α-Al2O3/430 stainless steel (SS430) joint brazed using a Cu-7Al-3.5Zr active brazing alloy. Brazing was conducted at above its eutectic temperature of 945 °C and below liquidus 1045 °C, where liquid and solid phases of the brazing alloys coexists. At 1000 °C, the liquid phase of the brazing alloy was wet onto the α-Al2O3 surface. Zr in the liquid phase reduced α-Al2O3 to form a continuous ZrO2 layer. As the dwell time increased, Zr in the liquid phases near α-Al2O3 interface was used up to thicken the reaction layers. The growth kinetics of the layer obeys the parabolic rate law with a rate constant of 9.25 × 10−6 cm·s−1/2. It was observed that a number of low yield strength Cu-rich particles were dispersed over the reaction layer, which can release the residual stress of the joint resulting in reduction of crack occurrence.

Influence of Laser Power on the Microstructure and Mechanical Properties of a Laser Welded-Brazed Mg Alloy/Ni-Coated Steel Dissimilar Joint

In this work, we describe a method to improve the bonding of an immiscible Mg/steel system using Ni as an interlayer by coating it on the steel surface. Laser welding-brazing of AZ31B Mg alloy to Ni-coated Q235 steel using Mg-based filler was performed in a lap configuration. The influence of laser power on the weld characteristics, including joint appearance, formation of interfacial reaction layers and mechanical properties was investigated. The results indicated that the presence of the Ni-coating promoted the wetting of the liquid filler metal on the steel surface. A thermal gradient along the interface led to the formation of heterogeneous interfacial reaction layers. When using a low laser power of 1600 W, the reaction products were an FeAl phase in the direct laser irradiation zone, an AlNi phase close to the intermediate zone and mixtures of AlNi phase and an (α-Mg + Mg2Ni) eutectic structure near the interface at the seam head zone. For high powers of more than 2000 W, the FeAl phase grew thicker in the direct laser irradiation zone and a new Fe(Ni) transition layer formed at the interface of the intermediate zone and the seam head zone. However, the AlNi phase and (α-Mg + Mg2Ni) eutectic structure were scattered at the Mg seam. All the joints fractured at the fusion zone, indicating that the improved interface was not the weakest joint region. The maximum tensile-shear strength of the Mg/Ni-coated steel joint reached 190 N/mm, and the joint efficiency was 70% with respect to the Mg alloy base metal.

The microstructural observation of brazing Ti–6Al–4V and TZM using the BAg-8 braze alloy

Microstructural evolution of the brazed Ti–6Al–4V and TZM joints using the BAg-8 braze alloy have been evaluated in this study. According to the dynamic sessile drop test, the molten braze alloy can effectively wet Ti–6Al–4V at 850 °C. In contrast, the TZM substrate cannot be effectively wetted by the molten braze below 900 °C. The microstructure of an infrared brazed specimen (800 °C, 60 s) mainly consists of eutectic Ag–Cu, with a reaction layer (Ti 3Cu 4) approximately 2 μm thick. The interfacial reaction is more pronounced in a specimen furnace brazed at 800 °C for 600 s. Both TiCu and Ti 3Cu 4 are observed at the interface with the thickness of about 10 μm. In specimens furnace brazed at 850 °C, the reaction layer is mainly comprised of TiCu. The application of the infrared brazing cannot completely prevent the formation of interfacial reaction layer(s), but it provides an effective way to inhibit the growth of intermetallics at the interface between the braze alloy and substrate. Additionally, the dissolution of the substrates into the molten braze alloy during infrared brazing is significantly decreased due to its rapid thermal cycle.

Joining of sialon ceramics by a stainless steel interlayer

In direct diffusion bonding of sialon to stainless steel, thermal residual stresses arise due to the difference in coefficient of thermal expansion of the two materials. These stresses frequently lead to failure of the bond. This behaviour is further influenced by the formation of interfacial reaction layers between ceramic and metal and the problem is essentially one of asymmetry of stresses in the interface between dissimilar materials. The present study demonstrates that a thin layer of austenitic stainless steel can be used as an interlayer to join two sialon components. In such a case the distribution of residual stresses is symmetrical across the composite join and provided that the thickness of the steel layer is less than a critical value, then fracture on cooling from joining temperature does not occur. The development of this process is described and a finite-element model has been used to predict the properties of the interfacial reaction layer between steel and ceramic which are consistent with the experimental observations.