Tem characterization of diffusion bonding of superplastic 8090 Al-Li alloy

Hot Isostatic Pressing (HIP) diffusion bonding with CLAM steel is the primary candidate fabrication technique for the first wall (FW) of DFLL-TBM. Surface state is one of the key factors for the joints quality. The effect of surface state prepared with grinder and miller on HIP diffusion bonding joints of CLAM steel was investigated. HIP diffusion bonding was performed at 140 MPa and 1373 K within 3 h. The mechanical properties of the joints were investigated with instrumented Charpy V-notch impact tests and the microstructures of the joints were analyzed with scanning electron microscopy (SEM). The results showed that the milled samples with fine surface roughness were more suitable for CLAM steel HIP diffusion bonding.

Airworthiness regulatory bodies are authorised and responsible for verifying and ensuring the safety and reliability of aircraft. There are many civil and military aviation organisations and regulatory bodies. The functions and responsibilities of several of these organizations are summarised in this chapter. Owing to the importance of aircraft structural fatigue, a survey of fatigue design philosophies is also given. This is followed by (i) a discussion of the airworthiness certification methodology for materials and structures, starting with the initial mill products and proceeding via incremental levels to the finished aircraft; and (ii) an example of material certification for an aluminium–lithium (Al-Li) alloy that is a candidate for use in the airframes of light combat aircraft (LCA).

Deformation of the Al–Al₄C₃ composites with different volume fraction of Al₄C₃ phase was tested at different temperatures and different strain rates. As shown, at temperatures 400–450 °C and the highest strain rate applied 10¹ s⁻¹, a significant ductility growth was observed. According to the results of Tunnelling Electron Microscope analysis, it is supposed to be the result of dynamic grain polygonization, grain slip and rotation, partial recrystallization and dislocation creep in the tested system, known as strain induced dynamic recovery. Increase of the volume fraction of secondary phase in the investigated composite changed the deformation mechanism (from more slip on grain boundaries to more grain rotation).

In the present work, the change in fracture for the Al–12Al₄C₃ system was investigated and analyzed at temperatures from 20 to 400 °C and strain rates from 2.5×10⁻⁵ to 10⁻¹ s⁻¹. At room temperature during tensile testing, the strain is controlled by dislocation movement and reactions. For high temperatures in the investigated region, the principal mechanism keying the strain is the presence of dynamic recovery processes. Strain rate influences on fracture are analyzed.

The deformation of Al–Al₄C₃ composites with different volume fraction of Al₄C₃ phase was tested at different temperatures and different strain rates. It is shown that at temperatures between 400 and 450 °C and the highest strain rate applied 10⁻¹ s⁻¹, a significant ductility growth was observed. According to the results of TEM analysis, this behaviour is supposed to be the result of dynamic grain polygonization, grain slip and rotation, partial recrystallization and dislocation creep in the tested system, known as strain induced dynamic recovery. The increase of the volume fraction of secondary phase in the investigated composite changed the deformation mechanism from more slip on grain boundaries to more grain rotation.

The effect of surface roughness on the properties of Al6061 joints fabricated by diffusion bonding in air at 450°C was studied. It was found that rougher surfaces yield superior ultimate tensile strength and linearized bonded ratio. Joints with ultimate tensile strength comparable to that of bulk metal were obtained for holding times of 75 min using rougher surfaces; however, the maximum linearized bonded ratio obtained was only about 75%. Incomplete bonding was attributed to air entrapment along the bond interface. This was due to good bonding occurring at the periphery of the bonded specimens during the early part of the bonding process.