This paper describes a model used to represent the cyclic mechanical behaviour of P91 martensitic steel. Low cycle fatigue tests were conducted at 600°C using a thermo-mechanical fatigue test machine. A unified, Chaboche viscoplasticity model, was used to model the behaviour of the steel. The micro structure of the steel at different life fractions of the tests was investigated using scanning and transmission electron microscope images. The viscoplasticity model, with two stages of softening period, has resulted in better prediction capability for the cyclic behaviour of the steel for an initially undamaged material prior to crack initiation

Purpose: This paper aims to investigate the characteristics of ultra-fine lead-free solder joints reinforced with TiO₂ nanoparticles in an electronic assembly. Design/methodology/approach: This study focused on the microstructure and quality of solder joints. Various percentages of TiO₂ nanoparticles were mixed with a lead-free Sn-3.5Ag-0.7Cu solder paste. This new form of nano-reinforced lead-free solder paste was used to assemble a miniature package consisting of an ultra-fine capacitor on a printed circuit board by means of a reflow soldering process. The microstructure and the fillet height were investigated using a focused ion beam, a high-resolution transmission electron microscope system equipped with an energy dispersive X-ray spectrometer (EDS), and a field emission scanning electron microscope coupled with an EDS and X-ray diffraction machine. Findings: The experimental results revealed that the intermetallic compound with the lowest thickness was produced by the nano-reinforced solder with a TiO₂ content of 0.05 Wt.%. Increasing the TiO₂ content to 0.15 Wt.% led to an improvement in the fillet height. The characteristics of the solder joint fulfilled the reliability requirements of the IPC standards. Practical implications: This study provides engineers with a profound understanding of the characteristics of ultra-fine nano-reinforced solder joint packages in the microelectronics industry. Originality/value: The findings are expected to provide proper guidelines and references with regard to the manufacture of miniaturized electronic packages. This study also explored the effects of TiO₂ on the microstructure and the fillet height of ultra-fine capacitors.