The effects of boriding and boronitrocarburising surface treatments on the microstructure and mechanical properties of AISI 4130 steel have been investigated. Pack boriding was carried out at 1223 K for 5 h and 8 h, while the double treatment of boronitrocarburising consisted of salt bath nitrocarburising at 853 K for 6 h followed by pack boriding at the same temperature and times as the boriding treatment. Microstructure examination of the borided and boronitrocarburised layers was carried out using optical and scanning electron microscopy, and phase identification was obtained using X-ray diffraction. Vickers hardness, wear and corrosion weight loss tests were used to evaluate the mechanical properties and corrosion behaviour. The results of X-ray diffraction analysis revealed the presence of superhard phases such as FeB, Fe₂B, CrB, MnB and MnB₂, indicating that pack boriding surface treatment conducted at 1223 K for 8 h exhibited the highest hardness, low coefficient of friction and the greatest wear resistance. Boronitrocarburising treatment, on the other hand, caused a reduction in both the depth of iron borides zone and mechanical properties compared to the boriding surface treatment. These recommended treatments offer to industrialists a particular contribution and interest in the development of these steels, which can be applied in various fields.

Solder joint reliability is dependent on both thickness and morphology of the intermetallics that form and grow at the solder joint interface during soldering and subsequent thermal ageing and examining the morphology of these intermetallics is of great importance. The focus of this paper is to present experimental results of a comprehensive study of the interfacial reactions during soldering of Sn-Ag-Cu lead-free solders on copper (Cu), immersion silver (ImAg), electroless nickel/ immersion gold (ENIG) and electroless nickel/ electroless palladium/ immersion gold (ENEPIG) surface finishes. Using scanning electron microscopy detailed a study of the 3-D morphology and grain size of the intermetallics was conducted. The results showed that when soldering on ENIG and ENEPIG finishes several morphologies of intermetallics with different grain sizes form at the solder joint interface compared to a single intermetallic morphology that forms when soldering on copper and immersion silver. An attempt was made to discuss the effect of several factors that may have an influence on the type of morphology the intermetallics may grow into. The results obtained in the present investigation also revealed that the technique of removing the solder by deep etching to examine the morphology of intermetallics is a convenient and efficient method to investigate the intermetallics formed at the solder joints.

Doping lead-free solders with minor additions of alloying and impurity elements such as Ni, Bi or Zn appears to have major effects on the growth of intermetallics (IMC) in solder joints during reflow soldering between the Sn-Ag-Cu lead-free solders and the surface finish metallurgy. In this paper, the results of the effect of small Nickel additions (0.05 and 0.1 wt%) on intermetallic formation during soldering with Sn-3Ag-0.5Cu (SAC305) are presented. The Ø500μm solder alloys of Sn-3Ag-0.5Cu, Sn-3Ag-0.5Cu-0.05Ni and Sn-3Ag-0.5Cu-0.1Ni were investigated in detail after reflow soldering at 250°C on copper finish and isothermally aged at 150°C for up to 2000 hours. The results show that after reflow soldering, scallop-type Cu ₆ Sn ₅ / (Cu, Ni) ₆ Sn ₅ was the only reaction product formed. A strong influence of Ni addition on the growth rate and thickness of the Cu ₃ Sn layer was also observed. Addition of as little as 0.05wt% Ni to SAC305 solder effectively slows down the growth of this Cu ₃ Sn phase while growth of the Cu ₆ Sn ₅ continued to increase with increasing in aging time.