Rahul Kumar Agrawal

This study demonstrates the simultaneous achievement of high strength and excellent corrosion resistance in a Ni-free, high N austenitic stainless steel fabricated by laser powder bed fusion (PBF-LB). The formation of a single-phase austenitic structure was confirmed through X-ray diffraction analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cyclic potentiodynamic polarization tests conducted in 0.6 M NaCl solution at room temperature revealed high breakdown potential (1187 ± 31 mV _SCE ), indicating excellent corrosion resistance for the additively manufactured Ni-free austenitic stainless steel compared to wrought 316L stainless steel. These findings were further supported by immersion tests in FeCl ₃ solution. The additively fabricated alloy’s yield strength and ultimate tensile strength exceeded 800 MPa and 1 GPa, respectively. The results highlight the potential for developing highly corrosion-resistant, high-strength Ni-free austenitic stainless steel by PBF-LB for possible applications for biomedical implants and structures relating to nuclear energy.

Magnesium-containing multi-principal element alloys (MPEAs) are promising for lightweight applications due to their low density, high specific strength, and biocompatibility. This study examines two Mg-Ti-Zn alloy compositions, equal molar MgTiZn (TZ) and Mg₄TiZn (4TZ), synthesized via ball milling followed by spark plasma sintering, focusing on their microstructures and corrosion behaviors. X-ray diffraction and transmission electron microscopy revealed the formation of intermetallic phases, including Ti₂Zn and Mg₂₁Zn₂₅ in TZ, while 4TZ exhibited a predominantly Mg-rich phase. Potentiodynamic polarization and immersion tests in 0.1 M NaCl solution showed that both alloys had good corrosion resistance, with values of 3.65 ± 0.65 µA/cm² for TZ and 4.58 ± 1.64 µA/cm² for 4TZ. This was attributed to the formation of a TiO₂-rich surface film in the TZ, as confirmed by X-ray photoelectron spectroscopy (XPS), which contributed to enhanced passivation and lower corrosion current density. Both alloys displayed high hardness, 5.5 ± 1.0 GPa for TZ and 5.1 ± 0.9 GPa for 4TZ, and high stiffness, with Young’s modulus values of 98.2 ± 11.2 GPa for TZ and 100.8 ± 9.6 GPa for 4TZ. These findings highlight the potential of incorporating Ti and Zn via mechanical alloying to improve the corrosion resistance of Mg-containing MPEAs and Mg-based alloys.

This paper reports the beneficial effects of strontium (Sr) on the sensitization kinetics and an unusually high passivation behavior in Al-5.7 wt% Mg alloy. The presence of strontium has aided not only in retarding the sensitization kinetics of Al-5.7 wt% Mg alloy but also significantly enhanced the intergranular corrosion resistance. The surface enrichment of Cr and Sr as oxides and hydroxides has caused an unusual increase in the passivity and pitting potential of Al-5.7 wt% Mg alloy. The presence of both Cr and Sr helped in retaining the passivity of the alloy even in the sensitized condition.

The effects of environments in altering the atomic strain distribution in AA 7004 while subjected to slow strain rate testing to environmentally assisted cracking are investigated. Two different temper conditions—one where predominantly G.P. zones are present and the other with predominantly η′/η precipitates were chosen for the present study. Three different test environments—glycerol (Gly), 3.5 wt% NaCl (OCP), and 3.5 wt% NaCl with 100 mV cathodic charging vs. open-circuit potential (CP) were used. Under the above environmental conditions, the alloy aged at 140°C for 24 h, containing predominantly G.P. zones, showed the existence of the tensile nonshear components of the strain. On the other hand, the alloy aged at 140°C for 48 h, containing predominantly η′/η precipitates, showed only one of the two nonshear strain components that were tensile in nature, with a simultaneous reduction in the shear component of strain. The work highlights that the effects of the environment on the deformation behavior of the alloy are evident by way of alterations in strain distribution at the atomic level, which could possibly explain the increase in dynamic recovery for the microstructure containing primarily the G.P. zones, and the decrease in dynamic recovery for microstructures consisting predominantly of η′/η precipitates.

Dental implants provide oral rehabilitation by mimicking bone topography, faster bone formation, and rapid bone healing to enable early loading protocol with better stability. The dental implant surface affects the mechanical stability of the implant affecting cell adhesion and osteogenic cell response. Different techniques have shown biological advantages through increase in surface wetta-bility, surface roughness, and altered surface topography. These have benefitted osseointegration in both healthy as well as a compromised bone through its underlying cellular mechanisms. The effects of nanostructuring are discussed in this chapter in terms of gene expression, biochemical stimuli, biocompatibility, corrosion resistance, cell metabolism, and its differentiation.

Gas tungsten arc welding is extensively used in the fabrication of 18Ni 250 maraging steel motor casings. In this work, the role of flux addition on the environmentally assisted cracking (EAC) and electrochemical corrosion behaviors of these welds in their peak-aged condition is presented. Studies were performed in order to bring out the potential influence of long-term exposure of maraging steel welds to neutral 0.1 M NaCl (mildly corrosive) and acidified 0.1 M NaCl (a relatively more corrosive) environments to understand the EAC behavior of the welds. The study showed that both the fluxed and unfluxed weld metals suffered 21% to 23% loss in ductility in neutral 0.1 M NaCl solution from that of obtained in air. The EAC of the welds in the neutral chloride solution was due to anodic dissolution, while in the acidified chloride solution it was found to be predominantly due to hydrogen embrittlement. The effect of flux in refining the weld microstructure was reflected in: (a) preventing intergranular mode of hydrogen embrittlement of the unfluxed welds and transforming the mode to transgranular cracking, (b) lowering a wide scatter in electrochemical corrosion rate, and (c) reducing the selective attack in the interdendritic regions of the unfluxed welds. Such a transition from intergranular to transgranular cracking might affect long-term service behavior of the welds to corrosion and EAC, though it is not reflected in the short-term tests.