Mixed (Ti,Zr)C offers significantly higher hardness compared to its monocarbide constituents owing to solid solution hardening. However, the (Ti,Zr)C system has a miscibility gap in which the carbide can decompose into TiC-rich and ZrC-rich phases at high temperature. This limits the utilization of (Ti,Zr)C, where structural stability at high temperatures is sought, but we here show, using in-situ neutron diffraction during aging at 1600 °C, how small additions of other carbides can significantly retard the decomposition. The effect on decomposition kinetics by addition of 1 mol% HfC or NbC is shown and thermodynamics calculations and scanning transmission electron microscopy experiments aid to propose that the altered decomposition kinetics can stem from a narrower miscibility gap and altered interface chemistry. Although the decomposition morphology suggests that phase separation proceeds through discontinuous precipitation, we find that only the TiC-rich decomposition product nucleates with a composition far from equilibrium and evolves with time.

This study investigates and compares the evolution of subsurface hardness and microstructure of Hybrid 60 and 52100 steels under rolling contact fatigue (RCF) testing. Similar microstructural decay was identified for both Hybrid 60 and 52100 steel, evidenced by the formation of elongated ferrite and ferrite microbands during the first stage of the microstructural decay. Nano-sized ferrite grains were also observed in the region with maximum Hertzian stress after 1×108 stress cycles for both steels. In addition to the common microstructural decay in the two steels, the 52100 steel experienced microstructural decay in the form of dissolution of residual cementite and tempered carbides. The present study shows that the Hybrid 60 steel develops less microstructural decay than the 52100 steel at the same RCF conditions suggesting that Hybrid 60 could be suitable for replacing 52100 in applications where higher RCF is needed. The improved microstructure stability in Hybrid 60 is attributed to the more stable secondary carbides and intermetallic precipitates as compared to the cementite in the 52100 steel.

The effect of blue light on atmospheric corrosion of Cu and on the antimicrobial properties was explored upon exposure mimicking the condition of hygienic surface disinfection. The results show that blue light illumination enhanced the formation of Cu2O, resulting in a slightly increased corrosion resistance of Cu without pre-deposited NaCl, whereas the enhanced formation of Cu2O, CuCl and/or Cu(OH)3Cl on copper with pre-deposited NaCl caused concomitant corrosion product flaking and a reduced corrosion resistance. The blue light induced enhancement of Cu corrosion led to increased surface roughness and more pronounced integration of bacteria within the corrosion products.

Material decay in bearing steels under rolling contact fatigue (RCF) leads to fatigue initiation and failure. This study examines the local structure-property relationship in decayed material through in-situ compression testing of micropillars prepared from a dual-hardening martensitic bearing steel (Hybrid 60) before and after RCF testing. The results demonstrate a pronounced enhancement in local yield strength for decayed regions (2200–2340 MPa) as compared to non-decayed regions (1755–1780 MPa). The higher initial stress for dislocations glide in the decayed regions and their discontinuous yield behavior are attributed to the presence of ferrite microbands. Crystal plasticity simulations corroborated these findings, showingincreased critical resolved shear stress (CRSS) and reduced strain hardening in decayed samples.

We investigate the microstructural degradation during rolling contact fatigue (RCF) in a martensitic dual-hardening bearing steel. The dual-hardening steel makes use of both carbide precipitation and intermetallic precipitation hardening. The microstructural degradation leading to fatigue failure is studied using electron microscopy, atom probe tomography, and synchrotron X-ray diffraction (SXRD). The initial microstructure of the steel consists of tempered martensite with a fine dispersion of secondary M7C3, and NiAl precipitates. During RCF testing at 2.2 GPa contact pressure, ferrite microbands develop and the partial dissolution of NiAl and M7C3 precipitates occur within the ferrite microbands. For the RCF testing at higher contact pressure of 2.8 GPa, nanosized ferrite grains develop in the ferrite microbands. The SXRD analysis reveals a decrease in dislocation density in the sub-surface region experiencing microstructural degradation. This is believed to be associated with the rearrangement of dislocations into low energy configuration cells. We conclude this manuscript by proposing a microstructure decay mechanism for martensitic dual-hardening bearing steel that provides insights in the fatigue initiation process.

Targeting to obtain fine dispersions of nanoscale precipitates to enhance the mechanical properties of a highperformance tool steel, re-engineering of the alloy composition and heat treatment was guided by computational thermodynamics and kinetics. A prototype alloy was prepared using the designed chemistry and heat treatment. Thereafter, advanced microstructural characterization and mechanical testing confirmed the successful design to reach a high number density of (V, Mo)C precipitates with an average diameter of about 5 nm in the peak-hardened condition, after tempering the martensite at 600 degrees C for 2 h.

Subsurface rolling contact fatigue (RCF) failure occurs beneath heavily loaded hard contacts like gears, bearings, and cams. This study investigates microstructural decay beneath a RCF-tested surface in AISI/SAE 52100 bearing steel tempered at 240 ℃. RCF tests were conducted at 100 ℃ with a maximum Hertzian contact pressure of 4 GPa for four stress cycles. Microstructural characterization utilized scanning electron microscopy, electron backscatter diffraction, transmission Kikuchi diffraction, and transmission electron microscopy. Due to high tempering temperature, white etching bands (WEBs) were observed without preceding dark etching regions. The microstructural decay sequence involved: (1) formation of elongated ferrite and ferrite microbands, (2) complete dissolution of tempered carbides and partial dissolution of residual cementite, (3) formation of WEBs composed of nano-sized ferrite grains (100–300 nm) transformed from ferrite microbands, and (4) appearance of lenticular carbides. Within the WEBs, most nano-sized grains had high-angle grain boundaries, while the fraction of low-angle grain boundaries increased in later stages of RCF. Lenticular carbides formed alongside elongated ferrite and coalesced nano-sized ferritic grains.

We investigate the microstructural degradation during rolling contact fatigue (RCF) in a novel martensitic dual-hardening steel. The microstructural decay that eventually leads to fatigue failure is studied by electron microscopy, atom probe tomography and synchrotron X-ray diffraction (SXRD). The initial microstructure of the steelconsists of tempered martensite with a fine dispersion of secondary M7C3, and NiAl precipitates. During RCF testing at 2.2 GPa contact pressure, ferrite microbands develop and the partial dissolution of NiAl and M7C3 precipitates occur within theferrite microbands. For the RCF testing at higher contact pressure of 2.8 GPa, nanosized ferrite grains develop in the ferrite microbands. The SXRD analysis reveals a decrease in dislocation density in the sub-surface region experiencing microstructural decay. This is believed to be associated with the rearrangement of dislocations into low energy configuration cells. We conclude this manuscript by proposing a microstructure decay mechanism for dual-hardening martensitic steels that provides insights in the fatigue initiation process.

Here we design a novel multi-principal element carbide system (Ti,Zr,Hf,W)C with a miscibility gap using computational tools and report on the formation of a single-phase (Ti,Zr,Hf,W)C after spark plasma sintering. The (Ti,Zr,Hf,W)C shows high nanohardness (32.7 GPa) and fracture toughness (5 MPa·m1/2). Aging studies at 1350 °C for 100 h show that the single-phase carbide solid solution is quite stable even though this temperature is within the predicted miscibility gap of the system. Detailed electron microscopy characterization shows that phase separation has initiated with minor decomposition after aging by forming rock-salt (Ti,W)C- and (Zr,Hf)C-rich phases as well as hexagonal WC precipitates. We show that the (Ti,W)C- and (Zr,Hf)C-rich phases form a lamellar structure upon aging and the interlamellar spacing is considerably coarser than what has been previously found for the binary (Ti,Zr)C system. The decomposition kinetics, on the other hand, is sluggish due to the reduced driving force for phase decomposition. 

The effect of prior deformation on the evolution of the martensite phase in Ti-6Al-4V alloy is reported by varying the hot-rolling temperature to have different stored energies. While the morphology of the martensite phase is greatly influenced by the prior deformation, the phase fraction is primarily dependent on the quenching temperature. The compositional deviation from the equilibrium condition, emerging from the differences in the diffusion of elements at different rolling temperatures, govern the nucleation and aspect ratio of the martensite laths. Higher stored energy in the deformed samples, calculated as the dislocation density, is found to derive the formation of a twinned plate martensite. Martensitic transformation, irrespective of the prior deformation condition, induces a strong variant selection based on the minimization of the transformation strain energy. However, a strong correlation between the morphology and the character of the intervariant boundaries of the martensite phase is established. The intervariant boundary distribution in martensite showed three major angle–axis pairs associated with the Burgers orientation relationship. The hardness of the martensite phase is determined by the solid solution strengthening, martensite morphology, and microstrain present in the sample.