This work developed an effective and promising lubricant containing Zn nanoparticles and polyethylene glycol (PEG) base oil to deal with the tough problem of boundary lubrication for steel/Ti6Al4V. Tribological tests were carried out to investigate the boundary lubrication performances and the generation process of boundary protective films on the worn surface. Results showed that low and steady friction coefficient curves could be obtained by PEG suspensions with Zn nanoparticles after a very short ‘run-in’ period, and the main wear volume of Ti6Al4V was occurred during the ‘run-in’ period. The ZnO boundary protective films generated on the counterfaces of the Ti6Al4V disk and steel ball during the friction process. This strong and steady oxide films could effectively prevent direct contact between frictional pairs and provide excellent boundary lubrication performances. This work will contribute to the development of high performance lubricants for titanium alloys

The effects of Al and Mo elements on the microstructure and hardness of TNM TiAl alloys (Ti-43.5Al-4Nb-1Mo-0.1B) were studied by decreasing 0.5 at.% Mo and/or increasing 1.5 at.% Al. The results showed that the changed composition of the alloy had a slight influence on the morphology, but had important effects on the volume fraction, size, and composition of each phase. All the alloys had nearly full lamellar (NL) microstructures, with a few β_o phases at the boundaries of the colony or in the lamellar colony. The lamellar colony size and the lamellar spacing increased with the decrease in Mo and the increase in Al. The reduction in Mo content reduced the content of each phase in proportion, but the increase in Al content in the alloys led to the corresponding increase in Al content in the α₂ and γ phases. The hardness of the alloys decreased with the increase in Al content and the decrease in Mo content. This is mainly due to the increase in lamellar spacing caused by the change in composition. Therefore, the increased content of Al and decreased Mo content are unbeneficial for the microstructure. The relationship between the Vickers hardness and the lamellar spacing obeyed the Hall–Petch relationship.

NO oxidation over LaMnO ₃ (001) surface was studied using first-principle calculations based on density functional theory (DFT). The calculated results indicate that the surface energies of (001) are lower than that of the (011) and (111) surfaces. Three adsorbates (O ₂ NO and NO ₂ ) after adsorption are activated due to remarkable elongation of bond length, notable change in DOS and large electron transfer. The analysis of the electron localization function (ELF) reveal the typical feature of a ionic bond in the Mn-N and Mn-O bond intersecting planes. Difference charge density (DCD) analysis show that electron accumulation occurs at the Mn-O and Mn-N bonds as charge is transferred from adsorbate (NO, O ₂ or NO ₂ ) to the substrate, so that the ability bonding of the adsorbate and substrate is enhanced. The reaction of NO adsorbed at Mn2 with O _c is faster and more feasible due to the low energy barrier and short O _c -N bond distance. Dissociation of O ₂ is an exothermic process (−1.290 eV) with a small activation energy (0.345 eV). The NO activation and desorption of NO ₂ are energetically the most demanding steps.

The element distribution and the microstructures of directionally solidified ingots of Ti-45Al-8Nb and Ti-46Al-8Nb alloys were studied by scanning electron microscope (SEM) and electron probe microanalyzer (EPMA) equipped with wavelength-dispersive X-ray spectroscope (WDS). At high solidification rates, e.g., more than 50 μm/s, the ingot solidified in columnar β dendrites, while at low solidification rates, e.g., less than 30 μm/s, the solidification path changed from initial β solidification to L + β→α peritectic solidification, forming cellular dendrites with the β phase matrix surrounded by the α phase. The difference of Ti content in dendritic arms and interdendritic regions was not pronounced. The composition segregation was mainly caused by the mutual conversion of Al and Nb contents. Therefore, it was difficult to distinguish the variation of Ti in microstructure by EPMA-WDS map and line profiles. The composition of the peritectic α phase was different from that of the α phase transformed directly from the β phase. The Al content of the former was about 1 at% higher than that of the latter, while the Nb content was about 1 at% lower. The change of solidification path in the final solidified part resulted from the more severe segregation caused by slow solidification.

The friction weldability of Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy has been investigated by optimizing process parameters and analyzing the microstructures and tensile properties of the joints. The as-cast alloy with a nearly lamellar (NL) microstructure and the as-forged alloys with a duplex (DP) microstructure have been successfully welded. All the joints have a severe deformation zone (SDZ) and a transition zone (TZ) between the parent metal (PM) and SDZ. SDZ, showing a biconcave lens geometry, has a maximum thickness of hundreds of micrometers at the periphery. TZ is hundreds of micrometers thick. All SDZs have a fine-grained DP microstructure with a grain size of a few micrometers. For the joint of the as-cast alloy, the TZ consists of deformed lamellar colonies as the major constituent and partially recrystallized grains as the minor constituent. For the joint of the as-forged alloy, the TZ is similar to both the PM and SDZ, showing a DP microstructure. The grain size, volume fraction of γ grains, and the remnant lamellar colonies all increase with the distance from the SDZ. All joints presented perfect metallurgical bonding. The strengths of the joints are higher than those of the corresponding PMs. This indicates that the studied alloy has good friction weldability.