Effect of Ni on microstructure and mechanical properties of Al−Mg−Si alloy for laser powder bed fusion

The microstructures and mechanical properties were systematically studied for the high-strength Al−5Mg_(2)Si−1.5Ni alloy fabricated by laser powder bed fusion(L-PBF).It is found that the introduction of Ni(1.5 wt.%)into an Al−5Mg_(2)Si alloy can significantly improve the L-PBF processibility and provide remarkable improvement in mechanical properties.The solidification range of just 85.5 K and the typical Al−Al3Ni eutectics could be obtained in the Ni-modified Al−5Mg_(2)Si samples with a high relative density of 99.8%at the volumetric energy density of 107.4 J/mm^(3).Additionally,the refined hierarchical microstructure was mainly characterized by heterogeneousα-Al matrix grains(14.6μm)that contain the interaction between dislocations and Al−Al3Ni eutectics as well as Mg_(2)Si particles.Through synergetic effects of grain refinement,dislocation strengthening and precipitation strengthening induced by Ni addition,the L-PBFed Al−5Mg_(2)Si−1.5Ni alloy achieved superior mechanical properties,which included the yield strength of(425±15)MPa,the ultimate tensile strength of(541±11)MPa and the elongation of(6.2±0.2)%.

Optimization of mechanical and antibacterial properties of Ti-3wt%Cu alloy through cold rolling and annealing

In this work,a process of cold rolling with 70%thickness reduction and different annealing temperatures was selected to regulate the microstructure of Ti-3wt%Cu alloy.Microstructural evolution,mechanical properties and antibacterial properties of the Ti-3wt%Cu alloy under different conditions were systematically investigated in terms of X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),tensile and antibacterial test.The results indicated that cold rolling could dramatically increase the ultimate tensile stress(UTS)from 520 to 928 MPa,but reduce the fracture strain from 15.3%to 3.8%.With the annealing temperature increasing from 400 to 800C for 1 h,the UTS decreased from 744 to 506 MPa and the fracture strain increased from12.7%to 24.4%.Moreover,the antibacterial properties of the Ti-3wt%Cu alloy under different conditions showed excellent antibacterial rate(>96.69%).The results also indicated that the excellent combination of strength and ductility of the Ti-3wt%Cu alloy with cold rolling and following annealing could be achieved in a trade-off by tuning the size and distribution of Ti2Cu phase,which could increase the applicability of the alloy in clinical practice.More importantly,the antibacterial properties maintained a good stability for the Ti-3wt%Cu alloy under different conditions.The excellent combination of mechanical properties and antibacterial properties could make the Ti-3wt%Cu alloy a good candidate for long-term orthopaedic implant application.

Antibacterial activity and mechanism of newly developed Zr-30Ta and Zr-25Ta-5Ti alloys against implant-associated infection

Infection is a common problem after implantation,and the currently used Ti-based implants have insufficient antibacterial activities.The newly developed Zr-30Ta and Zr-25Ta-5Ti alloys exhibited good mechanical properties,low elastic moduli,and high corrosion resistance.In this work,their antibacterial activities and antibacterial mechanisms were investigated.The surface roughness,wettability,and charge of the alloys were evaluated using a profilometer,drop shape analyzer,and electrokinetic analyzer,respectively.The antibacterial activity against Streptococcus mutans and Porphyromonas gingivalis was investigated using the inhibition zone assay,plate count assay,live/dead staining,and scanning electron microscopy(SEM).The reactive oxygen species release(ROS)was evaluated using the 2’7’-dichlorodihydrofluorescein diacetate(DCFH-DA)assay.The results demonstrated that Zr-30Ta and Zr-25Ta-5Ti alloys had favorable smooth,hydrophilic,negatively charged surfaces that decreased bacteria adhesion and prevented biofilm formation.Zr-30Ta and Zr-25Ta-5Ti alloys also exhibited a time-dependent decrease in the bacteria adhesion and viability.Zr-30Ta and Zr-25Ta-5Ti alloys were also found to induce direct membrane damage and increase ROS production,resulting in significantly better antibacterial activities than CP-Ti.Zr-30Ta and Zr-25Ta-5Ti alloys exhibited comparable antibacterial activities.This work suggests that the newly developed Zr-30Ta and Zr-25Ta-5Ti alloys have good antibacterial activity against Streptococcus mutans and Porphyromonas gingivalis and are promising candidate materials for dental and orthopedic implants.

Copper release and ROS in antibacterial activity of Ti-Cu alloys against implant-associated infection

Enhancing the antibacterial properties of the currently used implant materials is a major concern of healthcare providers to minimize the impact of peri-implant infection and improve implant survival rates.In this study,titanium-copper sintered alloys(3 wt% and 5 wt%Cu) were developed for medical implant applications.The phase identification,microstructure,copper ions release,and wettability of these alloys were evaluated using X-ray diffraction(XRD),optical microscope(OM),scanning electron microscope(SEM),transmission electron microscope(TEM),energy-dispersive X-ray spectroscope(EDS),inductively coupled plasma spectroscope(ICP) and drop shape analyzer.The antibacterial activities of Ti-Cu alloys against Porphyromonas gingivalis and Streptococcus mutans were evaluated using inhibition zone assay,plate counting assay,live/dead fluorescent staining,SEM and reactive oxygen species(ROS) staining assay.The results demonstrated that Ti-Cu alloys are composed of α-Ti and Ti_(2)Cu phases that increased with increased Cu content of the alloy.Ti-Cu alloys exhibited antibacterial activity against both bacteria species in a time-dependent manner.The antibacterial rates of Ti-3Cu and Ti-5Cu after72 h were 57% and 70% against Porphyromonas gingivalis and 63% and 78% against Streptococcus mutans,respectively.The highest amount of Cu^(2+) released from these alloys was 0.3 mg·L^(-1) during the first 24 h,within the safe range.The copper ions release and ROS production were suggested as the main antibacterial mechanisms.Overall,Ti-Cu sintered alloys are promising materials for dental and orthopedic implants.