Fabrication of Compact Magnesium Disk by Spark Plasma Sintering

Fabrication of pure magnesium (Mg) disk was performed by powder metallurgy with the compaction method of spark plasma sintering (SPS). The effect of mechanical milling time on the microstructure, density, and porosity of the disk specimen was investigated. At an identical temperature, the 4 and 5 h milled specimens exhibited a nearly overlapped displacement curves during SPS, and a higher value indicating a higher densification degree than that of the 3 h milling powder. In agreement, the specimen density increased consecutively from 1.76 to 1.77 and 1.80 g/cm3 for the milling time of 3, 4, and 5 h. However, the porosity increased from 1.21% to 1.49% when the milling time increased from 3 to 4 h and further to 3.44% for 5 h milled specimens. The microstructure observation revealed that the average grain size decreased, and the pores became smaller and elongated with increasing milling time. The number of pores was higher with the gain fraction of grain boundaries. The 3 h milled specimen contained the highest atomic fraction of oxygen (21.9 at%) than that of the 4 and 5 h milled specimens (5.6 at% and 7.9 at%). The optimum milling time for obtaining high density and low porosity of pure Mg disk was 4 h.

Numerical Simulation of Ice Fractures Process of the Yellow River Based on Disk Specimen

To study the influence of the changes in crystals on a micro scale as well as their effect on the macro mechanical properties of river ice and to mitigate the limitation of the objective conditions in a physical examination of river ice, it is necessary to analyze the fracture process of river ice using a micro numerical calculation method. Thus, a numerical model was established to simulate the cracking process of river ice based on disk specimen. Upon comparison with the physical experiment, the results of the numerical model show agreement with the fracture toughness and cracking process. Based on the numerical model, the obtained material parameters of Yellow River ice laid a foundation for the study of the cracking process of river ice on a macro-, meso-, and multiscale.

Effect of oxygen addition on the formation of isothermal ω phase in Ti-Fe alloys

The effect of the addition of oxygen on the formation of microstructure cooled from the β phase of Ti-Fe alloy was examined. The alloy ingots of Ti-(4, 5, 6, 7, 8, 9 and 10) at.% Fe and Ti-8 at.% Fe-(1 and 3) at.% O were arc-melted. They were homogenized at 1200 °C for 3.6 ks and then hot-rolled at 850 °C into 1.5-mm thick sheets. The disk specimen was fabricated and then put in the differential thermal analysis (DTA) apparatus. The disk in the DTA was heated at 1000 °C for 0.6 ks in the β phase and then cooled to room temperature at a rate of 50 °C/min. The microstructure was examined by an optical microscope after the DTA experiment. In the Ti-(7 and 8) Fe alloys the ω phase formed during cooling. The addition of oxygen in the Ti-8Fe alloy promoted the β→α transformation. Furthermore, the addition of one at.% oxygen in the Ti-8Fe alloy promoted β→ωi transformation, while the addition of three at.% oxygen suppressed the β→ωi transformation during cooling.

Effect of Halogen-Free Ionic Liquids as Additives of Biolubricants for Room Temperature Titanium-Steel Contact

The surface interactions and tribological behavior of titanium-steel contact have been previously studied under the application of several commercial Ionic Liquids (ILs). In certain cases, superior anti-wear characteristics have been experienced when lubricating using ILs. This is often attributed to the development of a protective tribolayer that forms during application. One anion in particular amide, [Tf2N], has exhibited these characteristics with particularly positive results. However, amide is an anion that contains halogens, which are toxic and can cause harm if not handled properly. Due to the toxicity of most lubricants there has been a growing need to transition to bio-lubricants due to their low impact to the environment. This particular work will investigate the use of Trihexyltetradecylphosphonium, [P6,6,6,14]-+, cation with anion decanoate [Deca] as a non-toxic alternative to amide [Tf2N]. [P6,6,6,14]-+[Deca] and [P6,6,6,14]-+[Tf2N] will be compared as additives (1.0 and 2.5 wt. %) in Coffee Bean oil (CB) for lubrication of titanium-steel contact at room temperature. In this work, tests are conducted using a ball-on-flat reciprocating tribometer as per ASTM G133 with lubricated titanium-steel contact. An AISI 420C stainless steel ball is used on a Grade 5 6Al-4V titanium alloy disk specimen. Friction and wear volume are measured, examined, and discussed.

Evaluation of Light-Activated Provisional Resin Materials for Periodontal Soft Tissue Management

The purpose of this study was to determine mechanical properties using a compressive test with cylinder specimen (h=6 mm andϕ=4 mm) as well as cytotoxicity using elutes from disk specimen (ϕ=10 mm andh=2 mm) against human gingival fibroblasts and oral keratinocytes with light-activated provisional resin materials (Revotek LC and Luxatemp Solar) compared to chemically activated counterpart (Snap, Trim II, and Jet). Significantly increased compressive strength (210~280 MPa) was detected in light-activated products compared to chemically activated ones (20~65 MPa,P<0.05) and similar compressive modulus was detected in both types (0.8~1.5 and 0.5~1.3 GPa). Simultaneously, the light-activated products showed less adverse effects on the periodontal soft tissue cells in any polymerization stage compared to the chemically activated products. Particularly, chemically activated products had significantly greater adverse effects during the “polymerizing” phase compared to those that were “already set” (P<0.05), as shown in confocal microscopic images of live and dead cells. In conclusion, light-activated provisional resin materials have better mechanical properties as well as biocompatibility against two tested types of oral cells compared to the chemically activated counterpart, which are considered as more beneficial choice for periodontal soft tissue management.