Brazing Characteristics and Bonding Strength of Pure Titanium Joints Brazed with Low-Melting Temperature Zi-17Ti-22Ni Filler Metal.

The brazing characteristics and bonding strengths of pure titanium joints are evaluated for joints brazed with Zr-17Ti-22Ni filler. Vacuum brazing was conducted at temperatures between the melting temperatures of the filler metals and the beta-transition temperature of pure titanium at 3 MPa of pressure for 5 min. Fracturing of the pure titanium joint brazed at 1,093 K occurred before yielding during the tensile tests owing to the presence of a serious segregation region containing harder and more brittle [Ti, Zr]2Ni intermetallic compounds. In contrast, in pure titanium joints brazed at and above 1,113 K, fracturing occurred at the base metal. The yield strengths of the samples brazed at 1,113 K-1,133 K were estimated to be in the range of 320-350 MPa and the ultimate tensile strengths likewise ranged from 350 to 380 MPa. The strength of pure titanium brazed at 1,153 K decreased rapidly. The results of this study show that the optimum temperature to ensure good performance after the brazing of pure titanium with Zr-17Ti-22Ni as a filler metal ranges from 1,113 K to 1,133 K.

Microstructural and Mechanical Characteristics of A356 Alloys as a Function of Mn Content and Cast Thickness.

In this study, the changes in the microstructural characteristics and mechanical properties of A356 alloys as a function of Mn content and cast thickness were evaluated using structural analysis and tensile tests. Five different A356+x%Mn alloys were prepared by casting in molds of different thicknesses followed by solid solution treatment at 813 K for 195 min and aging treatment at 423 K for 120 min. It was confirmed that the secondary dendrite arm spacing (SDAS) increased with increasing thickness of the cast sample, whilst, for a given thickness, the addition of small amounts of Mn resulted in a decrease of the SDAS. Mn contents of 0.05-0.15% resulted in ~7-9% improvements in the spheroid ratio of the primary Si particles compared to that of the commercial A356 alloy. Further, the spheroid ratio of the primary Si particles obtained in the thin cast samples were higher than that obtained in the thick cast samples. In particular, the addition of small amounts of Mn was also effective in suppressing the formation of the needle-like beta Al-Fe-Si intermetallic compound. The yield and tensile strengths of the thinner cast samples were higher than those of the thicker cast samples. Finally, Mn contents of 0.05-0.15% resulted in enhanced yield and tensile strengths, but Mn content ≥0.1% resulted in decreased elongation.

Evaluation of the Hot Workability of Commercially Pure Ti Using Hot Torsion Tests.

Optimum processing conditions were obtained by evaluating the hot working behavior of commercially pure Ti using hot torsion tests. Hot torsion tests were conducted at temperatures ranging from 800 °C-1000 °C and strain rates ranging from 0.1-10 s-1. The flow curves show that the peak stress increases as the temperature decreases and the strain rate increases. The optimum processing conditions were derived by comparing the processing and activation energy maps. The microstructure was characterized based on various regions of the processing map. The activation energy for plastic deformation was obtained using the constitutive equation. The activation energy differs depending on the constituent phases.

Hot Deformation Behavior of Hot-Extruded AA7175 Through Hot Torsion Tests.

The hot deformation behavior of hot-extruded AA7175 was investigated with flow curves and processing maps through hot torsion tests. The flow curves and the deformed microstructures revealed that dynamic recrystallization (DRX) occurred in the hot-extruded AA7175 during hot working. The failure strain was highest at medium temperature. This was mainly influenced by the dynamic precipitation of fine rod-shaped MgZn2. The processing map determined the optimal deformation condition for the alloy during hot working.

Microstructure and properties of cross-roll rolled and heat treated metastable TiNbSn alloy.

A (Ti-35mass%Nb)-4mass%Sn alloy was cross-roll rolled with a reduction ratio of 70% in which the roll axes are tilted by ± 5 degrees away from the transverse direction of the rolled sample and then aged at 250 degrees C for 2 h. Cross-roll rolling was found to increase yield strength and Young's modulus, simultaneously. Yield strength was higher in cross-roll rolled than in conventionally rolled at same reduction ratio. Yield and tensile strength further increased by a low temperature ageing by ψ precipitation hardening and microstructure refinement. Yield and tensile strength of the aged 70% cross-roll rolled sample were higher than those of the aged 70% conventionally rolled one.

Evaluation of paclitaxel rearrangement involving opening of the oxetane ring and migration of acetyl and benzoyl groups.

The stability of drug is a critical factor in quality control, drug efficacy, safety, storage, and production conditions. The rearrangement of paclitaxel, which involves opening of the oxetane ring and migration of acetyl group occurred on heating a powder of purified paclitaxel. Subsequently, the unusual migration of benzoyl groups progressed rapidly in organic solvents. These rearrangement derivatives were isolated carefully. The structures of the intermediate derivative A and the product derivative B were confirmed using (1)H NMR, high performance liquid chromatography (HPLC), and mass spectrometry. We proposed the rearrangement pathway here for the first time. Neither derivative exhibited bioactivity in SKOV3 (ovarian cancer) or MDA-MB-435 (breast cancer) cell culture assays.

Large-scale purification of 13-dehydroxybaccatin III and 10-deacetylpaclitaxel, semi-synthetic precursors of paclitaxel, from cell cultures of Taxus chinensis.

The taxane derivatives 13-dehydroxybaccatin III (13-DHB III) and 10-deacetylpaclitaxel (10-DAP) can be used as semi-synthetic precursors of paclitaxel. These precursors were isolated in a simple and economical procedure during purification of paclitaxel from plant cell culture extracts. No additional costs for cell culture or extraction by silica-gel low-pressure chromatography were incurred. Precipitation from dichloromethane/n-hexane followed by HPLC on ODS and silica-gel resins resulted in paclitaxel of 99.5% purity with 80% overall yield. ODS low-pressure chromatography and THF/n-hexane precipitation yielded 13-dehydroxybaccatin III at >99% purity with 87.1% overall yield, and ODS low-pressure chromatography alone yielded 10-deacetylpaclitaxel at >90% purity with 93.4% overall yield. These compounds are of sufficient purity for use in semi-synthesis of paclitaxel. Both compounds were obtained in high yield at >99.5% purity using ODS-HPLC. The procedures described allow the simultaneous purification of 13-dehydroxybaccatin III, 10-deacetylpaclitaxel, and paclitaxel with only minimal additional expense for reagents or equipment.