Gas formation and biological effects of biodegradable magnesium in a preclinical and clinical observation

Magnesium alloys are biodegradable metals receiving increasing attention, but the clinical applications of these materials are delayed by concerns over the rapid corrosion rate and gas formation. Unlike corrosion, which weakens mechanical properties, the gas formation issue has received little attention. Therefore, we evaluated the gas formation and biological effects for Mg implants through preclinical (immersed in Earle’s balanced salt solution and in vivo) and clinical studies. The immersion test examined the gas volume and composition. The in vivo study also examined gas volume and histological analysis. The clinical study examined the gas volume and safety after Mg screw metatarsal fixation. Gas was mainly composed of H₂, CO and CO₂. Maximum volumes of gas formed after 5 days for in vivo and 7 days in clinical study. Within the clinical examination, two superficial wound complications healed with local wound care. Osteolytic lesions in the surrounding metaphysis of the Mg screw insertion developed in all cases and union occurred at 3 months. Mg implants released gas with variable volumes and composition (H₂, CO, and CO₂), with no long-term toxic effects on the surrounding tissue. The implants enabled bone healing, although complications of wound breakdown and osteolytic lesions developed.     

Experimental study on moldability and segregation of Inconel 718 feedstocks used in low-pressure powder injection molding

Moldability and segregation of feedstock are linked to the rheological behavior of the powder-binder mixture. In this study, the impact of binders on viscosity and segregation of feedstocks was investigated. The experiments were conducted on several feedstocks obtained by mixing Inconel 718 powder with paraffin wax-based binder systems. The viscosity of feedstocks was measured by a rotational rheometer while the segregation within green parts was evaluated using a thermogravimetric analyzer. It was demonstrated that the variation in solid loading within a molded part can be measured with a sensitivity of at least ±0.25?vol% of powder. The results indicated that the predominant powder-binder separation appears clearly at the top and the bottom of the molded part. It was also shown that the viscosity profiles of feedstocks and the intensity of segregation depends significantly on the binder constituents used in feedstock formulation. The mixture containing only paraffin wax produced the best trade-off between high moldability and low segregation for an injection process requiring an extended time range between injection and solidification of the part (e.g. up to 10?min). For a short processing time (e.g. <1?min spent in molten state), the feedstocks containing paraffin wax with stearic acid or small amount of ethylene vinyl acetate can be also considered as good candidates for LPIM process because their viscosity and segregation potential are relatively low.     

快速充型对镁合金压铸件质量的影响

针对汽车发动机缸盖罩盖零件,采用压力传感器,通过对铸件的表观质量进行评定及铸件密度和抗拉强度的测定,系统研究了镁合金压铸过程中快速充型速度和起速位置对型腔内压力变化和铸件质量的影响.结果表明:随着充型速度增加,镁合金铸件的表观质量显著改善,达到一定值后,这种趋势变化不明显;铸件的表面缺陷随着起速位置的增大先增多后减少;铸件的强度与密度均随着充型速度和起速位置的增大先增大后减小,这与充型速度与起速位置对铸件型腔内压力的影响规律一致;当充型速度为70 m/s,起速位置为210 mm时,镁合金压铸件的质量与性能最佳.     

Effect of carnauba wax as a part of feedstock on the mechanical behavior of a part made of 4605 low alloy steel powder using metal injection molding

Metal injection molding is a growing technology for producing complex metallic components. Preparation of feedstock for metal injection molding is a very crucial step during this process. This is because the deficiencies in quality of the feedstock once made, cannot be corrected by subsequent processing steps. One of the challenges in producing the feedstock is its formulation. In this study, the effect of the percentage of carnauba wax along with other binder constituents of paraffin wax, polypropylene and stearic acid is investigated on the density, strength, hardness and rheological behavior of a part, made of 4605 low alloy steel powder using metal injection molding process. For this reason, six binder systems including paraffin wax, polypropylene and stearic acid having different percentages of carnauba wax have been produced. After preparation of the samples, tensile testing, Vickers hardness test, density and rheological behavior of the samples have been measured and compared. The results show that carnauba wax as a part of feedstock, has a positive effect on the strength and density while negative effect on the hardness of the final sintered part. Also with the increase in the percentage of the carnauba wax inside the polymer binder, the viscosity of the feedstock was reduced significantly.