Influence of glass-based dental ceramic type and thickness with identical shade on the light transmittance and the degree of conversion of resin cement

The purpose of this study was to assess the influence of the types and thicknesses of glass ceramic plates on light transmittance and compare the degrees of conversion(DC) of resin cement under the ceramic materials. Three ceramic plates with thicknesses of 0.5, 1.0, 2.0, and 4.0 mm were fabricated from each of five commercial ceramic blocks in shade A2: high-translucency and low-translucency IPS Empress CAD(EmpHT and EmpLT); high-translucency and low-translucency IPS e.max CAD(EmxHT and EmxLT); and Vita Mark Ⅱ(Vita). The translucency parameter was obtained using a colorimeter. The light transmittance rate was measured using a photodetector attached to an optical power meter. The DC of a resin cement(Variolink N) underneath the ceramic plates was examined by Fourier transform infrared spectroscopy. The translucency parameter, light transmittance rate, and DC showed significant differences by ceramic type and thickness(P < 0.05). The EmpHT specimens showed the highest light transmission and DCs, and the EmxLT showed the least light transmission and the lowest DCs. The high-translucency Empress showed significantly higher DCs than the low-translucency types(P < 0.05), but there was no significant difference in e.max(P >0.05). Both type and thickness of the glass ceramics significantly influenced the light transmittance and DC of the light-cured resin cement beneath the ceramic of the same shade.

Microstructure and mechanical behavior of cold-rolled CMnAlSi TRIP-aided steel sheets

The microstructure, mechanical properties and retained austenite stability of CMnAlSi-TRIP steels were investigated. Optical microscopy and X-ray diffractometry were used to analyze the microstructure, volume fraction and carbon concentration of retained austenite, while the tensile tests were performed to study the retained austenite stability against strain-induced martensitic transformation. The results show that the mechanical properties of the CMnAlSi cold-rolled TRIP-aided steels fabricated by proper heat treatment display good combination of strength and ductility after isothermal bainitic transformation (IBT) treatment at 420-450 ℃ for 60-120 s. The austenite transformation kinetics is influenced significantly by the IBT temperature, and the high mechanical stability of retained austenite, governed by its carbon concentration, and determines high strain hardening during deformation.

Counter-balancing effects of Si on C partitioning and stacking fault energy of austenite in 10Mn quenching and partitioning steel

Silicon is an essential alloying element in quenching and partitioning(Q&P)steels,because it is known to suppress carbide precipitation during partitioning step and promote carbon partitioning to stabilize austenite.When 2 wt%Si was added to 10Mn-2Al-0.2C steel,the size and fraction of the carbides formed during partitioning became smaller than in the Si-free counterpart.Moreover,the suppression of carbide formation promoted C partitioning into austenite as expected.However,austenite stability was always lower with Si under the equivalent partitioning condition because Si effectively decreased the stacking fault energy of austenite.As partitioning progressed,the both yield and tensile strengths of the Si-added steel exceeded that of the Si-free steel with the similar ductility level.This was because Si was an effective solid solution strengthener,and the austenite in the Si-added steel exhibited the appropriate stability to gradually transform into martensite throughout the deformation.The resulting strengthening effect compensated for the softening caused by martensite recovery.Consequently,strain hardening rate decreased continuously throughout deformation,which resulted in high tensile strength and ductility.