Low-temperature densification sintering and properties of CaAl_2Si_2O_8 ceramics with MeO·2B_2O_3(Me=Ca,Sr,Ba)

Dense CaAl2Si2O8 ceramics were prepared via a two-step sintering process at temperatures below 1000℃. First, pre-sintered CaAl2Si2O8 powders containing small amounts of other crystal phases were obtained by sintering a mixture of calcium hydroxide and kaolin powders at 950℃ for 6 h. Subsequently, the combination of the pre-sintered ceramic powders with MeO＇2B203 （Me = Ca, Sr, Ba） flux agents enabled the low-temperature densification sintering of the CaAl2Si2O8 ceramics at 950℃. The sintering behavior and phase formation of the CaAl2Si2O8 ceramics were investigated in terms of the addition of the three MeO·2B2O3 flux agents. Furthermore, alumina and quartz were introduced into the three flux agents to investigate the sintering behaviors, phase evolvements, microstructures, and physical properties of the resulting CaA12Si208 ceramics. The results showed that, because of their low-melting characteristics, the MeO·2B2O3 （Me = Ca, Sr, Ba） flux agents facilitated the formation of the CaAl2Si2O8 ceramics with a dense microstructure via liquid-phase sintering. The addition of alumina and quartz to the flux agents also strongly affected the microstructures, phase formation, and physical properties of the CaA12Si208 ceramics.

Influence of sintering temperature on the phases and photoelectric characteristics of BiOCl/ZnO composite powders

Zinc oxide is a typical functional oxide that has been widely researched for various industry applications due to its peculiar physical characteristics. However, to achieve its potential in promising applications, much work has been diligently performed to improve the physical properties of ZnO. In this work, an aqueous suspension route was used to prepare BiOCl/ZnO composite powders, and sintering processes were applied to investigate the influence of sintering temperature on the phase evolutions, microstructures, and photoelectric characteristics of BiOCl/ZnO composite powders. The results indicated that the photoelectric properties mainly depend on the relevant content of BiOCl in the composite powders and the sintering temperature. The photoelectric measurements in K_2SO_4 solutions show that the photoelectric properties of the samples with the appropriate BiOCl content(0.3 mol% and 2.0 mol%) are better than those of ZnO and commercial TiO_2(P_(25)) powders, but the photoelectric measurements in NaOH solutions indicate that the photoelectric characteristics of the as-sintered samples are only better than those of P_(25).

Mineral-phase evolution and sintering behavior of MO–SiO_2–Al_2O_3–B_2O_3 (M = Ca,Ba) glass-ceramics by low-temperature liquid-phase sintering

In this work, network former SiO_2 and network intermediate Al_2O_3 were introduced into typical low-melting binary compositions CaO·B_2O_3, CaO·2B_2O_3, and BaO·B_2O_3 via an aqueous solid-state suspension milling route. Accordingly, multiple-phase aluminosilicate glass-ceramics were directly obtained via liquid-phase sintering at temperatures below 950°C. On the basis of liquid-phase sintering theory, mineral-phase evolutions and glass-phase formations were systematically investigated in a wide MO–SiO_2–Al_2O_3–B_2O_3(M = Ca, Ba) composition range. The results indicate that major mineral phases of the aluminosilicate glass-ceramics are Al_(20)B_4O_(36), CaAl_2Si_2O_8, and BaAl_2Si_2O_8 and that the glass-ceramic materials are characterized by dense microstructures and excellent dielectric properties.

Microstructure and fatigue properties of TiAl-based alloy with different tungsten contents

Microstructure and fatigue properties of TiAlbased alloys with different W contents were investigated.The results indicate that the grain size and lamellar spacing can be significantly refined,and the optimal W content on both the microstructure and fatigue property is about1.00 at%.The amount of B2（ω） phase gradually increases with the increase in W content,and excessive B2（ω） phase located in the boundary of lamellar colony trends to be the weak region with low resistance against crack propagation.Another result is that with the increase in W content,the region of peritectic reaction is also enlarged.The interdendritic Al-rich region is another weak region against crack propagation.Both of these effects are responsible for the worse fatigue property of Ti-45.1Al-5Nb-1.40W-1.4B W alloy compared with that of Ti-45.7Al-5Nb-0.75W-1.4B alloy.Instability of fatigue property still exists,but it slightly reduces with the decrease in grain size and lamellar spacing.

Interfacial microstructure and mechanical properties of diffusion-bonded joints of titanium TC4 (Ti-6Al-4V) and Kovar (Fe-29Ni-17Co) alloys

Diffusion bonding is a near net shape forming process that can join dissimilar materials through atomic diffusion under a high pressure at a high temperature.Titanium alloy TC4（Ti-6 Al-4 V）and 4 J29 Kovar alloy（Fe-29 Ni-17 Co）were diffusely bonded by a vacuum hot-press sintering process in the temperature range of 700-850°C and bonding time of 120 min,under a pressure of 34.66 MPa.Interfacial microstructures and intermetallic compounds of the diffusion-bonded joints were characterized by optical microscopy,scanning electron microscopy,X-ray diffraction（XRD）and energy dispersive spectroscopy（EDS）.The elemental diffusion across the interface was revealed by electron probe microanalysis.Mechanical properties of joints were investigated by micro Vickers hardness and tensile strength.Results of EDS and XRD indicated that（Fe,Co,Ni）-Ti,TiNi,Ti_2Ni,TiNi_2,Fe_2 Ti,Ti_（17） Mn_3 and Al_6 Ti_（19） were formed at the interface.When the bonding temperature was raised from 700 to 850°C,the voids of interface were reduced and intermetallic layers were widened.Maximum tensile strength of joints at 53.5 MPa was recorded by the sintering process at 850°C for 120 min.Fracture surface of the joint indicated brittle nature,and failure took place through interface of intermetallic compounds.Based on the mechanical properties and microstructure of the diffusion-bonded joints,diffusion mechanisms between Ti-6 Al-4 Vtitanium and Fe-29 Ni-17 Co Kovar alloys were analyzed in terms of elemental diffusion,nucleation and growth of grains,plastic deformation and formation of intermetallic compounds near the interface.