Direct Comparison between Tensile Strength and Flexural Strength of Ceramic/Metal Brazing Joint

A design of the sandwich joint,steel/ ceramic/steel,was made for direct comparison be- tween tensile and flexural strength of ceramic/metal joint.The flexural strength is about twice as high as the tensile strength for the same joint.The results also showed that the flexural test is more excellent than tensile test for joint with a high interracial bond strength.

Effect of brazing temperature on microstructure and tensile strength ofγ-TiAl joint vacuum brazed with micro-nano Ti−Cu−Ni−Nb−Al−Hf filler

A novel micro-nano Ti−10Cu−10Ni−8Al−8Nb−4Zr−1.5Hf filler was used to vacuum braze Ti−47Al−2Nb−2Cr−0.15B alloy at 1160−1220℃ for 30 min.The interfacial microstructure and formation mechanism of TiAl joints and the relationships among brazing temperature,interfacial microstructure and joint strength were emphatically investigated.Results show that the TiAl joints brazed at 1160 and 1180℃ possess three interfacial layers and mainly consist of α_(2)-Ti_(3)Al,τ_(3)-Al_(3)NiTi_(2) and Ti_(2)Ni,but the brazing seams are no longer layered and Ti_(2)Ni is completely replaced by the uniformly distributed τ_(3)-Al_(3)NiTi_(2) at 1200 and 1220℃ due to the destruction of α_(2)-Ti_(3)Al barrier layer.This transformation at 1200℃ obviously improves the tensile strength of the joint and obtains a maximum of 343 MPa.Notably,the outward diffusion of Al atoms from the dissolution of TiAl substrate dominates the microstructure evolution and tensile strength of the TiAl joint at different brazing temperatures.

Microstructure and shear strength of reactive brazing joints of TiAl/Ni-based alloy

Reactive brazing of TiAl-based intermetallics and Ni-based alloy with Ti foil as interlayer was investigated. The interfacial microstructure and shear strength of the joints were studied. According to the experimental observations, the molten interlayer reacts vigorously with base metals, forming several continuous reaction layers. The typical interfacial microstructure of the joint can be expressed as GH99/（Ni,Cr）ss（γ）/TiNi（β2）＋TiNi2Al（τ4）＋Ti2Ni（δ）/δ＋Ti3Al（α2）＋Al3NiTi2（τ3）/α2＋τ3/TiAl. The maximum shear strength is 258 MPa for the specimen brazed at 1000°C for 10 min. Higher brazing temperature or longer brazing time causes coarsening of the phases in the brazing seam and formation of brittle intermetallic layer, which greatly depresses the shear strength of the joints.

The temperature-dependent fracture strength model for ultra-high temperature ceramics

Breaking down the entire structure of a material implies severing all the bonds between its atoms either by applying work or by heat transfer. Because bond-breaking is indifferent to either means, there is a kind of equivalence between heat energy and strain energy. Based on this equivalence, we assume the existence of a constant maximum storage of energy that includes both the strain energy and the corresponding equivalent heat energy. A temperaturedependent fracture strength model is then developed for ultrahigh temperature ceramics （UHTCs）. Model predictions for UHTCs, HfB2, TiC and ZrB2, are presented and compared with the experimental results. These predictions are found to be largely consistent with experimental results.

Fabrication and flexural strength of porous Si3N4 ceramics with Li2CO3 and Y2O3 as sintering additives

By employing sintering additives of Li2CO3 and Y2O3,porous Si3N4 ceramics are prepared after experiencing the processes of sintering and post-vacuum heat treatment at 1680 and 1550°C,respectively.The experimental results demonstrate the completed phase transformation fromαtoβ-Si3N4 in Si3N4 ceramic samples with a amount of 1.60 wt%Li2CO3(0.65 wt%Li2O)and 0.33 wt%Y2O3 additives.The as-synthesized porous Si3N4 ceramics exhibit high flexural strength((126.7±2.7)MPa)and high open porosity of 50.4%at elevated temperature(1200°C).These results are attributed to the significant role of added Li2CO3 as sintering additive,where the volatilization of intergranular glassy phase occurs during sintering process.Therefore,porous Si3N4 ceramics with desired mechanical property prepared by altering the addition of sintering additives demonstrate their great potential as a promising candidate for high temperature applications.

Vacuum brazing of Si/SiC ceramic composite and Invar alloy using TiSOCu-W filler metals

Si/SiC ceramic composite and lnvar alloy were successfidly joined by vacuum brazing using Ti5OCu-W filler metals into which W was added to release the thermal stress of the brazed joint. Microstructures of the brazed joints were irwestigated by scanning electron micrascope （SEM） and energy dispersive spectrometer （EDS）. The mechanical properties of the brazed joints were measured by shearing tests. The results showed that the brazed joints were composed of Ti-Cu phase, W phase and Ti-Si phase. W had no effect on the wettability and mobility of the .filler metals. The growth of Ti2 Cu phase was restrained, and the reaction between ceramic composite and filler metals was weakened. The specimen, brazed at 970°C for 5 rain, had the maximum shear strength of 108 MPa at room temperature.

Effect of Heat Treatment on High Temperature Stress Rupture Strength of Brazing Seam for Nickel-base Superalloy

In order to enhance the high-temperature stress rupture strength of brazing seam by heat treatment, it was diffusion treated, then solution heat treated, and finally aging treated. The microstructure of brazing seam especially morphology of gamma ' phase and boride was observed and the strength of brazing seam was measured in this process. The results show that heat treatment can enhance high-temperature stress rupture strength by improving the microstructure of brazing seam. The strength of brazing seam after solution heat treatment decreases in comparison with that only after diffusion treatment while aging treatment after solution heat treatment increases the strength of brazing seam.

Preparation and characterization of ceramic materials with low thermal conductivity and high strength using high-calcium fly ash

High calcium-fly ash(HCFA)collected from the Mae Moh electricity generating plant in Thailand was utilized as a raw material for ceramic production.The main compositions of HCFA characterized by X-ray fluorescence mainly consisted of 28.55wt%SiO_(2),16.06wt%Al_(2)O_(3),23.40wt%CaO,and 17.03wt%Fe_(2)O_(3).Due to high proportion of calcareous and ferruginous contents,HCFA was used for replacing the potash feldspar in amounts of 10wt%-40wt%.The influence of substituting high-calcium fly ash(0-40wt%)and sintering temperatures(1000-1200℃)on physical,mechanical,and thermal properties of ceramic-based materials was investigated.The results showed that the in-corporation of HCFA in appropriate amounts could enhance the densification and the strength as well as reduce the thermal conductivity of ceramic samples.High proportion of calcareous and ferruginous constituents in fly ash promoted the vitrification behavior of ceramic samples.As a result,the densification was enhanced by liquid phase formation at optimum fly ash content and sintering temperature.In addition,these components also facilitated a more abundant mullite formation and consequently improved flexural strength of the ceramic samples.The op-timum ceramic properties were achieved with adding fly ash content between 10wt%-30wt%sintered at 1150-1200℃.At 1200℃,the max-imum flexural strength of ceramic-FA samples with adding fly ash 10wt%-30wt%(PSW-FA(10)-(30))was obtained in the range of 92.25-94.71 MPa when the water absorption reached almost zero(0.03%).In terms of thermal insulation materials,the increase in fly ash addi-tion had a positively effect on the thermal conductivity,due to the higher levels of porosity created by gas evolving from the inorganic decom-position reactions inside the ceramic-FA samples.The addition of 20wt%-40wt%high-calcium fly ash in ceramic samples sintered at 1150℃reduced the thermal conductivity to 14.78%-49.25%,while maintaining acceptable flexural strength values(~45.67-87.62 MPa).Based on these promising mechanical and thermal characteristics,it is feasible to utilize this high-calcium fly ash as an alternative raw material in clay compositions for manufacturing of ceramic tiles.

Predicting model on ultimate compressive strength of Al_2O_3-ZrO_2 ceramic foam filter based on BP neural network

In present study, BP neural network model was proposed for the prediction of ultimate compressive strength of Al2O3-ZrO2 ceramic foam filter prepared by centrifugal slip casting. The inputs of the BP neural network model were the applied load on the epispastic polystyrene template （F）, centrifugal acceleration （v） and sintering temperature （T）, while the only output was the ultimate compressive strength （（7）. According to the registered BP model, the effects of F, v, T on 0 were analyzed. The predicted results agree with the actual data within reasonable experimental error, indicating that the BP model is practically a very useful tool in property prediction and process parameter design of the Al2O3-ZrO2 ceramic foam filter prepared by centrifugal slip casting.

Shear bond strengths between alumina-toughened zirconia cores and veneering ceramics and their susceptibility to aging

Objective:To evaluate the shear bond strength(SBS) between alumina-toughened zirconia (ATZ) cores and veneering ceramics,investigate the effect of aging in artificial saliva on SBS and compare it with that of yttria-stabilized tetragonal zirconia polycrystals(Y-TZP).Methods:Bars of ATZ and Y-TZP were layered with veneering ceramics in accordance to the recommendation of the manufacturer.Half of each group(n = 10) was aged at 134℃.(under 2 bar pressure) in an autoclave for 48 h.Subsequently,all specimens were subjected to shear force in a universal testing machine.The interface and fractured surface of the specimens were evaluated using scanning electron microscopy and X-ray energy dispersive spectroscopy.Results:The initial mean SBS values in MPa±SD were 28.9±8.0 for ATZ and 26.2±7.6 for Y-TZP.After aging,the mean SBS values for ATZ and Y-TZP were 22.9±4.9 MPa and 22.8±6.9 MPa,respectively.Neither the differences between the SBS values of the ATZ and Y-TZP groups nor the influence of aging on all groups were statistically significant.Conclusions:The SBS between the ATZ core and the veneering ceramics was not affected by aging.The SBS of ATZ to veneering ceramics was not significantly different compared with that of Y-TZP.

Behaviors of interfacial elements during the brazing of SiO2 glass ceramic to Ti-6AI-4V with AgCu/Ni interlayer

AgCu/Ni composite interlayer was used to join SiO2 glass ceramic to Ti-6AI-4V alloy successfully, obtaining the largest joint shear strength 110 MPa. Ag, Cu and Ni in the interlayer and Ti in the Ti-6AI-4V alloy affect the joint formation and interfacial products significantly. To understand the joint formation process better, behaviors of elements Ag, Cu, Ni and Ti during the brazing of SiO2 glass ceramic to Ti-6AI-4 V alloy were investigated in the present work. Active element Ti is the most important component in the joining, realizing the metallurgical bonding of SiO2 glass ceramic to braze alloy. Cu together with Ni reacts to Ti in the base material by Ti-Cu-Ni ternary eutectic reaction, which is beneficial for reducing the massive Ti- Cu and/or Ti-Ni brittle intermetallic compounds on the joint interface. Dispersion of Ag decreases the brittleness qf the whole joint effectively.

Effects of thermal cycling on shear strength of soldered joints of laminar ceramic resistor

The shear strength of two joints with different compositions (Sn63Pb37 and SnAg3.0Cu0.5) was compared under thermal cycling conditions, and the effects of thermal cycling times on the two different joints were studied. Results indicate that the shear force of the joints soldered with lead-free solder is higher than that of the joints soldered with Sn-Pb solder. After 120 times thermal cycling, the shear force of both the two kinds of joints declines obviously. The fractures are located at the two interfaces which is between the resistor’s side pad and the ceramic, the other is between the resistor’s bottom pad and the solder. Analysis result on the fractures by means of SEM indicates that the micrographs of fractures change obviously and the grains grow coarser after thermal cycling.

Bond Strength of the Sn-Ti-Ⅹ Ternary Active Solders on Sialon Ceramic

The bond strength of the Sn based ternary active solders,Sn-5Ti with various contents of Ag,Cu,In, Ni or AI on sialon ceramic was investigated by the ceramic/ceramic joint joining.The bond strength of Sn-STi (about 80 MPa) may increase to 90-100 MPa by small addition of Ag or Cu (about 5-10%).A little Ni (about 1-3%) in the solder is slightly beneficial,but too more Ni (more than 5%) is harmful.Small addition of In is trivial,but too more In is detrimental.On the other hand,small addi- tion of AI in the active solder decreases greatly the bond strength of the solder,therefore it is very harmful.In discussion,three suggestions for selection of the third element to increase the bond strength of the soft solders on ceramic,i.e.with a high surface energy,benefiting to wetting on ce- ramic and strengthening the soft solder itself,have been made.

Preparation and Properties of a New Mediumdensity and High-strength Ceramic Proppant

Based on the needs of the market,a new 52 MPa medium-density and high-strength ceramic proppant was prepared by adopting third grade bauxite and clay as raw materials and using the solid phase sintering method,and the effect of the firing temperature on the microstructure,phase composition and mechanical properties of the ceramic proppant was studied. The broken resistance mechanism of this ceramic proppant was also discussed. The results show that the main phases of the prepared ceramic proppant are mullite and corundum; the broken rates are 3. 92% and 7. 21% under 52 MPa and69 MPa,respectively.

Relationship between Leucite Content and Compressive Strength of K_2O-Al_2O_3-SiO_2 System Dental Glass Ceramics

Relationship between leucite content and compressive strength of K2O-Al2O3-SiO2 sys-tem dental glass ceramics were investigated. 10 groups of feedstock powder with different composi-tions were treated according to the same thermal treatment system of leucite micro-crystallization reported in some primary studies. The products of each group were analyzed by X-ray diffractometer, polaring microscope and scanning electronic microscope （SEM）, and then the compressive strength was tested by a material testing machine. A direct proportion was found between leucite content and the compressive strength when leucite content was less than 50 vol%, and compressive strength de-creased with the increasing of leucite micro-crystals when leucite content was more than 50vol%, The leucite content has a notable influence on the compressive strength of K2O-Al2O3-SiO2 system dental glass ceramics.

Synthesis of Xonotlite and Effects of Ceramic Fiber Addition on Its Compressive Strength

In order to improve the compressive strength of xonotlite, the pretreated quartz powder, slaked CaO, additive, deionized water(water-solid ratio of 30) were placed in a magnetically stirred autoclave, and the corresponding products were obtained after incubating at 220 ℃ for 0, 1, 3 and 6 h, respectively to explore the synthetic process of xonotlite. In the prepared xonotlite powder, 0, 5%, 10%, 15% and 20%(by mass, the same hereinafter) of pre-treated ceramic staple fibers were added, and two sets of specimen with the specifications of φ50 mm×35 mm were molded by pressed filtration.One set of specimens were not sintered, and the other group was fired at 1 000 ℃ for 2 h to explore the effect of ceramic fiber addition on the compressive strength before and after sintering of xonotlite. The results show that C-S-H gel is first synthesized in the synthesis of xonotlite, and then the C-S-H gel is transformed to form tobermlite, at last tobermlite fully reacts to produce xonotlite. The addition of ceramic fiber enhances the compressive strength of the xonotlite before and after sintering. When the 15% ceramic fiber is added, the compressive strength is the highest. The specimens before and after the high temperature firing contain xonotlite phase and calcium silicate phase, respectively, and the compressive strength of the fired specimens is higher than that of the green ones.

Interfacial Bonding Strength of TiN Film Coated on Si_3N_4 Ceramic Substrate

The fraction of TiN/Si3N4 in the cross section was observed with scanning electric microscope （SEM）, and residual stresses of TiN coated on the surface of Si3N4 ceramic were measured with X-ray diffraction （XRD）.The hardness of TiN film was measured, and bonding strength of TiN film coated on Si3N4 substrate was measured by scratching method. The formed mechanism of residual stress and the failure mechanism of the bonding interface in the film were analyzed, and the adhesion mechanism of TiN film was investigated preliminarily. The results show that residual stresses of TiN film are all behaved as compressive stress, and TiN film is represented smoothly with brittle fracture, which is closely bonded with Si3N4 substrate. TiN film has high hardness and bonding strength of about 500 MPa, which could satisfy usage requests of the surface of cutting Si3N4 ceramic.

The Influence of Ceramic Surface Treatments on the Microtensile Bond Strength of Resin Cements to Y-TZP Ceramic

The effects of surface conditioning methods on the microtensile bond strength of Y-TZP ceramic were studied based on airborne particle abrasion and resin cements.Eight square-shaped（φ12 mm×5 mm high） Y-TZP ceramic were studied blocks（LAVATM,3M ESPE,USA） and flat occlusal dentin blocks were fabricated,pre-treated（airborne abrasion with 125μm Al2O3 particles,tribochemical silica coating with 110 μm Al2O3 particles modified by silica oxide）,and bonded to each other using resin cements（Panavia F 2.0,RelyX Unicem）.Thereafter the trilayer specimens were cut into microbar specimens with a bonding area of approximately 1.0±0.1 mm2 and then microtensile bond strength tests were performed.The Y-TZP ceramic following airborne particle abrasion with 125μm Al2O3 and silicoating,the surface roughness of Y-TZP and its surface silica content were confirmed to increase.Overall,the Y-TZP ceramic surface treatment with a tribochemical silica coating showed the highest microtensile bond strength of the phosphate monomer-based resin cement to Y-TZP ceramic（mean MPa=18.11±0.27（Panavia F 2.0）,17.45±0.39（Rely X Unicem）.In cases in which a silica coating was applied,there was no significant difference in the bonding strength depending on resin cements（P0.05）.

Research on the High Strength Glass Ceramics/Mullite Ceramics Composites

In order to improve the bending strength of mullite ceramic thin tiles, SiO2-ZnO-Na2O-Y2O3 glass was prepared on the surface of the tiles. The influences of the thermal properties and thermal expansion coefficient of the glass and the sintering temperature on the structure and the property of the composites were investigated by differential thermal analysis (DTA), X-Ray Diffraction (XRD), Raman and scanning electron microscopy (SEM). The bending strength of the composites was measured with an universal testing machine. Results show that the crystallization temperature of the SiO2-ZnO-Na2O-Y2O3 glass is higher than that of SiO2-ZnO-Na2O glass. The corresponding crystallites show more complex structure for the SiO2-ZnO-Na2O-Y2O3 glass. The thermal expansion coefficients of both glasses are lower than the mullite ceramic tiles. The bending strength of the composites after sintering at 1150°C was obviously improved by 10.7% to 106.2 MPa, compared with the mullite ceramic tiles.

Modeling and analysis of porosity and compressive strength of gradient Al_2O_3-ZrO_2 ceramic lter using BP neural network

BP neural network was used in this study to model the porosity and the compressive strength of a gradient Al2Q-ZrO2 ceramic foam filter prepared by centrifugal slip casting. The influences of the load applied on the epispastic polystyrene template （F）, the centrifugal acceleration （V） and sintering temperature （T） on the porosity （P） and compressive strength （a） of the sintered products were studied by using the registered three-layer BP model. The accuracy of the model was verified by comparing the BP model predicted results with the experimental ones. Results show that the model prediction agrees with the experimental data within a reasonable experimental error, indicating that the three-layer BP network based modeling is effective in predicting both the properties and processing parameters in designing the gradient Al203-ZrO2 ceramic foam filter. The prediction results show that the porosity percentage increases and compressive strength decreases with an increase in the applied load on epispastic polystyrene template. As for the influence of sintering temperature, the porosity percentage decreases monotonically with an increase in sintering temperature, yet the compressive strength first increases and then decreases slightly in a given temperature range. Furthermore, the porosity percentage changes little but the compressive strength first increases and then decreases when the centrifugal acceleration increases.