Effects of various sintering methods on microstructure and mechanical properties of CP-Ti powder consolidations

Effects of various sintering methods such as spark plasma sintering(SPS), hot pressing(HP) and electric resistance sintering(ERS) on the microstructure and mechanical properties of commercial pure titanium(CP-Ti) powder consolidations with particle size of <147 μm, <74 μm and <43 μm were studied. The smaller particle powders are densified to proceed at a higher rate. Dense titanium with relative density up to 99% is found to take place at 850 °C under 30 MPa of SPS and HP condition. However, in case of ERS, CP-Ti powders were densified almost at 950 °C under 30 MPa. The microstructure of sintered titanium is composed of equiaxed grains at 850-950 °C. The yield strength of sintered body composed of <43 μm powder is 858 MPa by using SPS at 850 °C under 30 MPa. When there is a higher content of small particle, the higher yield strength value is obtained both by using SPS and HP. However, when ERS is introduced, the highest yield strength is 441 MPa at 950 °C under 30 MPa, which shows much lower values than those by SPS and HP methods. ERS method takes much less sintering time compared with SPS and HP. Nevertheless, higher sintering temperature results in lower strength and elongation because of brittle fracture.

Effect of nitrogen introduction methods on the microstructure and properties of gradient cemented carbides

Gradient cemented carbides with the surface depleted in cubic phases were prepared following normal powder metallurgical pro-cedures.Gradient zone formation and the influence of nitrogen introduction methods on the microstructure and performance of the alloys were investigated.The results show that the simple one-step vacuum sintering technique is doable for producing gradient cemented carbides.Gradient structure formation is attributed to the gradient in nitrogen activity during sintering,but is independent from nitrogen introduced methods.A uniform carbon distribution is found throughout the materials.Moreover,the transverse rupture strength of the cemented carbides can be increased by a gradient layer.Different nitrogen carriers give the alloys distinguishing microstructure and mechanical properties,and a gradient alloy with ultrafine-TiC0.5N0.5 is found optimal.

Effects of BN content on the mechanical properties of nanocrystalline 3Y-TZP/Al_(2)O_(3)/BN dental ceramics

3Y-TZP/3wt%Al_(2)O_(3) powder was coated with varying amounts of BN using the urea and borate reaction sintering method,and then multiphase ceramics were prepared by hot pressing sintering.The micro-topography and the compositional analysis of synthesized ceramics were conducted through scanning electron microscopy,transmission electron microscopy and X-ray diffraction.A mechanical tester was used to analyze the Vickers hardness,fracture toughness,and bending strength of the synthesized ceramics.The results showed that the ceramic with a BN content of 12wt%showed the best processability,but had diminished mechanical properties(such as fracture toughness and bending strength).The ceramic with a BN content of 9wt%showed better processability than those with 3wt%and 6wt%BN.However,the fracture toughness was affected by the addition of 9wt%BN,making this ceramic only usable as a base material for a three-unit fixed bridge.In contrast,the ceramics with a BN content of 3wt%or 6wt%fulfilled the criteria for use in multi-unit restoration,but their low processability made them unsuitable for milling after sintering.

Optimum Preparation Conditions of LiNi_(0.8)Co_(0.2)O_2 and LiNi_(0.95)Ce_(0.05)O_2 as Lithium-Ion Battery Cathode Materials

The preparation of LiNi_(0.8)Co_(0.2)O_2 was discussed by the multiply sintering method for solid reaction, in which the sintered material was smashed, ground and pelletted between two successive sintering steps. The optimum technological condition was obtained through orthogonal experiments by L_9(3~4) and DTA analysis. The result indicates that the factors of effecting the electrochemical properties of synthesized LiNi_(0.8)Co_(0.2)O_2 are molar ratio of Li/Ni/Co, oxygen pressure, homothermal time, the final sintering temperature in turn according to its importance. The oxygen pressure is reviewed independently and the technological condition is further optimized. With the same method, rare earth element Ce was studied as substitute element of Co and the cathode material of LiNi_(0.95)Ce_(0.05)O_2 with excellent electrochemical properties was prepared. The electrochemical testing results of LiNi_(0.8)Co_(0.2)O_2 and LiNi_(0.95)Ce_(0.05)O_2 experimental batteries show that discharge capacities of them reach 165 and 148 mAh·g^(-1) respectively and the persistence is more than 9 h at 3.7 V.

Gd_(3)Al_(3)Ga_(2)O_(12):Ce^(3+), Yb^(3+) fluorescent ceramic with highly increased trap density for optical information storage

Electron-trapping materials,due to their exceptional ability of energy storage and controllable photon release under external stimulation,have attracted considerable attention in the field of optical information storage(OIS).In this work,Gd_(3)Al_(3)Ga_(2)O_(12):Ce^(3+), Yb^(3+)fluorescent ceramics,were developed using air and vacuum sintering technology.By co-doping Ce^(3+)and Yb^(3+),the trap density was significantly increased by 7.5 times compared to samples containing only Ce^(3+).Vacuum annealing further enhanced trap density by 1.6 times compared to samples sintered solely in air,while generating deep traps(1.44 eV),making Gd_(3)Al_(3)Ga_(2)O_(12):Ce^(3+), Yb^(3+) an excellent OIS medium.This work is expected to facilitate the development of OIS materials.

Efficient and cost-effective method to synthesize highly purified Ti_(4)AlN_(3) and Ti_(2)AlN

Nitrides MAX have attracted ever-growing interest owing to its unique metallic and ceramic characteristics and properties.Here,we report on the synthesis of highly purified Ti_(2)AlN and Ti_(4)AlN_(3) powders from Ti,Al and TiN powders by a facile atmosphere sintering method.The obtained nitrides show highly pure phase and excellent layered structure.Except for the composition difference of raw materials,both the nitrides can be sintered and obtained by same sintering temperature and holding time,which thus makes less processing time and less usage of synthesis parameters as compared to previously synthesis methods.To our knowledge,present work is one of the few reports on synthesis of Ti_(4)AlN_(3) and Ti_(2)AlN using atmosphere sintering method.Furthermore,the lattice changes of the layered structure of Ti_(2)AlX(X/C=N)were studied by changing the composition of X position from the synthesis of Ti_(2)AlCN and Ti_(2)AlC,and the optimal formulation and synthesis mechanism of Ti_(4)AlN_(3) were also studied.