Densification and Sintering Kinetics of Rare Earth(α′+β′)-Sialon Composites

The sintering processes of Re-(α' + β')-sialon composites (Re=Sm, Dy, Yb) have been investigated by using a specially designed high temperature dilatometer. The initial densification of various samples starts at about 1200℃, and the maximum shrinkage rate of these sialon composites occurs at about 1500℃. The light rare earth sialon has a noticeably tower densification temperature and a higher final shrinkage. The sirtering kinetics of Re-(α' +β')-sialonare much more complex. The Kingery's liquid phase sintering model appears to be applicable,but the mechanism of mass transport in stage two appears to be changeable. The controlling factor shiffs from solution-precipitation to diffusion when densification process proceeds from the earlier part to the later part of this stage.

Densification of Mo Alloys at 1473 K by Adding Ni-Cu Solid Solution

Mo is difficult to sinter densely at a relatively low temperature due to its high melting point. In the present paper,by adding different weight contents of Ni and Cu additives, Mo alloys have been densified at 1473 K for an hour byhot-pressing method, and the optimum contents of Cu and Ni additives have been acquired: when the contents of Niand Cu are 3 and 2 wt pct respectively, the relative density of the sample reaches the maximum value. It was foundthat when the Ni-Cu solid solution was added into Mo alloys. the achieved density is higher than the case of Ni andCu additives. The experimental results indicate that, Ni and Cu play different roles in the process of sintering, theNi-Cu solid solution has the same function as Ni and Cu additives in the course of sintering Mo alloys, It shows moreactivating sintering feature for Mo than the Ni and Cu additives.

Preparation,Structures,Thermal Properties and Sintering Behaviors of B_2O_3-SiO_2-ZnO-BaO-Al_2O_3 Glass

B_2O_3-SiO_2-ZnO-BaO-Al_2O_3 glass with different Al_2O_3 contents（1mol%, 3mol%, 5mol%, and 7mol%） was prepared, and it was intended to be used as lead-free and low-melting glass sealants for solid oxide fuel cells. The effects of Al_2O_3 content on the structures, thermal properties, and sintering behaviors of the B_2O_3-SiO_2-ZnO-BaO-Al_2O_3 glass were investigated in detail. The Al_2O_3 content largely influenced the structures and thermal properties of the glass. When the Al_2O_3 content 5mol%, the transition temperature of the glass decreased with the Al_2O_3 content, while the crystallization temperature increased with the Al_2O_3 content. However, higher Al_2O_3 content degraded the stability of the glass. The B_2O_3-SiO_2-ZnO-BaO-Al_2O_3 glass with 5 mol% Al_2O_3 content exhibits the optimal sintering densification characteristics and can be used as glass sealants for solid oxide fuel cells.

Densification of Mo Alloys at 1473K

By choosing different weight contents of Ni and Cu,Mo alloys have been densified under 1473K-30MPa-1h in a vacuum furnace.The experimental results indicate that,when the contents of Ni and Cu are 3wt% and 2wt% respectively,the relative density of the sample reaches the maximum value.Ni and Cu play different roles in the process of sintering,the powder Ni,dissolved in the liquid Cu,shows more activating sintering feature for Mo than the solid Ni.

Factors influencing particle agglomeration during solid-state sintering

Discrete element method （DEM） is used to study the factors affecting agglomeration in three-dimensional copper particle systems during solid-state sintering. A new parameter is proposed to characterize agglomeration. The effects of a series of factors are studied, including particle size, size distribution, inter-particle tangential viscosity, tem- perature, initial density and initial distribution of particles on agglomeration. We find that the systems with smaller particles, broader particle size distribution, smaller viscos- ity, higher sintering temperature and smaller initial density have stronger particle agglomeration and different distribu- tions of particles induce different agglomerations. This study should be very useful for understanding the phenomenon of agglomeration and the micro-structural evolution during sin- tering and guiding sintering routes to avoid detrimental ag- glomeration.

Integrated high-performance and accurate shaping technology of low-cost powder metallurgy titanium alloys: A comprehensive review

The practical engineering applications of powder metallurgy (PM) Ti alloys produced through cold compaction and pressure-less sintering are impeded by poor sintering densification, embrittlement caused by excessive O impurities, and severe sintering deforma-tion resulting from the use of heterogeneous powder mixtures. This review presents a summary of our previous work on addressing the above challenges. Initially, we proposed a novel strategy using reaction-induced liquid phases to enhance sintering densification. Near- complete density (relative density exceeding 99%) was achieved by applying the above strategy and newly developed sintering aids. By focusing on the O-induced embrittlement issue, we determined the onset dissolution temperature of oxide films in the Ti matrix. On the basis of this finding, we established a design criterion for effective O scavengers that require reaction with oxide films before their dissol-ution. Consequently, a ductile PM Ti alloy was successfully obtained by introducing 0.3wt% NdB6 as the O scavenger. Lastly, a powder- coating strategy was adopted to address the sintering deformation issue. The ultrafine size and shell-like distribution characteristics of coating particles ensured rapid dissolution and homogeneity in the Ti matrix, thereby facilitating linear shrinkage during sintering. As a result, geometrically complex Ti alloy parts with high dimensional accuracy were fabricated by using the coated powder. Our fundament-al findings and related technical achievements enabled the development of an integrated production technology for the high-performance and accurate shaping of low-cost PM Ti alloys. Additionally, the primary engineering applications and progress in the industrialization practice of our developed technology are introduced in this review.

Influence of Mo on the microstructure and mechanical properties of TiC-based cermets

The microstructures and mechanics properties of TiC-based cermets composed of TiC, WC, Ni, Co, Mo, and Cr3C2 were investigated. The results show that Mo has a great effect on the sintering densification, microstructures, and mechanical properties. The microstructures and distribution of Mo and Ti in the TiC-based cermets were analyzed. It was indicated that a new phase with Ti, Mo, W, and C was formed on the rim of （Ti,W）C grains by means of an addition of Mo into the TiC-based cermets. The new phase with a surrounding structure was of great aid to improve the wettability of the liquid phase on the solid phase surface of TiC, decrease the porosity and refine the grains of the hard phase, which gave rise to the increase in strength and hardness. The properties of the TiC-based cermets could be further improved to some extent by adding WC, Cr2C3, and Co.

Structure properties and sintering densification of Gd_2Zr_2O_7 nanoparticles prepared via different acid combustion methods

Gadolinium zirconate（Gd2Zr2O7） nanocrystals were prepared via two different combustion methods： citric acid combustion（CAC） and stearic acid combustion（SAC）. The effects of the different preparation methods on the phase composition, microtopography, and sintering densification of the resulting Gd2Zr2O7 nanopowders were investigated by thermal-gravimetric and differential thermal analysis（TG-DTA）, Fourier transform infrared spectroscopy（FTIR）, X-ray diffraction（XRD）, and transmission electron microscopy（TEM） techniques. The results indicated that both methods could produce Gd2Zr2O7 nanopowders with an excellent defective fluorite structure. The reaction time was reduced by the SAC method, compared with the CAC method. The nanopowders synthesized by the two methods were different in grain size distribution. The resulting nanoparticle diameter was about 50 nm for CAC and 10 nm for SAC. After vacuum sintering, the sintered bodies also had a different relative density of about 93% and 98%, respectively. Thus the preparation of Gd2Zr2O7 nanopowders by SAC was the first choice to achieve the desired sintering densification.

Sintering densification behavior and kinetic mechanism of nano-tungsten powder prepared by sol-spray drying

Due to its excellent mechanical and radiation resistance performance,fine-grained tungsten becomes an ideal plasma facing material in fusion reactors.However,the preparation of fine-grained tungsten by ultrafine powder is faced with some problems,such as low density,coarse grain and not suitable for engineering production.In this paper,nano-tungsten powders prepared by“sol-spray drying-calcination-hydrogen thermal reduction”process were sintered by non-isothermal ordinary pressureless sintering,and the densification behavior and kinetic mechanism were investigated.The results show that there exists two stages during sintering process,namely significant densification process at low temperature(1300-1700℃)and grain growth stage at high temperature(1700-2000℃).Finally,bulk tungsten material with the relative density of 96.9%and average grain size of 2-6μm was prepared at 1900℃.Moreover,electron backscatter diffraction results show the grain size is uniform and fine.By mathematical calculation,the nanocrystallization of tungsten powder significantly reduces the sintering activation energy and promotes the densification of tungsten powder at low temperature.Surface diffusion is the main transport mechanism in grain growth stage.It is easy to find that the hardness of material increased with the sintering temperature increasing,at the end of sintering densification(>1700℃),TEM observation revealed that the inner pores formed by particle combine were gradually eliminated through grain boundary diffusion with the sintering temperature increasing,resulting in the intra-crystal densification to increase the hardness of tungsten material.

Enhancement of Sinter Densification of SrO-BaO-Nb_2O_5-SiO_2 Tungsten-Bronze Glass-Ceramics by Doping with P_2O_5

Densification behaviors of SrO-BaO-Nb2O5-SiO2 based glass-ceramics prepared by conventional sintering were investigated with an emphasis on the influence of P2O5 content. Although P2O5 dopant did not modify the surface crystallization mechanism, it resulted in a decrease of the glass transition temperature, which facilitates the viscous glass flow necessary for sintering. However, premature crystallization of （Sr, Ba）Nb2O6 induced by addition of excess amount of P2O5 essentially retarded sintering due to the formation of closed pores in the matrix. The SrO-BaO-Nb2O5-SiO2 glass with 1.0 mol% P2O5 （SBN-1P） showed the best sinter densification, which was accomplished at about 850 ℃.