densification

In this study, ZrB2-SiC ultra-high temperature ceramic composite was sintered using Spark Plasma Sintering (SPS) process with WC/HfB2 modifiers at different sintering temperatures of 1850, 1900, 2000, and 2050˚C for 8 and 25 minutes. The densification behavior of the composite was also examined using punch displacement-time and temperature-time measurement graphs during SPS. Phase and microstructure evaluations were also done based on XRD, EDS, and FESEM methods. The effect of SPS parameters on the densification of ZrB2-SiC-based composite was studied. In this case, there was no displacement until the pressure was applied due to the low sinterability of boride powders. A ZrB2-SiC-based composite with a relative density of 90% was obtained at 2050˚C under 30 MPa for a 25-minute soaking time. The densification curve of this sample showed a typical “S” shape. The best water absorption and apparent porosity values obtained as 1.3 and 6.7%, respectively. The minimum and maximum punch displacement of the samples was 2.2 and 3.6 mm, respectively. Use of WC/HfB2 modifiers led to the formation of byproducts of WB and HfB.

Microwave sintering has emerged as a promising technique for the fabrication of Ti-based alloys, offering unique advantages over conventional sintering methods. The selective and volumetric heating capabilities of microwaves can result in rapid densification, microstructural refinement, and enhanced properties in Ti-Cu alloy systems. Therefore, this study aimed to synthesize an intermetallic alloy of Ti-50 at. % Cu through high-energy mechanical milling and a microwave-assisted sintering method. The objective was to expedite the sintering process of the Ti-Cu alloy using microwave assistance and analyze how this method influences the phases formed and the properties of the alloy. A Ti-50 at. % Cu powder mixture was milled for 30 hours under an argon atmosphere, then uniaxially compacted to form green samples, which were subsequently sintered by microwave heating. This method allowed for rapid consolidation without significant grain growth within a short sintering period. The effects of the sintering method and temperature on microstructure and mechanical properties were studied. The density of the sintered samples increased with rising temperatures, with the highest density of 6.54 g/cm³ obtained at 900°C. Microstructural examination revealed that the Ti3Cu4 and TiCu phases primarily formed, with an average grain size of approximately 28 nm. A high micro-hardness of ~880 HV was achieved for the dense alloy prepared using this method.

Garnet-type Li7La3Zr2O12 (LLZO) solid-state electrolytes are promising candidates for application in next-generation solid-state batteries. Of note, the most controversial issue is to stabilize the cubic phase structure (c-LLZO) with high density after the sinter process to reach high ionic conductivity with the desired strength. Considering this issue, the current study aims to investigate the synthesis and sintering of LLZO with Al substituted and without any additive. The LLZO ceramic was synthesized through conventional solid-state reaction. The effect of heating temperature on the synthesis of the cubic structure was studied using X-Ray Diffraction (XRD). The ionic conductivity of the samples was examined by AC Impedance Spectroscopy. The obtained results indicated that Al doping led to the cubic phase stabilization and that it had a positive effect on the sintering regime so that the sample with Al dopant was densified at the lower temperature of 1140 °C. The total ion conductivity of Al-LLZO is 0.1 mScm-1 which is comparable to the values of high temperature-sintered samples.

In this research, densification and shape distortion of the Al-Cu-Mg (Al2024) pre-alloyed powder compact in the supersolidus liquid phase sintering process (SLPS) were investigated. The effect of Sn on the sintering process was also studied. The powders were compacted at pressures ranging from 100 to 500 MPa in a cylindrical die. The sintering process was performed in a dry N2 atmosphere at various temperatures (580-620 ºC) for 30 min at a heating rate of 10 ºCmin-1. Results showed that the onset of densification process was observed at 600ºC and onset of distortion was occurred at 610ºC. Addition of 0.1 wt. %Sn to the alloy has increased the distortion of the samples produced from Al-Cu-Mg pre-alloyed powder, but their densification has been improved. The compact pressure of 200MPa caused the complete densification at the optimum sintering temperature and at the compact pressures greater than 200MPa; the sintered density was independent of green density.

In this research study, the effects of aluminum nitride (AlN) additive on the densification behavior and microstructure development of titanium diboride (TiB2) based ceramic matrix composite were investigated. In this way, a monolithic TiB2 ceramic and a TiB2–5 wt% AlN ultrahigh temperature ceramic composite were fabricated by spark plasma sintering (SPS) process at a temperature of 1900 °C for a dwell time of 7 min under an externally applied pressure of 40 MPa in vacuum conditions. The relative density measurements were carried out using the Archimedes principles for evaluation of bulk density and rule of mixtures for calculation of theoretical one. Compared to the additive-free monolithic TiB2 ceramic sample with a relative density of ~96%, the addition of AlN as a sintering aid greatly improved the sinterability of TiB2 matrix composite so that a near fully dense sample with a relative density of ~100% were obtained by the spark plasma sintering process. The removal of harmful oxide impurities of titania (TiO2) and boria (B2O3) from the surfaces of starting TiB2 powder particles and in-situ formation of new phases such as aluminum diboride (AlB2) and Al2Ti as an intermetallic compound of aluminum and titanium, not only improved the sinterability of the composite ceramic, but also significantly prevented the extreme growth of TiB2 grains.

The effect of SiC content, additives, and process parameters on densification and microstructural properties of pressureless sintered ZrB2– (1–10 wt %) SiC particulate composites have been studied. The ZrB2–SiC composite powders mixed by Spex mixer with 1-2wt% C (added as graphite powder) and CMC have been cold-compacted and sintered in argon environment in the temperature range of 1800–2100ºC for 2hs. The amount of densification is found to increase with sintering duration and by prior holding at 1200-1650ºC for reduction of oxide impurities (ZrO2, B2O3 and SiO2) on powder particle surfaces via the formation of new phases such as ZrSi2 and ZrC in the system. Presence of SiC with average size smaller than that of ZrB2 appears to aid in densification by enhancing green density, increasing C content by erosion of milling media, and inhibiting matrix grain growth. Both of SiC and C appear to aid in reduction of oxide impurities. The shrinkage of samples was measured, and the microstructure of samples was examined using X-Ray Diffraction and scanning electron microscopy (SEM), equipped with EDS spectroscopy. Room temperature mechanical properties were examined. Sintering temperature has a great effect on relative density, porosity, water absorption, hardness, fracture toughness, oxidation resistance, Strength and microstructure of these composites. The highest relative density, (99.65%), was obtained in ZrB2–10wt. %SiC–2 wt. %C composites sintered at 2000ºC for 2hs.

The effective shear and bulk viscosity, as well as dynamic viscosity, describe the rheological properties of the ceramic body during the liquid phase sintering process. The rheological parameters depend on the physical and thermo-mechanical characteristics of the material such as relative density, temperature, grain size, diffusion coefficient, and activation energy. Thermal behavior of the ceramic body during sintering process including the viscose flow deformation, anisotropic shrinkage, heterogeneous densification, as well as sintering stress, have significant influence on the both final body dimensional precision and densification process. In this paper, the numerical-experimental method has been developed to study both rheological and thermal behavior of hard porcelain ceramic body during liquid phase sintering process. After raw materials analysis, the standard hard porcelain mixture as a ceramic body was designed and prepared. The finite element method for the ceramic specimens during the liquid phase sintering process are implemented in the CREEP user subroutine code in ABAQUS. Densification results confirmed that the bulk viscosity was well-defined with relative density. It has been shown that the shrinkage along the normal axis of slip casting is about 1.5 times larger than that of casting direction. The stress analysis proved that the sintering stress is more than the hydrostatic stress during the entire sintering time so, the sintering process occurs completely. The inhomogeneity in Von-Misses, pressure, and principal stress intensifies the relative density non-uniformity. Dilatometry, SEM, XRD investigations as well as bulk viscosity simulation results confirmed that the “mullitisation plateau” was presented as a very little expansion at the final sintering stage, because of the highly amount of mullite formation.

In this study the effect of nano meter size ZrO2 particles on the microstructure, densification and hydration resistance of magnesite –dolomite refractories was investigated. 0, 2, 4, 6 and 8 wt. % ZrO2 particles that were added to magnesite –dolomite refractories containing 35 wt. % CaO. The Hydration resistance was measured by change in the weight of specimens after 72 h at 25℃ and 95% relative humidity. The results showed with addition of nano meter size ZrO2 particles, the lattice constant of CaO increased, and the bulk density and hydration resistance of the specimens increased while apparent porosity decreased. With the addition of small amount ZrO2 the formation of CaZrO3 phase facilitated the sintering and the densification process. The mechanism of the nano meter size ZrO2 particles promoting densification and hydration resistance is decreasing the amount of free CaO in the specimens.

The main goal of this study is optimization of densification of ZrB2-SiC composites reinforced with chopped Cf prepared by SPS. Taguchi method is employed as statistical design of experiment (DOE) to optimize densification parameters including SiC, Cf, MoSi2, HfB2 and ZrC content, milling time of Cf and SPS parameters such as temperature, time and pressure. Each of these factors was examined on four levels in order to obtain the optimum conditions. A total of 32 samples were prepared in accordance to the L32 array proposed by the Taguchi method. By using statistical analysis of variance (ANOVA), it has been concluded that the most significant effect on the densification is related to temperature, MoSi2 and time by 50.2%, 20.7% and 9.8% portion, respectively. Also, the results showed that pressure with 0.8%, ZrC with 1.9% and HfB2 with 1.9% have the least portion on open porosity. The other parameters including SiC, M.t and Cf have 2.9%, 3.6% and 3.8% on open porosity respectively.

The rapidly solidified prealloyed alpha brass powder with a size range of 40 to 100 μm produced by water atomization process was consolidated using liquid phase sintering process. The relationships between sintering temperature, physic-mechanical properties and microstructural characteristics were investigated. Maximum densification was obtained at 930 °C, under 600 MPa compacting pressure, with 60 min holding time. The microstructure of the sintered brass was influenced by dezincification and structural coarsening during supersolidus liquid phase sintering. As a consequence of Kirkendall effect atomic motion between Cu and Zn atoms caused to dezincification at the grain boundaries and formation of ZnO particles on the pore surfaces. It was concluded that microstructural analysis is in a well agreement with obtained physical and mechanical properties. Also, the amount of liquid phase, which depends on sintering temperature, results in different load bearing cross section areas, and it affects the type of fracture morphologies.

The process of mullitization of kyanite concentrate was studied at different conditions of heat treatment (1400 – 1600 °C and 0.5 – 3.5 hours) and particle size of raw materials (38-300? m). Kyanite concentrate was obtained from ore-dressing of kyanite deposits of Mishidowan-Bafgh region at 100 km northeastern part of Yazd. The results of microstructure (shape, distribution and size of the grains) and phase evolution studies by SEM and XRD showed thattotal transformation of kyanite to mullite takes place by heat treatment between 1500 –1550 °C during 2.5 hours.. At temperatures below 1500 °C need-like mullite grains are always produced. At higher temperatures the mullite grains reveal rounded and platelet morphology. At 1550 °C, the rate of mullitization and densification were improved by increasing soaking time from 1h to 3h and decreasing particle size of materials from 300 to 38 m.