Correlations of grain boundary segregation to sintering techniques in a three-phase ceramic

Abstract

The effects of using different sintering techniques (conventional, flash and spark plasma sintering) on grain boundary segregation were investigated in a 3-phase polycrystalline ceramic containing cubic 8 mol% Y 2 O 3 stabilized ZrO 2 (YSZ), -Al 2 O 3 and MgAl 2 O 4 . Six types of interfaces for each sintered sample were analyzed for grain boundary chemistry. Using aberration-corrected STEM and EDS, we show Al segregation at YSZ-YSZ boundaries, and Y/Zr segregation at Al 2 O 3 -Al 2 O 3 , MgAl 2 O 4 -MgAl 2 O 4 and MgAl 2 O 4 -Al 2 O 3 boundaries. YSZ-MgAl 2 O 4 and YSZ-Al 2 O 3 heterointerfaces, in contrast, do not show elemental segregation. Our results show that the type of segregation at different boundaries does not change with different sintering processes, indicating that elemental segregation mainly depends on initial sample composition, although the amount of segregation can vary. Quantitative analyses reveal that spark plasma sintering (950°C for 5 min, 100 MPa) results in relatively higher average segregation at grain boundaries and heterointerfaces compared to conventional sintering (1550°C for 10 h), suggesting that low temperatures result in higher grain boundary segregation. The average segregation concentrations at the grain boundaries of our flash sintered sample (estimated to reach 1700°C for 6 s) were found to be consistently similar to long-annealed spark-plasma sintered sample (1350°C for 20 h), suggesting that very high temperatures reached during flash process can achieve similar segregation concentrations compared to a SPS sample annealed for several hours at lower temperature. The presence of other phases in multi-phase systems can modify the grain boundary chemistry and segregation compared to segregation in single-phase ceramics.

Flash Sintering Research Perspective: A Bibliometric Analysis

“…Despite its simplicity, FS is an extremely powerful sintering method that can be successfully used for most ceramic materials, from dielectrics (BaTiO 3 [41][42][43][44][45][46][47] or (Bi 0.2 Na 0.2 K 0.2 Ba 0.2 Ca 0.2 )TiO 3 [48]) to ionic (Zirconia, YSZ [2,[49][50][51][52], CeO 2 or doped-CeO 2 [53][54][55][56][57][58]) or electronic (TiO 2 [19,22,[59][60][61][62], BiFeO 3 or substituted-BiFeO 3 [24,27]) conductors. Interestingly, it can be also applied for processing ceramic composites of complex stoichiometry, metastable phases, or materials constituted by volatile species at the temperatures required for their sintering such as YSZ-Al 2 O 3 composites [63][64][65], different types of solid state electrolytes [25,66,67], BiFeO 3 [68,69], or K 0.5 Na 0.5 NbO 3 [26,[70][71][72][73]. Moreover, ceramics prepared by FS present very interesting properties rarely reported for materials obtained by convectional procedures.…”

Mechanical Properties of an Ultrahard In Situ Amorphous Steel Matrix Composite

“…The die and plunger assembly was then loaded into a current-activated pressure-assisted densification furnace. [68][69][70][71][72][73][74][75][76][77] After achieving a vacuum of 2.5 Â 10 À2 torr, the sample was uniaxially pressed to 100 MPa. As the final applied stress was reached, the sample was heated to temperatures between 903 and 948 K with a variation of AE5 K, at a rate of 500 K min À1 using a proportional-integral-derivative controller, monitored by a thermocouple inserted into the side of the die that was approximately 6 mm from the edge of the sample.…”

A Review of Grain Boundary and Heterointerface Characterization in Polycrystalline Oxides by (Scanning) Transmission Electron Microscopy

“…These methods have been applied readily for several decades, as described in books and reviews [99,[103][104][105]142]. STEM-EDXS is used to characterize GB and HI segregations in YSZ-Al 2 O 3 -MgAl 2 O 4 ceramic oxides (Figure 28) and correlate them with thermal properties of these composites [41]. In a work by Ikuhara et al [211], STEM-EDXS was used to study segregation behavior in YSZ bicrystal at atomic scale.…”