Study on the growth kinetics of Al2O3 columnar crystal in Al2O3 matrix composite ceramics prepared by microwave sintering

Chen, Lu; Ai, Yongfeng; Yu, Qingling; He, Wen; Zhang, Jianjun; Min, Xinxin

doi:10.1016/j.jcrysgro.2018.11.039

Cited by 20 publications

(5 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Therefore, it can be identified the temperature of molten pool T(r,x) is rising with the laser scanning speed v decreasing. In order to explore grain growth kinetics of fine columnar crystal near the joint boundary during LMD process, a classical grain growth kinetics equation was used [36]:…”

Section: Effects Of Thermal Behavior On Grain Dimension and Growth Directionmentioning

confidence: 99%

Effect of Thermal Behavior on the Grain Morphology and Dimension of 80mm-Thick Ti6Al4V Plates Joined by Laser Melting Deposition

Lyu¹,

Hu²,

Wang³

et al. 2021

Preprint

View full text Add to dashboard Cite

Individually fabrication forged parts and then joining them together through Laser Melting Deposition (LMD) is a viable way for manufacturing large components. For investigating the effect of the grain morphology of LMD joint, two 80mm-thick Ti6Al4V plates are successfully manufactured using three different scanning speeds (10, 15, and 20 mm/s). It is essential for understanding the thermal behaviour of melt pool during LMD to improve process quality. This study focuses on the energy density of heat source and the direction of heat flux, analyzing the effect of thermal behavior on the grain morphology and dimension of deposition area, equiaxed crystal zone (EQZ) and the substrate. The macrostructure is evaluated in the different thermal condition and scanning speeds. An extremely fine equiaxed crystal was observed near the joint boundary with a high temperature gradient and cooling rate. The curve epitaxial growth of fine columnar crystal rather than along straight lines is induced by the direction of heat conduction near the joint boundary. However, the orientation angle of epitaxial growth of the coarse columnar crystal is the same as previous deposition layer at the center of deposition area. Given the effect of high heat accumulation and low temperature gradient during LMD, the dimension of columnar crystal is coarsen significantly at the center of deposition area.

show abstract

Section: Effects Of Thermal Behavior On Grain Dimension and Growth Directionmentioning

confidence: 99%

Effect of Thermal Behavior on the Grain Morphology and Dimension of 80mm-Thick Ti6Al4V Plates Joined by Laser Melting Deposition

Lyu¹,

Hu²,

Wang³

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…[17,[33][34][35] Therefore, the self-toughening method for in situ growth of highaspect-ratio reinforcements has received extensive attention due to its lower cost and better effect. [36][37][38] Su et al [39] successfully designed and prepared a single-component Al 2 O 3 ceramic with bamboo-like structures using nanosized Al 2 O 3 as polycrystalline fibers and microsized Al 2 O 3 as boundaries. The DOI: 10.1002/adem.202200971 Strength and toughness are two vital and contradictory properties, especially in alumina structural ceramics.…”

Section: Introductionmentioning

confidence: 99%

“…[ 17,33–35 ] Therefore, the self‐toughening method for in situ growth of high‐aspect‐ratio reinforcements has received extensive attention due to its lower cost and better effect. [ 36–38 ] Su et al [ 39 ] successfully designed and prepared a single‐component Al 2 O 3 ceramic with bamboo‐like structures using nanosized Al 2 O 3 as polycrystalline fibers and microsized Al 2 O 3 as boundaries. The monolithic Al 2 O 3 ceramic exhibited high toughness and graceful failure behavior, and its values of fracture toughness exceeded 7.1 ± 1.1 MPa m 1/2 .…”

Section: Introductionmentioning

confidence: 99%

“…Additives such as CaO and SiO 2 can induce the heterogeneous growth of alumina grains into plate-like grains. [36,40] In addition, the seed grains will be induced to in situ produce uniformly distributed reinforcements such as large-aspect-ratio grains, whiskers, or plate-like grains, through adding seed grains to the alumina feedstock using composite technology and simultaneously controlling the process conditions. Xu et al [41] fabricated self-toughening alumina ceramics with high fracture toughness by introducing seeds and controlling processing.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Strong and Tough Alumina Ceramic from the Particle‐Stabilized Foam

et al. 2022

View full text Add to dashboard Cite

Strength and toughness are two vital and contradictory properties, especially in alumina structural ceramics. This mutual exclusion limits the widespread application of advanced alumina ceramics in harsh environments. To deal with this issue, self‐toughening alumina bulk ceramics without any ductile phase and with a unique combination of excellent toughness and reliable strength by combining the foam ceramics with hot‐pressing sintering are prepared. Foam ceramics with honeycomb cellular structures are prepared by particle‐stabilized foaming. Then, the foam ceramics is directly hot pressed sintered, in which the cellular structure is fractured into fragments and completely dense under pressure. Equiaxed grains that constituting the fragments grow anisotropically into plate‐like grains with a large diameter–thickness ratio during hot‐pressing sintering. Plate‐like grains improve the material's fracture toughness by exerting a toughening mechanism similar to that of fibers. The self‐toughening alumina ceramics exhibit a unique combination of high flexural strength (874 ± 31 MPa) and high fracture toughness (6.2 ± 0.1 MPa m1/2). The Vickers hardness also can reach 21 GPa. Herein, a new strategy with relatively simple processing to fabricate high‐performance ceramics based on the widespread ceramic processing techniques are provided.

show abstract

“…In situ self-generated whiskers or rod-like crystals can not only increase their content up to 30-50 vol%, but also improve the bonding strength between them and the matrix, which greatly exerts their toughening effect. The widely used in situ self-generated β-Si 3 N 4 rod-like microcrystal [15,16] ceramics and Al 2 O 3 ceramics with a small amount of α-Al 2 O 3 columnar microcrystals [17][18][19] can improve the ceramic toughness because of the rod-like/columnar structures. However, most of these ceramics need to add inducer or seeds, and the Si 3 N 4 usually undergo α→β phase transformation, which depends on the equilibrium phase diagram, so the method of rod-like/columnar crystals toughened ceramics is restricted.…”

mentioning

confidence: 99%

Making Ultra‐Tough Nanoceramics by Columnar Submicrocrystals with Three‐Level Micro‐Nano Structures

Yang

Zheng

Liu

et al. 2022

Small

View full text Add to dashboard Cite

leading to the intergranular fracture. The fracture surface area of equiaxed nanocrystalline ceramics is independent of grain size (Figure S1a,b and Equation S3, Supporting Information). Therefore, the total fracture energy (Equation S4, Supporting Information) of brittle ceramics does not change under the invariant interface energy, according to Griffith theory. This is the fundamental reason why the toughness of nanocrystalline ceramics cannot be greatly improved.The toughness of nanoceramics with high-strength can be greatly improved by changing the grain geometry or the way of grain fracture. In the past, high-toughness ceramics were mainly prepared by adding whiskers, [11] fibers, [12] and nanoparticles. [13] Due to the limitation of equilibrium phase transition, these ceramics can only form one-or two-level micro-nano structures (Figure 1b,c), which not only have low-content second-level structure but also cannot achieve three-level structure. In order to prepare high-density ceramics, the whisker content should not exceed 20-30 vol%, [14] and whiskers are damaged during the mixing process, thus limiting the improvement of ceramic toughness. In situ self-generated whiskers or rod-like crystals can not only increase their content up to 30-50 vol%, but also improve the bonding strength between them and the matrix, which greatly exerts their toughening effect. The widely used in situ self-generated β-Si 3 N 4 rod-like microcrystal [15,16] ceramics and Al 2 O 3 ceramics with a small amount of α-Al 2 O 3 columnar microcrystals [17][18][19] can improve the ceramic toughness because of the rod-like/columnar structures. However, most of these ceramics need to add inducer or seeds, and the Si 3 N 4 usually undergo α→β phase transformation, which depends on the equilibrium phase diagram, so the method of rod-like/columnar crystals toughened ceramics is restricted. Through the nonequilibrium phase transformation, the three-level or multi-level structure of high-content nanoparticles, whiskers, rod-like/ columnar crystals, or plate-like crystals can be realized by in situ growth, breaking the limit of the phase diagram. The multi-level structure of ceramics with intergranular fracture will increase the fracture surface area, thereby improving the toughness. The multi-level micro-nano structure is similar to the fractal structure (Figure 1a), so the higher the number of levels it has, the larger the fracture surface area of ceramics. We designed threelevel structure of crystals based on the fractal theory of romanesco broccoli [20] (Figure 1a). The intergranular fracture of these two three-level micro-nano grains (Figure 1b,c) can increase the The low fracture toughness of equiaxed nanocrystalline ceramics is the main bottleneck of its wide range of commercial applications. Here, the authors report a method to overcome this limitation for preparing ultra-tough nanoceramics from using amorphous and supersaturated Al 2 O 3 /ZrO 2 solid solution micro-powders, which is fabricated by Al-O 2 ultrahigh-temperature combustion ...

show abstract

Study on the growth kinetics of Al2O3 columnar crystal in Al2O3 matrix composite ceramics prepared by microwave sintering

Cited by 20 publications

References 25 publications

Effect of Thermal Behavior on the Grain Morphology and Dimension of 80mm-Thick Ti6Al4V Plates Joined by Laser Melting Deposition

Effect of Thermal Behavior on the Grain Morphology and Dimension of 80mm-Thick Ti6Al4V Plates Joined by Laser Melting Deposition

Strong and Tough Alumina Ceramic from the Particle‐Stabilized Foam

Making Ultra‐Tough Nanoceramics by Columnar Submicrocrystals with Three‐Level Micro‐Nano Structures

Contact Info

Product

Resources

About