Dissertation > Excellent graduate degree dissertation topics show

The Study of Mechanism of Crack Propagation of LaPO4 Coated Al2O3 Methinable Ceramics

Author: JiangGuiJun
Tutor: WangZuo
School: Ocean University of China
Course: Materials Physics and Chemistry
Keywords: coating LaPO4/Al2O3 machinable ceramic crack propagation R-curve
CLC: TQ174.1
Type: Master's thesis
Year: 2010
Downloads: 36
Quote: 0
Read: Download Dissertation

Abstract


In order to improve the performance of machinable ceramics, we treated LaPO4/Al2O3 composite ceramic with structure design, made LaPO4 evenly distributed in the ceramic matrix to cut down its reunion. This could reduce the amount LaPO4, greatly increase the poor interface between LaPO4/Al2O3. So give it a good processing performance, while maintaining good mechanical properties.First, we used the non-homogeneous nucleation synthesized coated LaPO4/Al2O3 powder. To detect the phase composition of powder by XRD, there wereα-Al2O3 and amorphous LaPO4 existed in powder without calcined. The calcined powder is obvious monoclinic LaPO4 andα-Al2O3; this fully proved that the amorphous LaPO4 existed before burning. This would only produce a very shallow crack layerIn the case of certain content LaPO4, the coated LaPO4/Al2O3 composite ceramic in relative density, fracture toughness have been improved than those using traditional methods, while the hardness and bending strength decreased, but the processability index has also been greatly enhanced. We can clearly see the LaPO4 is layered structure by fracture surface analysis materials. When the rupture occurred, the grains were lamellar or step-like detachment. The fracture surface showed that the alumina grains were pulled out. The traces showed that the fracture form is intergranular fracture. In the LaPO4/Al2O3 composite ceramic materials processing, this layered structure LaPO4 cleavage occurred along the lamellar direction. Rather than the deep layer left by transgranular fracture cracks. The coated LaPO4/Al2O3 ceramic composite materials improved the processing, while leaving less processing damage.We have studied crack propagation behavior of coated LaPO4/Al2O3 composite ceramic. The slope of composite ceramic was-0.26 between strength and indentation load, indicating it have crack resistance curve effect. Kr increase from 4.153MPa·m1/2 to 4.281 MPa·m1/2, and slight decreased in the latter part. When the material cracks propagated, the two planes would have a relative displacement, Cracks compressed between the uneven grains, they produced a self-locking, and enhanced resistance to crack propagation. When the crack extended to the alumina grains, the extension path would be obvious to change, resulting in bridging. The two crack surfaces would be restrained by the alumina grains, thereby increased the material crack propagation resistance, improved material properties. As the interface effect or the impact of internal stress generated by heat mismatch, in particular the interactions of heterogeneity of internal stress and interfacial crack, when in the main crack tip generated microcracks, microcracks perpendicular with the principal stress axes, and then microcracks may be connected between one another, crack deflection occurred. This will increase the crack propagation path; consumed a large amount of crack propagation.We established the mechanical model of indentation tests; according to the mechanical model we could get the stress field at any point. Meanwhile we can analysis the formation of indentation cracks of ceramic materials. According to the formula we got the critical pressure of LaPO4/Al2O3 composite ceramic materials prepared by the conventional method was 1.3 N, the critical pressure of ones prepared by the coating method was 3.2 N; the initial crack length of LaPO4/Al2O3 composite ceramic material prepared by the coating method was 3.46μm, the initial crack length of ones prepared by the conventional method was 2.14μm.We analyzed toughening mechanism of ZTA ceramics and LaPO4/Al2O3 composite ceramic materials. ZTA ceramics was phase transformation toughening. The toughening mechanism of LaPO4/Al2O3 composite ceramic materials:under the pressure, materials would produce a large number of microcracks at the interface, and absorbed a large amount of elastic strain energy. Meanwhile during the crack expansion process, under the tensile stress, extension to form larger microcracks would confluence with the main crack, leaded the main crack propagation path was distorted and bifurcation, and made the main crack propagation path was more tortuous. This could absorb more elastic strain energy, thus greatly improved the fracture toughness.

Related Dissertations

  1. Preparation of Micro-Arc Oxidation Ceramic Coating on Mg Alloy and the Research of Galvanic Corrosion,TG174.453
  2. The Effect of Current Density and Electric Field on Ni and Its Alloy Electrodeposition for Copper Crystallizer,TQ153.2
  3. Computing Minimum Distance between Curves/Surfaces Based on PSO Algorithm,O182
  4. Preparation and Anticorrosion Properties of Doped Polyaniline/Epoxy Coating,TQ637
  5. Research on Detecting Optical Fiber Geometric Parameter Based on Machine Vision,TN253
  6. LSGM electrolyte thin films and electrochemical properties of,TM911.4
  7. Anti-corrosion Property of Flake Zinc Epoxy Coating Doped with Rare Earth in SRB,TQ630.1
  8. Study on Monitoring and Early Warning for Heavy Metal in Textiles,TS107
  9. Study on Chitosan-Based Composiate Nano-Coating Dope and Its Effect of Fresh-Keeping for Coated Egg,TS253.2
  10. Development and Application of Biological Seed Coating Formulation for Soybean,S565.1
  11. Automotive CO 2 emissions Technology and Economic Assessment,F426.471
  12. The Simulation Technology Study of Marine Gas Turbine Based on Modular Modeling,U674.703
  13. Mechanical Property Analysis on Concrete Short Columns with Strengthened Style Hoop,TU375.1
  14. Research on Microstructures and Properties of FeMnCrNiAlBSi/Cr3C2 Coatings,TG174.44
  15. Studies of Plasma Spray Metal-Ceramic Compounds Coatings on Q245r Steels,TG174.44
  16. Stability of the SRAM Cells for Deep Sub-micron Technologies,TP333
  17. Study on the Silicone Modified Acrylic and Water-borne Anti-corrosion Coatings,TQ637
  18. Automotive the starter performance of high-precision high stability of the test method and application,U467
  19. Design and Optimize of LED Packaging Process,TN312.8
  20. Research and Design of a High-Performance Scalable Public Key Cryptographic Coprocessor,TN918.1
  21. Research and Software Development on the Basis of the Graph Theory in Road Alignments Modeling,U412.33

CLC: > Industrial Technology > Chemical Industry > Silicate > Ceramic Industry > Basic theory
© 2012 www.DissertationTopic.Net  Mobile