| Shape Forming via Colloidal Isopressing: Reformulating a Commerical Silicon Nitride Slurry with a Commercial Silane |
01 MAY 2003 |
14 pages |
| Authors:
Hannes Essmann; Ryan Bock; V. K. Pujari; F. F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
 | Colloidal Isopressing is a new shape forming method that requires a pre-consolidated slurry with a flow stress much less than that of a commercial throwing clay (< 0.1 MPa), so that it can be injected into a rubber cavity and isopressed. It is shown that the desired interparticle pair potential can be achieved with a commercial silane for a commercial Si3N4 aqueous slurry (NT 154- X12) containing densification aids. Unlike ... |
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| Reliable Ceramic Structural Composites Designed with Threshold Strength |
30 APR 2001 |
10 pages |
| Authors:
M. P. Rao; J. Roedel; F. F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| A stress intensity (K) function describing the extension of a crack through bounding compressive layers has been experimentally verified using two methods. For one method the crack length was measured using a replicating technique; in the other, the crack length was continuously measured in-situ with an optical microscope during loading. In both, cracks were observed to propagate in a stable, nearly straight path across the compressive layer with increasing applied ... |
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| Synthesis of Ceramics from Solutions: Functionally Graded Composites, NanoComposites and Single Crystal Thin Films. Lattice Mismatch Accommodation in Perovskite Films on Perovskite Substrates |
28 FEB 97 |
37 pages |
| Authors:
P. A. Langjahr; F. F. Lange; T. Wagner; M. Ruehle; CALIFORNIA UNIV SANTA BARBARA COLL OF ENGINEERING
|
| Cubic perovskite films with different compositions were grown on perovskite substrates to investigate the influence of a large lattice mismatch on growth phenomena via the chemical solution deposition method, using toluene solutions of different 2-ethylhexanoates and neodecanoates. The films were pyrolyzed to crystallize the perovskite of the desired composition and then heated to 1000 deg C to promote epitaxial grain growth. Pole figures obtained via X-ray diffraction as well as ... |
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| Synthesis of Ceramics from Solutions: Functionally Graded Composites, NanoComposites and Single Crystal Thin Films. Epitaxial Growth and Structure of Highly Mismatched Oxide Films with Rock-Salt Structure on MgO |
28 FEB 97 |
8 pages |
| Authors:
P. A. Langjahr; T. Wagner; F. F. Lange; M. Ruehle; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| CaO thin films were grown on (001) MgO single crystal substrates by a chemical solution deposition method to study the influence of a relatively high lattice mismatch (14%) on the epitaxial growth. In order to minimize an influence of a different crystal structure and chemistry between film and substrate, film and substrate were chosen to have the same structure (NaCl) and a similar chemistry. The films were heat treated until ... |
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| Mechanical Performance of Fiber Reinforced Metal Matrix Composites and Microstructural Development of Polycrystalline Alumina Fibers Synthesized from Liquid Precursors |
31 DEC 94 |
8 pages |
| Authors:
A. G. Evans; F. Zok; C. G. Levi; F. F. Lange; CALIFORNIA UNIV SANTA BARBARA
|
| The research of the Office of Naval Research grant at UCSB focused on the research concerns of mechanical properties of fiber reinforced metal matrix composites as well as the understanding of microstructural development in polycrystalline Al2O3 fibers synthesized from liquid precursors. It has been closely coordinated with the DARPA/ONR URI program dealing with the design of high performance composites. |
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| De-sintering, A Phenonmena Concurrent with Densification Within Powder Compacts: A Review |
94 |
12 pages |
| Authors:
F. F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| A morphological instability characterized by the separation of grain pairs and the disappearance of grain boundaries is a common feature in polycrystalline bodies that are constrained from skrinking during mass transport. This instability, know as de-sintering, occurs during grain coarsening as sequentially observed for thin films with columnar microstructures constrained by a substrate, fibers with a 'bamboo' microstructure constrained by a matrix, and powder matrices within composites. De-sintering is a ... |
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| Deformation Consolidation of Metal Powders Containing Steel Inclusions |
91 |
|
| Authors:
F. F. Lange; L. Atteraas; F. Zok; J. R. Porter; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
 | Two deformable metal powders (1100 Al and Pb5%Sb) containing various amounts of spherical steel inclusions underwent uniaxial consolidation experiments at room temperature; the experiments show that the inclusion phase offers little constraint to matrix deformation at volume fractions <0.20 but causes a rapidly increasing constraint at larger volume fractions; microstructural observations have revealed two constraining mechanisms: 1, the matrix must be deformed more within the composite due to the excluded ... |
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| Powder Processing of Ceramic Matrix Composites |
91 |
|
| Authors:
F. F. Lange; D. C. C. Lam; O. Sudre; B. D. Flinn; C. Folsom; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| Powder processing of ceramic matrix composites is reviewed with emphasis on (1) forming powder compacts containing reinforcements, (2) the effect of the reinforcement network on the shrinkage and strengthening of the powder matrix during a heat treatment, (3) a novel method for producing a metal- reinforced ceramic composite and (4) a novel method for producing a laminar ceramic composite containing brittle fibers. Preliminary properties of the two new composite-processing methods ... |
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| Processing and Properties of Al2O3-Al Composites |
91 |
|
| Authors:
B. D. Flinn; F. W. Zok; F. F. Lange; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| Metal-reinforced ceramic composites have been fabricated by infiltrating metal into ceramic pre-forms containing continuous open channels. The fracture resistance behavior of the composites has been characterized using both R curve measurements and work-of-rupture tests. The latter tests indicate that the steady state composite toughness is almost 10 MPa square root of m, a value which is about three times that of the ceramic matrix itself. The effect of matrix microstructure ... |
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| Partitioning Reactions to Control and Develop Unique Microstructures |
15 SEP 90 |
|
| Authors:
F. F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| Studies reported include: (1) Liquid precursor formulation, pyrolysis, compositional homogeneity, and densification, (2) Crystallization vs. compostion subsequent to pyrolysis, (3) High temperature phase partitioning of metastable structures produced during crystallization after pyrolysis, (4) Grain growth phenomena as related to different binary, solid-solution cations and composition with different binary systems, (5) Microstructural instabilities of polycrystalline thin films, (6) Microstructural instabilities of polycrystalline fibers constrained by composite matrices, (7) Formation of single ... |
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| Densification Behavior of Single-Crystal and Polycrystalline Spherical Particles of Zirconia |
90 |
|
| Authors:
E. B. Slamovich; F. F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| Micrometer size polydispersed spheres of zirconia were produced via electrostatic atomization and pyrolysis of aqueous zirconium acetate-yttrium acetate precursors. Varying the precursor composition in the ZrO2-rich region of the ZrO2-Y2O3 binary system resulted in the production of either single- crystal (0 and 10 mol% Y2O3) or dense polycrystalline (3 mol% Y2O3) zirconia spheres of similar size distribution for densification studies. Powders of either the single-crystal or the polycrystalline particles exhibited ... |
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| The Instability of Polycrystalline Thin Films: Experiment and Theory |
90 |
|
| Authors:
K. T. Miller; F. F. Lange; D. B. Marshall; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| Dense polycrystalline thin films of ZrO2 (3 and 8 mol% Y2O3) were produced by the pyrolysis of zirconium acetate precursor films, which were deposited on single crystal Al2O3 substrates by spin-coating aqueous solutions of zirconium acetate and yttrium nitrate. Dense films were heat treated to encourage grain growth. With grain growth, these films broke into islands of ZrO2 grains. Identical areas were examined after each heat treatment to determine the ... |
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| Contributions of Sintering and Coarsening to Densification: A thermodynamic Approach |
90 |
|
| Authors:
F. F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
|
| The Morphological Stability of Polycrystalline Fibers |
89 |
|
| Authors:
K. T. Miller; F. F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
|
| Single Crystal Zirconia Thin Films from Liquid Precursors |
89 |
|
| Authors:
K. T. Miller; F. F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
|
| Densification Behavior of Al2O3 Powders Containing ZrO2 Inclusions |
89 |
|
| Authors:
O. Sudre; D. C. C. Lam; F. F. Lange; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
|
| Transformation Toughening of Ceramics |
JAN 87 |
|
| Authors:
D. B. Marshall; F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| In situ optical observations during mechanical loading have been used to investigate R-curve behavior in a series for transformation toughened ceramics and to examine characteristics of the tetragonal-to-monoclinic transformation that is responsible for toughening. In high strength and high toughness materials, the strength is dictated by the R-curve and is independent of pre-existing flaws. The results explain observed strength-toughness relations in several zirconia systems (peak strength obtained at intermediate toughness) ... |
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| Structural Ceramics Based on Si(sub 3)N(sub 4)-ZrO(sub 2)(+ Y(sub 2)O(sub 3)) Compositions, |
JAN 1987 |
|
| Authors:
F. F. Lange; L.K.L. Falk; B. I. Davis
|
| An investigation was made of the effect of yttria in solid solution in zirconia on the phases that are formed when zirconia is reacted with either nitrogen or silicon nitride. The results suggest that the Zr-oxynitride phase can be precluded as a reaction product when the yttria content of the zirconia is >4 mol%. Dense silicon nitride/zirconia (+ yttria) composites were fabricated, which did not degrade during oxidation at temperatures ... |
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| Processing Science to Increase the Reliability of Ceramics |
SEP 86 |
|
| Authors:
Bruce J. Kellett; F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| Contents: Thermodynamics of Densification, Part I: Sintering of Simple Particle Arrays, Equilibrium Configurations, Pore Stability, and Shrinkage; Thermodynamics of Densification, Part II: Grain Growth in Porous Compacts and Relation to Densification; Thermodynamics of Densification, Part III: Experimental Relation between Grain Growth and Pore Closure; Experiments on Pore Closure during HIPing and Forging. |
|
| Low Density Ceramics Based on Open Cell Macrostructures Fabricated from Reticulated Polymer Substrates |
JUN 86 |
|
| Authors:
F. F. Lange; K. T. Miller; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| Processing procedures, and resulting mechanical properties, of open cell low density (relative density less that 0. 1) ceramic macrostructures were investigated. These macrostructures were fabricated by slurry coating reticulated polymer substrates. Cracks in the powder coating, which were produced during the pyrolysis of the substrate, remained after powder densification at high temperatures and were the major cause of suboptimum properties. Additionally, lack of slurry drainage during the coating process could ... |
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| Fracture Mechanics of Ceramics. Volume 7. Composites, Impact, Statistics, and High-Temperature Phenomena |
86 |
|
| Authors:
R. C. Bradt; D. P. Hasselman; F. F. Lange; UNIV OF WASHINGTON SEATTLE COLL OF ENGINEERING
|
| Recent developments in understanding failure mechanisms and in applying fracture mechanics to ceramic fiber composites are reviewed. Direct observations of failure mechanisms in a uniaxially reinforced SiC/glass-ceramic composite are first summarized, thereby establishing a basis for a fracture mechanics analysis. The key observation is that frictional forces exerted by the fibers on the matrix oppose the opening of matrix cracks. The fracture mechanics analysis defines transitions between several failure mechanisms, ... |
|
| Fracture Mechanics of Ceramics. Volume 8. Microstructure, Methods, Design, and Fatigue |
86 |
|
| Authors:
R. C. Bradt; A. G. Evans; D. P. Hasselman; F. F. Lange; UNIV OF WASHINGTON SEATTLE COLL OF ENGINEERING
|
| The influence of microstructure on defects in ceramics, and the consequences of their presence for the application of fracture mechanics theories are reviewed. The complexities of microstructures, especially the multiphase nature, the crystallographic anisotropy and the resultant anisotropic physical properties, and the variation of microstructure and surface finish from point to point in real components, all lead to considerable uncertainties in the actual performance of any particular component. It is ... |
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| Sintering Studies Project |
13 MAY 85 |
|
| Authors:
F. F. Lange; W. J. Knapp; CALIFORNIA UNIV LOS ANGELES DEPT OF MATERIALS SCIENCE AND ENGINEERING
|
| A new concept explains the factors which influence the sinterability of ceramic (and metal) powders. This theory, based on the thermodynamics consideration of pore disappearance, is centered on the coordination number of distributon of pores within the initial powder compact and on the changes in the pore coordination number during sintering. Thermodynamic arguments show that only pores with a coordination number less than a critical value (R > R sub ... |
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| Influence of Particle Arrangement on Sintering |
APR 85 |
|
| Authors:
F. F. Lange; B. J. Kellett; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| The change in free energy of identical cylinders arranged in rings to enclose one pore shows that the pore can either shrink to an equilibrium size or disappear depending on the number of cylinders coordinating the pore and the grain boundary energy to surface energy ratio as expressed by the dihedral angle. The same result is obtained for symmetric, closed arrays of spheres (rings and polyhedral). The shrinkage and strain ... |
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| Strengthening and Strength Uniformity of Structural Ceramics |
APR 85 |
|
| Authors:
F. F. Lange; D. B. Marshall; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| The results of a four year study aimed at improving the strength and reliability of structural ceramics are summarized. Strength-degrading flaw populations were identified and processing methods were developed to eliminate each flaw population, thereby increasing the strength of Al2O3-ZrO2 composites by a factor of three. The final year's work, which is reported in detail here, concentrated on the introduction of beneficial surface stresses by grinding, identification of strength-controlling characteristics ... |
|
| Processing Science to Increase the Reliability of Ceramics |
JUL 1984 |
|
| Authors:
F. F. Lange; D. J. Green; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| Contents: Sinterability of Zr02 and Al203 Powders The Role of Pore Coordination Number Distribution; Sinterability of Agglomerated Powders; Effect of Zr02 Inclusions On the Sinterability of Al203; and Relations Between Shrinkage Strain, Strain Rate and Rearrangement During Sintering: Experimental Observations with Al203, Zr02 and Al203/Zr02 Powder Compacts. |
|
| Strengthening and Strength Uniformity of Structural Ceramics |
APR 1984 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| The goal of this work is to identify the processing flaws that limit the strength of sintered ceramics, and to engineer uniform microstructures which either eliminate or minimize the size of these processing flaws. During the first year, a major advance was made by uncovering the fact that agglomerates in powders produce crack-like voids that severely limit the strength of sintered ceramics. Crack-like voids produced by the differential sintering of ... |
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| Sinterability of ZrO2 and Al2O3 Powders: The Role of Pore Coordination Number Distribution |
MAY 1983 |
|
| Authors:
F. F. Lange; B. I. Davis; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| The sinterability of two Zr02 powders containing 2.2 and 6.6 m/o Y203, respectively, a Al203 powder, and Al203/10 v/o Zr02 composite powder was investigated. Shrinkage was measured at a constant heating heating rate. Capillary size distributions were determined by mercury intrusion after heating compacts to various temperatures. Iso-pressing eliminated larger pores with larger coordination numbers which results in greater sinterability. Local densification, i.e., densification of multiple-particle packing units, enlarged pores ... |
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| Strengthening and Strength Uniformity of Structural Ceramics |
MAY 1983 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| Stresses created by differential sintering, due to differences in initial bulk density, were determined experimentally. The experiments entailed determining the shrinkage rates of a powder isostatically pressed to two different bulk densities. Using this information, stresses were determined by forcing the slower densifying compact to shrink at the same rate as the faster densifying compact and measuring the resulting forces with a load cell. Maximum stresses (between 200 and 400 ... |
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| Study Processing of Ceramic Material |
JAN 1983 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| A concept is presented which relates the sinterability of a powder compact to its particle arrangement as defined by the distribution of pore coordination numbers, i.e. the number of touching particles surrounding and defining each void space. Previous thermodynamic arguments suggest that pores will only disappear when their coordination number is less than a critical value. The coordination number distribution of an agglomerated powder is discussed with respect to the ... |
|
| Research of Microstructurally Developed Toughening Mechanisms in Ceramics. Part 1-4 |
OCT 1982 |
|
| Authors:
F. F. Lange; M. R. James; D. J. Green; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| An x-ray diffraction technique has been used to measure the residual surface stresses induced by surface grinding in A1203 and in transformation- toughened A1203/Zr02 composites. For the A1203, compressive stresses in the range 135 to 170 MPa were measured and were found to extend to a depth = 15 micron. It is believed that the compressive layer is produced by the elastic/ plastic interaction of the abrasive grains with the ... |
|
| Strengthening and Strength Uniformity of Structural Ceramics |
MAR 1982 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| The first year effort of this program has produced a major advance in uncovering the processing steps that result in strength degrading flaws in sintered ceramics. This advance was initiated when a dye-penetrant was used to examine sintered materials (namely, a series of tough A1203/Zr02 composites). As detailed in Appendix 1, successful attempts were made to eliminate the low density volume elements by HIPing (Hot-Isostatic Pressing), and strength increased as ... |
|
| High Temperature Mechanical Properties of Polyphase Ceramics Based on Silicon Nitride |
APR 1981 |
|
| Authors:
F. F. Lange; D. R. Clarke; B. I. Davis; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| Results for the four year effort concerning the high temperature mechanical properties of polyphase ceramics based on Si3N4 are described. Initial work showed that subcritical crack growth at high temperature was caused by cavitation. Phase equilibria work identified the lowest melting eutectic in the Si3N4-Mg2SiO4-MgO portion of the Si-Mg-O-N system and linked the volume fraction of the residual glassy phase to material composition. Subsequent creep studies related creep mechanism to ... |
|
| Research of Microstructurally Developed Toughening Mechanisms in Ceramics. Part 2. Contribution to Fracture Toughness. |
MAR 1981 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| The first part of this series described the thermodynamics of the constrained phase transformation with particular emphasis on the effect of the inclusion size. In this part, two different approaches, viz. Griffith's and Irwin's, will be used to determine the contribution of a stress-induced phase transformation to the fracture toughness of a brittle material. As in Part 1, special reference will be made to the ZrO2 (tetragonal) yields ZrO2 (monoclinic) ... |
|
| Research of Microstructurally Developed Toughening Mechanisms in Ceramics. Part 3. Experimental Observations in ZrO2-Y2O3 System. |
MAR 1981 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| Materials in the ZrO2-Y2O3 system (less than or equal to 7.5 m/o Y2O3) were fabricated to investigate the conditions required to retain the metastable, tetragonal phase and to determine the contribution of the stress-induced martensitic reaction to fracture toughness. Retention of the tetragonal phase was optimized by minimizing porosity and maintaining the grain size below a critical valve. The critical grain size increased from 0.2 micrometers to 1 micrometer for ... |
|
| Research of Microstructurally Developed Toughening Mechanisms in Ceramics. Part 4. Fabrication, Fracture Toughness and Strength of Al2O3/ZrO2 Composites. |
MAR 1981 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| Three Al2O3/ZrO2 composite series, containing O, 2 and 7.5 mole % Y2O3, were fabricated for fracture toughness determinations. Without Y2O3 additions, 2 m/o Y2O3 allowed full retention up to 60 v/o ZrO2. Cubic ZrO2 was produced with additions of 7.5 m/o Y2O3. Significant toughening and strengthening was achieved when tetragonal ZrO2 was present. (Author) |
|
| Research of Microstructurally Developed Toughening Mechanisms in Ceramics, Part 5. Effect of Temperature and Alloy on Fracture Toughness. |
MAR 1981 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| The critical stress intensity factor (Kc) of materials containing tetragonal ZrO2 was found to decrease with increasing temperature and CeO2 alloying additions, as predicted by theory. The temperature dependence of Kc was related to the temperature dependence of the chemical free energy change associated with the tetragonal yields monoclinic transformation. Good agreement with thermodynamic data available for pure ZrO2 was obtained when the size of the transformation zone associated with ... |
|
| Research of Microstructurally Developed Toughening Mechanisms in Ceramics. Parts 1-5. |
OCT 1980 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| Reseaech of microstructurally developed toughening mechanisms in ceramics: Part 1: Size effects associated with the thermodynamics of constrained transformations; Part 2: Contribution to fracture toughness; Part 3: Experimental observations in the ZrO2-Y2O3 system; Part 4: Fabrication, fracture toughness and strength of AL2O3/ZrO2 composite; Part 5: Effect of temperature and alloy on fracture toughness. |
|
| Research of Microstructurally Developed Toughening Mechanisms in Ceramics. Stress Induced Transformation Toughening. Part 1. Size Effects Associated with Constrained Phase Transformation Thermodynamics. |
OCT 1980 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| The thermodynamics of the constrained phase transformation is presented with particular reference to size effects introduced by surface phenomena concurrent with the transformation, e.g., the formation of solid-solid surfaces (twins, etc.) and solid-vapor surfaces (e.g., microcracks). It is shown that these surface phenomena not only introduce a size-dependent energy term into the total free energy change, but also reduce the strain energy associated with the transformation, which can result in ... |
|
| Microstructurally Developed Toughening Mechanisms in Ceramics. Stress-Induced Phase Transformations: Theory of Phase Retention and Fracture Toughness. |
OCT 1979 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| The thermodynamics of a constrained transformation has been examined with regard to the conditions for phase retension during fabrication and the effect of a stress-induced transformation on the fracture toughness. Constraint of the shape change associated with the transformation by an elastic matrix will lower the transformation temperature. Retention also requires that a critical grain size (or particle size) cannot be exceeded during fabrication. Two binding solutions for the critical ... |
|
| Microstructurally Developed Toughening Mechanisms in Ceramics--Transformation Toughening in the A1 sub 2 O sub 3/ZrO sub 2 Composite System. |
OCT 1979 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| Three A1203/ZrO2 composites series, containing 0, 2, and 7.5 mole % Y203, respectively, were fabricated. For the A1203/ZrO2(+2M/oY203) series, tetragonal ZrO2 was retained from one end-member to the other. Significant increases in fracture toughness and strength were observed for materials in this system. Strengths decreased with increasing temperature. These results are consistent with previous theoretical predictions. (Author) |
|
| High Temperature Mechanical Properties of Polyphase Ceramics Based on Si(sub 3)N(sub 4) |
APR 79 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
|
| Progress is summarized in the following study areas concerning the compressive creep behavior of silicon nitride/magnesium oxide alloys: effect of composition of compressive creep behavior, source of the viscoelastic effect, and effects of oxidation induced compositional change. Surface stresses induced during the oxidation of silicon nitride/cerium oxide alloys was also investigated. |
|
| MICROSTRUCTURALLY DEVELOPED TOUGHENING MECHANISMS IN CERAMICS--FRACTURE MECHANICS AND MICROSTRUCTURAL DESIGN |
JUL 78 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CALIF SCIENCE CENTER
|
| Two areas stand out among others where fracture mechanics concepts can be used in aiding the design of ceramic microstructures for optimum mechanical integrity. The first is the effect of microstructure size (viz. grain and/or inclusion size) on the formation of microcracks during fabrication. The second area is the effect of microstructure on fracture toughness. Review of this subject will include crack interaction with particulates, microcrack zones at crack fronts, ... |
|
| Microstructually Developed Toughening Mechanisms in Ceramics. Compressive Surface Stresses Developed in Ceramics by a Oxidation-Induced Phase Change. |
JUL 1978 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CALIF SCIENCE CENTER
|
| Although further work is required to quantify the oxidation kinetics to obtain detailed surface stress distributions, it has been amply demonstrated that significant surface stresses can be developed by an oxidation-induced phase change. This demonstration is important since it opens a new route to increase the reliability of ceramics in applications where the mechanical properties of the surface are important, viz application (e.g., bearing surfaces, erosion, etc.) which involve surface ... |
|
| Microstructurally Developed Toughening Mechanisms in Ceramics. Fracture Toughness of Si3N4 as a Function of the Initial Alpha-Phase Content. |
JUL 1978 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CALIF SCIENCE CENTER
|
| Mixtures of high alpha-Si3N4 and high Beta-Si3N4 powders were hot-pressed with 5 w/o MgO. The critical stress intensity factor of this series of materials increased from 4.16 MPa/m sq to 6.0 MPa/m sq as the initial alpha-Si3N4 increased from 26% to 70% respectively. These results are consistent with the concepts that the alpha/Beta ratio governs the aspect ratio of the fibrous grains and that fibrous fracture is responsible for the ... |
|
| Microstructurally Developed Toughening Mechanisms in Ceramics. Stress Induced Martensitic Reaction. II. Experiments in the ZrO2-Y2O3 System. |
JUL 1978 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CALIF SCIENCE CENTER
|
| Retention of the tetragonal phase was found to depend on both density and grain size. The dependence on density is consistent with the need for self-constraint and the concepts developed regarding the thermodynamics of the martensitic reaction in an elastically constrained system. The dependence on grain size and the effect of Y2O3 on the critical grain size is consistent with the theory relating the latent internal pressure (required to maintain ... |
|
| Microstructurally Developed Toughening Mechanisms in Ceramics -- Stress-Induced Martensitic Reactions. I. Theory of Metastable Phase Retention and Contribution to Fracture Toughness. |
JUL 1978 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CALIF SCIENCE CENTER
|
| Prevention of a martensitic reaction is explained by relating the internal pressure, which arises through matrix constraint, to pressure-temperature-compositional phase equilibria. To have a constraint, microcracking must be avoided by fabricating the material with a grain/particle size less than a critical value. This is a previous result of theories concerned with crack extension in highly localized stress fields. The contribution of a stress-induced martensitic reaction to fracture toughness is explained ... |
|
| High Temperature Mechanical Properties of Polyphase Ceramics Based on Silicon Nitride. |
MAR 1978 |
|
| Authors:
F. F. Lange; ROCKWELL INTERNATIONAL THOUSAND OAKS CALIF SCIENCE CENTER
|
| Progress is summarized in the following study areas: (1) eutectic studies in the Si3N4-MgO-SiO2 system relating eutectic compositions and temperatures to fabrication, microstructure and mechanical properties; (2) evidence for high temperature cavitation crack growth in polyphase Si3N4 materials; (3) estimates of the time required for the stress induced penetration of a liquid from triple points to locations between grains; (4) the reaction of Fe with polyphase Si3N4 to form surface ... |
|
| FRACTURE MECHANICS OF CERAMICS--FLAWS AND TESTING |
78 |
|
| Authors:
R. C. Bradt; D. P. H. Hasselman; F. F. Lange; PENNSYLVANIA STATE UNIV UNIVERSITY PARK MATERIALS SCIENCE LAB
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| Volume 3 investigates the statistics of flaws and their creation during impact and scratching events, and applies the results to engineering design with ceramics and to the development of new testing techniques. |
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| FRACTURE MECHANICS OF CERAMICS--CRACK GROWTH AND MICROSTRUCTURE |
78 |
|
| Authors:
R. C. Bradt; D. P. H. Hasselman; F. F. Lange; PENNSYLVANIA STATE UNIV UNIVERSITY PARK MATERIALS SCIENCE LAB
|
| Volume 4 concentrates on the fundamentals of crack growth and its analysis as well as its relationship to the microstructure of ceramic materials. |
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Reports by Author
