TRP 93-012

Laminated Object Manufacturing of an Advanced Ceramic Composite with Extremely High Toughness

Lone Peak Engineering, Inc.

I

The transition of DoD-developed technologies into the commercial market is needed to maintain a strong advanced materials industry. Cost is the primary consideration in the commercial market. Therefore, manufacturing processes are needed to fabricate components from advanced materials that are affordable and competitive on a cost basis with current materials. Lone Peak Engineering (LPE) proposes to combine two DoD-developed technologies to manufacture advanced ceramic matrix composites at affordable costs.

An AFOSR project has developed a new laminar ceramic matrix composite (CMC) of a ceria-zirconia matrix reinforced with layers of CeO2-ZrO2 and Al2O3 ceramics. These layered composites have the potential for fracture toughness as high as some tool steels, up to 40 MPa-Tm. In a separate ARPA project, LPE is developing a desktop manufacturing system for structural monolithic ceramics using a laminated object manufacturing (LOM) technique. The LOM technique is uniquely suited to manufacture layered ceramic matrix composites.

The objective of the Phase I project is to demonstrate the feasibility of manufacturing layered ceramic matrix composites using the LOM technique. The objective of a Phase II project will be to develop the equipment and processes so that layered composites can be manufactured for DoD and commercial applications at reasonable costs.

The combination of the LOM process and layered ceramic composites will provide a cost-effective, rapid method to produce reliable ceramic components with high fracture toughness in the shapes required for structural applications. These composites could be used as structural components in military and nonmilitary applications.

• Ceramics Matrix Composites
• Laminated Object Manufacturing
• Desktop Manufacturing
• Rapid Prototyping

Identification and Significance of the Problem or Opportunity

A strong advanced materials industry is vital to maintain US competitiveness in the global market. The Department of Defense (DoD) is the largest developer and consumer of advanced materials. The expected decrease in the DoD demand for advanced materials must be compensated by an increased civilian demand to maintain our leadership in this industry. This can be accomplished by a transition of DoD-developed technologies into the commercial sector. Cost is the primary consideration in the commercial market. Therefore, manufacturing processes are needed to fabricate components from these advanced materials that are affordable in the commercial sector and competitive on a cost basis with current materials. Lone Peak Engineering (LPE) proposes to combine two DoD-developed technologies to manufacture advanced ceramic matrix composites at affordable costs.

Under an AFOSR project, a new laminar ceramic matrix composite (CMC) has been developed. This composite consists of a ceria tetragonal-zirconia-polycrystal (Ce-TZP) matrix reinforced with continuous layers of a mixture of CeO2-ZrO2 and Al2O3 ceramics [1,2]. These layered composites have the potential for fracture toughness, i.e., to resist cracking, that is as high as some tool steels, up to 40 MPa-Tm. Already, these composites have fracture toughness of 17.5 MPa-Tm, which is one of the highest measures of fracture toughness recorded for a ceramic [1].

While the AFOSR project has proven the concept, little consideration has been given to manufacturing affordable components from these layered composites. Without affordable components, there will be few opportunities for the transition of this technology into civilian use. To date, only simple test specimens have been prepared using a special colloidal-sedimentation technique [1,3]. While this technique provides excellent specimens for basic research, it is not capable of producing structural components at reasonable costs. Also, the complexity and geometry of parts produced by the colloidal method is limited to simple shapes, which are generally not suitable for commercial applications. Conventional processes, such as pressing and extrusion, can not be used to manufacture these composites.

In a separate ARPA project, LPE is developing a desktop manufacturing system for structural monolithic ceramics using a laminated object manufacturing (LOM) technique [4]. The LOM technique offers the capability to produce ceramic components directly from a computer-generated design without the use of molds, dies, or hard tooling.

The LOM technique is uniquely suited to manufacture layered ceramic matrix composites. Lone Peak's LOM process uses flexible-tape-cast sheets of a structural ceramic to form the desired components. One sheet is placed in the LOM system, a computer-controlled laser cuts the sheet to outline the initial cross-section of the part being fabricated. The next sheet is laminated to the first one and then the laser cuts only the new sheet to form another layer of the part. The process is repeated layer-by-layer until the part is finished. The part is removed from the excess material. The bindera is removed and the resulting ceramic component is then sintered to a high density. By alternating the composition of the sheets during the LOM process, the layered composite described above could be fabricated.

Phase I Technical Objectives

The objective of the Phase I project is to demonstrate the feasibility of manufacturing layered ceramic matrix composites using the LOM technique. The results of the Phase I project will be benchmarked against the properties and costs of common ceramic materials.

In this Phase I demonstration, test bars of the layered ceramic composite will be fabricated using LPE's LOM process and evaluated. These bars will contain CeO2-ZrO2/Al2O3 layers in a Ce-TZP matrix. The questions this research project will answer are:

Can layered composites be formed by the LOM process? What are the resulting physical and mechanical properties of the composites made by LOM? What areas must be developed to manufacture these composites on commercial scale?

The objective of a Phase II project will be to develop the equipment and processes so that layered composites can be manufactured for DoD and commercial applications at reasonable costs. Those areas identified in the Phase I project will be developed during the Phase II project. Anticipated areas of development may include process refinement and automation, material composition, and optimal layer thickness and spacing between layers. These areas will help to optimize the material properties of these composites.

Phase I Work Plan

The work plan has been divided into five tasks, which are described below. A schedule for the tasks is shown in Figure 1.

Task Time, months 1 2 3 4 5 6 7 1 Materials Preparation ___________ 2 LOM Composite Test Bars _____ 3 Post-Forming Processes ________ 4 Mechanical Property Evaluations _______ 5 Benchmarking ___ 6 Final Report _________ Figure 1. Task Schedule

Task 1 Materials Preparation

The objective of Task 1 is to prepare the flexible-tape-cast sheets of the ceramic compositions needed for the layered composite. These sheets will be used in Task 2 to prepare the green (unsintered) layered-composite test bars using the LOM process. A procedure established by LPE will be used to prepare tape cast sheets [4].

The matrix of the composite will be ceria-partially-stabilized zirconia (CeO2-ZrO2). The layers will be a mixture of 50 vol% Al2O3 and 50 vol% CeO2-ZrO2. The addition of the CeO2-ZrO2 to the Al2O3 provides for a better thermal expansion match with the CeO2-ZrO2 matrix than pure Al2O3, which could also be used [1].

Commercial powders will be used to prepare the tapes. A 12 mol% CeO2-88 mol% ZrO2 powder will be obtained from Tosoh Corp, Tokyo, Japan (Grade TZ-12Ce). Presently, there is no US source for this type of powder. Lone Peak's production-grade alumina powder will be used to make the CeO2-ZrO2/Al2O3 mixture. This is a 99.8% alumina powder from Alcoa Corp, Pittsburgh, PA (Grade A-16SG).

The powders will be ball milled with a proprietary binder system to form a slurry for tape casting. This binder system contains a mixture of organic solvents, binders, plasticizers, and dispersants. The CeO2-ZrO2 and Al2O3 powders will be mixed during the milling step. The milled slurries will be de-aired under vacuum before tape casting.

The de-aired slurry will be tape cast onto a mylar surface using a doctor blade. The solvents in the cast tapes will be evaporated, leaving dry, flexible, green tapes of uniform thickness. The tape thickness will be approximately 0.051 mm (0.002") thick, which should result in sintered thicknesses of approximately 0.041 mm (0.0016"). Since this is a very thin tape, special care will be taken when it is handled. The green tapes will be cut into sheets that are approximately 101.6 x 152.4 mm (4" x 6"). LPE will use the facilities at EPH Engineering, Orem, Utah to prepare these tapes. These green sheets will be used in the LOM process outlined in Task 2.

Task 2 Laminated Object Manufacturing of Ceramic Test Bars

The objective of Task 2 is to prepare test bars from the tape-cast sheets that were prepared in Task 1. A commercially available LOM machinea that has been modified by LPE for ceramics will be used to prepare the composite bars by LPE's laminated object manufacturing process. The original machine, shown in Figure 2, was developed to produce parts directly from CAD files using paper and plastic materials. LPE demonstrated in a previous project that monolithic structural ceramic parts can be produced with the machine shown in Figure 2 [4]. The LOM machine will be purchased and modified under a separate project scheduled to start in October of 1993. Some of the specifications of this system include:

Working Envelope: 13"L x 10"W x 15"H Laser: 25 watt CO2 Beam Diameter: 0.010" Accuracy: +/- 0.005" in X, Y, or Z direction Speed: Up to 15"/second Computer System: 80486-based, IBM Compatible, MS-DOS 6.0 and MS- Windows NT Operating system

Models of the test bars will be generated using a three-dimensional solid modeling software operating on a UNIX-based workstation. The model will be converted into the proper format required to control the LOM system.

Initially, some laser cutting trials will be conducted to determine the cutting parameters, such as laser power and cutting speed, to insure that only the top layer is cut. These cutting parameters will be determined using the LOM-1015.

Once the cutting parameters are determined, then the test bars will be manufactured. Two different sizes of green bars will be made by the LOM process. One set will be approximately 4 x 6 x 50 mm for the strength and hardness tests. The other set

Figure not included Figure 2. Laminated object manufacturing system, Helisys Model LOM-1015.

will be 2 x 12 x 50 mm for the fracture toughness tests. Forty test bars will be prepared by the LOM process.

Lone Peak will use an established procedure to prepare the test bars by the LOM technique [4]. Because the composition of the layers will alternate, a manual process will be used. The LOM system can be used in an automatic mode if the material being used is only one composition. The LOM-1050 can only accommodate one roll of material at a time, and hence only one composition, Part of a Phase II project will be to modify the LOM equipment to accommodate the alternating compositions required for the layered ceramic composites, possibly by using a single-sheet feeder similar to a copy machine. The LOM procedure that will be used in this project consists of the following steps:

1. The coated sheet will be placed onto the previous layersa. If necessary, the tape cast sheet will first be coated with an bonding agent to help laminate the tapes together. 2. A heated plate will be placed on top of the layered sheets to laminate the top layer to the previous layer. A small amount of pressure will be applied to aid in the lamination. The temperature of lamination will be around 45oC. 3. The heated plate will be removed and the top most layer of the stack will be cut by the laser. The LOM system computer controls the laser path to cut out the cross section of the parts being made. The power and speed of the laser will be adjusted so that only the top-most layer will be cut by the laser. 4. The entire process will be repeated until the parts are finished. The composition of the layers will be alternated, i.e., Ce-TZP layer, CeO2-ZrO2/Al2O3 layer, Ce-TZP layer etc.

LPE has available all of the equipment necessary to prepare these test bars. After the LOM process is complete, the bars will undergo the post-forming processes outlined in Task 3 at LPE.

Task 3 Post-Forming Process

The objective of this task is to nondestructively evaluate the test bars, remove the binder, and sinter the test bars. The physical properties (density, porosity, shrinkage, and weight loss) will also be measured during this task.

Contact radiography by X-rays will be the nondestructive evaluation technique used in this task. It will be used to determine if any defects are generated during the forming processes in Task 2 or during any of the post-forming processes performed in this task.

The procedure for this task is outlined below: 1. Measure the green dimensions and calculate the green densities of the test bars. 2. X-ray the bars for internal defects that may have been generated during the LOM process. 3. Remove the binder using LPE's established thermal process for LOMed parts. 4. Measure the dimensions and determine the geometric densities of the bars after the binder has been removed. 5. Sinter the bars at 1600oC for three hours in air. 6. Measure the dimensions and calculate the densities of the sintered bars. Sintered density and open porosity will also be measured by an immersion technique (ASTM-STD-C373-56). 7. X-ray the bars for any internal defects that may have been generated during the binder removal and sintering processes.

Standard procedures already used at LPE will be employed in the procedures shown above.

The microstructure of the sintered composites will be examined using an optical microscope. Polished sections will be prepared from selected sintered parts. The polished sections will be prepared to view both parallel and perpendicular to the laminations made during the LOM process. The mechanical properties of the sintered bars will be determined in Task 4.

Task 4. Mechanical Property Evaluation

The objective of Task 4 is to determine the mechanical properties of the sintered test bars produced by LOM. Specifically, flexure strength, fracture toughness, and hardness will be determined using the procedures outlined below.

All four sides of the sintered bars will be surface ground using a diamond wheel to a finish of better than 30 mm. Grinding will be done parallel to the length of the bar. The edges of each bar will be chamfered to 45o.

Flexure strength of the ground and chamfered bars will be measured in four-point bending with an Instron testing machine. The fracture origins of the broken test bars will be determined by observation of the fracture surface as viewed under a stereo microscope.

The hardness will be determined from Vickers-type indentations into the polished specimens using standard techniques. These indentations will be made into the polished sections that were prepared for the microstructural examination in Task 3.

The fracture toughness measurements are not as straight forward as the strength or hardness measurements because these layered ceramic composites exhibit R-curve behavior [1]. R-curve behavior indicates that the fracture toughness is a function of crack length. Generally, the fracture toughness increases with the crack length. For these layered composites, the R-curve behavior is shown in Figure 3 [1].

The fracture toughness and R-curve behavior of the sintered test bars will be determined from controlled crack growth tests in notched beams, fracture of smooth bars, and indentation fracture toughness tests. These tests will be performed at the Rockwell Science Center in Thousand Oaks, CA under the direction

Figure not included Figure 3. R-curve behavior of layered composites showing very high fracture toughness [1].

of Dr. David Marshall using established procedures and equipment [1]. Dr. Marshall originally conceived of the idea of a layered composite [2] and is a recognized expert in the field of zirconia ceramics.

Task 5 Benchmarking

The results of this Phase I project will be benchmarked against properties of commercially available ceramic materials. The costs to manufacture the layered composites by the LOM process will be estimated based on this Phase I feasibility study.

The physical and mechanical properties determined in Tasks 3 and 4 will be compared to common ceramic materials such as alumina, zirconia, silicon nitride, and silicon carbide. This data will be obtained through technical and product literature. The Phase I data will also be compared to the latest data obtained by Dr. Lange using the colloidal-sedimentation fabrication method to prepare the layered composites.

Based on the Phase I process, an estimate of the cost to manufacture layered composites using the LOM process will be made. The cost estimates will be made using LPE's process to estimate the cost to manufacture ceramic components by injection molding. The cost estimate will be compared to the costs of conventional ceramic materials.

Task 6 Final Report

The final report will be prepared and submitted to the technical monitor by the end of the project's seventh month of the project. In this report, the observations and data gathered in the earlier tasks will be summarized and discussed. Monthly progress reports will be submitted as a basis for progress payments.

Related Work

Laminated object manufacturing offers possibly the only practical process to produce working components from the layered ceramic composites. Combining the layered-composite structure and the LOM process will result in a practical commercial process to produce tough ceramic components for DoD and commercial applications.

In this section, background information is provided on Ce-TZP ceramics in general. Then, the layer composite approach to increase the toughness of Ce-TZP is discussed. The LOM process is described and the potential use of the LOM technique to produce the layer composites is discussed.

Background on Ceria-Zirconia Ceramics

Ceria-zirconia monolithic ceramics have reported fracture toughness in the range of 10 to 14 MPa-Tm [5-8]. The fracture toughness of Ce-TZP is very high compared to most monolithic ceramics. Fracture toughness is a measure of a materials resistance to failure, a brittle material has a low fracture toughness, while a ductile material's fracture toughness is high. Most ceramics have low fracture toughness, since they are brittle. For example, alumina, a common structural ceramic, has a fracture toughness between 3 and 4 MPa-Tm and glass less than 3 MPa-Tm. Tool steel can have fracture toughness between 40 and 80 MPa-Tm [9].

High fracture toughness in toughened zirconia materials is generally attributed to stress-induced transformation of the tetragonal grains to the monoclinic form. This transformation creates a zone ahead and to the side of the crack. This transformation zone results in 3 to 5 % volume expansion and 1 to 7 % shear strain that leads to compressive stresses in the matrix. These compressive stresses shield the crack from further growth, i.e., crack tip shielding mechanism. This leads to an increase in the toughness of the material [10].

The shape of the transformation zone ahead of a crack in Ce-TZP is very different than in other toughened zirconia materials. The zone in magnesia-partially-stabilized zirconia (Mg-PSZ) extends equal distances ahead and to the side of the crack. In Ce-TZP, the zone is very narrow extending ahead of the crack 10 to 20 times the zone width [5-7].

This long narrow zone is thought to result from autocatalytic transformation, i.e., transformation of adjacent grains trigger the transformation of other grains [8]. Autocatalytic transformation is also believed to occur in Mg-PSZ. However, the tetragonal precipitates in Mg-PSZ are contained in larger grains whose grain boundaries restrict the growth of the transformation zone on a long-range scale.

There is no effective barrier to autocatalytic transformation in Ce-TZP. The transformed material far ahead of the crack reduces the overall fracture toughness of the Ce-TZP by a factor of two (2) [2,5]. In order to increase the fracture toughness of Ce-TZP, the shape of the transformation zone must be changed.

Layered Composites: Potential for Very Tough Ceramics

Marshall first suggested that microstructural modifications to Ce-TZP to reduce the elongation of the transformation zone could double the fracture toughness, to possibly as high as 40 MPa-Tm [2]. In a later paper, Marshall, Ratto, and Lange [1] demonstrated the effectiveness of using thin layers of Al2O3 or CeO2-ZrO2/Al2O3 mixtures to modify the microstructure and create the Ce-TZP layered composites. These layers acted as barriers that widened the transformation zone from 15 mm to 150 mm, increased the fracture toughness, and resulted in extensive R-curve behavior, i.e., fracture toughness increases with crack length. The effect on the transformation zone is shown schematically in Figure 4 and the R-curve behavior is shown in Figure 3.

The maximum fracture toughness of the Ce-TZP layered composites was 17.5 MPa-Tm. This is one of the highest fracture toughness reported for ceramics. It is only exceeded by weakly-bonded fiber-reinforced composites [10], weakly-bonded laminar composites [11], and some Mg-PSZa immediately after heat treatment [12].

Higher fracture toughness values could have been achieved, but the crack reached the end of the layered section and propagated through the rest of the specimen, Figure 4. It is difficult to use the colloidal-sedimentation method used to make specimens with more layers, which would have resulted in high fracture toughness. In addition, this method is not suitable to make complex components for actual use.

Laminated Object Manufacturing

Laminated object manufacturing offers a practical process to produce working components for structural applications from the layered ceramic composites. Combining the layered-composite

Figure not included Figure 4. Schematic representation of the effect of the CeO2-ZrO2/Al2O3 layers on the transformation zone in CeO2-ZrO2 matrix [1].

structure and the LOM process, the resulting composite structure will have:

1) the layered microstructure through out the part, 2) the microstructure in place that could result in fracture toughness of up to 40 MPa-Tm, and 3) the capability to form complex-shaped parts from these layered composites.

In the sections below, the general area of desktop manufacturing, of which LOM is one technique, is first discussed followed by a discussion of the LOM process in general terms. Finally, the work performed by LPE related to the LOM process for ceramics is discussed.

Desktop Manufacturing

Laminated object manufacturing is one of several desktop manufacturing systems that have been developed recently [13-26]. These techniques are summarized in Table 1. Most of these techniques were developed to prepare plastic, wax, or paper parts. These parts are primarily used in form and fit functions or as models for molds. Few are used as functional components. While the processes differ somewhat, they all produce a solid part directly from a three-dimensional CAD drawing, without the use of any hard tooling or dies.

The initial steps in each of the different desktop manufacturing techniques are very similar. First, the part to be manufactured is designed using a conventional CAD program.

Table 1. Summary of Various Flexible Manufacturing Systems. Material of Working Used With Technique Construction Envelope Tolerance Ceramics ---------------------------------------------------------------------------- Laminated Object Thin Sheets 13x10x15 0.005 Structural Al2O3, Manufacturing glass-Al2O3 [4,14] Fused Deposition Plastic Fiber 12x12x12 0.005 None reported Modeling Stereolithography L-S Polymerb 20x20x24 --- None reported PhotoChemical L-S Polymer --- --- None reported Machining SOMOS L-S Polymer 12x12x12 --- None reported Optical L-S Polymer 12x12x12 --- None reported Fabrication Solid Base Curing L-S Polymer 14x20x20 0.002 None reported Selective Laser Powders 12x15 0.005 Low Density Sintering Al2O3Phosphate[15] Ballistic Particle Powders No Limit 0.004 None reported Manufacturing 3-Dimensional Ceramic Powders 3 in3 --- Low density Printing ceramics for casting molds [16] ____________________________________________________________________________ a All dimensions are in inches. b Light-sensitive polymer.

A three-dimensional solid model or wire-form model is then created from the CAD. The 3-D CAD model is converted into a de facto standard format for flexible manufacturing called a .STL file. The .STL file is sliced into thin cross sections by a separate computer program. These slices become the program steps that control the equipment that actually produces the component slice-by-slice. Once the sliced .STL file is created, the various techniques can be differentiated by the materials used to form the component. Very few of these techniques have been used with ceramic materials.

Laminated object manufacturing uses sheets of materials to build up the component. The process is shown schematically in Figure 5a. The sheet material is rolled into place and heat-laminated to the previous layer. A CO2 laser cuts only the new sheet to outline the part. The laser is controlled by the sliced

Figures not included (a) (b) Figure 5. (a) A schematic representation of the LOM process and (b) Example of paper parts produced by the LOM process without the use of any hard tooling [17-19].

.STL file. Other "tiles" are cut into the surplus material to help with the removal of the finished component. The laminated layers are lowered slightly and a new sheet is rolled into place. The process repeats itself until the component is completed. An example of a LOMed part made from paper is shown in Figure 5b.

Lone Peak's Work Related to the LOM Process for Ceramics

Lone Peak Engineering has demonstrated the application of LOM process to prepare monolithic alumina ceramics [4]. Lone Peak's LOM process will be fully developed during a Phase II ARPA SBIR project scheduled to start in October 1993. The properties of the LOMed alumina components were very similar to the physical and mechanical properties of alumina ceramics that were prepared by a conventional pressing process, Table 2. The LOMed ceramics were also very similar in properties to commercially-available alumina ceramics. LPE has also demonstrated that complex-shaped, monolithic ceramic parts can be formed by the LOM process. These parts are shown in Figure 6.

The LOM process to be demonstrated in this Phase I effort will allow unique combinations of materials to be produced, such as the layered composites described in this proposal. Since the laminated object manufactured (LOMed) component can be produced directly from a CAD file without any tooling dies or molds, LOMed ceramic composites will have other advantages over conventionally-processed ceramics. Parts and prototypes can be prepared rapidly and cost-effectively. Design changes can be easily and inexpensively made, allowing wider design options to be investigated. Parts can be designed and engineered to take advantage of the stronger properties of ceramics, rather than

Table 2. Properties of LOMed Alumina Components Made at LPE Compared to Pressed Parts and Commercially Available Alumina [4]. Flexure Vickers Forming Direction1 Density Strength Hardness Fracture Toughness Process of Test g/cc MPa GPa MPa-Tm ---------------------------------------------------------------------------- LOM Parallel 3.88 314 20.2 4.3 LOM Perpendicular 3.88 311 20.1 3.9 Pressed Parallel 3.89 336 21.8 4.0 Pressed Perpendicular 3.89 325 19.8 3.7 ---------------------------------------------------------------- Commercial grade2 3.89 379 14.13 4-54 ------------------ 1 The test direction was either parallel to the direction of lamination (pressing) or perpendicular to it. 2 For Grade AD995 (99.5%) Alumina, Coors Ceramics Company, Golden, CO, Datasheet 7164C FP 20K 2/89, 3 Knoop hardness under a 1000 g load, whereas the other hardness shown in the table were measured using a Vickers indentor. 4 Measured by the single edge notched beam technique.

making the ceramic from an existing design for a metallic part, which is the common design procedure.

Lone Peak Engineering, Inc.

Lone Peak Engineering, Inc. was founded in 1986 to conduct contract research in the area of technical ceramics. The current focus at Lone Peak emphasizes ceramic production, service work, and contract research. The emphasis on production is a natural transition from the contract research conducted earlier in the company's history.

Lone Peak has won an awarda for its Phase III commercial activities resulting from a Phase II SBIR project. This project developed a method to injection mold whisker-reinforced ceramic matrix composites for the Navy. LPE's commercial work has grown four-fold from 1991 to 1992. Two-fold growth is anticipated in 1993.

The LOMed layered-ceramic composites strengthens LPE's overall business strategy. LPE's strategy is to provide current customers with affordable advanced ceramics. The knowledge gained during the commercialization of our previous Phase II

Figure not included Figure 6. Ceramic parts made by Lone Peak Engineering to demonstrate the complex-shape forming capability of the LOM process. Pyramid, angled- recessed, and bar shapes are shown.

project will be used to commercialized the technology developed during this SBIR project.

Relationship with Future Research or Research and Development

The Phase I project will successfully demonstrate the capability of the LOM process to form layered-ceramic composites. Furthermore, these LOMed composites will have been sintered to a high density and they will exhibit mechanical properties that exceed the properties of monolithic ceramic.

In the Phase II project, the laminated object manufacturing system and processes will be developed specifically for layered composites. This scaled-up equipment will be capable of automatically handling the multiple material compositions needed to produce the layered-ceramic composites. Phase II areas of investigation include: process automation, automatic feed of sheets with different material composition, layer thickness and composition, and material compositions. Flexibility and cost- and time-savings associated with the LOM process for ceramics will be addressed in Phase II project.

Potential Post Applications

The mission of the Technology Reinvestment Project (TRP) is "to stimulate the transition to a growing, integrated, national industry capability which provides the most advanced, affordable, military system and the most competitive commercial products" [27]. One strategy employed by the TRP project to achieve its mission is to stimulate the integration of military and commercial research and production activities.

The project outlined here by LPE directly supports the TRP mission. Preparing layered ceramic matrix composites by the LOM process will help the US maintain a technology leadership position in the use of advanced ceramic materials. This project will draw on DoD-funded CMC and LOM research results to develop an affordable manufacturing process. The nature of the LOM process will allow the integration of concurrent engineering principles into the overall manufacturing approach to aid the transition into the civilian market.

Structural designers are continually searching for ceramics that are much less brittle (higher fracture toughness) than currently available. The layered-ceramic composites combined with the LOM process offers the potential to form tough ceramics in the shapes required for structural applications.

Once fully developed, the LOM process for layered-ceramic composites will provide a cost-effective, rapid method to produce reliable ceramic components with high fracture toughness, i.e., much less brittle than monolithic ceramics. These composites could be used in many structural applications required by the Department of Defense. In addition, the LOM process can be used to easily and rapidly prototype ceramic components for new applications or to test new designs.

The LOM process offers a rapid, flexible method to make ceramic components. Many of the applications for ceramic components are small volume, custom parts. Sometimes ceramics are not considered for an application because conventional ceramic manufacturing is a costly, time-consuming, and inflexible process. The LOM process will provide an effective technique, with regard to both cost and time, to provide cost-competitive ceramic components for applications requiring only a few parts. It will also allow more rapid and less costly fabrication of ceramic prototypes for a broader range of applications. The LOM process will also allow the design engineer to consider more design options with the flexible LOM process.

Key Personnel

Lone Peak Engineering has assembled a well-qualified, multi-disciplinary team to successfully complete this project. Mr. Curtis Griffin will be the principal investigator for this project. Lone Peak Engineering has retained a consultant, Dr. Frederick Lange, who was instrumental in demonstrating the potential of the layered composites. Dr. Lange's resume is shown in section k. Dr. David Marshall of the Rockwell Science Center will perform the fracture toughness tests on a purchase order basis. He originally conceived the idea of incorporating the layer structure in the Ce-TZP matrix. Mr. Griffin's resume is given below.

CURTIS W.~GRIFFIN, Director,
Technical Ceramics Division,
Lone Peak Engineering, Inc.

Mr. Griffin joined LPE in 1990. As Director of the Technical Ceramics Division, he is responsible for the technical and fiscal management of all ceramics-related programs. His research experience and interest lies in the processing and characterization of ceramic materials for structural applications. Mr. Griffin lead Lone Peak's successful demonstration of the LOM process to prepare monolithic, structural ceramics. He will be the principal investigator on the Phase II effort for monolithic ceramics, which will begin in October 1993. He directed LPE's program for the Navy to develop an injection molding process for ceramic matrix composites. Mr. Griffin experience in ceramic processing will be particularly applicable to this program.

He was the Manager for Composite Programs at Ceramatec, Salt Lake City, Utah from 1987 until 1990. He was responsible for all ceramic composite programs. These programs included work on the reinforcement of Al2O3, Si3N4, TiB2 and ZrB2 matrices with various whiskers, fibers, or particulate materials. In addition, he developed new fabrication processes for Ceramatec such as injection molding and microwave sintering.

From 1977 until 1987, Mr. Griffin was a Senior Research Engineer at Battelle's Pacific Northwest Laboratories in Richland, Washington. He specialized in ceramic materials research, which included fabrication and characterization of high temperature ceramics. Mr. Griffin was a principal investigator on projects to develop ceramic matrix composites for applications in fossil energy systems and to characterize the fiber-matrix interfaces using microanalytical techniques.~ His other research activities at Battelle included development of electrode materials for solid oxide fuel cells and MHD systems, examination of the high-temperature thermal and electrical properties of ceramic materials, and development of nuclear fabrication processes.

Mr. Griffin received a BS and a MS in Ceramic Engineering from Alfred University and Iowa State University, respectively.~ Mr. Griffin has also taken a number of short courses to supplement his formal education. Some of Mr. Griffin's publications pertaining to his ceramic materials research are:

(1) Griffin, C.W., A.C. Hurford, A.V. Virkar, and D.W. Richerson, "Processing and Properties of Pressureless Sintered Alumina Composites with SiC Whiskers", Cer. Eng. Sci. Proc., R.E. Barks, ed. 10(7-8):695- 706, 1989. (2) Griffin, C.W., and S.C. Danforth, Injection Molding of Ceramic Matrix Composites, Final Report on a Phase I SBIR Contract, Naval Surface Warfare Center, Silver Springs, Maryland, 1989. (3) Griffin, C.W., D.K. Shetty, S.Y. Limaye, and D.W. Richerson, "Evaluation of Interfacial Properties in Borosilicate-SiC Composites Using Pullout Tests" Cer. Eng. Sci. Proc., D.E. Clark, ed. 9[7-8]:671- 678, 1988. (4) Bates, J.L., C.W.~Griffin, D.D. Marchant and J.E. Garnier, "Electrical Conductivity, Seebeck Coefficient and Structure of In2O3- SnO2", Bul., Am., Cer., Soc., 65(4):673-678, 1986. (5) Weber, W.J., C.W. Griffin and J.L. Bates, "Electrical and Thermal Transport Properties of the Y1-xMxCRO3 System", J. Mater. Res. 1(5):675-684, 1986.

Facilities/Equipment

The majority of the equipment required for this project is presently available at Lone Peak Engineering. The equipment available at LPE includes:

Powder Preparation Ball mills, milling media, mill containers Large capacity balances, up to 2 kg, Fume hood for powder handling Glove box to handle hazardous materials, e.g. ceramic whiskers Mixing Sigma blade mixer, 1.8 l capacity, stainless steel, jacketed High temperature bath for mixer, 0 to 150oC capability Forming 20-ton injection molder with 100 g shot capacity, 13,500 psi injection pressure, manual through automatic operation Assorted pressing and injection molding dies. Bench-scale tape cast system. Laminated object manufacturing equipment Furnaces Binder removal furnaces with off gas treatment system Assorted drying ovens Inspection and Measurement Electronic analytical balance, 1 mg readability Assorted calipers and micrometers Immersion density apparatus Miscellaneous Laboratory Equipment Laminar flow hood Ultrasonic cleaners Sieving equipment including shaker and assorted screens Data Reduction/Computers Various PCs and various software including spreadsheets, CAD, 3-D modeling, word processing, and graphics packages UNIX-based workstation.

Lone Peak is purchasing a LOM machine (Figure 2) from Helisys as part of the ARPA Phase II project. LPE is also purchasing on the ARPA project a UNIX-based workstation and 3-D modeling software, which will also be used on this Phase I project. All of this equipment is expected to be operational by January of 1994.

Lone Peak Engineering will use an Instron testing machine at the University of Utah to measure the strength and hardness of the LOMed composites. The fracture toughness tests will be conducted by Dr. David Marshall at the Rockwell Science Center in Thousand Oaks, CA on a purchase order basis.

Consultants

Dr. Frederick Lange, Consultant to Lone Peak Engineering. Dr. Lange along with Dr. Marshall, who will also participate in this project, were first to demonstrate the potential of the Ce-TZP layered composites. Dr. Lange is currently a Professor in the Material Science Department at the University of California, Santa Barbara (UCSB). Dr. Lange's work at UCSB is directed towards understanding relations between chemistry, processing, microstructure development, and properties enabling the engineering of new, more reliable advanced ceramics and their composites. Dr. Lange has been studying ZrO2 ceramics since 1976 and he has contributed to much of the present understanding of these materials. Prior to joining the faculty at UCSB, Dr. Lange was employed at the Rockwell Science Center (1976-1986), Westinghouse Research Laboratory (1967-1976), and United Kingdom Atomic Research Establishment (1965-1967). He received his degrees from Rutgers University, BS in Ceramics in 1961 and Pennsylvania State University, Ph.D. in Solid State Technology in 1965. Dr. Lange has published over 185 papers and holds 10 patents relating to the ceramics field.

Prior, Current, or Pending Support

A similar proposal was submitted on June 12, 1993 to the 1993 NSF Phase I SBIR solicitation. Curtis Griffin will be the PI for this project entitled "Laminated Object Manufacturing of an Advanced Ceramic Composite with Extremely High Toughness".

Cost Proposal

The total budget is shown in the attached Appendix C with details in Appendix C.1. The monthly and final reports will be established as contract line-item deliverables. Billing will be monthly through submission of a DD-250, Material Inspection and Receiving Report.

Prior SBIR Awards:

Lone Peak has not received more than 15 Phase II awards.

References

1. Marshall, D.B., Ratto, J.J., and Lange, F.F., "Enhanced Fracture Toughness in Layered Microcomposites of Ce-ZrO2 and Al2O3", J. Am. Cer. Soc., 74[12]:2979-2987, 1991 2. Marshall, D.B., "Crack Shielding in Ceria-Partially-Stabilized Zirconia", J. Am. Cer. Soc., 73[10]:3119-3121, 1990. 3. Chang, J.C., Velamakanni, B.V., Lange, F.F., and Pearson, D.S., "Centrifugal Consolidation of Al2O3 and Al2O3/ZrO2 Composite Slurries vs Interparticle Potentials: Particle Packing and Mass Segregation", J. Am. Cer. Soc., 74[9]:2201-2204, 1991. 4. Griffin, C.W., Daufenbach, J., and Feygin, M., "Flexible Manufacturing of Advanced Structural Ceramics Using Laminated Object Manufacturing Techniques", Final Report to DARPA, Arlington, Virginia under Contract DAAHO1-92-C-R244, 1992. 5. Yu, C-S., Shetty, D.K., "Transformation Zone Shape, Size, and Crack- Growth-Resistance (R-Curve) Behavior of Ceria-Partially-Stabilized Zirconia Polycrystals", J. Am. Cer. Soc., 72[6]:921-928, 1989. 6. Hannink, R.H.J. and Swain, M.V., "Metastability of Martenistic Transformation in a 12 mol% Ceria-Zirconia Alloy: I Deformation and Fracture Observations", J. Am. Cer. Soc., 72[1]:90-98, 1989. 7. Rose, L.R.F. and Swain, M.V., "Transformation Zone Shape in Ceria Partially Stabilized Zirconia" Acta. Metall., 36[4]:955-962, 1988. 8. Reyes-Morel, P.E. and Chen, I-W., "Transformation Plasticity of CeO2- Stabilized Tetragonal Zirconia Polycrystals: I Stress Assistance and Autocatalysis", J. Am. Cer. Soc., 72[8]:343-353, 1988. 9. Datasheet 7164C FP 20K, Coors Ceramics Company, Golden, CO, February 1989. 10. Stevens, R., Introduction to Zirconia, Magnesium Elektron Publication 113, London, England, pp 17-18, 1986. 11. Evans, A.G. and Marshall, D.B., "The Mechanical Behavior of Ceramic Matrix Composites", Acta. Metall., 37[10]:2607-2683, 1989. 12. Clegg, W.J., Kendall, K., Alford, N.M., Button, T.W., and Birchall, J.D., "A Simple Way to Make Tough Ceramics", Nature (London), 347:455- 457, 1990. 13. Heuer, A.H., Readey, M.J., and Steinbrech, R., "Resistance Curve Behavior of Supertough MgO Partially Stabilized ZrO2", Mater. Sci. Eng., A105/106:83-89, 1988 14. "Desktop Prototyping Experiment Produces Ceramic Blade", Design News, 3-25-91, pp.32-33. 15. Lakshminarayan, U., G. Zong, W. Richards, and H. Marcus, "Solid Free Form Fabrication of Ceramics", to be published in the Proceedings of the Synthesis and Processing of Ceramics Symposium, Fall Meeting of the Material Research Society, Boston, MA, December 2-6, 1991. 16. Lauder, A., M. Cima, T. Fan, and E. Sachs, "Three Dimensional Printing: Surface Finish and Microstructure of Rapid Prototyped Components", to be published in the Proceedings of the Synthesis and Processing of Ceramics Symposium, Fall Meeting of the Material Research Society, Boston, MA, December 2-6, 1991. 17. Feygin, M. and B. Hsieh, "Laminated Object Manufacturing: A Simpler Process", The Second FreeForm Fabrication Symposium, University of Texas at Austin, August 1991. 18. Feygin, M., B. Hsieh, and M. Melkanoff, "Laminated Object Manufacturing (LOM): A New Tool in the CIM World", submitted for publication in the proceedings of PROLAMAT 1992, Tokyo, Japan, June 1992. 19. "Laminated Object Manufacturing", Rapid Prototyping Report, Volume 1, Number 1 June 1991, pages 1,6-8. 20. Pacheco, Joselito M., "Rapid Prototyping", MTIAC Report TA-91-01, January 1991. 21. Wood, Lamont, "Desktop Prototyping", Byte, May 1991, pp. 137-142. 22. Bak, David J., "Quick Path to Prototype Tooling", Design News, 6-25- 90, pp.116-117. 23. Haase, Bruce, "Stereolithography at Chrysler Motors", Microcad News, August 1990. 24. Machlis, Sharon, "Cubital Claims Advantages Over Stereolithography", Design News, 10-22-90, page 30. 25. "Powerful Duo: CAD Plus Prototypes", Design News, 11-19-90, page 91, 1991. 26. Renault, T., Ogale, A.A., Dooley, R.L., Bagchi, A., Jara-Almonte, C.C., "Photolithography for Composites Manufacturing", Fiber-Tex 1990 The Fourth Conference on Advanced Engineering Fibers and Textile Structures for Composites, John D. Buckley, editor NASA Conference Publication 3128: 111-117, 1991. 27. Program Information Package for Defense Technology Conversion, Reinvestment, and Transition Assistance, March 10, 1993, pp 2-1.