No abstract
Poor thermal shock and resistance to crack propagation have had a negative influence on the acceptance of ceramics for components in air breathing engine applications. In comparison with their metallic counterparts, they are less predictable and there is limited historical in-use data available. They have therefore been considered primarily for non-load bearing applications such as flaps and seals, flame holders and covers. A fibrous monolith, ceramic hybrid between a Si 3 N 4 core with a weak BN interface has been evaluated for non-load bearing applications in air breathing engines where a high degree of thermal shock resistance is required. The fibrous monolith architecture confines damage to local regions and although the overall strength is typically reduced, the macroscopic damage tolerance and thermal shock resistance is improved over monolithic S 3 N 4 of similar compositions. Two different architectural scales with a cell size of 150µm and 30µm were investigated. Both architectures showed a similar response with no loss in strength when quenched from below 800°C and no loss in modulus when quenched from 1000°C into water. Cyclic thermal shock from 600°C showed no change in modulus but at 1000°C a gradual drop in the modulus was observed. Microstructural assessment of the Si 3 N 4 core and BN phases showed microcracking of the BN phase following thermal shock but no discernable changes in the Si 3 N 4 phase. The thermal shock resistance of the FM Si 3 N 4 / BN structure is improved over monolithic Si 3 N 4 due to the ability of the weak BN interface to preferentially microcrack and accommodate strain. Improved thermal shock resistance has been demonstrated in water quench tests as well as in a gas burner rig test where heating rates and temperatures more representative of those observed in engine applications have been investigated.
During this reporting period, work continued on development of formulations using the materials identified as contenders for the fibrous monolith wear resistant components. The FM structures fabricated were: diamond/WC-Co, B 4 C/WC-Co, TiB 2 /WC-Co, WC-Co/Co, WC-Co/WC-Co. Results of our consolidation densification studies on these systems lead to the down-selection of WC-Co/WC-Co, WC-Co/Co and diamond/WC-Co for further development for mining applications including drill bit inserts, roof bit inserts, radial tools conical tools and wear plates (WC-Co based system only) for earth moving equipment. Prototype component fabrication focused on the fabrication of WC-Co/WC-Co FM conical tools, diamond/WC-Co coated drill bit insert prototypes. Fabrication of WC-Co/WC-Co FM insert prototypes for a grader blade is also underway. ACR plans to initiate field-testing of the drill bit insert prototypes and the grader blade insert this summer (2002). The first WC-Co/WC-Co FM conical tool prototypes were sent to Kennametal for evaluation towards the end of the current reporting period.4
During the reporting period, work continued on development of formulations using the materials down-selected from the initially identified contenders for the fibrous monolith wear resistant components. The FM systems studied were: WC-Co/WC-Co, WC-Co/Co, diamond/WC-Co, and Al 2 O 3 /Al 2 O 3 -TiCN. Extrudable formulations for the materials listed were developed during the first twelve months of this effort, and work during the reporting period was focused on the development of optimized binder removal processes. A twostage binder removal process was developed that resulted in prototype parts free of voids and other internal defects. In addition, changes in the binder removal atmosphere resulted in the apparent elimination of residual carbon, an important consideration when consolidating WC-Co containing systems. Using the improved binder removal processes, parts were consolidated by both sintering and hot pressing to >99% theoretical density. Samples of these materials were sent to Kyocera for mechanical evaluations. Fabrication of drill bit inserts was begun, and binder removal begun during the reporting period. A total of 24 green inserts were fabricated, and will be consolidated and delivered for field testing during the upcoming reporting period.
The work performed on this program was to develop wear resistant, tough FM composite materials with efforts focused on WC-Co based FM systems. The materials were developed for use in mining industry wear applications. Components of interest were drill bit inserts for drilling blast holes. Other component applications investigated included wear plates for a variety of equipment such as pit shovels, wear surfaces for conveyors, milling media for ball milling operations, hydrocyclone cones, grader blades and dozer teeth. Cross-cutting technologies investigated included hot metal extrusion dies, drill bits for circuit board fabrication, cutting tools for cast iron and aluminum machining.An important part of the work was identification of the standard materials used in drilling applications. A materials trade study to determine those metals and ceramics used for mining applications provided guidance for the most important materials to be investigated. WC-Co and diamond combinations were shown to have the most desirable properties. Other considerations such as fabrication technique and the ability to consolidate shifted the focus away from diamond materials and toward WC-Co.Cooperating partners such as Kennametal and Kyocera assisted with supplies, evaluations of material systems, fabricated parts and suggestions for cross-cutting technology applications for FM architectures. Kennametal provided the raw materials (WC-Co and Al-TiCN powders) for the extent of the material evaluations. Kyocera shared their research into various FM systems and provided laboratory testing of fabricated materials.Field testing provided by partners Superior Rock Bit and Brady Mining and Construction provided insight into the performance of the fabricated materials under actual operational conditions. Additional field testing of cross-cutting technology, the extrusion of hot metals, at Extruded Metals showed the potential for additional market development. 4 INTRODUCTIONThis program addresses the mining industry's need for improved components for wear resistance. The cost/performance ratio drives the application of components and materials used in mining applications. The mining industry traditionally had little use for advanced wear resistant materials due to their high cost relative to their improved durability. The goal of this program is to offer advanced wear resistant materials, in the form of fibrous monolith composites, which will overcome the cost/performance barrier traditionally associated with advanced materials and significantly increase the wear life of targeted components. Materials systems that exhibit promise as a crosscutting technology where resistance to wear is important will also be developed. Research will be performed on other applications, such as metal cutting tools, as crosscutting technologies are developed and translated into other industries.The program is a collaborative effort of component manufacturers, end users, a national laboratory, and universities. The program will target three particular wear ...
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