Processing and characterization of high strength wear resistant materials

Abstract

This project plans to further consolidate and extend a previous PRONEX project No.664203/97-3. In the execution of the previous PRONEX project, significant progress took place, both in terms of improved collaborative work among the participants and results. The results of this interaction can be seen from the number of publications, the patent request, the products (inserts, punches, etc) and from the extent of interest shown by companies to test our products. These are shown in 'previous results' of this project. The objective of the PRONEX project was to extend further, two PADCT projects that were carried out in IPEN. The objective of one of these projects was to install and consolidate, in Brazil, the powder metallurgy based technology to manufacture high speed steel components. The objective of the other project was to master the techniques for processing advanced structural ceramic materials, using normal sintering, gas assisted sintering, hot pressing and hot isostatic pressing. These two projects had reached a stage that a decision was taken to redirect the objectives towards a more applied context, like the development of methods to obtain ceramic and metallic materials for use as cutting tools. In this context, partnership with the mechanical engineering departments of EPUSP and UFSC was very important for evaluating wear resistance and performance in the field, respectively. Finally, the support given to the materials characterization and processing laboratory in UFRN was based on the knowledge of the other participants in this area of material science. Organization in the form of a nucleus enabled large scale interaction among the participants. This type of organization a/so enabled abilities to be complemented, which resulted from interactions among the various groups involved in the project. The inclusion of an emerging group (UFRN/Physics Department) addressed the issue of expansion of human resource development and improvement of experimental infrastructure, besides overall development in science and technology The Materials Group in IPEN is well known for joint work in the areas of (a) metallic materials: The projects PADCT-NM 62.0102/94-2, RHAE-ME 610016/96-2, PRONEX 664203/1997-3, RECOPE-Finep-ref. 3780/96, FAPESP 99/07764-7 enabled mastering of the liquid phase vacuum sintering process, which in turn enabled the manufacture of complex shaped pieces (near net shape) and in requesting a patent: sintered high speed steel interchangeable insert (no pi 0202472-1); (b) ceramic materials: the project PADCT -NM initiated the development of covalent ceramic materials in Brazil; RHAE projects, thematic FAPESP project 97/01114-5 and two PROBRAL projects (with German institutions); all of which, permitted the extension and consolidation of this' area of research. Recently, another joint project between the Company Hurth-lnfer and the Powder Metallurgy Group of the Materials Science and Technology Center of IPEN was approved. This RHAE Innovation project, Process: 552293/02-4, titled: Development and Manufacture of Drills and Techno-Economic Evaluation of Vacuum Heat Treatment of Sintered High Speed Steels. The results obtained so far, which is proof of being able to consolidate, and the projects that were approved during these years, have been the motivating force behind this request to continue to work in this area and to propose a new PRONEX project. General Objective Processing, using powder technology, of ceramic materials and high speed steels with superior mechanical properties and wear resistance. Specific objectives Develop the complete process cycle for manufacturing liquid phase sintered high speed steels, including water atomization to obtain powders, vacuum sintering and pressing, forming and heat treatments. The high speed steels to be developed, will be with conventional compositions and will be composites with NbC additions, to improve wear resistance while fracture toughness is maintained. Obtain silicon nitride based and silicon carbide based covalent ceramic materials and alumina composites. Adequate processing methods will be used to obtain high density materials with controlled microstructures, to optimize properties related to wear resistance. Manufacture high speed steel and ceramic compacts cutting tools for machining and for other wear resistant tools. Develop coating processes for the compacts to improve its performance. Evaluate the performance of these materials, with respect to machinability and durability (wear) and compare with existing materials. Methodology The main activities are: .Obtain atomized metallic high speed steel powders; .Addition of additives/binding agents/lubricants; .Grinding/homogenization; .Drying (spray dryer); .Pressing (uniaxial/isostatic); .Removing binding agents/lubricants; .Densification (sintering; hot pressing; hot isostatic pressing); .Final finishing; .Chemical and physical characterization of the raw materials, through particle size analysis, specific surface area analysis, electron microscopy and x-ray diffraction; .Determine the desired composition from phase diagrams available in literature; .Pressing of the raw materials in the predetermined proportions; .Grinding and homogenization; .Forming; .Determination of green density by the geometric method; .Study the sintering variables such as heating rate, duration, temperature, sintering atmosphere and applied pressure; .Determine the phases present by x-ray diffraction; .Determine the density using geometric and hydrostatic methods; .Study specimens using scanning electron microscopy and determine the distribution, size and shape of the constituents .Transmission electron microscopic observations, involving light and dark fields, selected area electron diffraction, dark field de-focusing from the diffusely scattered electrons, to determine the crystalline structure of the grains, the existence of amorphous phases, the formation of crystalline interfaces, preferential orientation during crystallization or grain growth and study defects. Optimization of material processing parameters, based on results .Determination of mechanical properties .Obtain tools with specific geometries .Coating of tools .Machining tests to determine machinability .Wear tests on tools and tribological tests Activities of each institution involved in the project .IPT will be responsible for atomization of the high speed steel powders .IPEN will be responsible for the processing of both metallic and ceramic materials, preparation of the compacts and tools, physical, chemical and microstructural characterization and correlation of microstructure x performance results .Characterization of wear behavior will be carried out by EPUSP. EPUSP will be responsible for the characterization of fracture toughness by Chevron method. UFRN will be responsible for coating the compacts and the tools. (AU)