Functionally Graded Coating
The Production of Functionally Graded Coatings Using Intense Millimeter-Wave Beams
Tech Area / Field
- MAT-SYN/Materials Synthesis and Processing/Materials
8 Project completed
Senior Project Manager
Novozhilov V V
Russian Academy of Sciences / Institute of Applied Physics, Russia, N. Novgorod reg., N. Novgorod
- VNIIEF, Russia, N. Novgorod reg., Sarov
- National Aerospace Laboratory / Kakuda Research Center, Japan, Kakuda\nOsaka University / Joining & Welding Research Institute, Japan, Osaka
Project summaryThe objective of this Proposal is to develop a novel method for fabrication of functionally graded coatings using intense beams of millimeter-wave radiation for volumetric and controllable heating of the coating materials. Another principal objective is to develop both physical fundamentals and practical instruments for surface processing of materials by intense millimeter-wave beams. The need for novel, improved materials, capable of meeting the demanding performance requirements, is dictated by recent developments in such technologies as energy production, ceramic engines and cutting tools, gas turbines, nuclear fusion, etc. The most promising approach to this problem is based on the concept of functionally graded materials (FGM). The principal idea of the ongoing research activities within the field of FGM is to combine dissimilar materials in a way that takes advantages of each material type.
For most applications, the functionally graded materials are designed in the form of coatings whose composition, microstructure, and properties vary over their thickness. A great demand for such materials is most conspicuous among high temperature applications, mainly in the field of energy generation, conversion, and usage. Besides, many examples of laboratory-scale research prove the fruitfulness of the FGM approach in the development of thermal barrier coatings, corrosion and wear resistive coatings, materials for thermoelectric and thermoionic energy conversion, biomaterials, etc.
In recent years many processing methods have been extensively explored to create FGM, including thermal spray, powder metallurgy, chemical and physical vapor deposition, self-propagating high temperature synthesis, thermal diffusion treatment, and so on. The most acute problem challenging each of the processing methods is the need to minimize thermal and residual stresses in the coatings.
The main idea of the proposal is based upon the unique possibility to create functionally graded coatings with low thermal and residual stresses using selective and controllable volumetric deposition of the energy of electromagnetic waves in the millimeter-wave range. The most important advantage of the millimeter-wave beam processing technique in the development of functionally graded coatings with minimized thermal and residual stresses is controllable, internal absorption of the millimeter-wave radiation within the entire volume of the coating. In contrast to thermal treatment methods based on the heating from surface, the millimeter-wave beam processing technique offers an opportunity to control energy deposition and temperature in the bulk of FGM. Compositional selectivity of microwave energy absorption makes it possible to create purposely such temperature profiles across the coating thickness that provide controllable evolution of the coating microstructure and prevent excessive thermal stresses during processing. In that way, the millimeter-wave beam processing technique solves, by tailored energy deposition, the problem of thermal expansion mismatch that obstructs other processing methods.
Since microwave absorptivity of many materials increases with frequency, use of the millimeter-wave radiation (of frequency 30 GHz and higher) allows significant expansion of the range of materials which can be effectively and controllably heated and, as a result, the range of functionally graded coatings produced with the millimeter-wave beams, compared to the more commonly used microwave radiation of frequencies 915 MHz and 2.45 GHz. In particular, refractive materials based on oxides of transition metals and nitrides, commonly considered transparent for microwaves, can be effectively heated by the millimeter-wave radiation.
The scientists participating in this Proposal possess a unique opportunity to develop the method of FGM fabrication using millimeter-wave radiation. The IAP team has created a unique gyrotron system facility that includes two 30 GHz – 20 kW and a 83 GHz – 20 kW continuous operation gyrotron systems for materials processing and several 110 – 170 GHz gyrotrons with output power of hundreds kW in pulse operation. Among the researchers participating in this Proposal there are experts in applications of intense millimeter waves, including millimeter-wave methods of engineering and synthesis of materials with novel properties, experienced material scientists working in the field of ceramics and composites, and developers of power millimeter-wave devices. They have accomplished a broad range of experimental studies in the field of physics of millimeter-wave interaction with materials and developed the theory of non-thermal microwave field effect in crystalline solids.
The expected results of implementation of the proposed project are the following:
— knowledge will be gained that is needed for developing the technology for creating functionally graded coatings using millimeter-wave electromagnetic radiation. A novel approach to creation of functionally graded coatings based on their volumetric heating will be developed. Although the proposal is aimed at the development of functionally graded coatings for high-temperature applications, the resulting methodology can equally be applied to the creation of FGM for electronic, antiwear, biomedicine and other applications;
— upgrade and adaptation of the millimeter-wave processing equipment for purposes of surface processing of materials by intense beams of electromagnetic radiation will be accomplished. Test specimens of gas turbine blades with the thermal barrier coatings created by millimeter-wave processing will be produced. Upon completion of the proposed project, the technology development stage is planned by the teams participating in the proposal. The millimeter-wave processing equipment upgraded in the course of implementation of the proposed project will serve as a prototype for developing industrial-scale gyrotron systems needed for the transfer of the technology to industry.
The use of microwave energy in high temperature processing entails such benefits as energy and labor saving, increase in productivity, reduction in wastes and environmental impact. For example, the specific energy consumption for ceramics sintering is reduced about one order of magnitude compared to conventional methods. The most significant economic benefits, however, are not even due to these savings but rather due to the potential to fabricate reliable functionally graded materials with improved performance properties, not achievable with other processing methods.
More than 2/3 of the full number of the project personnel will be scientists and specialists previously involved in weapon development. Facilities available at VNIIEF, in particular, the comprehensive analytical equipment, and personnel expertise in materials science will be directed to the development of a novel technology aimed to produce materials of great demand at the civil market. The international nature of the proposed collaboration, publication of the scientific results and their presentation at international conferences will promote integration of the scientists of CIS states into the international scientific community. The planned commercialization of the technology resulting from the project will contribute to the development of a market-based economy responsive to civil needs in the country.
The proposed activities are based on the experience gained in the course of implementation of a previous ISTC project on the application of millimeter-wave radiation for development of materials with novel properties. The use and further refinement of physical models and numerical simulation codes will be correlated at each stage with the data obtained experimentally. The developed general approach will be validated by producing thermal barrier coatings on actual energy production/ conversion components such as gas turbine blades, nozzles, heat exchangers etc. Due to the need to optimize the process over many variables, both simulation and experimental tasks will be done on an iterative basis, i.e., the work on each task will be repeatedly adjusted based on the results of the subsequent tasks.
For purposes of implementation of the proposed project, a number of upgrades in the existing millimeter-wave processing equipment is foreseen. These include design of radiation conversion components for shaping the gyrotron output radiation into a wavebeam needed for coating processing, and adaptation of the process control equipment to monitoring fast processes. For purposes of coating structure optimization, numerical simulation methods will be extensively used for such tasks as assessing millimeter-wave absorption of porous composite materials, modeling the dynamics of temperature fields within the coatings, and investigating the relationships between the temperature profile shape and thermal stresses. The principal experimental tasks are green coating preparation, millimeter-wave sintering, and characterization of the resulting materials. For the latter, a wide range of characterization methods will be used: densitometry, porosimetry, electron microscopy, energy dispersion X-ray analysis, X-ray diffractometry, laser mass-spectrometry, atomic force microscopy, hardness and fracture toughness indentation measurements, etc. As the result, correlation will be found between the regimes of millimeter-wave processing and the final parameters of materials, in particular, residual stress distribution, microstructure, and mechanical properties. The optimized coatings will be tested for their high temperature performance parameters such as thermal conductivity, thermal shock resistance and operation period to failure. By doing so, the maximum temperature of reliable operation will be determined.
An important role in the proposed project will be played by foreign collaborators from Japan. Among them are world-renowned leaders in the FGM research and a recognized expert in the field of application of millimeter-wave radiation in technology. The scope of cooperation with the foreign collaborators will include information exchange in the course of project implementation, shared use of sample materials, cross checks of results obtained in the course of project implementation, and conduction of joint seminars and workshops.