Papers by Keyword: Alloy Development

Abstract: Indefinite-chill materials are used as shell materials for cast work rolls for surface-critical applications in hot rolling mills. Besides a smooth surface quality, a low sticking tendency and low sensitivity against incidents in the rolling mill, the work rolls need the highest wear resistance possible. The microstructure of the indefinite-chill material consists of various carbides (cementite up to 40 area-%) and up to 5 area-% of graphite embedded in tempered martensite. To increase the wear resistance of this material group, the comparably soft cementite has to be replaced by more wear resistant carbides such as MC, M₂C or M₆C. This can be achieved by increasing the amount of carbide forming elements such as Nb, V, Mo, W or Cr. Nevertheless it is important to maintain a certain amount of graphite in the microstructure to avoid sticking to the rolled material and to lower the sensitivity against mill incidents. It is well known that high amounts of carbide forming elements limit the graphite precipitation and therefore a sophisticated alloying concept is required for this material type. Not only the effects of matrix elements such as Si, Mn, Ni and Co but also the effects of Cr, Mo, W, Nb and V were studied in an intensive research project. This work gives an insight in the results of the project based on the example of the effects of Si and Cr on the phase amounts and the composition of the cementite phase.

Abstract: Challenging issues concerning energy efficiency and environmental politics require novel approaches to materials design. A recent example with regard to structural materials is the emergence of lightweight intermetallic TiAl alloys. Their excellent high-temperature mechanical properties, low density, and high stiffness constitute a profile perfectly suitable for their application as advanced aero-engine turbine blades or as turbocharger turbine wheels in next-generation automotive engines. Advanced so-called 3^rd generation TiAl alloys, such as the TNM alloy described in this paper, are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments.

Abstract: Urgent needs concerning energy efficiency and environmental politics require novel approaches to materials design. One recent example is thereby the implementation of light-weight intermetallic titanium aluminides as structural materials for the application in turbine blades of aero-engines as well as in turbocharger turbine wheels for the next generation of automotive engines. Each production process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and / or subsequent heat-treatments. To develop sound and sustainable processing routes, knowledge on solidification processes and phase transformation sequences in advanced TiAl alloys is fundamental. Therefore, in-situ diffraction techniques employing synchrotron radiation and neutrons were used for establishing phase fraction diagrams, investigating advanced heat-treatments as well as for optimizing thermo-mechanical processing. Summarizing all results a consistent picture regarding microstructure formation and its impact on mechanical properties in advanced multi-phase TiAl alloys can be given.

Abstract: After almost three decades of intensive fundamental research and development activities, intermetallic titanium aluminides based on the ordered γ-TiAl phase have found applications in aircraft and automotive engine industry. The advantages of this class of innovative high-temperature materials are their low density and their good strength and creep properties up to 750°C as well as their good oxidation and burn resistance. Advanced TiAl alloys are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments. The background of these heat treatments is at least twofold, i.e. concurrent increase of ductility at room temperature and creep strength at elevated temperature.

Abstract: The focus of this paper is set on technical achievements and challenges - however, these are most often closely linked to economical or ecological targets set by customers or society. Ideally, an alloy or process optimization leads to improved properties, reduced cost, and reduced emissions. With a continuously growing understanding of the underlying materials science, supported by novel computer simulation, improved alloys and processing routes have been developed. Many of the recent improvements were related to the thermal-mechanical treatment of high strength alloys for enhanced light weight design. Currently and in the future, the focus will be on sustainable development along the entire process chain, with special attention to the recycling of used products and high recycled content in new products. The optimized utilization of resources (e.g. materials, energy, etc.) will require the close cooperation of materials suppliers, product designers and manufacturers as well as R&D facilities to reconsider given material specifications and processing routes.

Abstract: The main alloys which have been semi-solid processed commercially are based on aluminium (particularly the cast compositions) and magnesium. There is a strong drive to broaden the range of alloys to the wrought compositions for aluminium, more creep-resistant magnesium recipes and to higher temperature alloys such as those based on copper, steels, stellites and cast irons. This paper will summarise the issues with such development including the scientific and practical issues for alloy design and the thermodynamic prediction of alloys suitable for semi-solid processing. After an initial introduction to semi-solid processing routes, the most important alloy systems for semi-solid processing from a development point of view (aluminium, magnesium, steels and composites- including nanocomposites) will be discussed. The key issues of alloy design specifically for semi-solid processing will be drawn out through the text.

Abstract: Currently most commercial magnesium alloys are based on the Mg-Al system and it is reasonably well developed. Although the Mg-Al based alloy system has excellent castability and adequate ambient temperature mechanical properties, it shows poor creep resistance. Therefore, our group has focused on finding the way to improve the creep properties of Mg alloys. This paper presents a brief summary of the research achievements in this area recently made by AFML(Advance Functional Materials Lab in PNU, Korea). The properties of newly designed Mg alloys in our group are presented and compared with the properties of commercial A356 alloy.

Abstract: This paper summarizes the development of new cast and wrought magnesium alloys using computational thermodynamics tools and experimental approach. The Mg-Al-Ca alloys show excellent creep resistance due to the formation of high-temperature (Mg,Al)₂Ca phase. The Mg-Al-Sn alloys are designed for mechanical properties and corrosion resistance through the optimization of Mg₁₇Al₁₂ and Mg₂Sn phases in the microstructure. In the Mg-Zn-Ce system, Zn provides strength through solid solution strengthening while Ce increases the ductility via improved texture. Mg-Nd-Zn is a heat-treatable alloy system based on the precipitation hardening of Mg₁₂Nd phase.

Abstract: Development and processing of high-temperature materials is the key to technological progress in engineering areas where materials have to meet extreme requirements. Examples for such areas are the aerospace and automotive industries. New structural materials have to be stronger, stiffer and lighter to withstand the extremely demanding conditions in the next generation of aero- and automotive engines. Intermetallic -TiAl based alloys exhibit numerous attractive properties which meet these demands. These properties include high melting point, low density, high specific elastic modulus, good oxidation and burn resistance, and high specific strength up to application temperatures of 700 to 800°C. Thus, current -TiAl based alloys outperform advanced Ti-based alloys and have the potential to replace heavy Ni-based superalloys.

Abstract: Although Ni-base superalloys meet the gas turbine needs of today, they are used very close to their melting range. Demands for applications at higher temperatures are presently met partly through component cooling and application of thermal barrier coatings. However, this approach can not be sustained indefinitely unless the base metal melting temperature is also significantly increased. Rhenium addition can substantially increase the melting point in Co-base alloys and thereby provide a unique opportunity in the development of new alloys for very high temperatures – e.g. for applications at +100°C metal temperature above present day single crystal Ni-base superalloys. The design considerations behind the Co-Re alloy development are presented in this paper. Selected results from the alloy development studies are also presented.