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The developtment of microstructure and its influence on creep properties has been studied in two Ti-48Al-2Cr-2Nb alloys. The addition of 0.9 atomic % Mo to the Ti-48Al-2Cr-2Nb composition results in the formation of the ordered B2 phase. The presence of this phase along with a small amount of alpha2 at grain boundaries was found to effectively limit grain growth at 1125 deg C during heat treatments that produce equiaxed gamma microstructures. The gamma -> alpha transformation produces a2 plates with several orientation variants within gamma grains during subsequent anneallng of the equiaxed gamma microstructures below the a-transus. Formation of this a2 morphology results from rapid up-quenching and this structure persists through annealing, cooling, and creep testing. Differences in minimum creep rates for several microstructures containing varying amounts multi or single variant gamma/a2 grains are shown to be minimal. The presence of Mo has also resulted in improved creep resistance in equiaxed gamma, and gamma + a2 + B2 structures as compared to similar microstructures in the Ti-48Al-2Cr-2Nb alloy. Deformation during creep at 760 deg C at stresses between 200 and 400 MPa occurs by a combination of twinning and dislocation glide without recrystallization, resulting in power-law stress exponents in the range of 6 to 9. On]y minimal strain path dependence of the minimum creep rate was detected in a comparison of creep rates in stress jump, stress drop and single stress tests.
The first book entirely dedicated to the topic emphasizes the relation between basic research and actual processing technologies. As such, it covers complex microstructures down to the nanometer scale, structure/property relationships and potential applications in key industries. From the contents: * Constitution * Thermophysical Constants * Phase Transformations and Microstructures * Deformation Behaviour * Strengthening Mechanisms * Creep * Fracture Behaviour * Fatigue * Oxidation Resistance and Related Issues * Alloy Design * Ingot Production and Component Casting * Powder Metallurgy * Wrought Processing * Joining * Surface Hardening * Applications and Component Assessment
A March 2003 meeting provided a forum for scientists to share information on progress in gamma TiAl alloys. Selected papers from the meeting, 77 in all, are presented here, and cover applications, fundamentals, alloy design and development, processing, joining, microstructure-property evaluation, an
The objective of this program was to investigate how carbon additions and Al content variation affects RT tensile properties and creep performance in gamma TiAl alloys. On the basis of the results from the work four alloys were selected within the composition range of Ti-(44.7-47.0) Al-(1.0-1.7)Cr-3.0Nb-0.2W-0.2B-(0.23-0.43)C-(0, 0.2)Si. Through extensive annealing/aging experiments, detailed observations of microstructure evolution, property measurements and analyses, comprehensive understanding was made in the carbide formation process. It was found that creep properties depend on the distribution of carbide particles, which is controlled not only by the aging process but also the amount ratio fo Al and carbon. From the results and analysis, new creep-resistant alloy compositions are suggested for further development.Kim, Young-Won and Kim, Sang-LanGlenn Research CenterCARBON; TENSILE PROPERTIES; CREEP STRENGTH; MICROSTRUCTURE; CREEP PROPERTIES; ANNEALING
Creep of a TiAl alloy, having a composition of Ti-47Al-2Cr-2Nb (in atom%) and a fine-grained, fully-lamellar structure, was carried out at 760 C and stresses between 69--723 MPa. It was found that, in addition to having good room temperature properties, the alloy exhibits higher creep resistance than other TiAl alloys with a similar composition. Both the creep data and microstructures of the alloy suggest that there exists a change in deformation mechanism from a glide-controlled process at high stresses to a recovery-controlled process at low stresses. Also, microstructural evidence indicates that the rate-controlling recovery mechanism is the climb of dislocation segments pinned by ledges at[gamma]/[alpha][sub 2] interfacial boundaries.
The first book entirely dedicated to the topic emphasizes the relation between basic research and actual processing technologies. As such, it covers complex microstructures down to the nanometer scale, structure/property relationships and potential applications in key industries. From the contents: * Constitution * Thermophysical Constants * Phase Transformations and Microstructures * Deformation Behaviour * Strengthening Mechanisms * Creep * Fracture Behaviour * Fatigue * Oxidation Resistance and Related Issues * Alloy Design * Ingot Production and Component Casting * Powder Metallurgy * Wrought Processing * Joining * Surface Hardening * Applications and Component Assessment
* Numerous line drawings with consistent format and units allow easy comparison of the behavior of a very wide range of materials * Transmission electron micrographs provide a direct insight in the basic microstructure of metals deforming at high temperatures * Extensive literature review of over 1000 references provide an excellent reference document, and a very balanced discussion Understanding the strength of materials at a range of temperatures is critically important to a huge number of researchers and practitioners from a wide range of fields and industry sectors including metallurgists, industrial designers, aerospace R&D personnel, and structural engineers. The most up-to date and comprehensive book in the field, Fundamentals of Creep in Metals and Alloys discusses the fundamentals of time-dependent plasticity or creep plasticity in metals, alloys and metallic compounds. This is the first book of its kind that provides broad coverage of a range of materials not just a sub-group such as metallic compounds, superalloys or crystals. As such it presents the most balanced view of creep for all materials scientists. The theory of all of these phenomena are extensively reviewed and analysed in view of an extensive bibliography that includes the most recent publications in the field. All sections of the book have undergone extensive peer review and therefore the reader can be sure they have access to the most up-to-date research, fully interrogated, from the world’s leading investigators. · Numerous line drawings with consistent format and units allow easy comparison of the behavior of a very wide range of materials· Transmission electron micrographs provide a direct insight in the basic microstructure of metals deforming at high temperatures· Extensive literature review of over 1000 references provide an excellent reference document, and a very balanced discussion