A new approach to increase the tensile performance of high entropy alloys (HEAs) by producing a duplex ultrafine-grained (UFG) structure was reported in this work. A novel HEA based on the CoCrFeNiMn system with substantial amounts of Al and C was used for the illustration of this approach. In the as-cast condition the alloy had almost entirely a single face-centered cubic (fcc) phase structure with an insignificant amount of M 23 C 6 carbides. After cold rolling and annealing at 800-1000°C an increased amount of fine second phases, namely M 23 C 6 carbides and B2 phase, effectively pinned boundaries of recrystallized fcc grains. As a result, a duplex UFG structure composed of the recrystallized fcc grains and M 23 C 6 and B2 particles was produced. The alloy with the UFG structure demonstrated attractive mechanical properties. For example, after annealing at 900°C the alloy had the yield strength of 785 MPa, the ultimate tensile strength of 985 MPa, and elongation to fracture of 32%. The phase composition of the alloy in different conditions was compared with the equilibrium phase diagram obtained using a Thermo-Calc software. Strengthening mechanisms were qualitatively analyzed, and some possibilities for further improvement of strength of the alloy were discussed.
This work aims to establish a scientific and engineering background in the production of cast multicomponent alloys and metal-martix composite (MMCs) via Self-Propagating High Temperature Synthesis (SHS, combustion synthesis) which is a novel process technique regarding fast and low-cost production ability. We carried out the search for reactive systems and process parameters that would ensure preparation of cast multicomponent materials in a single process. The principles and methods of the SHS thermite-type reaction processes have been investigated under high-gravity values applying loads up to 1000 g with special centrifuge set-up. In this way we expected to improve the yield of target product, remove gaseous byproducts, diminish the grain size in the product, and make product composition more uniform. The obtained results can be expected to make a theoretical background for industrial-scale manufacturing of heat-resistant intermetallic alloys, master alloys, catalysts, MMCs etc.
Самораспространяющийся высокотемпературный синтез марки ПА4 в количестве 5 % в СВСсмесь позво ляет на порядок уменьшить размер синтезируе мых частиц карбидной фазы TiС с 2-4 до 0,17-0,35 мкм, т. е. достичь уровня ультрадисперсной армирующей фазы в литом композите Al-10%TiС. А замена 30 % металлического титана в СВСсмеси на галоидную титансодержащую соль Na 2 TiF 6 дает возможность синтезировать частицы TiC разме ром менее 100 нм, т. е. достичь уровня наноди сперсной армирующей фазы в этом композите.
Работа выполнена при поддержке Министерства образования и науки РФ в рамках ФЦП «Исследования и разработки по приоритетнымнаправлениям развития научно-технологического комплекса России на 2007-2013 годы» (государственный контракт № 14.513.11.0042).
Pilot-scale series of cast Ti-Al, Ti-Al-Nb, (Ni, Co, Mn)Al x , Ni-Cr-Al-Si-C, and Co-V-Al-Si-C alloys were produced by thermit-type SHS under high gravity for their potential use as heat-resistant materials, master alloys, precursors for catalysts, etc.
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