| Zirconium metal has excellent resistance to radiation damage and atomic oxygen corrosion.In addition,zirconium has a low expansion coefficient,so it has the potential to serve in an alternate temperature environment.Compared with alloy steels and titanium alloys which are widely used in active components of space vehicles,zirconium has more potential applications in aerospace industry.Because of the infinite mutual solubility of zirconium and titanium,titanium element can be added to the zirconium matrix to meet the performance requirement of the structural material.Therefore,Zr-Ti-based alloys have a very broad application prospect in aerospace.In this paper,by means of electron baskscatter diffraction?EBSD?,electron channeling contrast?ECC?,X-ray diffraction?XRD?,optical microscope?OM?and microhardness technologies,we focus on noe novel?-51.1Zr40.2Ti4.5Al4.2V alloy and systematically investigate the microstructure evolution and the effect of prior?grain sizes on the variant selection of?phase during the furnace cooling period as well as the microstructure evolution during room temperature compression progress.The main conclusions are summarized below:???transformation will occur during the furnace cooling progress in?-ZrTiAlV alloy.During this period,?phase firstly nucleates at the grain boundaries,and the orientation of?GB is effected by the adjacent prior?grains,so the?GB with{0001}?pole parallel to the common{110}?pole of adjacent?grains will present preferred nucleation at?grain boundaries.The major nucleation mechanism of?WGB is interface instability nucleation mechanism,and sympathetic nucleation mechanism can be rarely observed.Therefore,?WGB grains nucleate and grow into the interior of prior?grains by inheriting the orientation of?GB.In order to coordinate the strain energy formed during the???transformation,?WI developes three-variant cluster by so-called self-accommodation mechanism,the three variants are related to each other by an angle/axis pair 60°/<112?0>.With the decrease of furnace-cooling temperature,the relative volume fraction of?phase increases,resulting in the increasement of hardness.There is a linear relationship between hardness and the relative volume fraction of?phase.Theoretical 12?variants can be obtained during the furnace cooling from 750?to550?in?-ZrTiAlV alloy.All?variants formed within one parent?grain meet the axle/angle relationships predicted by Burgers theory.For smaller prior?grains,only?GB grain with{0001}?paralleling to the common{110}?pole of adjacent?grains nucleates at the grain boundary,according to the interface instability nucleation mechanism of?WGB,the orientation of?GB can propogate to the inside of the parent?grain.As a result of this,?variant holding the same orientation with?GB the will widely distribute within the parent?grain,resulting in stronger variant selection in smaller prior?grains.For bigger prior?grains,besides the formation of aforementioned?GB,?GB grains with other orientations also nucleate at the grain boundary.Although the former preferentially nucleate,?variants with different orientations obstruct each other during the next period,so?variants whose orientations are parallel to the common{110}?poles just gather near the grain boundaries,and these variants uniformly distribute inside the parent?grain,which cause weaker variant selection in bigger prior?grains.Stress induced martensitic transformation??????will occur during the room temperature compression progress of?-ZrTiAlV alloy.As the compression strain increases,several prior?grains totally transform to??phase.{101?2}<101?1>twin is also observed in??phase and the number of twin increases with the continuous compression.The misorientation distribution near the grain boundaries in??phase shows that grain boundaries will hinder the growth of??phase during compression,so the area near the boundaries will accumulate a lot of strain,which will promote stress induced martensitic transformation in adjacent prior?grains and form new??phase. |
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