The influence of grain size on the twinning stress of an Fe-15Mn-2Al-2Si-0.7C twinning induced plasticity (TWIP) steel has been investigated. Five grain sizes were obtained using a combination of cold rolling and annealing. Electron backscatter diffraction (EBSD) analysis revealed that the material exhibited a typical cold rolled and annealed texture. Tensile testing showed the yield stress to increase with decreasing grain size, however, the ductility of the material was not substantially affected by a reduction in grain size. Cyclic tensile testing at sub-yield stresses indicated the accumulation of plastic strain with each cycle, consequently the nucleation stress for twinning was determined. The twin stress was found to increase with decreasing grain size. Furthermore, the amount of strain accumulated was greater in the coarser grain material. It is believed that this is due to a difference in the twin thickness, which is influenced by the initial grain size of the material. SEM and TEM analysis of the material deformed to 5 % strain revealed thinner primary twins in the fine grain material compared to the coarse grain. TEM examination also showed the dislocation arrangement is affected by the grain size. Furthermore, a larger fraction of stacking faults was observed in the coarse-grained material. It is concluded that the twin nucleation stress and also the thickness of the deformation twins in a TWIP steel, is influenced by the initial grain size of the material. In addition grain refinement results in a boost in strength and energy absorption capabilities in the material.
Precipitate evolution in Ti-5Al-5Mo-5V-3Cr-0.3Fe wt.% (Ti-5553) has been studied in-situ by small angle neutron scattering (SANS) during a two step ageing heat treatment of 300• C/8 h + 500• C/2 h. The first heat treatment step precipitates ω, with a corresponding increase in hardness of ∼ 15% compared to quenched material. The second heat treatment step precipitates fine scale α from the ω phase, with a ∼ 90% increase in hardness compared to quenched material.The SANS measurements are complemented by atom probe tomography (APT) to give compositional information, ex-situ transmission electron microscopy (TEM) to confirm phase identification and size distribution locally, and X-ray diffraction (XRD) for additional confirmation of phase identification.The ω phase is depleted in all the solute additions following 300• C/8 h ageing heat treatment. The volume fraction of the ω phase from APT is estimated to be ∼ 7%. SANS modelling is consistent with disc shaped particles for the ω phase. The mean particle diameter increases from ∼ 7.5 nm to 9.5 nm diameter between 1 h and 8 h heat treatment at 300• C, while the thickness increases from ∼ 4 nm to ∼ 5 nm. The SANS model estimates the volume fraction to be ∼ 10% for the 8 h heat treatment, using the phase compositions from APT.
This paper represents the first application of small angle neutron scattering (SANS) to the study of precipitate nucleation and growth in -Ti alloys in an attempt to observe both the precipitation process in-situ and to quantify the evolving microstructure that a↵ects mechanical behaviour. TEM suggests that athermal ! can be induced by cold-rolling Gum metal, a -Ti alloy. During thermal exposure at 400 C, isothermal ! particles precipitate at a greater rate in cold-rolled material than in the recovered, hot deformed state. SANS modelling is consistent with disc shaped nanoparticles, with length and radius under 6nm after thermal exposures up to 16 h. Modelling suggests that the nanoprecipitate volume fraction and extent of Nb partitioning to the matrix is greater in the cold-rolled material than the extruded. The results show that nucleation and growth of the nanoprecipitates impart strengthening to the alloy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.