Grain boundary strengthening

About: Grain boundary strengthening is a research topic. Over the lifetime, 8585 publications have been published within this topic receiving 286232 citations.

Developing stable ne-grain microstructures by large strain deformation

Abstract: Methods of deforming metals to large strains are reviewed and the process of equal channel angular extrusion is analysed in detail. The development of microstructure during large strain deformation is discussed, and it is concluded that the main cri- terion for the formation of a sub-micron grain structure is the generation of a suf- ciently large fraction (greater than 0.7) of high-angle grain boundary during the deformation process. For aluminium alloys, it is found that a low-temperature anneal is required to convert the deformed microstructure into an equiaxed grain structure. The material, microstructural and processing factors that influence the formation of such ne-grain microstructures are discussed, and the stability of these microstruc- tures at elevated temperatures is considered. The grain size of a metal has a large eect on its properties, and renement of the grain size has many technological benets. For example, at low temperatures, a small grain size may increase the strength and toughness of the material, and, at high temperatures, ne-grained alloys may become superplastic. This paper discusses the application of novel deformation processing methods to the production of sub-micron grain structures that are considerably smaller than those produced by conventional processing. There are a number of methods of producing metallic materials with sub-micron grain sizes, including rapid solidication, powder metallurgy, and vapour condensa- tion methods, and the production and properties of nanostructured materials is now a well-established eld of materials science. However, most of these methods are only applicable to the production of very small quantities of material, often of unusual compositions, whereas the emphasis in this paper is on the production of ne-grain structures by methods that are based on the deformation of bulk metal, and that are applicable to larger quantities of conventional structural alloys. The as-cast grain size of most industrial alloys is generally large (greater than 100 μm), and further grain renement is achieved by thermomechanical processing. In alloys that undergo massive solid-state phase transformations, such as steels and titanium alloys, grain renement may be obtained via such transformations, and for steels, controlled rolling during the phase transformation (! ) may result in fer- rite grain sizes of less than 5 μm. For aluminium alloys, ne-grain microstructures are often produced by the recrystallization of a cold worked material, the smallest

Grain Boundary Misorientation Changes during Grain Growth in Pure Aluminium

Abstract: A new method is described for data-logging large amounts of grain boundary misorientation information from channelling patterns in the scanning electron microscope (SEM). The method relies on producing specimens where the grain size is larger than the specimen thickness and where the grain boundary planes are perpendicular to the specimen plane (the so-called columnar structure). Results for grain growth in pure aluminium at 460 and 500°C are presented. There is an increase in the proportion of low angle boundaries at the expense of high angle boundaries during growth times of up to a few hours. The reasons are thought to be partly connected with lower low angle boundary mobility compared with high angle boundaries. However, the growth kinetics appear to be normal over the entire growth time range.

A quantized statistical model of flow stress and generalized Hall-Petch law for deformable polycrystalline materials. A temperature-dimension effect

Abstract: A theory of flow stress (FS), reviewing and developing our research,e.g. arXiv:1803.08247;1908.09338, is proposed,including yield strength (YS) of PC materials for quasi-static plastic loading for grain of average size d in range 10^{-8}-10^{-2}m. It's based on statistical model of energy spectrum distribution in each grain of 1-mode PC sample under plastic loading,with highest level equal to maximal dislocation energy. Found distribution of scalar dislocation density leads to FS due to Taylor strain hardening containing usual and anomalous HP laws for coarse and NC grains, respectively, and reaches maximum for extreme grain size d_0 of order 10^{-8}m. Maximum undergoes shift to region of larger grains for decreasing T and increasing strains. Coincidence is established among theoretical and experimental data on YS for BCC(\alpha-Fe), FCC(Cu,Al,Ni),HCP(\alpha-Ti,Zr) PC materials at T=300K.The T-dependence of strength quantities is studied. It is shown using Al that YS grows with decrease in T for all grains with d>3d_0,and then YS decreases in NC region,thus determining a temperature-dimension effect (TDE).1-phase model of PC sample is extended by including softening GB phase into 2-phase model,and then by dispersion (un)hardening. A quasi-particle interpretation of crystallite energy quantization is suggested.Analytic and graphic forms of HP laws are obtained in above samples with different values of small-,large-angle GB and constant pores.The maximum of YS and respective extremal grain size of the samples are shifted by change of 2-nd phase.The T-dependence of YS in range of 150-350K for Al demonstrates the validity of TDE. An enlargement of 2-nd phase neutralizes TDE.Deformation curves for 1- and 2-mode 2-phase \alpha-Fe PC model are constructed with Backofen-Considere fracture criterion,as compared to experimental,1-phase model data, and strongly depend on multimodality and GB

Effect of Continuous Heating on Grain Growth in Fe-40Ni-Ti Alloy

Abstract: The grain growth of Fe-40Ni-Ti alloy was investigated by means of metallographic observation during continuous heating. The experimental results indicate that: the microstructures consist of multi-polygon austenite. No transformation happens of tested alloy during heating only the grain size increases gradually. The size of grain grows steadily below 1160°C until 1200°C, the grain size growth unusually. The process of grain growth has relations with the dissolving of TiN particles. Finally, the mathematical model of grain growth in continuous heating process was obtained for the tested alloy.