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The theory of transformations in metals and alloys
01 Jan 1965-
TL;DR: In this paper, the authors present a general introduction to the theory of transformation kinetics of real metals, including the formation and evolution of martensitic transformations, as well as a theory of dislocations.
Abstract: Part I General introduction. Formal geometry of crystal lattices. The theory of reaction rates. The thermodynamics of irreversable processes. The structure of real metals. Solids solutions. The theory of dislocations. Polycrystalline aggregates. Diffusion in the solid state. The classical theory of nucleation. Theory of thermally activated growth. Formal theory of transformation kinetics. Part II Growth from the vapour phase. Solidification and melting. Polymorphic Changes. Precipitation from supersaturated solid solution. Eutectoidal transformations. Order-disorder transformations. Recovery recrystalisation and grain growth. Deformation twinning. Characteristics of martensic transformations. Crystallography of martensitic transformations. Kinetics of martensitic transformations. Rapid solidification. Bainite steels. Shape memory alloys.
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TL;DR: In this paper, a selective laser melting experiment was carried out with Ti6Al4V alloy powders, and the results were analyzed using analyses of variance (ANOVA) and the signal-to-noise (S/N) ratios by design-expert software for the optimal parameters, and a regression model was established.
Abstract: In this study, a selective laser melting experiment was carried out with Ti6Al4V alloy powders. To produce samples with maximum density, selective laser melting parameters of laser power, scanning speed, powder thickness, hatching space and scanning strategy were carefully selected. As a statistical design of experimental technique, the Taguchi method was used to optimize the selected parameters. The results were analyzed using analyses of variance (ANOVA) and the signal-to-noise (S/N) ratios by design-expert software for the optimal parameters, and a regression model was established. The regression equation revealed a linear relationship among the density, laser power, scanning speed, powder thickness and scanning strategy. From the experiments, sample with density higher than 95% was obtained. The microstructure of obtained sample was mainly composed of acicular martensite, α phase and β phase. The micro-hardness was 492 HV0.2.
171 citations
TL;DR: In this article, the isothermal crystallization of thin amorphous Ge2Sb2Te5 films, sandwiched between Si3N4 dielectric layers, was followed in real time using in situ transmission electron microscopy.
Abstract: The isothermal crystallization of thin amorphous Ge2Sb2Te5 films, sandwiched between Si3N4 dielectric layers, was followed in real time using in situ transmission electron microscopy. A temperature-dependent incubation time is observed. After this incubation time, the crystallization is found to follow Johnson–Mehl–Avrami–Kolmogorov (JMAK) transformation kinetics. The JMAK parameters were determined, as well as the individual nucleation and growth parameters. The relationships between the JMAK parameters and the nucleation and growth parameters were tested and found to be valid. Nucleation was found to occur at the interfaces with the dielectric layers. The average grain size after crystallization did not show appreciable temperature dependence in the temperature range investigated.
170 citations
TL;DR: In this paper, the anatase-to-rutile phase transformation kinetics were studied using the Avrami model, and the effect of surface reduction and pore growth were anatase crystallite growth and the enhanced sintering of rutile during transformation.
Abstract: Textural evolution in sol–gel derived nanostructured unsupported titania membranes has been studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), thermal gravimetry (TG), X-ray diffraction (XRD) and N2 adsorption. The anatase-to-rutile phase transformation kinetics were studied using the Avrami model. The precursor gel had a surface area of ca. 165 m2 g–1, which after heat treatment at 600 °C for 8 h reduced to zero. Undoped titania-gel layers transformed to more than 95% rutile after calcination at 600 °C for 8 h. The causes of surface-area reduction and pore growth were anatase crystallite growth and the enhanced sintering of rutile during transformation. Lanthanum oxide was identified as a suitable dopant for shifting the transformation temperature to ca. 850 °C. Lanthanum oxide doped titania showed an improved stability of porous texture compared to that of the undoped titania membranes.
170 citations
TL;DR: The nonlinear viscosity change as a result of structural relaxation near equilibrium, at temperatures below and above the fictive temperature, has been measured for amorphous Pd77.5Cu6Si16.5 as discussed by the authors.
169 citations
15 Aug 1998-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: The influence of quench rate on the microstructure and the ageing response of a Zr-containing Al-Zn-Mg alloy was investigated in this article, where it was shown that Al3Zr dispersoids are efficient nuclei for precipitation of coarse, equilibrium η precipitates during quench.
Abstract: The influence of the quench rate on the microstructure and the ageing response of a Zr-containing Al–Zn–Mg alloy was investigated It is shown that Al3Zr dispersoids are efficient nuclei for precipitation of coarse, equilibrium η precipitates during the quench Dispersoids are heterogeneously distributed in bands, resulting in bands of quenched-induced precipitates after a slow quench The ageing response after a slow quench is characterized by various levels of heterogeneities resulting in a `composite' material On a microscopic scale, quench-induced η precipitates are surrounded by a precipitate-free zone On a mesoscopic scale, the material is separated in unperturbed regions and regions of high density of coarse precipitates and low density of hardening precipitates Finally, a slow quench makes the material more sensitive to the heating rate to the ageing temperature, due to slower GP zone precipitation during natural ageing because of annihilation of vacancies during quenching
168 citations