Like this presentation? Why not share! Diagrama de equilibrio hierro car Embed Size px. Start on. Show related SlideShares at end. WordPress Shortcode. Next SlideShares. Download Now Download to read offline and view in fullscreen. Technology , Business. Download Now Download Download to read offline. Diagrama de equilibrio hierro carbono. Diagrama de equilibrio de las aleaciones hierro carbono.
Diagrama hierro carbono y curvas ttt. Diagrama de hierro carbono. Diagrama de fases. Diagrama fe c. Iron Carbon Phase Diagram. Diagrama Fe C. Related Books Free with a 30 day trial from Scribd. Related Audiobooks Free with a 30 day trial from Scribd. Ramy Antar. Shivayou Pandey.
BhuVan Zutshi. Samta Nayak. Hemant Kumar. You know by now that in both cases the nucleation of the new phase occurs most easily at the grain boundaries and especially at the nodes of grain boundaries of the austenite.
Later we will see that certain impurity atoms also help to form cemenite. As soon as both steels hit the all-important K o C, o F transformation temperature , the still present austenite in both cases must change to a ferrite-cementite mixture striped in the picture below.
This is shown in the figure below. Formation of the structure of hypoeutectic and hypereutectic steel during slow cooling down. I'm going to discuss that figure in some detail by looking at the various state points in the phase diagram and the schematic! In both case we start with pure austenite or fcc iron with some dissolved carbon at a temperature somewhat above 0 C 0 C We can't image the structure at such a high temperature but we can be sure that it consists of large grains without many defects.
This is indicated by the two topmost structure figures. We now need to form some a ferrite or some Fe 3 C cementite, respectively. How much of these new phases are needed will be given by the "lever rule" that we will get to know quite soon. Whatever, in the beginning we don't need all that much and the precipitation of the new phases will start at good nucleation sites, in particular grain boundary nodes.
This is shown in the second structure figure in going downwards. As the state points move to lower temperatures within the mixed phase regions, more ferrite or cementite needs to be formed, and the new phases grow. This may happen along the grain boundaries indicated in the third structure figure on the right , more uniformly right figure , or in some other way.
Laporkan Dokumen Ini. Deskripsi: iron carbon phase theory. Tandai sebagai konten tidak pantas. Unduh sekarang. Judul terkait. Karusel Sebelumnya Karusel Berikutnya. Lompat ke Halaman. Although real solidification is generally expected to be between the Scheil and equilibrium solidification conditions, in the case of the investigated Mg—Si system, the curves calculated according the Scheil model and in equilibrium conditions were practically the same due to the negligible solubility of silicon in magnesium.
It should also be noted that the eutectic formed in the investigated materials had irregular morphology—typical for a faceted—nonfaceted eutectic. The primary Mg 2 Si phase has a regular polygonal morphology typical for faceted crystals and assumes the shape of a hexahedron, octahedron or tetrakaidecahedron.
This morphology of primary Mg 2 Si crystals has been observed in different composites reinforced with this compound; however, it was also mentioned in the Introduction Section that dendritic morphology with visible dendrite arms of the primary Mg 2 Si phase was also observed. Mirshahi R. They observed that at high cooling rates, Mg 2 Si formed with polygonal morphology, while at lower cooling rates Mg 2 Si precipitated dendritically.
These results are in contradiction to the results of Pan X et al. On the other hand, in work [ 19 ], dendrites of the Mg 2 Si phase were observed in composites cast in an iron mold preheated to K. In contrast, polygonal Mg 2 Si crystals were disclosed in work [ 30 ] in composites with 2. In our previous study [ 36 ], typical dendrites of Mg 2 Si were identified in a composite based on an AM50 magnesium matrix alloy with 9. In the presented study, dendritic growth of the Mg 2 Si crystals was not observed.
The observed differences in the primary Mg 2 Si phase morphology in various works could be the effect of not only the cooling rate but also the chemical composition of the composite and the presence of further elements or impurities and super-cooling during solidification which also depends on the casting temperature.
These factors need very detailed studies especially in the context of impurities. It is most likely that a very small amount of surface-active third elements influenced the phase morphology, similar to the aluminum—silicon system in which a content of up to 9 ppm phosphorus causes changes in the microstructure of hypereutectic alloys. The sequence of solidification according to these curves described the crystallization of the Mg 2 Si phase at the beginning and eutectic transformation at the end.
These dendrites of magnesium arose due to local fluctuation of the chemical composition of the composite during nonequilibrium solidification.
The Mg 2 Si crystals, formed as the first, needed a relatively high amount of silicon, which caused impoverishment of this element in the surrounding liquid. On one hand, this impoverishment blocked the growth of primary Mg 2 Si crystals, and on the other hand, there were advantageous conditions for the nucleation of magnesium.
Below the temperature of K, the magnesium dendrites nucleated in these regions and quickly grew. Mg dendrites are visible in Figure 4 and, additionally, in the micrographs presented in Figure 6. The dendrites were of different sizes and some of them also had secondary arms, visible especially in Figure 4 a and Figure 6 , which can indicate local fluctuation of the chemical composition in the liquid.
The distribution of magnesium dendrites was caused by the distribution of elements in the liquid during nonequilibrium solidification conditions, but the presence of the primary Mg 2 Si phase inside all the dendrites could also suggest heterogeneous nucleation of magnesium on the Mg 2 Si crystals. It is well known that one of the necessary conditions for heterogeneous nucleation is the formation of a low energy interface between the nucleus and substrate, i. According to typical crystallographic calculations in the main directions of the basal planes, Mg and Mg 2 Si exhibited an interatomic spacing misfit of less than 0.
Figure 8 a presents the ultimate tensile strength UTS and yield strength TYS obtained in the uniaxial tensile test for both composites and compared with those obtained for technically pure magnesium cast in the same conditions. The analogical results presenting the compression strength CS and yield strength YS values obtained in the uniaxial compression test are shown in Figure 8 b. Both the fabricated composites exhibited higher mechanical properties than technically pure magnesium.
The obtained results of the ultimate tensile strength of both the investigated composites were also higher than those presented by Mirshahi F. These values are comparable with the results obtained by gravity cast magnesium alloys, for example AM50 or AME [ 50 ].
On the other hand, the presented composites had a yield strength of more than twice as high, especially under compression. The investigated materials exhibited different fracture surfaces. Refinement of the composite microstructures with the increase in the weight fraction of the Mg 2 Si compound observed during the comparison of Figure 4 a and Figure 5 a is also visible when comparing Figure 9 a,b produced at the same magnification.
The failure of magnesium is usually brittle through cleavage or quasi-cleavage due to the hexagonal closed packed structure. Figure 11 and Figure 12 show SEM micrographs of the fracture surfaces of this composite at higher magnification. The primary Mg 2 Si phase was clearly visible on the fracture surface. In Figure 11 and Figure 12 , the surface distributions of the main element were also added 11b, 12b. Although the energy dispersive X-ray spectrometry EDX results from the fracture surfaces were burdened with errors especially quantitatively , they confirmed the presence of primary Mg 2 Si crystals in the obtained micrographs.
It should also be noted that the particles of the primary Mg 2 Si phase were cracked and exhibited intrinsic brittleness. The micrographs presented in Figure 11 c,d and Figure 12 show that the cracking process proceeded through the Mg 2 Si with the propagation of secondary cracks. All the Mg 2 Si phases designated as 1—3 in Figure 11 c and as 1—2 in Figure 12 a had visible effects of brittle cracking. The presented SEM results also indicate that primary Mg 2 Si crystals and the surrounding magnesium phase were strongly connected, which could also be an additional argument for the heterogeneous nucleation of magnesium dendrites on the Mg 2 Si phase.
The magnesium dendrite surrounding the Mg 2 Si cracked particle described as 3 is especially visible in Figure The main conclusions drawn are as follows:.
Magnesium matrix composites with 1. The microstructure of the material with 1. The composites exhibited a rise in tensile and yield strength in both the tensile and compression tests with an increase in the weight fraction of the Mg 2 Si phase.
The fracture surface observations revealed that during the uniaxial tensile test, the cracking process of the fabricated composites proceeded through all structural constituents. Conceptualization, K. All authors have read and agreed to the published version of the manuscript. National Center for Biotechnology Information , U.
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