Effect of dispersed particles on microstructure evolved in iron under mechanical milling followed by consolidating rolling (original) (raw)
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Study of the Nanometric Grain Size Distribution in Iron Compacts Obtained by Mechanical Milling
Materials Science Forum, 2006
A study has been carried out on the grain size distribution of cylindrical compacts obtained by consolidation of iron powder severely deformed by mechanical milling. Consolidation has been performed in two consecutive steps: cold and hot conditions. The hot one was done at two temperatures, namely 425 and 475°C. After milling, the iron powder has a grain size of 8 nm (± 4 nm) with an average hardness of 800 HV. After hot compaction the grain size increases up to 50 nm, especially at 475°C where a small fraction of grains reach larger values than the average. The grain size was evaluated by two different techniques, X-Ray Diffraction and Transmission Electron Microscopy. Results showed some differences between both methods. The advantage of using TEM is that grain size distribution, and not only the average size, can be obtained. Small discs were also obtained from the compacted specimen in order to fracture them on a “ball on three balls” equipment. The fracture behaviour of the sam...
Influence of Iron Oxide Particles on the Strength of Ball-Milled Iron
MATERIALS TRANSACTIONS, 2006
Detailed microstructural and mechanical property studies of ball-milled iron, in the powder and consolidated states, are reviewed and assessed. The analyses cover three and one-half orders of magnitude in grain size (from 6 nm to 20 mm) and focus on the influence of oxide particles on the strength. The study includes the early work of Jang and Koch, Kimura and Takaki and continues with the more recent work of Umemoto et al. and Belyakov, Sakai et al. It is shown that the major contributors to strength are the nano-oxide particles. These particles are created by adiabatic shear banding during ball-milling leading to a bimodal distribution of particles. The predicted strength from particles, p , is given by p ¼ B Á ðD s Ã Þ À1=2 where D s à is the surface-to-surface interparticle spacing, and B ¼ 395 MPaÁmm 1=2. A model is proposed that accounts for the influence of the bimodal particle size distribution on strength.
Journal of Thermal Analysis and Calorimetry, 2019
Fe-14Cr-3 W-0.4Ti-0.25Y 2 O 3 ferritic steels were produced by ball milling of initial mixture of elemental powders with various amounts of process control agent (PCA), ethanol (0.25 mass%, 2.5 mass%, 4 mass% and 20 mass%) under an Ar atmosphere and spark plasma sintering (SPS) consolidation at 1070°C. The influence of the quantity of PCA on the properties (microstructure, density and Vickers hardness) of the as-milled powders and of the consolidated steels was investigated. X-ray diffraction shows a bcc-a-phase with fine crystallite size, 6.7-11 nm, for all powders. The particle size and the lattice constant of a-ferrite of the as-milled powders decrease as the amount of PCA increases. The powder milled with the highest amount of PCA, 20 mass%, contains carbides (M 3 C) and oxides ((Fe,Cr) 2 O 3). The thermal analysis shows that as the amount of PCA increases, (1) the Curie temperature, T c , increases, (2) the temperature of a ? c transition, T a?c , decreases, (3) the mass loss with CO/CO 2 degassing increases, and (4) the milling with PCA hinders the nitrogen incorporation from milling media and air. The density and Vickers hardness of the SPS-consolidated and post-SPS annealed steels show an increasing trend with the increase in the amount of PCA. Carbides and oxides were detected in the post-SPS annealed steels derived from the powders milled with 2.5 mass% PCA and 4 mass% PCA (M 23 C 6 and (Fe,Cr) 2 O 3), and 20 mass% PCA (M 3 C and (Fe,Cr) 2 O 3). The obtained results were discussed in terms of: (1) dissolution into the alloy matrix of carbon and oxygen released after the disintegration of PCA, (2) carbides and oxides precipitation during milling and/or upon heating and (3) promotion of thermally activated processes (such as carbothermal reaction) upon heating which can develop as well at the contact points/particle surfaces during SPS consolidation and can influence the process of densification.
Effect of Milling Periods on the Iron Mill Scale Particle Size and Properties
2007
Abstract: The relations between the milling periods with the iron mill scale particle size have been studied. Iron mill scale has been chosen for this research due to the nature of itself, as a by-product. From this research, the average optimum size for the final iron mill scale particle size intended to produce is at 300μm. Raw iron mill scale received from the industries was in the form of chip with the average size of 10 mm across and 1.5 mm thickness.
Effect of Nano-Sized Oxides on Annealing Behaviour of Ultrafine Grained Steels
MATERIALS TRANSACTIONS, 2004
The annealing behaviour of ultrafine grained steels containing nano-scale dispersed oxides was studied in a temperature range of 600-900 C by means of microstructural observations and hardness measurement. The starting materials with submicrocrystalline structures were developed by mechanical milling of Fe-Fe 3 O 4 powders followed by consolidating bar rolling at 700 C. Depending on the initial oxygen content and the mechanical milling time, the fraction of dispersed oxides varied from 0.3 to 3.0 vol%. During the heating up to 800 C (i.e. within the ferrite region), the initial ultrafine grained microstructures were essentially stable against any discontinuous grain growth. The grain coarsening and the softening can be roughly expressed by power-law functions of annealing time. The main mechanism of microstructure evolution that operated during annealing is considered as a normal grain growth accompanied by recovery. The grain coarsening is characterized by a rather high value of the grain-growth exponent of about 20. The grain growth kinetics correlates with the oxide coarsening. The effect of dispersed oxides on the annealing behaviour of submicrocrystalline oxide bearing steels is discussed in some detail.
Nucleation and growth of selective oxide particles on ferritic steel
Corrosion Science, 2010
In the continuous annealing process, steel sheets are annealed at 800°C in an atmosphere of nitrogen and hydrogen (5 vol.%) containing low partial water pressure (20-50 Pa). Under these conditions, the most oxidizable alloying elements in the steel segregate towards the surface where they form oxide particles. The nucleation and growth of those oxides were examined. Oxide nucleation mainly occurs between 650 and 750°C. During their growth, the oxides take the form of a spherical cap and are composed of MnO, Mn 2 SiO 4 (or MnSiO 3), MnAl 2 O 4 , SiO 2 , Al 2 O 3 and B 2 O 3. Particle nucleation and growth are favored on grain boundaries.
Journal of Materials Processing Technology, 2012
The microstructure and mechanical properties of a gravity die and sand cast Al-10%Si-0.4%Mg alloy, which is one of the most important and frequently used industrial casting alloys, were examined. Tensile test samples were prepared from fan blades and sectioned through three positions which experienced different cooling rates. Furthermore, the inherent strength potential of the alloy was revealed by producing homogeneous and well fed specimens with a variety of microstructural coarseness, low content of oxide films and micro-porosity defects, solidified in a laboratory environment by gradient solidification technology. The solidification behaviour of the alloy was characterized by thermal analysis. By means of cooling curves, the solidification time and evolution of the microstructure was recorded. The relation between the microstructure and the mechanical properties was also assessed by using quality index-strength charts developed for the alloy. This study shows that the microstructural features, especially the ironrich needles denoted as β-Al 5 FeSi, and mechanical properties are markedly affected by the different processing routes. The solidification rate exerts a significant effect on the coarseness of the microstructure and the intermetallic compounds that evolve during solidification, and this directly influences the tensile properties.