The effect of time of ball milling on the morphology of the powders based Iron and
Chromium
S.TRIAA
1, L.FAGHI
1et F.KALI-ALIi
2, M. AZZAZ
1S.TRIAA, L.FAGHI et M. AZZAZ
* Laboratoire Sciences et Génie des Matériaux LSGM Département Sciences Des Matériaux
Université des Sciences et de la Technologie Houari Boumediene
E-Mail : salimtria@yahoo.fr
F.KALI-ALI
Laboratoire de physique théorique
Département de physique théorique. Faculté de physique Université des Sciences et de la Technologie Houari
Boumediene
BP 32 El Alia 16111 Bab Ezzouar – Alger – Algérie
Abstract: This work is to examine the conditions of milling on the alloys based on iron and chromium in powders prepared by ball milling and their structural properties.
A first step was the preparation of alloys based on the Fe-Cr vacuum in jars after studying beforehand optical microscope and the scanning electron microscope morphology of the powders our constituents pure alloy.
The characterization of alloys has been developed on : The dispersion and morphology powder after different milling time, and then we studied the distribution and size of powders by electron microscopy and image processing.
We were able to highlight the influence of some milling parameters on the morphology, size and distribution of various powders constituting our alloys based on Fe-Cr.
Nanostructures, Mechanical alloying, Fe-Cr powder, XRD and SEM.
I. INTRODUCTION
Chromium cast irons have high corrosion resistance, good abrasion and toughness, and give good service with oxidizing acids, numerous salt solutions and in marine or industrial atmospheres. Further, these alloys are resistant to shock and can be machined.
The properties of high chromium iron based alloys are very desirable for advanced nuclear reactor applications (1). Such alloys, however, have a big disadvantage when the sigma phase is formed. This phase causes a drastic deterioration in mechanical proprieties such as ductibility and impact toughness. Recently it has been found that the formation of sigma phase can be greatly retarded by purification (2).
It is generally accepted that mechanical proprieties are improved when a material is found to be in the nano-
structured state, due to the reduction of grain size and the decrease of the density of defects inside the grains.
Mechanical alloying is well known solid state reaction technique used amongst others to synthesise alloys with nanometer-scale crystallites and to obtain extended solid solutions.
The proprieties of ball-milled alloys are known to be sensitive to the conditions of preparation. In Fe-Cr alloys prepared by this method, the formation of the sigma phase was found to be highly accelerated when an amorphous phase is formed (3). In this work, the preparation and characterization of alloys obtained under different milling times are described.
II. EXPERIMENTAL PROCEDURE
In order to prepare the alloys required for these studies, a mixture of appropriate amounts of Fe (99.9%, powder grain size < 40 µm), Cr (99.2%, powder, grain size 100 µm) were ball milled in a vial with eleven balls. Both the vials (45 ml in volume) and the balls (20 mm in diameter) were made of stainless steel. The samples were prepared taking into account the contamination from the vial and balls. The average weight of the powders was 26.2 g and the powder to ball weight ratio was 1/13. The powders were sealed in the vials under a pure argon atmosphere. Mechanical alloying was performed with a planetary-type mill (reutsh P200) at a rotating speed of 250 rpm.
The total milling time was 36 h, interrupted for either 20 min every 1, in order to minimise excessive temperature rise and limit the adherence of the powders to the vial walls.
III. RESULTS AND DISCUSSION
Photographs of the samples, obtained by scanning electron microscopy are shown in figure; the powders deposited on a conducting support. It can be seen that the size of the particles decreases with increasing amounts of times.
We notices
• What cycle time become increasing the grain of our alloy becomes decreasing (small)
• What cycles combinations then cracking successive assemblies is observed, we can develop the homogeneous aggregate over time.
XRD spectra of our sample are presented in figure.
The diffraction patterns show a bcc structure with broad line widths, particularly with increasing of milling time. This is attributed to the reduction in crystallite size and accumulation of stresses in the bcc lattice during mechanical alloying process.
After 1 h of milling
After 3 h of milling
After 18 h of milling
After 36 h of milling
After 1 h of milling
After 3 h of milling
IV. CONCLUSIONS
Using untreated vials and balls in the milling process, the following were noted :
The size of particles and crystallites decreases with increasing of milling time.
The diffraction patterns show a bcc structure with broad line widths attributed to the reduction in crystallite size and accumulation of stresses in the bcc lattice during mechanical alloying process
References
[1] A. Hishinuma, S. Isozaki, S. Takaki, K. Abiko, Phys. Stat.
Sol. (a) 160 (1997) 431.
[2] K. Yano, K. Abiko, Phys. Stat. Sol. (a) 160 (1997) 449.
[3] B.F.O. Costa, PhD. Thesis, Coimbra. (1998).
After 18 h of milling
After 36 h of milling
