Abstract
This paper deals with the (Ni-Cr- xAl2O3) metallic composites (MCCs). Restraining of of thermal expansion at adequate mechanical and corrosion properties is the main objective of this work. Composites are fabricated with four weight percentages of (x = 1, 2, 5 and 10% Al2O3). Compacting and sintering has accomplished at (636 MPa) and 1250oC for 7 hrs. All sintered compacts were examined for phases and microstructure featuring. Results have indicated, the incorporation of Al2O3 with the matrix is due to the efficient sintering conditions, that diminishing the grain growth and increasing the softening temperature from 850°C to become 1350°C. Volume expansion appeared in the base sintered composites (NiCr-xAl2O3) due to pores evolution according to SEM observation. As, the Al2O3 has increased, the microhardness and corrosion resistance have improved. DSC results show a clear one exothermic and one endothermic reaction were occurred during the heating cycle. Corrosion behavior of fabricated composites was estimated by polarization curves using Potentiostat at scan rate 3 mV.sec-1. Potential-time measurements showed the formation of protective layer on surface composites compared with Ni-Cr base composite through an obtaining of the nobler open circuit potentials for composites. Corrosion parameters were estimated by the Tafel extrapolation method, these parameters indicated that the corrosion potential shifted toward a positive direction in addition to get lower corrosion current density especially for Ni-Cr/5%Alumina composite.
Highlights
Composite materials defined as macroscopic level mixtures of non-soluble constituents with two or more distinct compositions
The weight percentages of the Al2O3 increase, the thermal expansion percentages will decrease and the dimensions is withstanding the gradual increase of temperature
The softening occurs at different temperatures, according to the weight percentage of added Al2O3
Summary
Composite materials defined as macroscopic level mixtures of non-soluble constituents with two or more distinct compositions. An attempt has made to fabricate a new metal matrix composite material. This composite contains Ni, Cr and variable weight percentages of Al2O3. The increases of variable percentages of ceramic constituents (i.e. Al2O3) is one of the feasible methods in improving the working properties of these composites. A great deal of efforts passed in the direction of fabrication and characterization of new Ni-Cr metal matrix composite (MMCs). These efforts were concentrated on the development of corrosion resistance properties of these materials at high temperature applications
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