Carbon fiber reinforced AA7075 is known for good thermal properties and thus used as heat dissipating material. However, few such applications involve corrosive environments too, and hence there is a need to study the behavior of these composite materials under corrosive environment. In the present work, milled carbon fiber reinforced AA7075 composites were produced by vacuum hot pressing with varying amounts of milled carbon fibers. The relative densities of the composites were measured. SEM-EDS, TEM and XRD techniques were also employed for characterization. The composites were then characterized for electrochemical behavior in 3.5 wt.% aqueous NaCl solution by electrochemical polarization technique. Results showed that the corrosion potentials E corr have shifted to more negative direction and thus showed increase in corrosion current density, leading to increase in corrosion rate with increasing vol.% of carbon fibers. These results were complemented by SEM micrographs of the composites after corrosion test, which revealed that corrosion occurred at the interface of carbon fiber and matrix due to formation of galvanic coupling between carbon fiber and matrix. Thus, reduced corrosion resistance in composites as amount of fibers increases, is attributed to increase in number of galvanic cells that form at the interface.
Laser surface hardening is one of the effective method to enhance the mechanical properties of localised surface area of engineering parts made of different types of steels and other metals like titanium etc. Laser surface hardening has many advantages over conventional hardening process like, self-quenching, very fast, control over energy input and localised hardening etc. This work presents the effect of different laser parameters on the micro hardness of SS316L after laser hardening. The experimental work was carried out using 30W Diode-pumped nanosecond (ns) pulsed laser. Design of Experiments One Variable at a Time (OVAT) approach was used for experimentation. Laser power, laser scanning speed, frequency and number of passes were the process parameters used for the experiments. Effects of these parameters over the micro hardness of the surface are described. Along with this, discussion of features of microstructures using optical microscope are done. It has been found that, there is around 25% increase in hardness after laser hardening. Hardened depth up to 400 microns was obtained.
The coating quality of nickel is important factor in improvement of wettability of carbon fibers to be used as reinforcing material in the production of carbon fiber reinforced metal matrix composites. In this research work, Polyacrylonitile (PAN) based carbon fibers have been Ni coated in Sodium hypophosphite reduced acidic bath by electroless plating method. These carbon fibers are coated using 4, 4.5, 5 and 5.5 pH values for 5, 10, 15, 20, 25 and 30minutes. Coating thickness is found to increase with time linearly. Nickel deposition rate per unit time increases with pH, however it reaches a maxima and then declines. The surface condition of fibers reveals that coating becomes more and more rough due to non uniform coating, as coating time and pH goes on increasing.
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