U. K. Chatterjee

Gibb’s free energy for the crystallization of glass forming liquids

This letter gives an approximation for the Gibb’s free energy change for the crystallization of undercooled liquid (ΔG). The present ΔG expression is arrived at by the modification of existing models. Calculations based on the present expression have shown that the ΔG values obtained for seven glass forming alloys (Au81.4Si18.6, La50Al30Ni20, Mg65Cu25Y10, Mg50Ni30La20, Pd40Ni40P20, Zr65Cu17.5Ni10Al7.5, and Zr41.2Ti13.8Cu12.5Ni10Be22.5) compare well with the experimental ones in all the cases with a maximum deviation of 6% up to the glass transition temperature (Tg). The present expression is able to calculate the ΔG values accurately in a variety of glass forming alloys ranging from binary to quinary systems with a wide range of reduced glass transition temperature (Trg=Tg/Tm) of 0.45–0.75.

Mechanism of scc of α-brass in Mattsson's solution under potentiostatic conditions

Abstract SCC of α-brass in Mattssons solution has been studied under potentiostatic anodic and cathodic polarization. In annealed samples, anodic polarization brings in a minimum in cracking time accompanied by a transition in cracking mode from intergranular to transgranular. The range of potential giving maximum susceptibility to cracking has been found to be independent of Cu content and pH of the test solution, but dependent on cold work. Cathodic polarization increases the resistance to cracking, and in cold-worked samples, where the cracking is initially transgranular, a transition to intergranular has been observed on cathodic polarization. SCC has been encountered also in a non-Cu-containing solution. These observations strongly suggest a mechanism based on a shift in active anodic and cathodic sites on polarization and adsorption playing an important role in the cracking process.

Wear and Corrosion Behaviour of In-Situ Al-TiB2 Metal Matrix Composites

In-situ Al-TiB2 metal matrix composites containing 5 wt% and 10 wt% TiB2 have been synthesized through master alloy and mixed salt routes. The composites have shown five times increase in wear resistance compared to commercially pure aluminium. Corrosion evaluation by polarization technique carried out in NaCl, H2SO4 and NaOH solutions indicates a lower corrosion resistance of the composites than the corresponding base metals. The composites produced through mixed salt route suffered higher corrosion than those prepared by master alloy route. The results have been explained from the physical and electrochemical effects of TiB2 in the matrix.