Ramesh and Prabhu Nanoscale Research Letters 2011, 6:334 http://www.nanoscalereslett.com/content/6/1/334 Page 2 of 15 Figure 1 Typical boiling (a) and temperature-time (b) curves for a hot surface quenched in a liquid bath. The important factors, which influence the heat trans- fer/metallurgical transformation during quench harden- ing, are shown in Figure 2 [5]. Of all these factors listed, only a few can be changed in the heat treatment shop. The selection of optimum quenchant and quenching conditions both from the technological and economical point of view is an important consideration [5]. Water, brine solution, oil, polymer etc. are used as conventional quenching media. Water and brine Figure 2 Factors influencing the metallurgical transformation during quench hardening. solution are restricted to quenching simple shapes and steels of comparatively low hardenability because of the occurrence of intolerable distortion, warpage and quench cracks [6]. On the other hand, convective cool- ing in oil is less intensive due to relatively high viscosity and lower heat capacity. A variety of different quenching oils tend to show a prolonged vapour blanket stage, a short nucleate boiling stage with a much lower cooling rate, and finally a prolonged convective cooling stage with a very modest cooling rate [1]. Polymer quenchants show low cooling rate and it cannot be used with some common additives and anti oxidants. Continuous moni- toring of polymer quenchant is required for optimal per- formance and it is not suitable for steels requiring high temperature quenching [7]. Therefore, it is necessary to develop new type of quenchants capable of producing desired property distribution, acceptable microstructure and residual stress distribution in section thicknesses of interest with avoidance of cracking and reduced distortion. Modern nanotechnology provides new opportunities to process and produce materials with average crystallite sizes below 50 nm [8]. The unique properties of these nanoparticles are (i) size dependent physical properties, (ii) large surface area, (iii) large number density and (iv) surface structure [9]. Fluids with nanoparticles sus- pended in them are called nanofluids [8]. Commonly used materials for nanoparticles are oxide ceramics (Al2O3, CuO), metal carbides (SiC), nitrides (AlN, SiN),