Ajay Likhite

Effect of Cryogenic Processing on Surface Roughness of Age Hardenable AA6061 Alloy

The aging phenomenon in age hardenable aluminum alloys is complex and well under research. The supersaturated solid solution of these alloys, during aging, undergoes complex precipitation causing increase in strength with time. These alloys have wide range of applications in the aviation and automotive industry. The properties such as electrical conductivity and hardness of these alloys are well related to its precipitation behavior. Cryogenic treatment (CT) has been tried on tool and alloy steels where it has been found that this treatment positively affects the wear resistance and also causes uniformity in structure. The CT has become an important step in the manufacturing of tool steels. This work comprises applying CT at −185°C to AA 6061 aluminum alloy for various time periods. The treatment was sequenced in the conventional solutionizing and artificial aging. This sequence of treatment has not been reported in the literature. The characterization was done using scanning electron microscopy. The behavior of this alloy to the treatment was identified by measuring electrical conductivity and hardness. The surface roughness of this alloy was also found to be highly influenced by this treatment.

Compressive, tensile and wear behavior of ex situ Al/AlN metal matrix nanocomposites

The mechanical strength and wear behavior of Al–AlN metal matrix nanocomposites synthesized using melt metallurgy technique is investigated. Uniformly dispersed nanostructured AlN particulates in nanocomposites are found to improve the mechanical properties. Detailed study on compressive and tensile test is attempted in the present work to understand the mechanism of deformation in nanocomposites. Adhesive dry wear test results indicate that applied load has strong influence on wear behavior of nanocomposites compared to the sliding distance. Porosity and weak agglomeration of nanoparticles are found to significantly affect the wear behavior and mechanical strength of synthesized nanocomposites. It is revealed that the transfer of load from matrix to reinforcement particulate is not an instantaneous phenomenon but initiates after some incubation period depending on the fraction of porosity in nanocomposites during compressive and tensile testing.

Nucleation Criteria for the Formation of Aluminum Nitride in Aluminum Matrix by Nitridation

Synthesis of in situ metal matrix composites using liquid metallurgy technique involves processing the melt to generate ceramic particles and entrap them into the matrix during solidification. The process parameters such as temperature, holding time and buoyancy effect generated in the molten bath are crucial factors governing the size and distribution of ceramic particles into the matrix. Temperature being most important parameter and its role is easy to comprehend for in situ formation of ceramic particles using established nucleation criteria. In the present research paper, thermodynamic study is carried to understand the role of temperature on formation of aluminum nitride by nitridation of aluminum melt using ammonium chloride and calcium oxide. Mechanism of aluminum nitride formation by heterogeneous nucleation and its growth has also been discussed based on the nucleation theory. An attempt is also made to correlate nucleation theory for the formation of AlN in Al matrix at different temperatures. The mechanical behavior under compressive loading is carried out on synthesized composites to understand its capability to withstand static loading. Composite strength is analyzed and attempt is made to correlate nucleation dynamics of AlN particles.

Study on Quantification of Oxide Phases in Ex-situ AlN/Al Metal Matrix Nanocomposites

Al based metal matrix nanocomposite (MMNC) is synthesized by dispersing nanocrystalline aluminium nitride (AlN) particles in Aluminum matrix using ex-situ melt metallurgy method. The entrapment of atmospheric oxygen along with ex-situ particulate has been a long standing issue during fabrication of metal matrix composites. In the present investigation, presence of oxygen has been quantified in synthesized Al-AlN MMNCs with varying AlN content. The high resolution scanning electron microscopy is used to study morphology and distribution of AlN in Al matrix. Energy dispersive spectroscopy analysis is used to quantify in situ oxide phases along with AlN particles in the synthesized MMNCs using thermodynamic mass balance calculations. Present study also attempts to understand the role of in-situ oxide phases on the mechanical properties of MMNCs using microindentation hardness and nanoindentation test.

Effect of austenitization temperature on microstructure and mechanical properties of low-carbon-equivalent carbidic austempered ductile iron

The wear resistances of austempered ductile iron (ADI) were improved through introduction of a new phase (carbide) into the matrix by addition of chromium. In the present investigation, low-carbon-equivalent ductile iron (LCEDI) (CE = 3.06%, and CE represents carbon- equivalent) with 2.42% chromium was selected. LCEDI was austenitized at two different temperatures (900 and 975°C) and soaked for 1 h and then quenched in a salt bath at 325°C for 0 to 10 h. Samples were analyzed using optical microscopy and X-ray diffraction. Wear tests were carried out on a pin-on-disk-type machine. The effect of austenization temperature on the wear resistance, impact strength, and the microstructure was evaluated. A structure–property correlation based on the observations is established.

On the Mechanism of the Effect of the Cryogenic Treatment on High Speed Steels

The effect of subzero treatment on tool steels is well known, and is commercially practiced for certain varieties of tool steels. Substantial research is being carried out on the behavior of tool steels after cryogenic treatment (CT). While it has been established that CT improves the wear properties in some steels, the mechanism of this behavioral aspect is not yet fully known. Most work has been focused on AISI M2 high speed steel related to the effect on different properties, but the microstructural change is not yet conclusively identified. Neither the past research has brought forth the exact principles on which CT should be based. Some of these important issues are addressed in this paper.